NEC 310.4 Distribution Block Question

[jajohnson977]

I have an application where I have a 1500 amp circuit and on the load side of my distruibution block I have 32 legs (which all go to contactors for heating elements). I am not aware of any block that has that many load legs that is UL listed or recognized. What I have been doing is using (3) 3 pole distribution blocks that have 12 load side legs each. I use (1) 3 pole block (giving me 36 load side legs)for each phase assuming each line side has an equal amount of the same size conductor. However, someone was telling my I was voilating 310.4 stating that parallel conductors must be tied to each other at both ends. (1) Am I truly voilating NEC by doing this? (2) How else could I satisfy NEC and UL at the same time? (I've found a block from marathon that has 18 load side legs but has not been evaluated to accept two wires per leg, so that is out).

Any help would be appreciated.

Thanks,

 

[augie47]

Is this application a machine or piece of equipment (as opposed to a field installation) ?

 

[jajohnson977]

It is a power distribution cabinet mounted to a steam generator. The Customer is coming in with (6) 500kcmil wires per phase. We wire 32 contactors for heating elements each with a set of fuses in between them and the load side of the distribution blocks. Does that help? Thanks

 

[roger]

What you are describing would be three individual loads in lieu of one load, as long as the three sets are covered ampacity wise you are fine

IOW's, you do not have one 1500 amp parallel circuit, you have three 500 amp circuits being fed from a 1500 amp source. This would be no different than feeding two 200 amp panels from two sets of conductors originating on a 400 amp breaker.



Roger

 

[don_resqcapt19]

... you have three 500 amp circuits being fed from a 1500 amp source. This would be no different than feeding two 200 amp panels from two sets of conductors originating on a 400 amp breaker.
...Roger

In this case smaller conductors are being connected to the load end of the "500 amp" circiuts.
The 500 amp circuits are taps and connecting smaller wires at the load end would be tapping a tap and a code violation.

 

[roger]

In this case smaller conductors are being connected to the load end of the "500 amp" circiuts.
The 500 amp circuits are taps and connecting smaller wires at the load end would be tapping a tap and a code violation.

Don, I may be wrong in my interpretation of the OP's piece of equipment but it sounded to me in his second post that the smaller conductors are part of a manufactured piece of equipment. I was addressing the fact the he wouldn't actually have a 1500 amp "parallel" feed using the definition of conductors in parallel

Roger

 

[don_resqcapt19]

Don, I may be wrong in my interpretation of the OP's piece of equipment but it sounded to me in his second post that the smaller conductors are part of a manufactured piece of equipment. I was addressing the fact the he wouldn't actually have a 1500 amp "parallel" feed using the definition of conductors in parallel

Roger

Roger,
I didn't read it that way.

 

[roger]

Roger,
I didn't read it that way.

And there is a good chance that you read it correctly.

Roger

 

[jajohnson977]

This is what I have in the attached picture. Those are (3) 3 pole distribution blocks (each pole is rated for 510 amps which x3 meets my 1500 amp capacity). Each 3 pole block is for one phase. I'm hoping that this may clear up my application. If this is in violation, would you have any alternative suggestions? My issue is that I have 32 sets of contactors. I have not found a block that either has more than 32 holes per pole, or a block with that ampacity that has been evaluated to use two wires per hole. Thanks in advance.