Originally posted by Redsy:
I don't see how that would cause unequal division of current on a parallel feeder.
That is exactly my question!
Parallel feeders are resistors in parallel. Ohms law says that if the currents are unbalanced, we know the voltage is the same, the resistance has to be out of balance by the same amount as the current.What kind of amperage numbers are we talking? How many conduits?
The feeders are run through the switchgear, no raceways, except a nipple between the two cabinets. Downstream the load is very diverse. Sub-panels for lighting and HVAC. Three phase loads for equipment, every other type of load you would expect in the typical commercial/industrial setting.
We were measuring with two different cheap Amprobe clamp on meters. Both meters showed the same results, I don't know if these read true RMS or not.
The load was very light. We did this on Saturday, with the factory shut down. No equipment was operating.....the only loads were lighting and Hvac. Normal load with the plant operating is 760A on this feeder.....on Saturday we were seeing about 200A.....the three parallel feeders were showing numbers like 55A/63A/78A....all three phases were similar.
FWIW there is considerable phase imbalance. At full load of 760A the neutral is carrying about 150A of current. This seems to be a separate issue. Some of the load needs to be shifted from A & B to C phase to balance everything.
[This message has been edited by golf junkie (edited 09-23-2001).]