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    EMarkwick's Avatar
    EMarkwick Posts: 1, Reputation: 1
    New Member
    		  
    #1

    Dec 11, 2006, 11:32 AM
    Feeder size
    Hi,

    We are building a small art studio in our backyard. The power requirements for the building are:
    1 dedicated 110V 20 amp circuit for a small kiln
    1 dedicated 220V 20 amp circuit for a larger kiln
    1 dedicated 110V 15 amp circuit for small wall-mounted heater/ac unit
    1 dedicated 110V 15 amp circuit for a 2 gallon water heater
    1 general purpose 110V 15 amp circuit for lights and small plug-in electrical devices like radio, etc.

    So my question is this: What size wiring does the feed to studio need? The electrician has put a 70 Amp 220V breaker in the main panel for the feed (which I agree with), but he has run only #8 AWG wire. If I'm reading code correctly, the feed should be #4 AWG, shouldn't it?

    Thanks!
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
    Uber Member
    		  
    #2

    Dec 11, 2006, 03:59 PM
    The wire insulation is probably either THHN/THWN or XHHW, and I am assuming copper wire.

    The highest ampacity rating of both insulation types is 55 amps in the 90 Deg C column.

    This column can only be used if the terminals are rated 90 Deg C also. The terminals of the 70 amp breaker and the subpanel is most likely only rated at 75Deg C, and the wire is only rated at 50 amps.

    You are correct, the wire should be #4 copper THHN/THWN or XHHW.

    Did the electrician apply for a permit? And will this work be inspected?

    Either the breaker needs to be changed to a 50 amp breaker, or the wire changed to #4 copper.
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