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Thread: What is the maximum amperage for #4 awg?

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    radstorm is offline Handyman
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    What is the maximum amperage for #4 awg?

    Hi all, I wish to know what the max amps for #4 awg copper wire is, not aluminum wire. Don't need a formula or anything, just how much it can carry. It will be a very short run, about 5 foot.. thanks

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    #4 copper cable, type TW and UF, not more than three in a raceway or cable at 140 degrees fahrenheit, 70 amp
    THHN. THWN, not more than three in a raceway or cable at 167 degrees, 85 amps
    THHN, THHW, XHHW not more than three in a raceway or cable at 194 degrees, 95 amps

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    radstorm is offline Handyman
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    Thank you, HayZee, that is just what I wanted. A simple and straight answer I did notice you mention THHN twice though..is that according to temps?

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    its the composition of the thermoplastic that makes up the insulation. if you strip off the nylon coating of type thhn and thwn, the basic wire is tw.
    THHN wire stands for Thermoplastic High Heat Resistant Nylon which is fully approved and stamped on the wire. THWN is a different approval that came long after THHN and South Wire used to make two separate wires with the different approvals. Now they just make one wire and dual rate it with both approvals. THWN stands for Thermoplastic Heat and Water Resistant Nylon which just adds that it's water resistant. So manufacturers just started to dual rate the THHN wire for both so that they didn't have to run two separate wires everytime.

    TFFN is only used on 16 and 18 awg wire. It stands for Thermoplastic Flexible Fixture Wire Nylon which is slightly different than the THHN wire because it has a lower heat resistance and it's not good for wet locations. You can't even get TFFN in any bigger awg sizes because they're all dual rated THHN and THWN.

    All of these types of wire fall under the electrical wire category and they're sometimes called building wire as well. The reason is electrical contractors use it and most of the time in buildings and homes. Romex is made with THHN conductors and a ground wire so that you can pull two or three wires through a home or building at once.

    Article Source: http://EzineArticles.com/2965021
    Last edited by HayZee518; 09-11-2011 at 11:11 AM. Reason: added info

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    Quote Originally Posted by HayZee518 View Post
    Romex is made with THHN conductors and a ground wire
    Is that why Romex is not allowed outdoors? If Romex was made with THWN conductors, it would be?
    Dan

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    romex is a jacketed assembly of two THHN, THWN wires and a bare or fiber wrapped ground wire. The external jacket is not sunlight resistant. the assembly is not recommended for outside use even though the inner conductors may be. type UF is recommended because the jacket is sunlight and moisture resistant and is listed as direct burial. the majority of the above quote is taken from the EZineArticles dot com.

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    radstorm is offline Handyman
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    Quote Originally Posted by HayZee518 View Post
    #4 copper cable, type TW and UF, not more than three in a raceway or cable at 140 degrees fahrenheit, 70 amp
    THHN. THWN, not more than three in a raceway or cable at 167 degrees, 85 amps
    THHN, THHW, XHHW not more than three in a raceway or cable at 194 degrees, 95 amps
    HayZee, would it be necessary to run this wire inside a conduit / raceway in my attic space? I am going about 15 feet in with it from outdoors. It will be pretty insulated (r-49) once I get done up there. I dont know how hot it actually gets up there in summer, never wanted to climb in there and find out..haha. According to what you say only 3 wires, would I need a separate conduit to run a ground wire back outdoors from the panel?

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    the ground wire is not considered a current carrying conductor, therefore it would not be considered into the calculation. a short run of what you are proposing, i.e. a sub-panel, two hots, a neutral and a ground in one conduit is ok.

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    Thanks HayZee, just want to do it right for safety purposes

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