ground wire question

[olly]

If I have a 250 aluminum triplex URD and I need the fourth ground wire what size should I make the ground? This will be a feed from a meter socket to a residential house 200a breaker. I increased the size of wire for voltage drop.

 

[charlie b]

A 200 amp breaker would call for a ground wire of #4 AL. But a 250 AL only has an ampacity of 205 amps. It is not increased in size at all. What size do you think you are increasing from?

 

[olly]

I would be increasing from 4/0 AL because you get and allowance since it is a single family residential dwelling service. You can apply the 83 percent factor. Right?

 

[GerryB]

I would be increasing from 4/0 AL because you get and allowance since it is a single family residential dwelling service. You can apply the 83 percent factor. Right?

Do you need a ground wire? The breaker is not at the meter, right? I have purchased the triplex with 3 insulated conductors and a bare ground, think it's called quadplex. Table 310.15 (B) 7

 

[charlie b]

I would be increasing from 4/0 AL because you get and allowance since it is a single family residential dwelling service. You can apply the 83 percent factor. Right?

You can, but you don't have to. The article to which you refer speaks in terms of "shall be permitted." You can start by saying you have a load at or under 200 amps. You can then use table 310.15(B)(16) to discover that a 250 MCM AL conductor has sufficient ampacity. You next do your VD calculation and discover that you are under 3%, and you declare that that is an acceptable value. Finally, you look at table 250.122 and verify that a #4 AL is sufficient for the EGC. You didn't increase the ungrounded wire, and therefore you don't have to increase the EGC.