skeshesh
Senior Member
- Location
- Los Angeles, Ca
I'm putting together a load summary for a client who wants to obtain a city permit to add in some floor-standing distribution panels. There's going to be two 800A distribution panels added, both lightly loaded (100-150kVA each) with a few spare breakers for possible future expansion.
These panels will be fed from an existing double-ended unit substation with a normaly-open tie breaker. The bus is rated at 3000A and each end is tied in with a 3000A breaker to individual 2000/2666kVA, 4160V-480/277V, 3ph transformers fed from 4.16kV main switchgear.
The question is should I consider only the loads to one side of the tie breaker (the bus we'll be connecting the new load to) while still using the full 3000A capacity? It seems to me that for the new load to be allowable I need to look at the unit while the tie breaker is closed in case of one of the transformers failing/OCPD at secondary tripping, in order to consider the worst case. I ran it by one of the senior engineers and he said just do it with the tie normally open, and mumbled something about them having load shedding - but I havent seen anything mentioned on the as-built single lines I have... Any comment/advise is much appreciated.
These panels will be fed from an existing double-ended unit substation with a normaly-open tie breaker. The bus is rated at 3000A and each end is tied in with a 3000A breaker to individual 2000/2666kVA, 4160V-480/277V, 3ph transformers fed from 4.16kV main switchgear.
The question is should I consider only the loads to one side of the tie breaker (the bus we'll be connecting the new load to) while still using the full 3000A capacity? It seems to me that for the new load to be allowable I need to look at the unit while the tie breaker is closed in case of one of the transformers failing/OCPD at secondary tripping, in order to consider the worst case. I ran it by one of the senior engineers and he said just do it with the tie normally open, and mumbled something about them having load shedding - but I havent seen anything mentioned on the as-built single lines I have... Any comment/advise is much appreciated.