Multiple Phase A Conductors in one conduit

[ricomichigan]

Does the NEC allow for multiple 120V/20A branch circuit conductors of the same phase to be installed in one conduit?

The proposed installation would have a separate neutral conductor (3 total) and a shared ground conductor (1 total) with three phase "A" conductors in one conduit. The conductors would be terminated in separate 120V/20A circuit breakers and separate 120V/20A receptacles.

Would inductive heating of the conduit be an issue?

 

[roger]

Re: Multiple Phase A Conductors in one conduit

With the individual neutrals there is no problem.

Roger

 

[websparky]

Re: Multiple Phase A Conductors in one conduit

No problem.

As long as I read your question right, 3 "A" phase conductors with 3 neutrals and 1 grounding conductor in the same raceway.

 

[roger]

Re: Multiple Phase A Conductors in one conduit

Hi Dave, I snuck that one in on you.

Roger

 

[charlie b]

Re: Multiple Phase A Conductors in one conduit

The magnetic field created by current flowing out the phase conductor would be essentially cancelled by the magnetic field created by current flowing back along the neutral conductor. Thus, inductive heating is not a problem, and I agree with what the other members have already said. The problem with running only the phase A conductors in a conduit (i.e., no neutral and no phase B or C conductors) is that the magnetic field created by current flowing out each of the phase conductors would add together. Instead of the cancellation effect that I mentioned above, you get three times the magnetic field. That is what causes the inductive heating of the conduit.

By the way, I?m sure you?ll not forget to de-rate the ampacities to 80%, based on having 6 current-carrying conductors in a single conduit.

 

[pierre]

Re: Multiple Phase A Conductors in one conduit

Charlie
What if you are using the raceway as a heat supplement for the space it travels in

Pierre

BTW - I am only kidding for those who may think I am serious about my response to Charlie

[ November 14, 2003, 07:14 AM: Message edited by: pierre ]

 

[gwz2]

Re: Multiple Phase A Conductors in one conduit

The way I read the question, the installation is 3 Phase " A " or " L 1 " conductors and 1 Grounded Conductor.

If so, then the grounded conductor must be sized for 60 Amps. ie. 20A + 20A + 20A = 60A possible on the grounded conductor.

As for the inducted heat generated in the metal raceway, the answers are correct, except for the ambient heat generated by an under-sized grounded conductor.

gwz2

[ November 14, 2003, 04:42 PM: Message edited by: gwz2 ]

 

[websparky]

Re: Multiple Phase A Conductors in one conduit

Hi Roger!

You type faster than I do!

The proposed installation would have a separate neutral conductor (3 total)