Grounding A Separately Derived System

[blues]

I have a transformer feeding a 480volt switchgear with a 3200 main circuit breaker. We are supplying this switchgear with 9-3 conductor #500kcmil tray rated cable. My question is the multi-conductor cable is provided with 1-#2awg ground conductor. I am still required to provide the proper size ground conductor per table 250.66.

Thanks Dan

 

[Smart $]

I have a transformer feeding a 480volt switchgear with a 3200 main circuit breaker. We are supplying this switchgear with 9-3 conductor #500kcmil tray rated cable. My question is the multi-conductor cable is provided with 1-#2awg ground conductor. I am still required to provide the proper size ground conductor per table 250.66.

Thanks Dan

Yes (assuming you mean supply-side bonding jumper). Each cable would have to have a 1/0 copper grounding conductor to be compliant.

 

[bob]

Smart, If all of the cables are in the same tray, does he need more than one 1/0 ground for the 9 cables?

 

[Smart $]

Smart, If all of the cables are in the same tray, does he need more than one 1/0 ground for the 9 cables?

1/0 per cable is compliant with 250.102(C)(2).

The only alternative is to use a single SSBJ. 250.102(C)(2) refers that to 250.102(C)(1) sizing, which over 1100 kcmil copper is 12.5%.

500kcmil ? 9 = 4500kcmil .... ? 12.5% = 562.5kcmil

​

I don't know of any allowance to use metal tray as an SSBJ. 392.60 only says it can be used as an EGC.

 

[bob]

Thanks for your detail post. I was trying to point out the use of 1 conductor rather that the 9.

 

[topgone]

Thanks for your detail post. I was trying to point out the use of 1 conductor rather that the 9.

That would be nice but didn't the OP say those 9 x 3C cables have a #2awg each?

9 x 66,360 Cmils = 597,240 Cmils, which is almost 6 times bigger than a single 1/0 awg (105,600 Cmils).

 

[david luchini]

That would be nice but didn't the OP say those 9 x 3C cables have a #2awg each?

9 x 66,360 Cmils = 597,240 Cmils, which is almost 6 times bigger than a single 1/0 awg (105,600 Cmils).

A #2awg in each cable is too small. As Smart$ pointed out, EACH cable would have to have a 1/0awg. Or a single SSBJ would have to be 600mcm.

 

[bob]

Mike has a good explaination here http://www.youtube.com/watch?v=WlwVP43JxlQ
ECMag here http://www.ecmag.com/section/codes-standards/clarifying-intent