GFCIs or ground fault circuit interrupters

Scott Gibson, Contributing Editor

I'm told that if I were building a house today, I'd be required to use ground-fault circuit interrupters. What about an older house? It is a good idea to upgrade the wiring to include this type of outlet -- and, if so, how are they wired into an existing circuit that doesn't have a separate ground?

You're right about ground-fault circuit interrupters - better known as GFCIs. In new construction they're required in kitchens and bathrooms and in other areas that might get wet -- a garage or basement or around a pool, for instance.

GFCIs ... or ground fault circuit interruptersGFCIs are designed to trip when they sense even a minor imbalance in current between the hot (black) and neutral (white) legs of an electrical circuit. They shut off power to the receptacle in a fraction of a second -- fast enough so a potentially fatal shock is avoided.

They make just as much sense in an old house as they do in a new one. And they're easy to wire into an existing circuit so there's no reason not to tackle this upgrade.

And it's not the only requirement. Since 2002, the National Electric Code also has required devices called arc-fault circuit interrupters in bedroom circuits. That's in new construction, not existing houses.

Not all electricians think they're such a great idea. You may want to think twice before investing in an AFCI upgrade for an older house.

Wiring in a GFCI to an existing circuit

There's no such thing as too careful when you're working around wiring. (I know this because I once cut through a 240-volt line after my father, an electrical engineer, told me the line was dead. It wasn't.)

Start at the main panel by turning off the power to the outlet you want to upgrade. Then use a circuit tester to make sure the receptacle you're about to dismantle is really dead.

Disconnect the wires from the back of the old receptacle and wire in the new GFCI -- black wire to the gold colored screw, white to the silver screw. There are test buttons on the front of the receptacle to make sure it works.

The process is about that simple.

Many old houses have antiquated wiring systems with no separate ground -- that's the bare wire you'll find in modern cable along with the white and black wires.

A GFCI works just fine without that ground and will still protect you against shock.

Protect the whole run of receptacles

One other thing to remember. Branch circuits usually include a number of receptacles, one wired to the next. You can give all of them GFCI protection by wiring in a single GFCI receptacle at the start of the branch circuit.

In the outlet box, connect the black and white wires that come from the main panel to the screws marked "line" on the back of the GFCI receptacle. Then feed the next outlet from the screws marked "load."

Downstream receptacles will now behave just like GFCIs. If you get "line" and "load" mixed up, this will not be the case.

You can also use a GFCI circuit breaker to protect all of the receptacles on a branch circuit. It replaces a standard breaker in the main panel. Of course if your electrical system has never been upgraded from fuses to circuit breakers you're out of luck.

AFCIs work differently

When current jumps across a gap it's called an electrical arc. That can produce very high temperatures and result in a fire.

An AFCI is designed to sense an arc and turn off the power before it can cause any harm. It replaces a conventional breaker in the main panel, so if you've got an old fuse panel you're not a candidate for this upgrade.

Some electricians think that AFCIs have limited value in ungrounded wiring systems -- knob and tube, for instance, or non-metallic cable without an integral ground.

If you're really interested in adding AFCI protection, get some guidance from a licensed electrician first.

About the Author
An accomplished woodworker and carpenter, Scott Gibson is the former editor of Fine Woodworking magazine, and a former editor at Today's Homeowner and Fine Homebuilding magazines. He also is former managing editor of the Kennebec Journal, a daily newspaper in Maine.


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