The Ground Fault Circuit Interrupter is a case of necessity being the mother of invention. According to the National Electrical Manufacturers Association, in the mid-1970s, more than 600 people were electrocuted each year. By the turn of the 21st century, that number had dropped to fewer thanthan 200. Among the biggest reasons for that drop was the GFCI.
Distinct from general circuit breakers, which are for appliance protection, a ground fault circuit interrupter is for human protection against electrocution or shock.
Like fuses and circuit breakers, GFCIs are fast-acting circuit breakers designed to shut off electricity when it detects that current is flowing along an unintended path, such as water or a person. It works by measuring the current leaving the power source, or the hot wire, into the load, and comparing that current to the return side, or the neutral wire. If the current is not equal, then there must be a leak somewhere, so the GFCI turns the power off. A GFCI turns off the power if the current on the neutral side is less than the current on the load side by a very small amount (from 4 to 6 milliamps) because in normal operation, the flow of electricity will be equal. A difference causes the GFCI to trip within 25 milliseconds and open the circuit.
Local laws require GFCIs to be installed in kitchens, bathrooms, unfinished basements, anywhere near a sink, and outdoors. In other words, they are required anywhere where water could allow a short circuit to occur.
Specifically, NEC code requires GFCI protection for luminaries, lighting outlets, circulation, sanitation system equipment, and pump motor receptacles located near swimming pools. All 125V receptacles located within 20 feet of the walls of a pool must be protected by GFCI devices. Furthermore, the receptacles that supply pool pump motors that are rated 15A or 20A, 120V to 240V must have GFCI protection. If the pool has an electrically operated pool cover, it must be GFCI protected. It’s also essential to have GFCI protection for circuits supplying luminaries operating at greater than 15V.
When a GFCI is tripped, the device must be reset manually by pressing the reset button. If the problem has not been fixed, the GFCI will continue to shut off.
For permanent installation, GFCIs are available in two types. Most consumers are familiar with the receptacle type GFCI, which is similar to a common wall outlet. A receptacle type is installed in an electrical outlet box. Also available is a circuit breaker type that is installed in an electrical panel. These provide protection for every receptacle on that individual circuit.
There are also GFCIs that are attached to appliance cords like hair dryers and electric tools. These are temporary GFCIs and should not be used as an alternative to a permanent GFCI.
GFCIs should be tested on a monthly basis to ensure that they are still functional. They are electronic devices that can become damaged or wear out. Even if the GFCI circuit no longer works, the electrical receptacle may still continue to function, and this can
Figure 1. Source: National Electrical Manufacturers Association. Graphic shows the number of electrocutions has gone down with the prevalence of GFCIs.
Figure 2. GFCI receptacle present a dangerous situation. With either the circuit breaker GFCI or the receptacle GFCI, pushing the test button should turn off the power to the circuit. With receptacle GFCIs, pressing the test button should cause the reset button to pop up. With circuit breaker GFCIs, pressing the test button should cause the handle to move to the tripped position. In either case, remember to press the reset button or reset the handle to re-establish power and protection.
Many locations require GFCI protection, so it’s important to know how to install these devices. Installers need to understand how GFCIs function in order to provide their customers with the best installation.
But before attempting any electrical work, turn off the power at the service panel, and lock the electrical power box to prevent an unauthorized person from turning the power on.
GFCI receptacles have input holes or screws and output holes or screws referred to as the “line” leads and “load” leads. The line terminals are for connections from the service panel. The load terminals are to deliver power to another receptacle in the circuit. If there are no other receptacles on the circuit, the load lead should not be used. See Figure 2 on page 19.
The electrical cable coming from the service panel consists of two or three wires. It has a black hot wire, a white neutral wire, and a green grounding wire. From the service panel, the black hot wire is connected to a black or brass hot line terminal. The white wire is connected to the white or silver line terminal. The green wire is connected to the green grounding terminal.
One aspect of GFCI protection to consider is placement.
That is because the GFCI’s location along the circuit determines whether or not it also protects other receptacles along the circuit. See Figure 3 on GFCI placement.
If the GFCI is placed in position A, it will also provide protection to the load side, or receptacles B, C and D. If instead, the GFCI is in position D, it will not provide protection to receptacles A, B, and C.
When replacing an old receptacle, the situation can get complicated. For example, the existing receptacle may also be connected to another receptacle, and it’s important to identify its position in the series.
Remove the old receptacle from the electrical box. If there is only one cable consisting of 2 to 3 wires, the receptacle is probably in position D or else it is the sole receptacle for the circuit. See the graphic for GFCI placement.
On the other hand, when the old receptacle has been removed and there are two cables for a total of 4 to 6 wires, the receptacle is in position A, B, or C. Don’t assume that the old receptacle was correctly wired.
One common installation mistake that workers and even electricians make is what is called line load reversal. Current standards for GFCI devices make it so that if the line and load cables are acci- dently reversed, the device simply will not work. In older devices, however, it was possible to reverse the line and load connections.
In the case of some of the older GFCIs where the line and load cables are reversed, the outlet will continue to provide electricity, even when the test button has been pressed. Generally, people test their GFCIs by pressing the test button. This makes the reset button pop out, a signal that the outlet is now dead, and the GFCI has done its job. But with GFCIs where the line and load are reversed, that indicative pop still occurs, but the outlet is still live-a false positive. Furthermore, all outlets that are connected downstream of this outlet, presumed to be GFCI protected from the upstream GFCI, are also still live. It is common to find this mistake, and there are GFCI three-light testers that are available at most hardware stores that can diagnose this and other potentially dangerous situations.
Another installation mistake is called reversed polarity, where the hot wire is connected to the neutral terminal, while the neutral wire is connected to the hot terminal. See Figure 4. Appliances plugged into outlets whose polarity was reversed will still work, but they are dangerous. That’s because most appliances are wired to have the hot side of the circuit, not the neutral, controlled by their on/off switches.They present a shock hazard because even when they are off, if they are still plugged into an outlet and the hot and neutral wires were reversed, they are still getting electricity. People touching the outside metal of light bulbs and other appliances have been known to get shocked.