ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Working in an existing highrise building in NY:
Downstream of an existing 8MW 480/277V standby generator plant (Article 702 if interested), there are some 3 pole transfer switches serving 3ph, 4 wire loads. The phase to neutral loads are very small, but they are there.
Because it is a 3 pole transfer, I guessed that the upstream generator plant is not a separately derived system (SDS) to be in compliance with the code.
I was brought in to design a new 480/277V 14MW generator plant, also Article 702 type, that was to serve new loads.
Because the large ampere (>1000A) rated overcurrent protective devices, I knew I would need ground fault protection, so I decided that the plant would be SDS's and the new downstream transfers would be specified as 4 pole transfers, if it were 4 wire equipment.
So .... yesterday, the client tells me he wants to shed some existing 4 wire type loads from the old gen plant and connect it to the new plant when it is ready.
Here's the rub. I don't think I can do it without having to replace the the 1600A transfer switches from 3 pole to 4 pole.
That's where I'm looking for confirmation or suggestions from you smart folks.
Downstream of an existing 8MW 480/277V standby generator plant (Article 702 if interested), there are some 3 pole transfer switches serving 3ph, 4 wire loads. The phase to neutral loads are very small, but they are there.
Because it is a 3 pole transfer, I guessed that the upstream generator plant is not a separately derived system (SDS) to be in compliance with the code.
I was brought in to design a new 480/277V 14MW generator plant, also Article 702 type, that was to serve new loads.
Because the large ampere (>1000A) rated overcurrent protective devices, I knew I would need ground fault protection, so I decided that the plant would be SDS's and the new downstream transfers would be specified as 4 pole transfers, if it were 4 wire equipment.
So .... yesterday, the client tells me he wants to shed some existing 4 wire type loads from the old gen plant and connect it to the new plant when it is ready.
Here's the rub. I don't think I can do it without having to replace the the 1600A transfer switches from 3 pole to 4 pole.
That's where I'm looking for confirmation or suggestions from you smart folks.