parallel conductors

[rustyryan34]

Why does the nec allow in 310.4 that if their is separate raceways of the same physical characteristics for each different phase of parallel conductors that you can use different conductors, like aluminum for phase A and copper for B,and C phase.
Wouldn't that cause problems?

 

[peter d]

Why does the nec allow in 310.4 that if their is separate raceways of the same physical characteristics for each different phase of parallel conductors that you can use different conductors, like aluminum for phase A and copper for B,and C phase.
Wouldn't that cause problems?

It would not cause any problems assuming the copper and aluminum conductors are sized correctly.

 

[iwire]

Pete's got it right, phase A can be different then phase B and both of those can be different from phase C.

What the NEC does require is that all conductors of the same phase be identical.

 

[steve holt]

Parallel Conductors

Parallel Conductors

The reason they can be different from phase to phase but not within the same phase has to do with resistance. If all the properties of each conductor along with it's means of termination, the resistance should be the same. If one of the conductors is short, it will have less resistence thereby allowing more of the current to flow through that conductor than the other conductors which have a higher resistance. If this happens, you can exceed the max allowable amperage through that one conductor

 

[LarryFine]

Another way to look at it: each phase's conductor having different characteristics is no different that each phase having a different load. The neutral still carries the difference current.

Paralleling conductors has to do with each carrying its equal share when the OCP is greater than each conductor's ampacity.