<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.powellind.com/role/CommitmentsAndContingencies" xlink:href="powl-20170630.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/CommitmentsAndContingenciesDetails" xlink:href="powl-20170630.xsd#CommitmentsAndContingenciesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/CondensedConsolidatedBalanceSheetsUnaudited" xlink:href="powl-20170630.xsd#CondensedConsolidatedBalanceSheetsUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/CondensedConsolidatedBalanceSheetsUnauditedParenthetical" xlink:href="powl-20170630.xsd#CondensedConsolidatedBalanceSheetsUnauditedParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/CondensedConsolidatedStatementsOfCashFlowsUnaudited" xlink:href="powl-20170630.xsd#CondensedConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/CondensedConsolidatedStatementsOfComprehensiveIncomeLossUnaudited" xlink:href="powl-20170630.xsd#CondensedConsolidatedStatementsOfComprehensiveIncomeLossUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/CondensedConsolidatedStatementsOfOperationsUnaudited" xlink:href="powl-20170630.xsd#CondensedConsolidatedStatementsOfOperationsUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccounts" xlink:href="powl-20170630.xsd#DetailOfSelectedBalanceSheetAccounts" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsActivityInAllowanceForDoubtfulAccountsDetails" xlink:href="powl-20170630.xsd#DetailOfSelectedBalanceSheetAccountsActivityInAllowanceForDoubtfulAccountsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsActivityInProductWarrantyAccrualDetails" xlink:href="powl-20170630.xsd#DetailOfSelectedBalanceSheetAccountsActivityInProductWarrantyAccrualDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsComponentsOfInventoriesDetails" xlink:href="powl-20170630.xsd#DetailOfSelectedBalanceSheetAccountsComponentsOfInventoriesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsCostAndEstimatedEarningsOnUncompletedContractsDetails" xlink:href="powl-20170630.xsd#DetailOfSelectedBalanceSheetAccountsCostAndEstimatedEarningsOnUncompletedContractsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsTables" xlink:href="powl-20170630.xsd#DetailOfSelectedBalanceSheetAccountsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/DocumentAndEntityInformation" xlink:href="powl-20170630.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/EarningsPerShare" xlink:href="powl-20170630.xsd#EarningsPerShare" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/EarningsPerShareDetails" xlink:href="powl-20170630.xsd#EarningsPerShareDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/EarningsPerShareTables" xlink:href="powl-20170630.xsd#EarningsPerShareTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/FairValueMeasurements" xlink:href="powl-20170630.xsd#FairValueMeasurements" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/FairValueMeasurementsDetails" xlink:href="powl-20170630.xsd#FairValueMeasurementsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/FairValueMeasurementsTables" xlink:href="powl-20170630.xsd#FairValueMeasurementsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/GoodwillAndIntangibleAssets" xlink:href="powl-20170630.xsd#GoodwillAndIntangibleAssets" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/GoodwillAndIntangibleAssetsNarrativeDetails" xlink:href="powl-20170630.xsd#GoodwillAndIntangibleAssetsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/GoodwillAndIntangibleAssetsScheduleOfIntangibleAssetsSubjectToAmortizationDetails" xlink:href="powl-20170630.xsd#GoodwillAndIntangibleAssetsScheduleOfIntangibleAssetsSubjectToAmortizationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/GoodwillAndIntangibleAssetsTables" xlink:href="powl-20170630.xsd#GoodwillAndIntangibleAssetsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/IncomeTaxes" xlink:href="powl-20170630.xsd#IncomeTaxes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/IncomeTaxesNarrativeDetails" xlink:href="powl-20170630.xsd#IncomeTaxesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/IncomeTaxesScheduleOfEffectiveTaxRateDetails" xlink:href="powl-20170630.xsd#IncomeTaxesScheduleOfEffectiveTaxRateDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/IncomeTaxesTables" xlink:href="powl-20170630.xsd#IncomeTaxesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/LongTermDebt" xlink:href="powl-20170630.xsd#LongTermDebt" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/LongTermDebtComponentsOfLongTermDebtDetails" xlink:href="powl-20170630.xsd#LongTermDebtComponentsOfLongTermDebtDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/LongTermDebtNarrativeDetails" xlink:href="powl-20170630.xsd#LongTermDebtNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/LongTermDebtTables" xlink:href="powl-20170630.xsd#LongTermDebtTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/OverviewAndSummaryOfSignificantAccountingPolicies" xlink:href="powl-20170630.xsd#OverviewAndSummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/OverviewAndSummaryOfSignificantAccountingPoliciesDetails" xlink:href="powl-20170630.xsd#OverviewAndSummaryOfSignificantAccountingPoliciesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/OverviewAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:href="powl-20170630.xsd#OverviewAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/RestructuringAndSeparationCosts" xlink:href="powl-20170630.xsd#RestructuringAndSeparationCosts" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/RestructuringAndSeparationCostsDetails" xlink:href="powl-20170630.xsd#RestructuringAndSeparationCostsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/StockBasedCompensation" xlink:href="powl-20170630.xsd#StockBasedCompensation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/StockBasedCompensationNarrativeDetails" xlink:href="powl-20170630.xsd#StockBasedCompensationNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/StockBasedCompensationScheduleOfRestrictedStockUnitsActivityDetails" xlink:href="powl-20170630.xsd#StockBasedCompensationScheduleOfRestrictedStockUnitsActivityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/StockBasedCompensationTables" xlink:href="powl-20170630.xsd#StockBasedCompensationTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/SubsequentEvents" xlink:href="powl-20170630.xsd#SubsequentEvents" xlink:type="simple" />
