Mike Dolt Enterprises
Mike Dolt Enterprises
User: mshields, Location: Boston, MA
Asked on: Monday, March 28, 2011 at 4:28 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:23 am EDT
Question: I believe that the EGC for a motor feeder needs be sized based on the upstream OCPD and in accordance with Table 250.122. This means for example if you had a motor with FLA of say 50A, the wire size would have to be 125% of that (let's say based on 70Amps) and the OCPD could be as large as 125A. The EGC would need to be #6 to mach the OCPD. Is that correct or am I oversizing the EGC?Thanks,Mike
Yes, you are correct. The Equipment Grounding Conductor (EGC) for a motor feeder needs to be sized based on the upstream Overcurrent Protective Device (OCPD) and in accordance with Table 250.122 of the National Electrical Code (NEC).According to Table 250.122, the minimum size of the EGC for a motor feeder is:- 125% of the ampacity of the ungrounded conductors supplying the motor, for motors rated 100 amperes or more- 100% of the ampacity of the ungrounded conductors supplying the motor, for motors rated less than 100 amperesIn your example, the motor has an FLA of 50 amperes. The OCPD could be as large as 125% of the FLA, which is 70 amperes. Therefore, the EGC would need to be sized for 125% of the OCPD, which is 87.5 amperes. The closest standard conductor size to 87.5 amperes is #6 AWG.Oversizing the EGC is not necessarily a problem, but it can lead to increased material and installation costs. However, it is important to ensure that the EGC is sized properly to provide adequate protection against electrical faults. Flag for review