Updating electrical outlets
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.
There are a couple of ways to change your old two-prong, ungrounded receptacles to three-prong, grounded receptacles safely without having to rewire your house.
As with any work on existing wiring, the first step is shutting off the power to the circuit that you will be working on.
If testing shows that the box is properly grounded, insert a 10/32 machine screw into the hole in the back of the box and attach the ground wire from the grounding screw on the new receptacle here.
The hot and neutral wires then can be attached to their proper terminals and the new receptacle screwed into the electrical outlet box.
In most cases, this work is all you’ll need to do to replace your receptacles.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.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.
Search for updating electrical outlets:
Take off the cover plate and unscrew the outlet from the box. At the back of the GFCI are screw terminals marked "load" and "line." The single screw at the bottom is the grounding screw.