Single Phase Breakers, Three Phase Panel
Single Phase Breakers, Three Phase Panel
(OP)
Our company sometimes builds trailers with some of the equipment being three-phase and single phase motors. We'll take the trailers to a site and have the utility company build us a bank of transformer(s) for power. The power is normally 120/240 3-phase 200A 4-wire delta.
My question is this: suppose we have all single phase equipment (one and two pole breakers) in a three-phase panel. We go to the site and have the utility company connect 3-phase power. The breaker panel is configured so that the 'B' phase does not have any breakers assigned to it. Typically, the 'B' phase is the "high-leg".
Later, if we want to add a 3-phase motor, the power is available and the panel will accept the 3-pole breaker.
Are there any problems with leaving the 'B' phase unoccuppied?
thanks,
SB
My question is this: suppose we have all single phase equipment (one and two pole breakers) in a three-phase panel. We go to the site and have the utility company connect 3-phase power. The breaker panel is configured so that the 'B' phase does not have any breakers assigned to it. Typically, the 'B' phase is the "high-leg".
Later, if we want to add a 3-phase motor, the power is available and the panel will accept the 3-pole breaker.
Are there any problems with leaving the 'B' phase unoccuppied?
thanks,
SB






RE: Single Phase Breakers, Three Phase Panel
RE: Single Phase Breakers, Three Phase Panel
It's not a good choice when most of your loads are single-phase 120V.
RE: Single Phase Breakers, Three Phase Panel
For example, there are only 5 single pole 120V breakers occupying the A & C phases. The rest of the breakers (30 circuit panel) are 240V 2-pole that occupy phases
C & A. 'B' phase is not occuppied at all in the panel. A & C to ground is 120V. 'B' to ground is about 212V because of the delta.
Is there any concern for an unbalanced utility company transformer bank load since there are three transformers providing the three-phase power?
I realize that one of the poles of the the 240V 2-pole breaker could occupy the 'B' phase. I was just wondering what would happen if 'B' phase was MT.
thanks again,
SB
RE: Single Phase Breakers, Three Phase Panel
To appease the masses, one could install ±two three-pole breakers with the requisite installed/visible 3 conductors on each set of breaker-load terminals, but with one of the three leads surreptitiously dead-ended in the utilization-equipment terminal boxes.
Near-ultimate fruition and authenticity could then be realized by serving one 2-wire 240-volt load Aø-to-Bø, and another Bø-to-Cø.
RE: Single Phase Breakers, Three Phase Panel
RE: Single Phase Breakers, Three Phase Panel