skadee
Member
- Location
- Indianapolis
Where does NEC dictate whether the neutrals from two separately-derived systems can be connected? We have a 3-P manual transfer switch, fed by 120/208 1-ph, feeding a 120/208 panel. Our design engineer is specifying that the neutrals from the two two source panels are tied together at the neutral bus of the panel fed by the transfer switch.
Logically, I see that there's a potential to energize the neutral bar of one of the source panels with some un-balanced load, when that panel is not supplying the load, but I can't find any articles that nail down the direction to take in this case. The generator section heads down that path when mentioning whether the neutral is bonded to the generator, but this is not a case where we are using a gen set.
Our two sources are typically online 24/7, the transfer switch is primarily a switch that allows us to selectively choose the source feeding critical loads, when one source may be out of service for maintenance.
Logically, I see that there's a potential to energize the neutral bar of one of the source panels with some un-balanced load, when that panel is not supplying the load, but I can't find any articles that nail down the direction to take in this case. The generator section heads down that path when mentioning whether the neutral is bonded to the generator, but this is not a case where we are using a gen set.
Our two sources are typically online 24/7, the transfer switch is primarily a switch that allows us to selectively choose the source feeding critical loads, when one source may be out of service for maintenance.