Ground Fault Protection Methods
A Ground Fault Circuit Interrupter, or GFCI, is a device that
functions to de-energize a circuit when it senses the potential
risk of electric shock. GFCIs are very sensitive, and will trip
when sensing an abnormal difference of current in excess of 4-6
milliamps – significantly below the level that would cause injury
to a healthy person. For example, if you are using a hairdryer in
your bathroom, the hairdryer is typically drawing 15 amps from
the GFCI receptacle, all the while comparing current on the hot
wire with current on the neutral wire. If the GFCI senses the same
current level, up to 15 amps, on both the hot and neutral wires, the
face and feed-through output circuits remain connected, allowing
the hairdryer to function normally. If the hairdryer is dropped into
a sink full of water, then current can escape through the water as a
path to ground. This creates an imbalance in the current on the hot
versus the neutral wire, and would typically result in an electrical
incident or possible electrocution. With a GFCI device installed,
power to the hairdryer would instantly be shut off upon the sensing
of an imbalance in the current.