Almost everyone has heard of a GFCI (Ground Fault Circuit Interrupter). These devices precisely monitor the balance of electrical current moving through a circuit and immediately cut off the electricity when a short occurs. For more on the basics of a GFCI see our article on Ground Fault Interrupter Circuits.

Wiring a GFCI may vary slightly from manufacturer to manufacturer, but for the most part they follow the same general principles. We'll try to simply and succinctly outline those below so that you understand how to correctly connect a GFCI into your electrical circuit and provide protection for an outlet or series of outlets and fixtures.

About Ground Faults
Any electric path between a source of current and a grounded surface is referred to as a "ground-fault." A ground-fault occurs when current is "leaking" and escaping to the ground. How this occurs is significant in t hat, if your body provides a path to the ground for this leakage, you could be injured, burned, severely shocked, or electrocuted. Since water is such a good conductor, ground-faults are especially common in areas where water can provide a conduit for electricity to "escape" and find an alternate path to the ground.

Method 1: Simple Replacement of a Traditional Receptacle

A standard receptacle can always be replaced with a GFCI receptacle and wiring it up is very straightforward. This should go without saying, but always cut power to the circuit (and verify with a circuit tester) before replacing an outlet. As shown below, you simply wire the ground connection and then connect both the hot and neutral wires to the GFCI's LINE terminals as indicated to complete the replacement.

GFCI receptacle - The LOAD terminals are only used if you are passing power through the GFCI to protect additional receptacles downstream.

Breakdown of Installation Steps:

1. Turn off the breaker at the panel which controls the circuit you are working on. If the circuit breakers aren't labeled (as is often the case), you can find the right one by plugging a light or clock radio into the receptacle you are updating. Then you simply turn off the breakers one by one until the light or radio goes off. It helps to have an assistant during this phase. Once you turn off the correct breaker it's always a good idea to mark it with tape to make sure a "helpful" person doesn't accidentally flip it back on while you're still working.
2. Test the outlet with a circuit tester to be verify that the power is indeed off (there's nothing worse than finding out the hard way).
3. Remove the receptacle's cover plate and the screws holding the outlet in place and unscrew/disconnect the wires from the outlet.
4. Re-strip and connect the power-supply wires to the terminals marked "LINE". Remember, the White wire connects to the Silver LINE screw and the Black wire connects to the Brass LINE screw. Connect the bare ground wire to the green (Ground) screw. (See Diagram A).
5. Replace the receptacle, screw it back into the box and attach the cover plate.
6. Turn the power back on at the circuit-breaker panel.
7. Plug a clock radio or light into the outlet.
8. Test the GFCI by pressing the Black "Test" button on the outlet. If the radio turns off, the outlet is working.
9. Reset the GFCI by pressing the Red "Reset" button on the outlet until it clicks into place. The clock radio or light should come back on.

Diagram A - Connections for LOAD and LINE circuits

Note: While you can opt for the less expensive models, many 20A outlets will enable you to simply strip the ends of the 12/2 wire and insert it into the back of the receptacle in order to make the electrical connection. You then screw down the retention screws which internally clamp down on the wire. Less expensive models will require you to make a bend in the wire so that it may wrap around the outside screw terminal and get locked in place in that manner.

Method 2: Replacement of a Traditional Receptacle & Downstream Circuit Protection

When you replace a standard receptacle with a GFCI, you can also protect any outlets or fixtures which exist downstream from the GFCI. To do this you'll need to use the LOAD terminals on the GFCI which are typically covered by a yellow (or other color) sticker.

GFCI receptacle - The LOAD terminals are only used if you are passing power through the GFCI to protect additional receptacles downstream.

Breakdown of Installation Steps:

1. Turn off the breaker at the panel which controls the circuit you are working on. If the circuit breakers aren't labeled (as is often the case), you can find the right one by plugging a light or clock radio into the receptacle you are updating. Then you simply turn off the breakers one by one until the light or radio goes off. It helps to have an assistant during this phase. Once you turn off the correct breaker it's always a good idea to mark it with tape to make sure a "helpful" person doesn't accidentally flip it back on while you're still working.
2. Test the outlet with a circuit tester to be verify that the power is indeed off (there's nothing worse than finding out the hard way).
3. Remove the receptacle's cover plate and the screws holding the outlet in place and unscrew/disconnect the wires from the outlet.
4. At this point you'll need to take note as to which wires are the power supply "LINE" wires and which are the downstream "LOAD" wires (which allow the GFCI to work as intended and protect all the outlets on the "LOAD" side.) To do this, make certain the wires are completely separate from one another then turn the circuit-breaker back on in the panel box.
5. Use a circuit tester to determine which set of wires carries the power (the "LINE" wires).
6. Turn the power back off and re-tape the breaker in the panel box to avoid accident re-activation.
7. Re-strip and connect the power-supply wires to the terminals marked "LINE" and the downstream wires to the terminals marked "LOAD". Remember, White wires connect to Silver screws and Black wires connect to Brass Screws. Connect the bare ground wire(s) to the green (Ground) screw. (See Diagram B).
8. Replace the receptacle, screw it back into the box and attach the cover plate.
9. Turn the power back on at the circuit-breaker panel.
10. Plug a clock radio or light into the outlet.
11. Test the GFCI by pressing the Black "Test" button on the outlet. If the clock radio or light turns off, the outlet is working.
12. Reset the GFCI by pressing the Red "Reset" button on the outlet until it clicks into place. The clock radio or light should come back on.

 

Diagram B - Connections for LOAD and LINE circuits

Conclusion

Ground Fault Circuit Interrupters are critical in any home. If you are doing any rewiring or simply updating your house to bring it up to code you should pay attention to where GFCIs may be required. This is one of the least expensive things you can do to provide an incredibly beneficial level of safety to your family. It is important to understand exactly how the GFCI circuits can be wired (specifically, the LOAD function). In this way you can protect entire areas without having to replace each receptacle with the more expensive GFCI versions.