  <link:roleRef roleURI="http://www.powellind.com/role/SubsequentEventsDetails" xlink:href="powl-20170630.xsd#SubsequentEventsDetails" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/CommitmentsAndContingenciesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsLineItems" xlink:label="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfGuaranteeObligationsTable" xlink:label="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_6C906377D0B0186E1027960F7BD144B9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:to="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_6C906377D0B0186E1027960F7BD144B9" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_A5CCE9BA73374FEB4C939644080C1DE4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_6C906377D0B0186E1027960F7BD144B9" xlink:to="loc_us-gaap_CreditFacilityAxis_A5CCE9BA73374FEB4C939644080C1DE4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_EEFE316DA55DD7BE1E03964408113C67_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_A5CCE9BA73374FEB4C939644080C1DE4" xlink:to="loc_us-gaap_CreditFacilityDomain_EEFE316DA55DD7BE1E03964408113C67_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_EEFE316DA55DD7BE1E03964408113C67" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_A5CCE9BA73374FEB4C939644080C1DE4" xlink:to="loc_us-gaap_CreditFacilityDomain_EEFE316DA55DD7BE1E03964408113C67" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DomesticLineOfCreditMember" xlink:label="loc_us-gaap_DomesticLineOfCreditMember_8B78F17E4F6C5DCA2424964408E570ED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_EEFE316DA55DD7BE1E03964408113C67" xlink:to="loc_us-gaap_DomesticLineOfCreditMember_8B78F17E4F6C5DCA2424964408E570ED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsByNatureAxis" xlink:label="loc_us-gaap_GuaranteeObligationsByNatureAxis_6DF954953798E703CBB2960F7BD1A506" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_6C906377D0B0186E1027960F7BD144B9" xlink:to="loc_us-gaap_GuaranteeObligationsByNatureAxis_6DF954953798E703CBB2960F7BD1A506" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsNatureDomain" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_B4D5EC4A7026D82193A7960F7BD16EC3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_6DF954953798E703CBB2960F7BD1A506" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_B4D5EC4A7026D82193A7960F7BD16EC3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsNatureDomain" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_B4D5EC4A7026D82193A7960F7BD16EC3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_6DF954953798E703CBB2960F7BD1A506" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_B4D5EC4A7026D82193A7960F7BD16EC3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FinancialStandbyLetterOfCreditMember" xlink:label="loc_us-gaap_FinancialStandbyLetterOfCreditMember_D4220B3466B9351D0C64960F7BD11B91" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_B4D5EC4A7026D82193A7960F7BD16EC3" xlink:to="loc_us-gaap_FinancialStandbyLetterOfCreditMember_D4220B3466B9351D0C64960F7BD11B91" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SuretyBondMember" xlink:label="loc_us-gaap_SuretyBondMember_6857A0EF3A72E27588D2960F7BD1D46D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_B4D5EC4A7026D82193A7960F7BD16EC3" xlink:to="loc_us-gaap_SuretyBondMember_6857A0EF3A72E27588D2960F7BD1D46D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_0492DF3DDB340FD63F56960F7BD1D17B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_6C906377D0B0186E1027960F7BD144B9" xlink:to="loc_us-gaap_DebtInstrumentAxis_0492DF3DDB340FD63F56960F7BD1D17B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7CC2EA846F104048C931960F7BD17545_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_0492DF3DDB340FD63F56960F7BD1D17B" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7CC2EA846F104048C931960F7BD17545_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7CC2EA846F104048C931960F7BD17545" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_0492DF3DDB340FD63F56960F7BD1D17B" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7CC2EA846F104048C931960F7BD17545" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_FacilityAgreementMember" xlink:label="loc_powl_FacilityAgreementMember_628A3959025F0C1EAECB960F7BD2585A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7CC2EA846F104048C931960F7BD17545" xlink:to="loc_powl_FacilityAgreementMember_628A3959025F0C1EAECB960F7BD2585A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_56E892D281DF8ACAB0B5960F7BD299CC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGuaranteeObligationsTable_6C906377D0B0186E1027960F7BD144B9" xlink:to="loc_dei_LegalEntityAxis_56E892D281DF8ACAB0B5960F7BD299CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_2A8C55EB5737C2FBBE79960F7BD26DB3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_56E892D281DF8ACAB0B5960F7BD299CC" xlink:to="loc_dei_EntityDomain_2A8C55EB5737C2FBBE79960F7BD26DB3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_2A8C55EB5737C2FBBE79960F7BD26DB3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_56E892D281DF8ACAB0B5960F7BD299CC" xlink:to="loc_dei_EntityDomain_2A8C55EB5737C2FBBE79960F7BD26DB3" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_PowellUKLimitedMember" xlink:label="loc_powl_PowellUKLimitedMember_9C3024E577151A360D20960F7BD253B7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2A8C55EB5737C2FBBE79960F7BD26DB3" xlink:to="loc_powl_PowellUKLimitedMember_9C3024E577151A360D20960F7BD253B7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsCurrentCarryingValue" xlink:label="loc_us-gaap_GuaranteeObligationsCurrentCarryingValue_4EA9FB91FBF2DA270DC9960F7BD2FF68" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:to="loc_us-gaap_GuaranteeObligationsCurrentCarryingValue_4EA9FB91FBF2DA270DC9960F7BD2FF68" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_CommitmentsAndContingenciesAdditionalBondingCapacity" xlink:label="loc_powl_CommitmentsAndContingenciesAdditionalBondingCapacity_BCFD6FB8E43A10CF56C6960F7BD26869" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:to="loc_powl_CommitmentsAndContingenciesAdditionalBondingCapacity_BCFD6FB8E43A10CF56C6960F7BD26869" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_A76953DDAA55EE28C8C2960F7BD2CA86" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_A76953DDAA55EE28C8C2960F7BD2CA86" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_82DB8A95A6EDC5A60AAE960F7BD25A2F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_82DB8A95A6EDC5A60AAE960F7BD25A2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingencyLossInPeriod" xlink:label="loc_us-gaap_LossContingencyLossInPeriod_28C7DEAE2A4351A931B9960F7BD2F269" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:to="loc_us-gaap_LossContingencyLossInPeriod_28C7DEAE2A4351A931B9960F7BD2F269" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_LossContingencyProbableLossInPeriod" xlink:label="loc_powl_LossContingencyProbableLossInPeriod_E5A09FC1CFDF53A5986D960F7BD29CAF" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:to="loc_powl_LossContingencyProbableLossInPeriod_E5A09FC1CFDF53A5986D960F7BD29CAF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_9340A78EB4474103C1F0960F7BD3F702" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsLineItems_B30995AA51255F8A9B15960F7BD24DA1" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_9340A78EB4474103C1F0960F7BD3F702" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/CondensedConsolidatedBalanceSheetsUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/CondensedConsolidatedBalanceSheetsUnauditedParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/CondensedConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/CondensedConsolidatedStatementsOfComprehensiveIncomeLossUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