Q on what codes apply within J-Boxes re wire separation/bracing etc..........

[dionysius]

I would like to know what NEC rules govern wiring runs within J-Boxes......

Here is the scenario:

There is a very large J-Box (actually more like a blank panel) 6' hi; 3 ft deep; 2' wide.
All wires are 277/480 volt conductors. 350 kcmil.
Define a 'boat' as 3 phases + Neut tied into a group with wire ties, thus magnetically balanced.
4 boats run through from bottom to top at the rear.
3 boats run from bottom to top at the front.
A couple of single phases run through diagonally.
2 boats run from left to right.

What codes are applicable in this situation.

What bracing is required.

Are there any caveats which an Inspector could complain about?????

 

[Coppersmith]

Sounds like a box fill problem. See this link for details:

http://www.ecmweb.com/code-basics/box-fill-calculations

 

[petersonra]

have you closely reviewed 314.28 (A)?

 

[Smart $]

I don't see any just from your description.

 

[GoldDigger]

It may not be directly addressed by code, but when run in the open space of the box for a long distance (i.e. 6' in the OPs case) as a practical matter there will be no interaction between boats but the individual wires of each boat will see a mutual magnetic repulsion which could be significant during events like motor starting.
I would consider at least lacing or tying the conductors of each boat together over large runs inside this box. Just twisting the wires would probably be good enough.

I am sure most of us have either directly experienced or heard a first person description of the loud (loud enough to be disturbing) noises that can happen during motor starting in some cases of wires run in conduit. Imagine where they would go if not restricted in motion by the conduit.

Fault currents are one or two orders of magnitude worse.

350 kcmil wires are going to be carrying considerable current. Enough to justify tie downs even in an ordinary disconnect, controller or panel. Imagine what could happen over a 6' clear unsupported run.

Still might not be a code violation, but I do not like it at all.

 

[dionysius]

have you closely reviewed 314.28 (A)?

From my understanding I see no constraints given the sizes I posted. Anybody disagree??? It will be expensive if an overly meticulous Inspector disagrees with my interpretation. Let me know if I am on solid ground.

 

[GoldDigger]

Given that you did specify that each group was bundled with wire ties, I can only ask whether you have any calculations as to the strength of the ties you are using compared to the forces of normal or abnormal currents?

 

[dionysius]

Given that you did specify that each group was bundled with wire ties, I can only ask whether you have any calculations as to the strength of the ties you are using compared to the forces of normal or abnormal currents?

That would be a good exercise. I do not have the time to pursue that right now. Just empirical usage of large ties every 6" is my intuitive feeling of more than an overkill solution and that is without twisting the boat wires.