ECN Forum Forums General Topics of the Trade General Discussion Area sub panel in seperate structure

I would too. EGC's are good things. As Roger said, welcome. And do come back often, there is a lot of knowledge here (like Roger)!

that is my thought also,thanx

In this case the size of the conductors will determine the size of the EGC.


It is a 100 amp panel but you are running 1/0 awg I imagine for voltage drop reasons.

If we figure the normal size for a 100 amp feeder is 3 awg with a circular mil area of 52,620, and now you increase to 1/0 awg with a circular mil area of 105,600 the ratio between these two conductors is essentially 2.

Table 250.122 shows a 8 awg ground for a 100 amp breaker.

8 awg has a circular mil area of 16,510.

16,510 x 2 = 33,020 circular mils.

The smallest conductor that is more than 33,020 circular mils is a 4 awg with a circular mil area of 41,740.

So even though Table 250.122 shows an 8 awg ground for a 100 amp over current device we have to follow 250.122(B) and increase the size in proportion to the ungrounded conductors.

In this case that means a 4 awg ground with the 1/0 copper ungrounded conductors.

For extra fun,

What size grounding conductor would be needed on a 30 amp circuit using 4 awg as the ungrounded conductors?

Think of this as a long circuit for site lights around a building.

Bob

Edit: I agree with Roger and Ryan, I also would pull an EGC.




[This message has been edited by iwire (edited 11-12-2003).]

Iwire, my guess is 6.

Where do you get the circular mils chart?

Spark Master Flash, table 8 in chapter 9.

Roger

Thanks, Rog!