cforrester97
Member
- Location
- Colorado Springs
- Occupation
- Engineer
I'm having a hard time understanding what the actual requirements are per NEC.
The step down (480-208, 3PH) transformer GEC is sized per NEC 250.102(C)(1) of the secondary, supply side OCPD.
The secondary feed to the 208 panel is sized for GEC per NEC 250.102(C)(1) as well, not EGC as it typically would be sized for.
For example, 175A breaker from 480 panel to transformer. Secondary OCPD (208 panel) is sized at 400A. Ground on transformer is sized #1/0 per NEC 250.102(C)(1). The secondary to the 400A, 208 panel is sized with #1/0 gnd. instead of #3.
If any of this is incorrect, please let me know. This is my understanding currently. I have usually sized secondary per EGC requirement, not GEC, and have also seen it this way on many electrical plans. However, I recently got dinged by the building department for not sizing the secondary feeder ground as GEC and would like a clear answer on why.
Thank you!
The step down (480-208, 3PH) transformer GEC is sized per NEC 250.102(C)(1) of the secondary, supply side OCPD.
The secondary feed to the 208 panel is sized for GEC per NEC 250.102(C)(1) as well, not EGC as it typically would be sized for.
For example, 175A breaker from 480 panel to transformer. Secondary OCPD (208 panel) is sized at 400A. Ground on transformer is sized #1/0 per NEC 250.102(C)(1). The secondary to the 400A, 208 panel is sized with #1/0 gnd. instead of #3.
If any of this is incorrect, please let me know. This is my understanding currently. I have usually sized secondary per EGC requirement, not GEC, and have also seen it this way on many electrical plans. However, I recently got dinged by the building department for not sizing the secondary feeder ground as GEC and would like a clear answer on why.
Thank you!