250.30C Restrictions On Main Disconnect Bonding


The last sentence of 250.30A1, which references 250.30C, would seem to indicate that regardless of use, the GEC and SBJ must be at the xfmr and not at the main disconnect. This would seem to include things like overhead “can” type xfmr’s that may be covered by the NEC due to being in an oilfield or for 240V power in a non-utility owned substation. However, this rule seems to have been written with buildings in mind. And, while these can xfmr’s aren’t prohibited for applications covered by the NEC, they are primarily developed for and sold to utilities. As such, things like the factory bonding strap are quite small – they are intended for things like lightning protection or protection from contact with a higher voltage line – they may not have been intended to carry the short circuit current required to trip the breaker.

Do you think these specific NEC rules were really intended for some of the applications described here?