How GFCIs Work
Most household circuits have electrical current flowing to and from receptacles, switches and other devices on two wires: the hot wire (usually covered in black insulation) and the neutral wire (usually covered in white). Each wire should have an equal amount of current flowing on it. If not, electricity is leaking from the circuit in search of a path back to the ground, a condition known as ground fault. If you happen to be using a receptacle or other device on that circuit, that electricity could flow through you and give you a bad shock.
GFCIs constantly monitor the difference between the hot and the neutral wires and instantly break the circuit if they detect an imbalance. While a standard breaker won't trip until it reaches its rated amperage, a GFCI trips when it detects a ground fault that measures in milliamps rather than amps. Installing GFCI protection is well worth the time and money, and it's almost as easy as wiring a receptacle.
Where to Install GFCIs
Ground fault protection has been creeping into building codes since 1968, when it was first required in swimming pool lighting. Now, GFCIs are required in all new bathrooms, garages, unfinished basements, outbuildings, whirlpool tubs, crawl spaces, small-appliance receptacles along the kitchen countertop, and other potentially damp places. The National Electric Code also requires that repairs or replacements of older wiring in these areas be GFCI-compliant. In other words, if you're replacing a receptacle in an area that requires ground-fault protection, you need to replace it with a GFCI receptacle, even if the existing receptacle isn't grounded. This is particularly important in kitchen and bathroom repairs and remodels. Wherever there's water and electricity in close proximity, there's a chance that you can be severely shocked or even electrocuted water is a dangerously efficient conductor.
GFCIs also work in older, ungrounded electrical systems. (A giveaway that wiring isn't grounded: the receptacles only take plugs with two, not three, prongs.) In fact, it's even more important to protect these systems with GFCIs: Since they contain no ground wire to allow stray current to flow back to the panel and trip the fuse or breaker, the current could flow through you instead, especially in a damp location. But, again, if you have a GFCI-protected circuit, the stray current would trigger the GFCI and open the circuit, breaking the flow of current in time to keep you alive and healthy.
There are two ways to add GFCI protection to your home: install a GFCI breaker in the main service panel to protect an entire circuit, or install individual GFCI receptacles. Typical GFCI breakers are more expensive they cost $30 or $40, while GFCI receptacles run only $7 or $8. However, installing a GFCI breaker is sometimes easier than trying to identify where on a circuit to install a GFCI receptacle to protect a particular area, especially in older homes that have had wiring added and additional boxes spliced into existing lines. You also need GFCI protection for appliances like spas that don't plug in but rather are wired directly to a power source. All in all, installing a GFCI breaker is the only way to go.
Step by Step: Installing a GFCI Breaker
Safety: You'll be working in a hot electrical panel. If this idea makes you uncomfortable, hire a qualified electrician. If you choose to do it yourself, wear safety glasses, use a screwdriver with an insulated handle, and stand on a rubber mat or another dry, nonconductive surface. Also, have a flashlight handy for when you turn off the house power you may need some additional light to work by.
1. Locate the breaker you need to change. If you're not sure which one it is, a radio turned up loud will help you find it. Plug it into the circuit you want to protect, and flip the breakers off one at a time until the radio falls silent. (Put a piece of tape on the breaker so you can find it easily.) Jot down the breaker's amperage (it's usually embossed on the toggle) and the panel's manufacturer name and box model number, and have the information handy when you're looking for a GFCI replacement. (Even though many brands may work in your panel, your panel's warranty may not apply if you use a brand that the panel manufacturer hasn't explicitly approved. That's why it's best to buy breakers from the manufacturer that made your panel.) Once you have your replacement, it's time to remove the old breaker and install the new GFCI breaker.
2. Turn off the power. At the top of the panel you'll see one large breaker, called the "main." It controls all power to the individual breakers. Turn it to the OFF position.
Safety: The wires that bring electricity into the service panel (usually at the top) will still be hot even after you switch off the main breaker, so never touch them.
3. Remove the panel face to expose the breakers. Each breaker will have a wire attached to its screw terminal. On the breaker you plan to replace, loosen the screw, unwrap the wire, and pull the wire aside. To remove the breaker, pull it up at one end normally the end toward the panel center then at the other.