/CondensedConsolidatedStatementsOfOperationsUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccounts" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsActivityInAllowanceForDoubtfulAccountsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsActivityInProductWarrantyAccrualDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsComponentsOfInventoriesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsCostAndEstimatedEarningsOnUncompletedContractsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/DetailOfSelectedBalanceSheetAccountsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/DocumentAndEntityInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/EarningsPerShare" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/EarningsPerShareDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/EarningsPerShareTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/FairValueMeasurements" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/FairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7F3C2AD3EA2298BE2FA166C5BBBEC1D8" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_65F9014BD38F05AA557C66C5BBBED06F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7F3C2AD3EA2298BE2FA166C5BBBEC1D8" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_65F9014BD38F05AA557C66C5BBBED06F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8D51DFC2B87384F6E91166C5BBBE688E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_65F9014BD38F05AA557C66C5BBBED06F" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8D51DFC2B87384F6E91166C5BBBE688E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_FA6ECD2923C9CCF288A966C5BBBEC6F4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8D51DFC2B87384F6E91166C5BBBE688E" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_FA6ECD2923C9CCF288A966C5BBBEC6F4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_FA6ECD2923C9CCF288A966C5BBBEC6F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8D51DFC2B87384F6E91166C5BBBE688E" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_FA6ECD2923C9CCF288A966C5BBBEC6F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_642E66FE931D588F0DC366C5BBBE8590" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_FA6ECD2923C9CCF288A966C5BBBEC6F4" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_642E66FE931D588F0DC366C5BBBE8590" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_BDD97C2C481E5B8C34B566C5BBBE49E2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_FA6ECD2923C9CCF288A966C5BBBEC6F4" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_BDD97C2C481E5B8C34B566C5BBBE49E2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_536933A6CF8C4AB2B48F66C5BBBE2A6A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_FA6ECD2923C9CCF288A966C5BBBEC6F4" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_536933A6CF8C4AB2B48F66C5BBBE2A6A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_D26E9DF38AD8C25697DA66C5BBBEB460" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7F3C2AD3EA2298BE2FA166C5BBBEC1D8" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_D26E9DF38AD8C25697DA66C5BBBEB460" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_230F21078CE670E1888066C5BBBED012" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_D26E9DF38AD8C25697DA66C5BBBEB460" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_230F21078CE670E1888066C5BBBED012" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_9C185D62670C21495CA166C5BBBE0A48" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_D26E9DF38AD8C25697DA66C5BBBEB460" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_9C185D62670C21495CA166C5BBBE0A48" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_RestrictedCashFairValueDisclosure" xlink:label="loc_powl_RestrictedCashFairValueDisclosure_EA1CA1E1D7F61013F49B66C5BDD15742" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_D26E9DF38AD8C25697DA66C5BBBEB460" xlink:to="loc_powl_RestrictedCashFairValueDisclosure_EA1CA1E1D7F61013F49B66C5BDD15742" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_DeferredCompensationPlanAssetsFairValueDisclosure" xlink:label="loc_powl_DeferredCompensationPlanAssetsFairValueDisclosure_4FA4B14D7D39E96760EE66C5BBBE0E67" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_D26E9DF38AD8C25697DA66C5BBBEB460" xlink:to="loc_powl_DeferredCompensationPlanAssetsFairValueDisclosure_4FA4B14D7D39E96760EE66C5BBBE0E67" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7D00CD9A1693A95FDA7966C5BBBE5122" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7F3C2AD3EA2298BE2FA166C5BBBEC1D8" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7D00CD9A1693A95FDA7966C5BBBE5122" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent" xlink:label="loc_us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent_5E78274FA3C51B0317D066C5BBBE0C2A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_7D00CD9A1693A95FDA7966C5BBBE5122" xlink:to="loc_us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent_5E78274FA3C51B0317D066C5BBBE0C2A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/FairValueMeasurementsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/GoodwillAndIntangibleAssets" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/GoodwillAndIntangibleAssetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_D1C6BDFD9BB08B375B18960F7BF148CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_D1C6BDFD9BB08B375B18960F7BF148CA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_4EC27AD9A0F153B8A631960F7BF13D80" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_D1C6BDFD9BB08B375B18960F7BF148CA" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_4EC27AD9A0F153B8A631960F7BF13D80" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8EDD8DAB3E5C4B36B5D0960F7BF11A3A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_4EC27AD9A0F153B8A631960F7BF13D80" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8EDD8DAB3E5C4B36B5D0960F7BF11A3A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8EDD8DAB3E5C4B36B5D0960F7BF11A3A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_4EC27AD9A0F153B8A631960F7BF13D80" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8EDD8DAB3E5C4B36B5D0960F7BF11A3A" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_SupplyAgreementMember" xlink:label="loc_powl_SupplyAgreementMember_FBAF6BADB7520C1D05A5960F7BF1240D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_8EDD8DAB3E5C4B36B5D0960F7BF11A3A" xlink:to="loc_powl_SupplyAgreementMember_FBAF6BADB7520C1D05A5960F7BF1240D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_216EB559E3747D4832D8960F7BF15723" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_D1C6BDFD9BB08B375B18960F7BF148CA" xlink:to="loc_dei_LegalEntityAxis_216EB559E3747D4832D8960F7BF15723" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_790900906EF45EA6A594960F7BF1FFEE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_216EB559E3747D4832D8960F7BF15723" xlink:to="loc_dei_EntityDomain_790900906EF45EA6A594960F7BF1FFEE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_790900906EF45EA6A594960