Mike Dolt Enterprises
Mike Dolt Enterprises
User: frnkhr, Location: Lockport, IL
Asked on: Friday, June 3, 2011 at 9:17 am EDT
Answered on: Tuesday, May 14, 2024 at 6:09 am EDT
Question: I understand the equipment grounding conductor is sized based on NEC 250.122(A): "General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122,??. Table 250.122 lists the minimum size equipment grounding conductor per the "Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment,...".On a 4,160 volt circuit, is this the setting of the 50/51 relay (2000 Amp setting which requires a 250 kcmil copper equipment grounding conductor in my case), or the setting of the 51G relay (400 Amp setting which would require a #3 copper equipment grounding conductor in my case)?
The rating or setting of the automatic overcurrent device in circuit ahead of the equipment, as referred to in NEC 250.122(A) and Table 250.122, is typically the setting of the 50/51 relay, which provides overcurrent and ground fault protection for the circuit.In this case, the 50/51 relay has a setting of 2000 Amps, which requires a 250 kcmil copper equipment grounding conductor according to Table 250.122.The setting of the 51G relay, which provides sensitive ground fault protection, is not typically used to determine the size of the equipment grounding conductor. Flag for review