1600amp service

[doug glasscock]

We have a pull box nippled with 4-4" nipples (each 4" long) to the top of an outdoor mounted CT cabinet. There is a service rated transfer switch on the other side of the wall which is nippled to the same pull box with 4-4" nipples (each 6" long).

4" Long Nipples (from CT to pull box)
All A's in one
All B's in one
All C's in one
All N's in one.

6" Long Nipples (from pull box to ATS)
a,b,c,n in each nipple.

I know there is a problem with the 4" part of the installation, but I need some someone to extend their knowledge of the exact problem to me and why it is a problem?

 

[tom baker]

Re: 1600amp service

Inductive heating from hysterisis. the currents will not cancel, will overheat and burn up the conductors. One way to solve this is to slot between the nipple KO's. But the code compliant way is to have one conductor of each phase in each nipple.

 

[george t. everett]

Re: 1600amp service

I read some where that you can do this, but I can't back it up.

 

[iwire]

Re: 1600amp service

NEC 2002 300.3(B) Paralleled Installations, short version: you must have A,B,C,N in each pipe except for Nonmetallic raceways underground.

The slotting is referenced in 300.20(B) and is for other installations, one that I can think of is single conductor MI cable.

[ April 08, 2003, 05:49 PM: Message edited by: iwire ]

 

[doug glasscock]

Re: 1600amp service

If I have the contractor remove the 4" long nipples connecting the pull box to the CT cabinet and make one big opening between the two enclosures,...this would be a solution?? Does anyone see anything wrong with this??

 

[iwire]

Re: 1600amp service

This should work as derating does not apply to nipples less than 24" (2002 NEC 310.15(B)(2) Exception No. 3).

But if you have to take it apart why not put A,B,C,N in each nipple?

 

[doug glasscock]

Re: 1600amp service

iwire,
our contractor had it installed correctly, the power company's contractor came along and fished the wires back through the nipples and then re-fished them through the nipples to make it easy for termination to the CT cabinet lugs. Some of the conductors are now too short to re-fish them through correctly. The power company assumed responsibility for this and this idea was just a possible solution to keep them from having to pull all new wire from the CT cabinet to the ATS

 

[iwire]

Re: 1600amp service

WOW, I would be flipping out if the POCO did that to my work.

Goodluck with the fix, Bob