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Old 05-16-2013, 09:58 AM   #1
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Wire size question


Hello everyone, I was wondering if some of you electric pros could answer a question for me. I am installing a new heat pump and my air handler has a 10k back up heat strip. Now my air handler calls for a 60 am breaker with 8-2 wire. Now the old furnace that I am replacing had very large wire which I think was 6-2 or possibly even 4-2. I have a non fused 60 amp disconnect switch installed by the air handler. My question is can I reuse the old large wire to the disconnect and then use a smaller guage 8-2 from the disconnect to the air handler. The large guage wire from the breaker panel to the disconnect is around 15 ft long and the 8-2 from the disconnect to the air handleris only 3 ft. Any advice is greatly appreciated. Paul

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Old 05-16-2013, 10:02 AM   #2
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Wire size question


Yes. You can always go bigger as long as the OCD (breaker) is sized properly. Sized to the smaller wire.

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Old 05-16-2013, 10:19 AM   #3
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Wire size question


Great, Thanks for your help
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Old 05-16-2013, 04:34 PM   #4
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Wire size question


Who said you can use # 8 AWG? What wiring method are you using?
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Old 05-16-2013, 05:34 PM   #5
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Wire size question


Please post the Minimum Circuit Ampacity(MCA), and the Maximum Breaker/Fuse/Overcurrent Protection.
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Old 05-16-2013, 06:59 PM   #6
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the tag on the air handler says motor 5.2 amps and then it list the six different heat kits that can be installed in this air handler. mine is a hkr-10c which is 10kw. for my heat kit the MCA is 49/56 and the MOP is 50/60
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Old 05-16-2013, 07:06 PM   #7
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Wire size question


Assuming 240v, #4 AWG would be required using NM Cable, 60 Amp Breaker.

#6 AWG if using THHN individial wires in conduit
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Old 05-16-2013, 07:08 PM   #8
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yes it is 240 v and i made a mistake i was using 6-2 not 8-2. so you are saying 6-2 will not work?
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Old 05-16-2013, 07:09 PM   #9
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the 6-2 wire was the same wire i purchased for my cooktop and double oven they are both 60 amp breakers also
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Old 05-16-2013, 09:53 PM   #10
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the 6-2 wire was the same wire i purchased for my cooktop and double oven they are both 60 amp breakers also
The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
  1. The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.
  2. The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
  3. The next higher standard rating selected does not exceed 800 amperes.
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Old 05-16-2013, 09:56 PM   #11
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Wire size question


The manufacturer is sneaky here, due to the "56 Amp" minimum rating on the nameplate.

#6 NM cable is limited to 55 Amps, 60C column.

One measly amp ---

Most professionals still would use #6 romex, and many inspectors will pass it. But the manufacturer is off the hook if any problems develop, since a strict interpretation of the Code would require #4 if NM cable is utilized.

I would install #6 THHN in conduit if possible.

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