F7BF1FFEE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_216EB559E3747D4832D8960F7BF15723" xlink:to="loc_dei_EntityDomain_790900906EF45EA6A594960F7BF1FFEE" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_GeneralElectricCompanyMember" xlink:label="loc_powl_GeneralElectricCompanyMember_E7CE390876B10771C890960F7BF18580" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_790900906EF45EA6A594960F7BF1FFEE" xlink:to="loc_powl_GeneralElectricCompanyMember_E7CE390876B10771C890960F7BF18580" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_D7F23DBD49E471BF2FAB960F7BF1B0C5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_D1C6BDFD9BB08B375B18960F7BF148CA" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_D7F23DBD49E471BF2FAB960F7BF1B0C5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_327A552A447CA25F4315960F7BF283BE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_D7F23DBD49E471BF2FAB960F7BF1B0C5" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_327A552A447CA25F4315960F7BF283BE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_327A552A447CA25F4315960F7BF283BE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_D7F23DBD49E471BF2FAB960F7BF1B0C5" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_327A552A447CA25F4315960F7BF283BE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherIncomeMember" xlink:label="loc_us-gaap_OtherIncomeMember_6125E49D7A8E4734DC70960F7BF291E3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_327A552A447CA25F4315960F7BF283BE" xlink:to="loc_us-gaap_OtherIncomeMember_6125E49D7A8E4734DC70960F7BF291E3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_DB6C81716ECC8085295C960F7BF23B85" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_DB6C81716ECC8085295C960F7BF23B85" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_6DA5BB90C97711D384B9960F7BF29BB9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_6DA5BB90C97711D384B9960F7BF29BB9" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_CashReceivedFromAmendedSupplyAgreement" xlink:label="loc_powl_CashReceivedFromAmendedSupplyAgreement_56025198D0D0B367A31E960F7BF26F6B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_powl_CashReceivedFromAmendedSupplyAgreement_56025198D0D0B367A31E960F7BF26F6B" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_AdditionalAmountPaidOnExecutionOfAgreement" xlink:label="loc_powl_AdditionalAmountPaidOnExecutionOfAgreement_19D0F6CFE95886710E76960F7BF2D2D4" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_powl_AdditionalAmountPaidOnExecutionOfAgreement_19D0F6CFE95886710E76960F7BF2D2D4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_6E17CD305C4063182880960F7BF20CD5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_6E17CD305C4063182880960F7BF20CD5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherAssetsCurrent" xlink:label="loc_us-gaap_OtherAssetsCurrent_099FE46AB5F206D92F65960F7BF28E81" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_us-gaap_OtherAssetsCurrent_099FE46AB5F206D92F65960F7BF28E81" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredRevenueAndCredits" xlink:label="loc_us-gaap_DeferredRevenueAndCredits_C56766046FCCDCDDCC4C960F7BF25814" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_us-gaap_DeferredRevenueAndCredits_C56766046FCCDCDDCC4C960F7BF25814" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_9103281B366FC48DE65E960F7BF23550" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_9103281B366FC48DE65E960F7BF23550" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_3A9D392CDC46F350E6E4960F7BF2806C" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_E0AE6473C83B63F4DF77960F7BF216BB" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_3A9D392CDC46F350E6E4960F7BF2806C" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/GoodwillAndIntangibleAssetsScheduleOfIntangibleAssetsSubjectToAmortizationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_629D1AB9AF205C0F8E707EEFE9F60A72" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_EF5C0EAF3D7259BB9DDBB2C4C0DB0212" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_629D1AB9AF205C0F8E707EEFE9F60A72" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_EF5C0EAF3D7259BB9DDBB2C4C0DB0212" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1911339D1B1958839E6EDC766B0ED77E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_EF5C0EAF3D7259BB9DDBB2C4C0DB0212" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1911339D1B1958839E6EDC766B0ED77E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_479B33742C7BF39EEFA6A6053D8BA282_27F9CFF852D25E0A88882277ACD012C3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1911339D1B1958839E6EDC766B0ED77E" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_479B33742C7BF39EEFA6A6053D8BA282_27F9CFF852D25E0A88882277ACD012C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_527D1A11503054929D2AFF303CF462B9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1911339D1B1958839E6EDC766B0ED77E" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_527D1A11503054929D2AFF303CF462B9" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_PurchasedTechnologyMember" xlink:label="loc_powl_PurchasedTechnologyMember_E0631203D3365061981FD7C702890B79" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_527D1A11503054929D2AFF303CF462B9" xlink:to="loc_powl_PurchasedTechnologyMember_E0631203D3365061981FD7C702890B79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_CC506156BF585E778ED77BCB5B661AB1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_629D1AB9AF205C0F8E707EEFE9F60A72" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_CC506156BF585E778ED77BCB5B661AB1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_7704B0A498545B1FAE2332D447680E97" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_629D1AB9AF205C0F8E707EEFE9F60A72" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_7704B0A498545B1FAE2332D447680E97" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_EFF113C9C31B5DA98E734740E28D10C6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_629D1AB9AF205C0F8E707EEFE9F60A72" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_EFF113C9C31B5DA98E734740E28D10C6" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/GoodwillAndIntangibleAssetsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/IncomeTaxes" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/IncomeTaxesScheduleOfEffectiveTaxRateDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/IncomeTaxesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/LongTermDebt" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/LongTermDebtComponentsOfLongTermDebtDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/LongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_EA2BC247719BF03E9773B4A6A49F1866" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_EA2BC247719BF03E9773B4A6A49F1866" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsByNatureAxis" xlink:label="loc_us-gaap_GuaranteeObligationsByNatureAxis_DD6A2208AE668F593160B4A6A49F86D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_EA2BC247719BF03E9773B4A6A49F1866" xlink:to="loc_us-gaap_GuaranteeObligationsByNatureAxis_DD6A2208AE668F593160B4A6A49F86D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsNatureDomain" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_1B75E9736D871CFE3B00B4A6A49F983D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_DD6A2208AE668F593160B4A6A49F86D8" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_1B75E9736D871CFE3B00B4A6A49F983D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsNatureDomain" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_1B75E9736D871CFE3B00B4A6A49F983D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_DD6A2208AE668F593160B4A6A49F86D8" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_1B75E9736D871CFE3B00B4A6A49F983D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FinancialStandbyLetterOfCreditMember" xlink:label="loc_us-gaap_FinancialStandbyLetterOfCreditMember_195A8036F38AB1F3FD5EB4A6A49FCC95" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_1B75E9736D871CFE3B00B4A6A49F983D" xlink:to="loc_us-gaap_FinancialStandbyLetterOfCreditMember_195A8036F38AB1F3FD5EB4A6A49FCC95" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_1130C84945B159EA59F6B4A6A49FA60A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_EA2BC247719BF03E9773B4A6A49F1866" xlink:to="loc_us-gaap_DebtInstrumentAxis_1130C84945B159EA59F6B4A6A49FA60A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_12A6449A09A96CC7CFACB4A6A49FCA36_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1130C84945B159EA59F6B4A6A49FA60A" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_12A6449A09A96CC7CFACB4A6A49FCA36_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_12A6449A09A96CC7CFACB4A6A49FCA36" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1130C84945B159EA59F6B4A6A49FA60A" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_12A6449A09A96CC7CFACB4A6A49FCA36" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_TheThirdAmendmentMember" xlink:label="loc_powl_TheThirdAmendmentMember_84A6EBD44592E74648EAB4A6A49F408A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_12A6449A09A96CC7CFACB4A6A49FCA36" xlink:to="loc_powl_TheThirdAmendmentMember_84A6EBD44592E74648EAB4A6A49F408A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_56DB2CBB18388709F527B4A6A4A01DE7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_EA2BC247719BF03E9773B4A6A49F1866" xlink:to="loc_us-gaap_CreditFacilityAxis_56DB2CBB18388709F527B4A6A4A01DE7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_070FD306A4179331434FB4A6A4A01545_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_56DB2CBB18388709F527B4A6A4A01DE7" xlink:to="loc_us-gaap_CreditFacilityDomain_070FD306A4179331434FB4A6A4A01545_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_070FD306A4179331434FB4A6A4A01545" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_56DB2CBB18388709F527B4A6A4A01DE7" xlink:to="loc_us-gaap_CreditFacilityDomain_070FD306A4179331434FB4A6A4A01545" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DomesticLineOfCreditMember" xlink:label="loc_us-gaap_DomesticLineOfCreditMember_34BD2BB7753DA151C568B4A6A4A0A9FE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_070FD306A4179331434FB4A6A4A01545" xlink:to="loc_us-gaap_DomesticLineOfCreditMember_34BD2BB7753DA151C568B4A6A4A0A9FE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignLineOfCreditMember" xlink:label="loc_us-gaap_ForeignLineOfCreditMember_FA88CCD991E9D4EDFB59B4A6A4A06D64" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_070FD306A4179331434FB4A6A4A01545" xlink:to="loc_us-gaap_ForeignLineOfCreditMember_FA88CCD991E9D4EDFB59B4A6A4A06D64" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_IndustrialDevelopmentRevenueBondsMember" xlink:label="loc_powl_IndustrialDevelopmentRevenueBondsMember_CB135FD2DE9841B24953B4A6A4A0D6CF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_070FD306A4179331434FB4A6A4A01545" xlink:to="loc_powl_IndustrialDevelopmentRevenueBondsMember_CB135FD2DE9841B24953B4A6A4A0D6CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="loc_us-gaap_VariableRateAxis_1293CE063F81F20BF9DAB4A6A4A0C192" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_EA2BC247719BF03E9773B4A6A49F1866" xlink:to="loc_us-gaap_VariableRateAxis_1293CE063F81F20BF9DAB4A6A4A0C192" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_9B719DA5760F99184CD2B4A6A4A0282A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_1293CE063F81F20BF9DAB4A6A4A0C192" xlink:to="loc_us-gaap_VariableRateDomain_9B719DA5760F99184CD2B4A6A4A0282A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_9B719DA5760F99184CD2B4A6A4A0282A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_1293CE063F81F20BF9DAB4A6A4A0C192" xlink:to="loc_us-gaap_VariableRateDomain_9B719DA5760F99184CD2B4A6A4A0282A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FederalFundsEffectiveSwapRateMember" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_F427844CF1C148C88EB5B4A6A4A03401" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_9B719DA5760F99184CD2B4A6A4A0282A" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_F427844CF1C148C88EB5B4A6A4A03401" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EurodollarMember" xlink:label="loc_us-gaap_EurodollarMember_03CDEE10A7AC0A1C5F1DB4A6A4A08FE5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_9B719DA5760F99184CD2B4A6A4A0282A" xlink:to="loc_us-gaap_EurodollarMember_03CDEE10A7AC0A1C5F1DB4A6A4A08FE5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_39DF4F4756B01D77CEE7B4A6A4A09E8F" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_EA2BC247719BF03E9773B4A6A49F1866" xlink:to="loc_us-gaap_RangeAxis_39DF4F4756B01D77CEE7B4A6A4A09E8F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_1BC2ECA291532C6545D0B4A6A4A003D8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_39DF4F4756B01D77CEE7B4A6A4A09E8F" xlink:to="loc_us-gaap_RangeMember_1BC2ECA291532C6545D0B4A6A4A003D8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_1BC2ECA291532C6545D0B4A6A4A003D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_39DF4F4756B01D77CEE7B4A6A4A09E8F" xlink:to="loc_us-gaap_RangeMember_1BC2ECA291532C6545D0B4A6A4A003D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_2F15C5F3993B6B73A403B4A6A4A03CDD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_1BC2ECA291532C6545D0B4A6A4A003D8" xlink:to="loc_us-gaap_MaximumMember_2F15C5F3993B6B73A403B4A6A4A03CDD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_6A12785D07FD18A736BBB4A6A4A0F8F5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_6A12785D07FD18A736BBB4A6A4A0F8F5" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_LineofCreditFacilityCollateralFeePercentage" xlink:label="loc_powl_LineofCreditFacilityCollateralFeePercentage_9D509DAE4C0ADC7B883DB4A6A4A14116" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_powl_LineofCreditFacilityCollateralFeePercentage_9D509DAE4C0ADC7B883DB4A6A4A14116" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_65C87EFF155EDFA68A1BB4A6A4A144AE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_65C87EFF155EDFA68A1BB4A6A4A144AE" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_LineOfCreditFacilityCovenantTermsCashCollateralPercentOfDebtOutstanding" xlink:label="loc_powl_LineOfCreditFacilityCovenantTermsCashCollateralPercentOfDebtOutstanding_F8DE2FD43486483EF45BB4A6A4A1319F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_powl_LineOfCreditFacilityCovenantTermsCashCollateralPercentOfDebtOutstanding_F8DE2FD43486483EF45BB4A6A4A1319F" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_LineOfCreditFacilityCovenantTermsConsolidatedCurrentRatio" xlink:label="loc_powl_LineOfCreditFacilityCovenantTermsConsolidatedCurrentRatio_D78605609AD04289CFB6B4A6A4A10FD5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_powl_LineOfCreditFacilityCovenantTermsConsolidatedCurrentRatio_D78605609AD04289CFB6B4A6A4A10FD5" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_LineOfCreditFacilityCollateralAmount" xlink:label="loc_powl_LineOfCreditFacilityCollateralAmount_359E709DE59E4A15B036B4A6A4A1D86F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_powl_LineOfCreditFacilityCollateralAmount_359E709DE59E4A15B036B4A6A4A1D86F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:label="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_D2EE17D068D51E892118B4A6A4A15A8B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis_D2EE17D068D51E892118B4A6A4A15A8B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_7C672A248C08A0DCF436B4A6A4A14292" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_7C672A248C08A0DCF436B4A6A4A14292" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsCurrentCarryingValue" xlink:label="loc_us-gaap_GuaranteeObligationsCurrentCarryingValue_00A88120E8F462C4D46BB4A6A4A197E4" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_GuaranteeObligationsCurrentCarryingValue_00A88120E8F462C4D46BB4A6A4A197E4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCredit" xlink:label="loc_us-gaap_LineOfCredit_12A5044DED61516DD21EB4A6A4A1B4D5" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_LineOfCredit_12A5044DED61516DD21EB4A6A4A1B4D5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_A155F8365BA8A02AFC39B4A6A4A184A2" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_A155F8365BA8A02AFC39B4A6A4A184A2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityExpirationDate1" xlink:label="loc_us-gaap_LineOfCreditFacilityExpirationDate1_A5662D32517180CBB612B4A6A4A16641" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_LineOfCreditFacilityExpirationDate1_A5662D32517180CBB612B4A6A4A16641" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_PercentageOfDomesticCapitalStockPledgedAsCollateralForCreditFacility" xlink:label="loc_powl_PercentageOfDomesticCapitalStockPledgedAsCollateralForCreditFacility_FB3EE403E34CE257753EB4A6A4A1EC54" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_powl_PercentageOfDomesticCapitalStockPledgedAsCollateralForCreditFacility_FB3EE403E34CE257753EB4A6A4A1EC54" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_PercentageOfNonDomesticCapitalStockPledgedAsCollateralForCreditFacility" xlink:label="loc_powl_PercentageOfNonDomesticCapitalStockPledgedAsCollateralForCreditFacility_A2B6978CD383BE43BA7CB4A6A4A1D90A" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_powl_PercentageOfNonDomesticCapitalStockPledgedAsCollateralForCreditFacility_A2B6978CD383BE43BA7CB4A6A4A1D90A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_2462B355475DD68FE59CB4A6A4A14F08" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_2462B355475DD68FE59CB4A6A4A14F08" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_3D813BA70BC19B883996B4A6A4A14116" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_3D813BA70BC19B883996B4A6A4A14116" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentAnnualPrincipalPayment" xlink:label="loc_us-gaap_DebtInstrumentAnnualPrincipalPayment_040F489F1C715CE9CAE7B4A6A4A14429" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_DebtInstrumentAnnualPrincipalPayment_040F489F1C715CE9CAE7B4A6A4A14429" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_778FA2C300A6BC1B81F7B4A6A4A19D2E" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_227EAD41ADCBA68BAEEBB4A6A4A0881E" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_778FA2C300A6BC1B81F7B4A6A4A19D2E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/LongTermDebtTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/OverviewAndSummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/OverviewAndSummaryOfSignificantAccountingPoliciesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ChangeInAccountingEstimateLineItems" xlink:label="loc_us-gaap_ChangeInAccountingEstimateLineItems_9429E772753D7FE893E0C3EB2095FD5A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfChangeInAccountingEstimateTable" xlink:label="loc_us-gaap_ScheduleOfChangeInAccountingEstimateTable_B326F4BDD2D69E1F386BC3EB20955A84" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ChangeInAccountingEstimateLineItems_9429E772753D7FE893E0C3EB2095FD5A" xlink:to="loc_us-gaap_ScheduleOfChangeInAccountingEstimateTable_B326F4BDD2D69E1F386BC3EB20955A84" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ChangeInAccountingEstimateByTypeAxis" xlink:label="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_3840C9FA7A85B967A114C3EB209527AD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfChangeInAccountingEstimateTable_B326F4BDD2D69E1F386BC3EB20955A84" xlink:to="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_3840C9FA7A85B967A114C3EB209527AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_361BD7527585101A3FF8C3EB2095C91B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_3840C9FA7A85B967A114C3EB209527AD" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_361BD7527585101A3FF8C3EB2095C91B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_361BD7527585101A3FF8C3EB2095C91B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_3840C9FA7A85B967A114C3EB209527AD" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_361BD7527585101A3FF8C3EB2095C91B" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_ChangeinContractRevenueEstimatesMember" xlink:label="loc_powl_ChangeinContractRevenueEstimatesMember_F6B1163C5687308C5D7FC3EB2095CA88" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_361BD7527585101A3FF8C3EB2095C91B" xlink:to="loc_powl_ChangeinContractRevenueEstimatesMember_F6B1163C5687308C5D7FC3EB2095CA88" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_D0654FEEEC70E2775419C3EB2095FB17" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingEstimateLineItems_9429E772753D7FE893E0C3EB2095FD5A" xlink:to="loc_us-gaap_OperatingIncomeLoss_D0654FEEEC70E2775419C3EB2095FB17" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/OverviewAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/RestructuringAndSeparationCosts" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/RestructuringAndSeparationCostsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestructuringCostAndReserveLineItems" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_53CBBE7356B48591418A960F7B94AB3A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_73B8FC53FFDE3C05A83D960F7B92CEDE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