I have an office in a building supplied with 3 phase electricity in the United States. There are several standard household 120V outlets in my office, each connected to a dedicated, 20 amp circuit with an 80% rated breakers. Assuming I will plug in an appliance continuously with a power factor of 1, am I correct in assuming that each receptacle on one of these dedicated circuits will support up to a maximum of 120V x 20A x 1PF x sqrt(3) x. 80 = 3325.5 watts? Or is it standard to somehow downgrade the electricity to single phase 120V when the 208V comes through the panel, effectively eliminating the square root of 3 term in my calculation above,leaving a maximum wattage of 1920? Thanks.
Electrical – Max wattage on 120v outlet on 20A 80% breaker on 3 phase
electrical-panel
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Best Answer
No. You don't multiply by the square root of 3 unless you're drawing all 3 phases in a delta configuration, and then, you multiply the pole-pole voltage (208) not the pole-neutral voltage (120).
When dealing with a single phase of wye or split-phase, it's exactly what it says on the tin:
120V x 20A x PF1.00 x 80%. 1920W.
It's not "downgraded somehow", 3-phase wye service is simply three single-phase supplies that happen to be out of phase with each other 120 degrees. Just as split-phase is two single-phase supplies that happen to be 180 deg out of phase with each other.