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Thread: 70 Amp Breaker on 6 AWG?

  1. #1

    70 Amp Breaker on 6 AWG?

    I know this may sound really ignorant to alot of you with this forum, but I would really appreciate some help understanding this.

    I just replaced a 70 amp breaker that was melted in a load center. Under the breaker terminal were 6 awg thhn. This branch circuit is feeding a pool heat pump with a minimum circuit ampacity of 36 amperes, along with a 2 hp 230v 1 phase motor and a couple of 300 watt pool light transformers.

    Know I did my calculations and replaced the 6 with 4 awg thhn for the branch circuit, replacing the melted 70 amp breaker on the same day.
    Someone told me I shouldn't have done that and the wire and breaker were just fine.

    I have looked up code references in articles 210, 220, 430 and 440. Am I going in the right direction? And if so, I would appreciate some other code references to back my up on my call since I am feeling confident I did the right thing.

    Regards

  2. #2
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    With heat pumps the nameplate is what you need to look for. The Minimum circuit amp. , the max cir. amp and the max. fuse or hacr breaker. With heat pumps you would be allowed to protect a wire with a fuse that is higher than the amp. of the unit. Again look for the max. fuse. As long as your wire is large enoughtfor the min cir. amp. then you can protect it at the max. fuse or hacr breaker.

  3. #3
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    Quote Originally Posted by Dennis Alwon
    With heat pumps the nameplate is what you need to look for. The Minimum circuit amp. , the max cir. amp and the max. fuse or hacr breaker. .
    I agree except the feeder supplies more than just a heat pump.

    This branch circuit is feeding a pool heat pump with a minimum circuit ampacity of 36 amperes, along with a 2 hp 230v 1 phase motor and a couple of 300 watt pool light transformers.
    The 'normal' rules must be applied.

  4. #4
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    Quote Originally Posted by iwire
    I agree except the feeder supplies more than just a heat pump.
    The 'normal' rules must be applied.
    Well if I read the rest of the sentence I could have told him that. Amazing I got caught up in the heat pump thought.

    Thanks Bob

  5. #5
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    Smile

    Quote Originally Posted by Dennis Alwon
    I got caught up in the heat pump thought.
    So did I, I was ready to give the answer you did.

    I am hoping the 70 amp breaker is supplying a panel and then the other items.

  6. #6
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    meltdown

    dj,
    as bob states, I hope the 70 amp feeds a "sub-panel" and proper protection is supplied for the motor and lighting.
    That said, I would tend to investigate a bit closer as to the possible cause of the "meltdown"..loose connection on the breaker terminals, or loose on the buss,etc.. IMHO, the loads you showed would not be sufficient to damage a #6 THHH under normal working conditions. The 36 amp MCA heat-pump number would have some "safety" in that number, the motor running load would be approx, 14 amps and lights would be about 5 amps even if they were on the same phase. Although, I agree, I would prefer the #4, I personally would be suprised to see these loads cause a "meltdown" using the #6. An opinion.

  7. #7
    Yes, there is a subpanel feeding all the said equipment.

    Thats really the interesting part, the meltdown. Loose terminals on the breaker would contribute the then meltdown. How about the breakers operating temperature beening excessed for a long period of time and the breaker not tripping? After all a 70 amp breaker is only rated 56 amperes for continuous operation, right? The applied load was over 59 to 60 when I took a measurement.

    Regards.

  8. #8
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    Curious to know if the conductor's insulation also appeared to have failed, other than right where it terminated to the failed breaker?

  9. #9
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    If your feeder was wired with NM cable then you were absolutely correct to change out the wire. Even if it were not were with NM but rather conduit or mc it was probably a wise idea to change the wire. #6 thhn is good for 90C but we must use 75C rating because of the termination.

    That being said #6 thhn is good for 65 amps but art. 240.4(B) would allow us to use a 70 amp breaker as long as the load is not over 65 amps.

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