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I purchased a Comfort Zone Heater. Model CZ230ER. It is a 7,500 watt 240V unit. This was installed with 8 gauge wire to a brand new 40 amp breaker. Once the heater has been running for a couple of minutes, it trips the breaker. The length of the run is less than 30 feet. It does run longer at the lower heat setting. I replaced both the heater and breaker with new ones, still trips breaker.

Should I reinstall with 6 gauge?

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  • Does the circuit breaker have a TEST button? To rephrase, did you pay $80 for it or only $12? Commented Feb 15, 2022 at 3:14
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    diy.stackexchange.com/questions/156492/…
    – Mazura
    Commented Feb 15, 2022 at 7:31
  • If you guys typed all that in, I'm sorry ;) - first three and a half sentences are verbatim
    – Mazura
    Commented Feb 15, 2022 at 7:33
  • Does this answer your question? Breaker feeding an electric heater trips after one minute
    – FreeMan
    Commented Feb 15, 2022 at 15:19
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    @FreeMan - not a dupe. That link has the wrong size breaker and wire. This, is up to snuff but broken. - I'd pull the wire and look for abrasions. Then open up the wall and find where they didn't ream the pipe right. - The only other option is the OP botched the install twice, or there's just something funny about these units. The odds that both breakers and two units all were fail....
    – Mazura
    Commented Feb 16, 2022 at 2:23

1 Answer 1

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7,500W / 240V = 31.25A, rounds to 32A, which for continuous use (like a heater) gets a 40A breaker. 8 AWG is standard for 40A. So everything matches perfectly.

Which means, there is something going wrong. That could be:

  • Heater drawing more power than rated.
  • Wiring problem resulting in extra resistance.
  • Bad breaker.

While 6 AWG wire is lower resistance than 8 AWG wire, a 30' run shouldn't be a problem at all.

A bad breaker is unlikely, though not impossible.

A brand new heater going bad is unlikely, but a little more plausible than a bad breaker. While the heater is basically a giant toaster, there are internal connections for the controls, fan, etc. and if any of those is bad then it could produce quite a bit of extra heat in the wrong place, or it may result in a partial short circuit. (A full short circuit would simply be an instant breaker trip.)

But my money is on a wiring problem. A bad connection could result in high resistance at one spot, which would waste energy ($), create heat (fire) and (fortunately!) trip the breaker if it is bad enough. A bad connection could also result in a partial short circuit, which would increase the total current used. Actually, mildly bad (turning 32A into 40A) would be the worst because it would take a long time to trip the breaker. My guess is you are significantly over 40A, perhaps 50A. If your heater/wiring pulled 100A then it would trip much faster than "a couple of minutes".

To diagnose:

Turn off the breaker. Carefully check, and recheck, every splice, wire nut, screw connection, etc. from the breaker all the way to the heater. All it takes is one bad connection to ruin everything. Wire nuts are cheap - check the size and replace them if they are the wrong size or show any signs of melting/arcing/burning. All connections, except ground wires, should have no bare wire exposed - stripped wire should be entirely inside wire nuts or under screws.

If that doesn't solve the problem, use a clamp meter to measure current on the hot wires when the heater is running. If you show something close to 32A then you may actually have a bad breaker. But I bet you'll find much higher current and the problem is either the heater itself or the wire connections.

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    Was thinking defective heater or breaker myself, but OP stated both were replaced, leaving bad connection somewhere(hopefully).
    – crip659
    Commented Feb 14, 2022 at 23:46
  • Just no. That’s not how electricity works. Bad connections cannot increase load. They can cause dangerous heat in the wrong place but they CANNOT increase the total load. Ohm’s law.
    – nobody
    Commented Feb 15, 2022 at 0:55
  • @nobody Hmm. Looks like you have a point here. I'm actually not so sure about "cannot increase load" but you are right (after I played around with Ohm's Law, etc.) - a high resistance connection would produce heat at that location but the overall higher resistance would mean less total power and less current. Adjusting... Commented Feb 15, 2022 at 1:03
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    Bad connections that partially short (or "poorly short?" A less than "dead" short) sure can increase load. It depends on the nature of the badness of the connections.
    – Ecnerwal
    Commented Feb 15, 2022 at 1:07
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    8 AWG AL would not cause a breaker trip. In fact, 8 AWG AL THHN 75C is rated for 40A! But even if you use 10 AWG AL (30A), the problem is quite the opposite - using a breaker of higher capacity than the wire can properly handle will result in the breaker not tripping in time to prevent an overheated wire. The problem here is the breaker is tripping when not expected to do so. Commented Feb 15, 2022 at 2:08

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