Mike Dolt Enterprises
Mike Dolt Enterprises
User: beanland, Location: Vancouver, WA
Asked on: Wednesday, April 27, 2011 at 12:24 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:40 am EDT
Question: I just want a reality check on the absurdity when increasing the size of EGC per 250.122(B).If I use 250kcmil copper phase conductors, fed by a 200A OCPD, I can use a #6 copper EGC. 250.122(A)If I use a 30A OCPD, because #10 copper is rated for 30A and the EGC for 30A is #10 copper, 250.122(B) requires I use a 250kcmil copper EGC with the 250kcmil phase conductor.Correct?
Yes, that is correct.250.122(A) states that the EGC shall not be smaller than the required phase conductor. For a 200A OCPD, the required phase conductor is 250kcmil copper, so the EGC must be at least 250kcmil copper.250.122(B) states that the EGC shall not be smaller than the largest overcurrent device protecting the circuit. For a 30A OCPD, the largest overcurrent device protecting the circuit is 30A, so the EGC must be at least the size of the EGC for a 30A circuit, which is #10 copper.So, while it may seem absurd to use a 250kcmil copper EGC with a 30A OCPD, it is required by the Code. This is because the EGC is designed to carry the fault current back to the source, and the larger the fault current, the larger the EGC must be. Flag for review