-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 Gm3QJ8r7td197+StGxWS/KWB2Y7urlkAChalbprTeiaRPVYlGLcWWTk09nzbX+up
 GlHjDbV/DZQa7oRgzMJweg==

<SEC-DOCUMENT>0001140361-08-001621.txt : 20080118
<SEC-HEADER>0001140361-08-001621.hdr.sgml : 20080118
<ACCEPTANCE-DATETIME>20080118132327
ACCESSION NUMBER:		0001140361-08-001621
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080117
FILED AS OF DATE:		20080118
DATE AS OF CHANGE:		20080118

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MARSHALL DAVID
		CENTRAL INDEX KEY:			0001208444

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-26091
		FILM NUMBER:		08538185

	BUSINESS ADDRESS:	
		STREET 1:		997 WANDER WAY
		CITY:			INCLINE VILLAGE
		STATE:			NV
		ZIP:			89451
		BUSINESS PHONE:		7758331811

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TC PIPELINES LP
		CENTRAL INDEX KEY:			0001075607
		STANDARD INDUSTRIAL CLASSIFICATION:	NATURAL GAS TRANSMISSION [4922]
		IRS NUMBER:				522135448
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		110 TURNPIKE ROAD SUITE 203
		CITY:			WESTBOROUGH
		STATE:			MA
		ZIP:			01581
		BUSINESS PHONE:		5088717046

	MAIL ADDRESS:	
		STREET 1:		110 TURNPIKE RD
		STREET 2:		SUITE 203
		CITY:			WESTBOROUGH
		STATE:			MA
		ZIP:			01581
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-01-17</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001075607</issuerCik>
        <issuerName>TC PIPELINES LP</issuerName>
        <issuerTradingSymbol>TCLP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001208444</rptOwnerCik>
            <rptOwnerName>MARSHALL DAVID</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>110 TURNPIKE ROAD</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 203</rptOwnerStreet2>
            <rptOwnerCity>WESTBOROUGH</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01581</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Deferred Share Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2008-01-17</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>540</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common units representing limited p/ship interests</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>540</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>540</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">N/A - Upon termination of board service, Common Units representing limited partnership interests may be purchased on the open market on behalf of Mr. Marshall whereby he would receive Common Units in a number equal to the number of Deferred Share Units (&quot;DSUs&quot;) recorded in his account less any applicable withholdings. Alternatively, Mr. Marshall may elect to receive the value of his DSU entitlement in cash.  The cash payment amount shall be determined by multiplying the number of DSUs recorded in his account by the Fair Market Value of a Common Unit less any applicable withholdings.</footnote>
        <footnote id="F2">N/A - the DSUs are fully vested and are redeemable only following Mr. Marshall's termination of Board service.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Donald J. DeGrandis, Attorney for David Marshall</signatureName>
        <signatureDate>2008-01-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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