GF Protection on LV 3-Wire Unbalanced Systems

[recs]

If a 3-phase, 3-Wire (no Phase to neutral loads), Y-G, 480V system has several phase-to-phase loads unbalancing the system.

I would like to provide GF protection at the service disconnect and a second level at the feeder.

All 600 A frame breakers I have seen (Eaton, GE, and Square D) have GF protection using ONLY residual sensing. I believe that if the unbalance in the system due to the phase-to-phase loads, could trip the breaker.

Any thoughts about this? Is it necessary to measure the unbalance before setting the pick-up of the GF function on the circuit breaker?

I am interpreting this wrongly?

Thanks.

 

[dpc]

If you have no 277 V loads, the sum of three phase currents must equal zero under normal load conditions, regardless of whether the phases are balanced or not. There is no other current path available.