sfriedberg
Diamond
- Joined
- Oct 14, 2010
- Location
- Oregon, USA
SeymoreDumore, a GFCI intended for multi-phase supply is a bit more complicated than one intended for single-phase, but the principle is the same. The currents on all the supply conductors (3 hots for Delta, 3 hots and a neutral for Wye) are summed. If the sum isn't (almost exactly) zero, the breaker pops.
As I described earlier, a GFCI is really comparing incoming and outgoing currents. A ground fault will produce an imbalance, but so will lots of other conditions! In a multi-phase system, as long as all the outgoing current returns on the same set of 3 or 4 wires, things are OK. So imbalances between phases are not considered a fault. But if the currents on all the wires don't sum to (almost exactly) zero, that's a fault.
As I described earlier, a GFCI is really comparing incoming and outgoing currents. A ground fault will produce an imbalance, but so will lots of other conditions! In a multi-phase system, as long as all the outgoing current returns on the same set of 3 or 4 wires, things are OK. So imbalances between phases are not considered a fault. But if the currents on all the wires don't sum to (almost exactly) zero, that's a fault.