What is a GFI/GFCI?
A GFCI is a ground-fault circuit interrupter. It measures the current current flowing through the hot wire and the neutral wire. If they differ by more than a few milliamps, the presumption is that current is leaking to ground via some other path. This may be because of a short circuit to the chassis of an appliance, or to the ground lead, or through a person. Any of these situations is hazardous, so the GFCI trips, breaking the circuit.
GFCIs do not protect against all kinds of electric shocks. If, for example, you simultaneously touched the hot and neutral leads of a circuit, and no part of you was grounded, a GFCI wouldn’t help. All of the current that passed from the hot lead into you would return via the neutral lead, keeping the GFCI happy.
The two pairs of connections on a GFCI outlet are not symmetric. One is labeled LOAD; the other, LINE. The incoming power feed *must* be connected to the LINE side, or the outlet will not be protected. The LOAD side can be used to protect all devices downstream from it. Thus, a whole string of outlets can be covered by a single GFCI outlet.
Where should GFCIs be used?
The NEC mandates GFCIs for 110V, 15A or 20A single phase outlets, in bathrooms, kitchen counters within 6′ of the sink, wet-bar sinks, roof outlets, garages, unfinished basements or crawl spaces, outdoors, near a pool, or just about anywhere else where you’re likely to encounter water or dampness. There are exceptions for inaccessible outlets, those dedicated to appliances occupying fixed space, typically refrigerators and freezers, and for sump pumps and laundry appliances.
The NEC now requires that if your replace an outlet in a location now requiring GFCI, you must install GFCI protection. Note in particular – kitchen and bathroom outlets.
When using the “fixed appliance” rule for avoiding GFCI outlets, single outlet receptacles must be used for single appliances, duplex receptacles may be used for two appliances.
The CEC does not mandate as many GFCIs. In particular, there is no requirement to protect kitchen outlets, or most garage or basement outlets. Basement outlets must be protected if you have a dirt floor, garage outlets if they’re near the door to outside. Bathrooms and most exterior outlets must have GFCIs, as do pools systems and jacuzzi or whirlpool pumps.
There are many rules about GFCIs with pools and so on. This is outside of our expertise, so we’re not covering it in detail. See your inspector.
When replacing an outlet, it must now be GFCI-protected if such would now be required for a new installation. That is, a kitchen outlet installed per the 1984 code need not have been protected, but if that outlet is ever replaced, GFCI protection must now be added (under NEC). This is explicit in the 1993 NEC, and inspector-imposed in Canada.
Even if you are not required to have GFCI protection, you may want to consider installing it anyway. Unless you need a GFCI breaker (see below), the cost is low. In the U.S., GFCI outlets can cost as little as US$8. (Costs are a bit higher in Canada: C$12.) Evaluate your own risk factors. Does your finished basement ever get wet? Do you have small children? Do you use your garage outlets to power outdoor tools? Does water or melted snow ever puddle inside your garage?
Where shouldn’t I use a GFCI?
GFCIs are generally not used on circuits that (a) don’t pose a safety risk, and (b) are used to power equipment that must run unattended for long periods of time. Refrigerators, freezers, and sump pumps are good examples. The rationale is that GFCIs are sometimes prone to nuisance trips. Some people claim that the inductive delay in motor windings can cause a momentary current imbalance, tripping the GFCI. Note, though, that most GFCI trips are real; if you’re getting a lot of trips for no apparent reason, you’d be well-advised to check your wiring before deciding that the GFCI is broken or useless.
What is the difference between a GFCI outlet and a GFCI breaker?
For most situations, you can use either a GFCI outlet as the first device on the circuit, or you can install a breaker with a built-in GFCI. The former is generally preferred, since GFCI breakers are quite expensive. For example, an ordinary GE breaker costs ~US$5; the GFCI model costs ~US$35. There is one major exception: if you need to protect a multi-wire branch circuit (two or more circuits sharing a common neutral wire), such as a Canadian-style kitchen circuit, you’ll need a multi-pole GFCI breaker. Unfortunately, these are expensive; the cost can range into the hundreds of dollars, depending on what brand of panel box you have. But if you must protect such a circuit (say, for a pool heater), you have no choice.
One more caveat — GFCI outlets are bulky. You may want to use an oversize box when installing them. On second thought, use large (actually deep) boxes everywhere. You’ll thank yourself for it.
Incidentally, if you’re installing a GFCI to ensure that one specific outlet is protected (such as a bathroom), you don’t really have to go to all of the trouble to find the first outlet in the circuit, you could simply find the first outlet in the bathroom, and not GFCI anything upstream of it. But protecting the whole circuit is preferred.
When you install a GFCI, it’s a good idea to use the little “ground fault protected” stickers that come with it and mark the outlets downstream of the GFCI. You can figure out which outlets are “downstream”, simply by tripping the GFCI with the test button and see which outlets are dead.
Note that the labels are mandatory for GFCI-protected-but-ungrounded three prong outlets according to the NEC.
Learn about the Purpose of Ground Prong here>>