A general power and lighting feeder tap that consists of 1/0 AWG THHN conductors has been made to 500 kmcil THHN feeder conductors in a properly sized junction box. The 500 kcmil feeder conductors are protected by a 400A OCPD at the point where they receive their supply. The 1/0 AWG feeder tap conductors are protected at their termination point by a 150A overcurrent device. The feeder equipment grounding that runs with the 500 kcmil feeders is 3 AWG. What's the minimum size equipment grounding conductor required as part of the feeder tap circuit conductors?
A) 8 AWG
B) 6 AWG
C) 3 AWG
D) 1/0 AWG
Explanation: Per a 2005 change, 250.122(G) requires that when sizing equipment grounding conductors for feeder taps, the minimum size of the equipment grounding conductor to be installed with the feeder tap conductors shall be based on the rating of the overcurrent device protecting the feeder conductors.
A feeder protected by a 400A OCPD requires a 3 AWG equipment grounding conductor. According to this change, the feeder tap conductor would also have to be a 3 AWG equipment grounding conductor.
Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at [email protected].