4. Install the GFCI breaker. Switch your new GFCI breaker to OFF. Snap it into the panel, then take the black (or red) wire that was attached to the old breaker and attach it to the breaker terminal marked Line Power. (That terminal may also be black.)
5. Find the circuit's white (neutral) wire. Follow the wire that you attached to the breaker back to the cable where it comes into the box. You'll see a white wire coming in from the same cable. Follow the white wire to the neutral bus bar and loosen the screw terminal. Unwrap the wire from the screw, and attach it to the GFCI breaker terminal marked Load Neutral. Finally, attach the coiled wire (also called a pigtail) on the GFCI breaker to the neutral bus bar, either to the same screw from which you removed the circuit's neutral wire, or to another convenient open screw on the bus. Replace the panel face, make sure the GFCI is still off, and turn the panel's main switch back ON.
6. Test your installation. With the radio plugged in and turned up, switch the GFCI breaker to ON. The radio should start playing. Then, press the breaker's Test button. The breaker should trip, and the radio should fall silent as the circuit is broken. To reset the breaker, snap the toggle all the way to OFF, and then back to ON. Be sure to test the GFCI circuit about once a month thereafter to make sure it's in good working order.
1. Turn off the power. Start by turning the breaker for the circuit OFF at the main service panel. If you're not sure which breaker to use, see the radio trick above. Tape down the breaker switch and post a sign close by so that no one turns the breaker back on. Test the receptacle with a voltage tester to be sure the power's off.
2. Remove the old receptacle and test the circuit. Take off the receptacle cover, remove the screws that hold the old receptacle in place, and pull it from the box. Remove the wires from the terminals. If there are two or more cables coming into the box, separate the wires and group them together according to which cable they come from, so it's clear which ones come from the incoming feeder and which ones carry power downstream. Pull one cable's wires out to one side; if there's another, pull its wires to the opposite side.
In general, bare copper wires are ground, white are neutral, and black are hot. Make sure all wires are completely separate from one another, and then turn the power back on. Be careful not to touch any of the wires. Use your voltage tester to find the incoming hot wire. The wire should be black. The white wire in the same cable will be the neutral. Additional white and black wires will be extensions of the same circuit test them as well. With testing complete, turn the power off again.
3. Install the GFCI receptacle. Connect the black and white wires of the incoming power cable to the LINE terminals on the GFCI receptacle. Make sure the neutral wire goes to the LINE terminal marked neutral or white and the black or hot wire goes to the LINE terminal marked black or hot. Connect the bare copper wire (the ground wire) to the green screw on the receptacle.
If there's a second cable, it's there to carry power to other receptacles or perhaps to a light. If you want this cable to also have ground-fault protection, connect it to the LOAD screws on the GFCI receptacle. The second cable's neutral wire goes to the LOAD white or "neutral" screw, and the hot wire goes to the black or "hot" LOAD screw. If you don't want the second cable to have ground-fault protection, splice its hot, neutral and ground wires with the corresponding wires from the incoming feeder cable, and use short lengths of wire as jumpers between the spliced wires and the GFCI receptacle. (The idea is to never connect more than one wire to a terminal.) If there's more than one ground wire in the outlet box, splice them all together along with a 6-inch jumper wire and connect it to the receptacle's ground terminal.
Fold the wires carefully and stuff them into the box. Then screw the receptacle back into place and attach the cover that came with the receptacle.
4. Test your installation. Remove the tape you put on the breaker and switch the breaker back on. Plug in your radio. Press the receptacle's Test button, and the radio should go off. Press the Reset button, and the power should go back on. If there's no sound when you plug in your radio, chances are the Reset button popped to the "out" position during installation. Press the Reset button back in.
Testing and Resetting
Test your GFCI receptacles monthly, and replace any that don't trip when you push the Test button. A defective GFCI receptacle can still provide power without protecting you from shock. If a receptacle trips while you're using a device plugged into it, try resetting it once. If the receptacle trips again, there's probably a problem with the device. Have it checked and repaired before using it again.
GFCI receptacles can occasionally go bad and trip for no reason. Should this become a problem, replace the receptacle. If the new one trips, you may have a wiring problem. Consult an electrician.