U5 and U6 are the optocouplers for this circuit. The top and bottom circuits are identical, so I will focus only with one of them. Power is provided to the circuit by the 17 VAC coming from the ...

Any phase/circuit to ground condition is called a ground fault. Among all faults, a balanced 3-phase short circuit is the most critical and serious. However, it is one of the least likely of faults to ...