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I need to wire a 220v 55 amp circuit in the attic for a new HVAC system. I would normally run a single 6 gauge wire to handle the 55 amps. However, I already have 2 10 gauge wires run to the attic. Can I connect the 2 10 gauge wires together at both the MSP and the box in the attic and protect it with a 55 amp breaker and have it function the same way as a single 6 gauge wire?

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No, you cannot parallel that size conductor. Rule 12-108 states that conductors smaller than 1/0 AWG cu or al cannot be paralleled. You will need to run the larger wire.

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  • Is that a CEC reference, perchance? (The NEC ref for this would be 310.10(H), BTW) – ThreePhaseEel May 19 at 1:54
  • @ThreePhaseEel Yes, and I don't know why I thought he was from Canada.... mixed up with another qustion. – JACK May 19 at 12:07
  • What is the reason? If the connections are reliable and if the sum of the cross sections is the same, physically it should be even a better solution, since the cooling surface is much bigger and the mechanical stress should be smaller where the cables are bended. – xeeka May 19 at 15:16
  • @xeeka: legalese about code. they have to cater for lowest common denomators, so even though it would be measurably better, it's not allowed, probably because if half breaks, all the load is on one over-rated wire, whereas when one wire breaks the load is zero. – dandavis May 19 at 16:24
  • @dandavis The famous nail or screw run into the wall or ceiling could also decrease the cross section of a single bigger wire. Wouldn't that be the same overrated wire situation? – xeeka May 19 at 16:28

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