_53CBBE7356B48591418A960F7B94AB3A" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_73B8FC53FFDE3C05A83D960F7B92CEDE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestructuringCostAndReserveAxis" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_47C1D38143DDE9F04B2B960F7B93EC36" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_73B8FC53FFDE3C05A83D960F7B92CEDE" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_47C1D38143DDE9F04B2B960F7B93EC36" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TypeOfRestructuringDomain" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_42A55898445490D6644F960F7B93E94C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_47C1D38143DDE9F04B2B960F7B93EC36" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_42A55898445490D6644F960F7B93E94C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TypeOfRestructuringDomain" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_42A55898445490D6644F960F7B93E94C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_47C1D38143DDE9F04B2B960F7B93EC36" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_42A55898445490D6644F960F7B93E94C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeSeveranceMember" xlink:label="loc_us-gaap_EmployeeSeveranceMember_B94A31BA676348D34BC7965159655E28" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_42A55898445490D6644F960F7B93E94C" xlink:to="loc_us-gaap_EmployeeSeveranceMember_B94A31BA676348D34BC7965159655E28" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContractTerminationMember" xlink:label="loc_us-gaap_ContractTerminationMember_83D35473F8D539F15A4F960F7B9405EF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_42A55898445490D6644F960F7B93E94C" xlink:to="loc_us-gaap_ContractTerminationMember_83D35473F8D539F15A4F960F7B9405EF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestructuringCharges" xlink:label="loc_us-gaap_RestructuringCharges_C2A61DF15978B63363EC960F7B9429F1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_53CBBE7356B48591418A960F7B94AB3A" xlink:to="loc_us-gaap_RestructuringCharges_C2A61DF15978B63363EC960F7B9429F1" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/StockBasedCompensation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2167FD545F3DF813EC64C3EB1FD9FE44" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2167FD545F3DF813EC64C3EB1FD9FE44" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_06C04CA865244DEF32BEC3EB1FD9D5F8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2167FD545F3DF813EC64C3EB1FD9FE44" xlink:to="loc_us-gaap_AwardTypeAxis_06C04CA865244DEF32BEC3EB1FD9D5F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_AAF95FF946461AE4690DC3EB1FD94D6E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_06C04CA865244DEF32BEC3EB1FD9D5F8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_AAF95FF946461AE4690DC3EB1FD94D6E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_AAF95FF946461AE4690DC3EB1FD94D6E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_06C04CA865244DEF32BEC3EB1FD9D5F8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_AAF95FF946461AE4690DC3EB1FD94D6E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_269D3D2A3E4F6EFFAB1AC3EB1FD9ED2F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_AAF95FF946461AE4690DC3EB1FD94D6E" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_269D3D2A3E4F6EFFAB1AC3EB1FD9ED2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_879D654C1516C1AABB67C3EB1FDA9A71" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_AAF95FF946461AE4690DC3EB1FD94D6E" xlink:to="loc_us-gaap_RestrictedStockMember_879D654C1516C1AABB67C3EB1FDA9A71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_8725508DF4C3BAC7B342C3EB1FDA8A09" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2167FD545F3DF813EC64C3EB1FD9FE44" xlink:to="loc_us-gaap_StatementClassOfStockAxis_8725508DF4C3BAC7B342C3EB1FDA8A09" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_1BE8874DCF99B242042AC3EB1FDAB8E1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8725508DF4C3BAC7B342C3EB1FDA8A09" xlink:to="loc_us-gaap_ClassOfStockDomain_1BE8874DCF99B242042AC3EB1FDAB8E1_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_1BE8874DCF99B242042AC3EB1FDAB8E1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8725508DF4C3BAC7B342C3EB1FDA8A09" xlink:to="loc_us-gaap_ClassOfStockDomain_1BE8874DCF99B242042AC3EB1FDAB8E1" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_TimeBasedRestrictedStockUnitMember" xlink:label="loc_powl_TimeBasedRestrictedStockUnitMember_0D0E15E8643CC7C74F6DC3EB1FDA9257" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1BE8874DCF99B242042AC3EB1FDAB8E1" xlink:to="loc_powl_TimeBasedRestrictedStockUnitMember_0D0E15E8643CC7C74F6DC3EB1FDA9257" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_PerformanceBasedRestrictedStockUnitMember" xlink:label="loc_powl_PerformanceBasedRestrictedStockUnitMember_4D9B014D16825037832EC3EB1FDAD84F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1BE8874DCF99B242042AC3EB1FDAB8E1" xlink:to="loc_powl_PerformanceBasedRestrictedStockUnitMember_4D9B014D16825037832EC3EB1FDAD84F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VestingAxis" xlink:label="loc_us-gaap_VestingAxis_9B985C8939F1FFEA6CA5C3EB1FDA2D71" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2167FD545F3DF813EC64C3EB1FD9FE44" xlink:to="loc_us-gaap_VestingAxis_9B985C8939F1FFEA6CA5C3EB1FDA2D71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_668333BFA7C074E54C26C3EB1FDAFF88_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_9B985C8939F1FFEA6CA5C3EB1FDA2D71" xlink:to="loc_us-gaap_VestingDomain_668333BFA7C074E54C26C3EB1FDAFF88_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_668333BFA7C074E54C26C3EB1FDAFF88" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_9B985C8939F1FFEA6CA5C3EB1FDA2D71" xlink:to="loc_us-gaap_VestingDomain_668333BFA7C074E54C26C3EB1FDAFF88" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_2ED2F8321E9D03EB1AB4C3EB1FDA0E4F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_668333BFA7C074E54C26C3EB1FDAFF88" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_2ED2F8321E9D03EB1AB4C3EB1FDA0E4F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C76A10BA7B528149A2ADC3EB1FDAB5EA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_668333BFA7C074E54C26C3EB1FDAFF88" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_C76A10BA7B528149A2ADC3EB1FDAB5EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_1CC227237E12F246619CC3EB1FDA0E8E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_1CC227237E12F246619CC3EB1FDA0E8E" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentOfActualAmountOfUnitsEarned" xlink:label="loc_powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentOfActualAmountOfUnitsEarned_C71B2D5740BC01A7ACEDC3EB1FDAD796" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentOfActualAmountOfUnitsEarned_C71B2D5740BC01A7ACEDC3EB1FDAD796" xlink:type="arc" />
