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Is it legal per the NEC to connect two 115v branches (outlets, motors, etc) on a 12-3 cable which is connected to a 20amp 2pole breaker back in the service panel? Since the red and black cable connections to the breakered power will be out of phase, the current which the single neutral wire returns to the panel will never be the sum of the two circuits loads.
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Generally yes -- there is a lot on this in the archinves here.
The neutral WILL carry current whenever the loads on each side of the circuit are not in perfect balance. It is not a question of phase, but rather the two loads acting as if they were a single 240 V load (lots on this in the archives too). A risk if the neutral ever comes loose -- the 115 V loads will be subjected to 240 V.
Ground must also be run separate.
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And don't forget that the breaker handles must be tied together with an approved tie--no wire thru the handle holes (at least around here).
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Hmm, just noticed that 115 times 2 isn't 240 -- what are the "standard" (nominal) voltages anyway?
*120/240. 110 & 115 are residual terminologies from long ago. Although you may find 120/208 in 3-phase or single phase derived from 3-phase. 208 = 120 x sqrt 3.
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Is it legal per the NEC to connect two 115v branches (outlets, motors, etc) on a 12-3 cable which is connected to a 20amp 2pole breaker back in the service panel? Since the red and black cable connections to the breakered power will be out of phase, the current which the single neutral wire returns to the panel will never be the sum of the two circuits loads.