Probably a silly question.....

[daleuger]

We were pulling wire today and I had to explain to the help today that we needed an extra white in the pull because 2 circuits on the same phase cannot share a neutral, and he asks why? That's when it dawned on me that nobody ever explained it to me and I never asked. Just sort of took it as common knowlege and didn't question it. I imagine it has something to do with load balancing or how much is liable to backfeed on the neutral if you do but I'm not exactly sure.

 

[480sparky]

When more than one circuit the same phase share a neutral, the amperage is additive ( Circ 1=10 amps, circ 2=15 amps, neutral is 25 amps).

When they're on different phases, they are subtactive (5 amps in the above example).

 

[raider1]

If two ungrounded conductors of the same phase share a common grounded conductor the current from each ungrounded conductor would add together. For example if hot #1 has 10 amps and hot #2 has 13 amps the grounded conductor would have a load of 23 amps. It is permissible by code to do this provided that the grounded conductor is sized for the maximum combine load of the ungrounded conductors. It is not common practice to do that though.

Chris

 

[daleuger]

When more than one circuit the same phase share a neutral, the amperage is additive ( Circ 1=10 amps, circ 2=15 amps, neutral is 25 amps).

When they're on different phases, they are subtactive (5 amps in the above example).

That's kind of what I meant by backfeed on the neutral but I couldn't quite word it right and wasn't positive if that was the only reason. Thanks guys.

 

[chris kennedy]

( Circ 1=10 amps, circ 2=15 amps, neutral is 25 amps).

For example if hot #1 has 10 amps and hot #2 has 13 amps the grounded conductor would have a load of 23 amps.

Furthermore, if cir. one has 10 amps and cir. two has 14 amps, then ....

 

[raider1]

Furthermore, if cir. one has 10 amps and cir. two has 14 amps, then ....

Chris

 

[LarryFine]

Chris

Moderators. :roll:

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