    <link:loc xlink:href="powl-20170630.xsd#powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetRSUGrantedRange" xlink:label="loc_powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetRSUGrantedRange_5E98AEBD6843E643466FC3EB1FDA6A61" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_powl_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetRSUGrantedRange_5E98AEBD6843E643466FC3EB1FDA6A61" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_B0534C625A3A2332AD64C3EB1FDA38C8" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_B0534C625A3A2332AD64C3EB1FDA38C8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_9912A73F23D87CD742A7C3EB1FDAE69F" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_9912A73F23D87CD742A7C3EB1FDAE69F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_E1A13D40328BF5744D27C3EB1FDAACF5" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_E1A13D40328BF5744D27C3EB1FDAACF5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_FEC8465C641DF522527FC3F92EB05004" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_FEC8465C641DF522527FC3F92EB05004" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="loc_us-gaap_SharesIssuedPricePerShare_6791280C6EAF3A9C4266C3EB1FDAEC8B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8955F4AE42EE20A8697BC3EB1FDAEDF9" xlink:to="loc_us-gaap_SharesIssuedPricePerShare_6791280C6EAF3A9C4266C3EB1FDAEC8B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/StockBasedCompensationScheduleOfRestrictedStockUnitsActivityDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_329D6890864389317CB9960F7BBD856B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4BA59293D8CF791EE642960F7BBD150D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_329D6890864389317CB9960F7BBD856B" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4BA59293D8CF791EE642960F7BBD150D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_00BFC33DDF6FC3F9EDCE960F7BBD88A4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4BA59293D8CF791EE642960F7BBD150D" xlink:to="loc_us-gaap_AwardTypeAxis_00BFC33DDF6FC3F9EDCE960F7BBD88A4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8081FC9136240FBA27D0960F7BBD8322_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_00BFC33DDF6FC3F9EDCE960F7BBD88A4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8081FC9136240FBA27D0960F7BBD8322_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8081FC9136240FBA27D0960F7BBD8322" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_00BFC33DDF6FC3F9EDCE960F7BBD88A4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8081FC9136240FBA27D0960F7BBD8322" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_7348F4E50895BB746DAE960F7BBDA0A6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8081FC9136240FBA27D0960F7BBD8322" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_7348F4E50895BB746DAE960F7BBDA0A6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_32807A03ADD45B48F244960F7BBE5848" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_329D6890864389317CB9960F7BBD856B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_32807A03ADD45B48F244960F7BBE5848" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_8DAB55BE2A4BCD4929DA960F7BBE9F96" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_32807A03ADD45B48F244960F7BBE5848" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_8DAB55BE2A4BCD4929DA960F7BBE9F96" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_AFC199E4C27E2CCB433D960F7BBEF169" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_8DAB55BE2A4BCD4929DA960F7BBE9F96" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_AFC199E4C27E2CCB433D960F7BBEF169" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_934FECFDC0F82A6B1774960F7BBE32DC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_8DAB55BE2A4BCD4929DA960F7BBE9F96" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_934FECFDC0F82A6B1774960F7BBE32DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_36C393F3ECB8E54B79C3960F7BBE6779" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_8DAB55BE2A4BCD4929DA960F7BBE9F96" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_36C393F3ECB8E54B79C3960F7BBE6779" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_952DF97FF97D3585C3A6960F7BBE75F0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_32807A03ADD45B48F244960F7BBE5848" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_952DF97FF97D3585C3A6960F7BBE75F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_96CC77A75231271B8FAB960F7BBE67F6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_952DF97FF97D3585C3A6960F7BBE75F0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_96CC77A75231271B8FAB960F7BBE67F6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_403B92D51C0D8EEB0D5B960F7BBEBE15" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_952DF97FF97D3585C3A6960F7BBE75F0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_403B92D51C0D8EEB0D5B960F7BBEBE15" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_9E26C23018844510D131960F7BBE38C2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_952DF97FF97D3585C3A6960F7BBE75F0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_9E26C23018844510D131960F7BBE38C2" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.powellind.com/role/StockBasedCompensationTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/SubsequentEvents" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.powellind.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventLineItems" xlink:label="loc_us-gaap_SubsequentEventLineItems_75F785DB956F0DD29DD1C2F614F82EB6" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventTable" xlink:label="loc_us-gaap_SubsequentEventTable_08BFABF0725CEE22E299C2F614F7090D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_75F785DB956F0DD29DD1C2F614F82EB6" xlink:to="loc_us-gaap_SubsequentEventTable_08BFABF0725CEE22E299C2F614F7090D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_6CADC33874FB92DE52C9C2F614F7622A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_08BFABF0725CEE22E299C2F614F7090D" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_6CADC33874FB92DE52C9C2F614F7622A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_75E255F13DCFD6E418B9C2F614F7B0AD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_6CADC33874FB92DE52C9C2F614F7622A" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_75E255F13DCFD6E418B9C2F614F7B0AD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_75E255F13DCFD6E418B9C2F614F7B0AD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_6CADC33874FB92DE52C9C2F614F7622A" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_75E255F13DCFD6E418B9C2F614F7B0AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_5D2EE316A32B9ADC7711C2F614F8BC42" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_75E255F13DCFD6E418B9C2F614F7B0AD" xlink:to="loc_us-gaap_SubsequentEventMember_5D2EE316A32B9ADC7711C2F614F8BC42" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_7176028B9398D7BA2766C2F7BFA25AE5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_75F785DB956F0DD29DD1C2F614F82EB6" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_7176028B9398D7BA2766C2F7BFA25AE5" xlink:type="arc" />
  </link:definitionLink>
</link:linkbase>
