JohnMcNutt
Industrial
- Mar 3, 2013
- 111
Looked at a facility that has 208Y/120 power throughout.
Their automatic genset is a 120/240 1Φ set that only powers selected circuits.
The way this is accomplished is by interrupting or transferring phases A and B before they hit the subpanel. Phase C is going straight from the utility-supplied breaker to the subpanel without interruption.
All loads on this circuit are 1Φ, so no risk of single-phasing any 3Φ motors.
But it occurs to me that under certain conditions, a heavy heating element from A-C or B-C could sufficiently energize C (reference neutral) to cause a hazard to personnel on line.
When utility returns but time has not elapsed for retransfer, voltages A-C and B-C could be wild and fluctuating.
Voltage of 208V equipment connected A-C or B-C would remain >120V during the duration of the outage.
I don't know where to look for the code violation here, but there must be one somewhere.
Their automatic genset is a 120/240 1Φ set that only powers selected circuits.
The way this is accomplished is by interrupting or transferring phases A and B before they hit the subpanel. Phase C is going straight from the utility-supplied breaker to the subpanel without interruption.
All loads on this circuit are 1Φ, so no risk of single-phasing any 3Φ motors.
But it occurs to me that under certain conditions, a heavy heating element from A-C or B-C could sufficiently energize C (reference neutral) to cause a hazard to personnel on line.
When utility returns but time has not elapsed for retransfer, voltages A-C and B-C could be wild and fluctuating.
Voltage of 208V equipment connected A-C or B-C would remain >120V during the duration of the outage.
I don't know where to look for the code violation here, but there must be one somewhere.