Updating electrical outlets
A GFCI has a built-in circuit breaker that interrupts the flow of electricity the instant it senses a ground fault or current leak.But a GFCI won't work unless it's properly connected.The conduit is clamped to the electrical outlet box on one end and to a known ground, such as the grounding stake on the other end (at the main panel).The electrical outlet box then can act as a ground for the receptacle.Any receptacles downstream of the GFCI, hooked up to the load side of the GFCI, should be replaced with a standard three-prong outlets, but again with no wire attached to the grounding screw.This system works because the GFCI monitors the difference in current between the black and the white wires and does not depend on a ground wire to protect the circuit.After you’ve finished the installation of the new outlet, I recommend testing the outlet with a three-light tester (see Ground-Fault Protection) to confirm that the outlet is functioning properly.
On older homes, the flexible metal conduit on armored cable is normally used in place of a ground wire.Another replacement solution can be found in a special exception granted by the National Electric Code in section 210-7D of the 1993 codebook.As strange as it may seem, the code recommends replacing a two-prong receptacle with a ground fault circuit interrupter (GFCI) without attaching a wire to the GFCI’s grounding screw.If your electrical system has not been upgraded for 20 years or more, you probably need to install GFCIs.
Here's how: First, turn off the power to the circuit you'll be working on.
In my experience, if an outlet box is not grounded, it’s usually due to corrosion that has broken the connection or rusted out the metal conduit at some point between the box and the main panel.