100% Duty Breaker and Table 250.122

[dburkhardt]

Hi All,

I have a 800A OCPD rated for 100% duty. I sized the equipment ground to 1/0 per Table 250.122 (2008 NEC). A comment came back stating that Table 250.122 is based on OCPD rated for 80% duty, therefore I need to size my ground to 2/0 for a 1000A OCPD. Does anyone know where in the code this is stated?

Thanks.

 

[Dennis Alwon]

It is stated in the mind of some authority. I have never heard that. 250.122 does not make mention of that, it is based on the breaker size not the actual load. BTW, welcome to the forum

 

[infinity]

What would the 80% vs. 100% rating of the breaker have to do with the EGC being able to open the OCPD in a ground fault situation?

 

[charlie b]

A comment came back stating that Table 250.122 is based on OCPD rated for 80% duty. . . .

The code says no such thing. The table only says to base the EGC on the rating or setting of the OCPD. If you have a breaker that has a frame size (i.e., rating) of 1000 amps, and you have it set (i.e., setting) to trip at 800 amps, then you base the EGC on 800 amps.

 

[dburkhardt]

That's what I thought, but was looking for a confirmation.

Thanks!