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Thread: what size wire for a 10kw heater

  1. #1
    Join Date
    Apr 2008
    Chalmette(New Orleans)

    what size wire for a 10kw heater

    10kw heater with a 60 amp breaker on board. I have been told 8 gauge but I know that 8 gauge does not handle 60 amps. but I can get away with the 60 because we can rate the OCPD at 125% which brings it up to around 52.7 amps the next highest breaker is 60 amps does this sound right. the reason I ask is I have the ac man telling me he will fail inspection for the wire but I have done this before and I have been told b y inspectors that this is okay does this sound right thanks Ryan

  2. #2
    Join Date
    Feb 2003
    Seattle, WA
    What is the voltage? Let me presume it is 240 volts, single phase. 10,000 watts divided by 240 is 41.6 amps. This is a "continuous load" so the wires must have an ampacity of 125% of 41.6 amps, which is 52 amps. I don't have my book handy, so I don't know if a #8 will suffice. I will say that you must have a wire with an ampacity of at least 52. You can use a 60 amp breaker on such a wire, since it is the next higher rated overcurrent device.

    Welcome to the forum.
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

  3. #3
    Join Date
    Jul 2004
    Louisville, Kentucky
    What type wiring method will be used, NM or conduit? If NM I would feel comfortable with #6 @ 55amp, on 60amp breaker. Table 310.16 60deg due to 334.80 Ampacity requirement.
    Last edited by 1793; 04-30-08 at 11:22 AM.
    My Boss is a Tyrant and my Employee is an Idiot.

  4. #4
    Join Date
    May 2005
    Richmond, Virginia
    I use #6 Cu NM for 10kw/240v, also. If it were 208v, you could get away with #8, but with a 50a breaker.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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