<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-07-27</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000038725</issuerCik>
        <issuerName>FRANKLIN ELECTRIC CO INC</issuerName>
        <issuerTradingSymbol>fele$210</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001228301</rptOwnerCik>
            <rptOwnerName>BROWN DAVID T</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>10858 EAST WILDCAT HILL RD.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SCOTTSDALE</rptOwnerCity>
            <rptOwnerState>AZ</rptOwnerState>
            <rptOwnerZipCode>85262</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>stock units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>31.79</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-07-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>47.18</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>47.18</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13591.79</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Pursuant to terms of the Nonemployee Directors' Deferred Compensation Plan approved by the board of directors on February 11, 2000 and amended and restated on April 28, 2006, Mr. Brown elected to receive his 2010 board of directors meeting fees in Franklin Electric Co., Inc. common stock, issuance of such shares deferred until he retires or otherwise leaves the board of directors (e.g. Stock Units).  On July 27, 2010 Mr. Brown was credited with 47.18 Stock Units for board meeting attendance.  At distribution, Mr. Roberts may elect pursuant to the terms of the Plan to receive his deferred compensation either in shares of Franklin common stock or in cash.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Angela M. Hughes, power of attorney for David T. Brown</signatureName>
        <signatureDate>2010-07-28</signatureDate>
    </ownerSignature>
</ownershipDocument>
