Ground Fault Circuit Interrupter (GFCI).

A ground fault circuit interrupter is the device used to de-energize the circuit.

One of the most important requirements is to deenergize all circuits at a work station. A rubber or deck mat must be used to check all energized equipment. A distribution board should always be connected to the breaker/ fuse box and control load box.

The two windings are in parallel with each other. Some motors have a capacitor placed between the two windings. Other connections find a switch between the two windings. When the motor gets up to speed, the switch opens and the start winding is taken out of the circuit and the motor runs on the run winding.

I am going to assume that you are asking about a differential relay. It is basically just that- it compare two different sources and will trip at a set value value of the difference. These can be directional as well. A couple of examples are transformer protective relays and bus differential. A transformer relay will measure the amount of current coming into the transformer and the amount of current going out. If there is a disparity due to an internal fault the relay will trip the supply source and deenergize the transformer. Same for the Bus differential.