Every year tens of thousands of Americans are injured in electrical accidents in and around the home according to a DOE (Department of Energy) report. Every year approximately 300 Americans die from accidental electrocutions in the home with thousands more being hospitalized with serious burns and other consequences resulting from this accidental contact with electricity. Most of these electrocutions, at least 66 percent of them, could have been prevented if the home was properly equipped with GFCI (Ground Fault Circuit Interrupter) receptacles where required by the NEC (National Electric Code). Let’s begin by taking a look at the difference between a “Ground Fault” and a “Short Circuit.”
“Short Circuit” Vs “Ground Fault”
A “Short Circuit” occurs when the “Hot” conductor makes direct contact with the “Grounded” or with the “Grounding” conductor of the circuit. When a short circuit occurs, the CB (Circuit Breaker) trips open or the fuse blows. Fuses and circuit breakers are designed to protect the electrical system against short circuits. Circuit breakers and fuses protect the structure against fires caused by short circuits; they do not protect human beings and animals against electrical shocks. A “Ground Fault” occurs when the normally insulated grounded conductor, the “Neutral” conductor, makes direct electrical contact with an ungrounded metal surface such as the metal case of a household toaster. When such a ground fault occurs the potential for a fatal electric shock to occur is present because electricity will always take the path of least resistance to ground. If a person while multitasking touches the toaster with the ground fault and the sink at the same time, they become the path of least resistance to ground. The electrical current will travel up one arm, across their heart, and out their other arm. This shock could easily be fatal because it takes less than 20 Milliamps or 0.020 Amperes to cause fibrillation of the heart muscles and paralysis of the diaphragm.
Circuit breakers and fuses are not designed to protect human beings and animals from shocks caused by a ground fault condition. They aren’t even aware that a problem exists because the fault occurs on the circuits return path. The person or animal receiving the shock is simply replacing the normal return path, the circuits grounded conductor, with his or her body because his or her body is the least resistant path to ground. GFCIs (Ground Fault Circuit Interrupters), on the other hand, are designed specifically to protect humans and animals against shocks caused by ground fault conditions. Ground Fault Interrupters measures the current flow in both the hot and neutral conductors and compare them one to the other. In a properly functioning circuit, these two currents are equal in amplitude but flowing in opposite directions so they cancel one another out in the detection circuitry. When a ground fault is present the amplitude of the current flowing in the hot conductors exceeds the amplitude of the current flowing in the neutral or grounded conductor. When such an imbalance is detected and exceeds the trip threshold of 6 Milliamps or 0.006 Amperes the GFCI trips open, opening both the neutral and hot legs of the circuit. The imbalance is detected by a differential amplifier using miniscule toroidal coil as an input source. The output from the differential amplifier feed a tiny solenoid coil that is mechanically connected to the GFCIs internal trip mechanism. Now that we know what a GFCI is and how they operate, let’s look at where GFCI protected receptacles need to be installed.
Mandatory GFCI receptacle locations for dwellings
According to the Electrician’s Bible, the NEC (National Electric Code) Handbook, Article 210-8 (A), GFCI protection is required for all receptacles located in
- Bathrooms, Article 210-8(A)(1)
- Garages and other out buildings with a floor at or below grade level , Article 210-8(A)(2)
- All outdoor receptacles located at grade level , Article 210-8(A)(3)
- Crawl spaces at or below grade level , Article 210-8(A)(4)
- All receptacles located in unfinished basements , Article 210-8(A)(5)
- All receptacles installed to service kitchen countertop areas , Article 210-8(A)(6)
- All receptacles within 1.8 meters or 6 feet of the outside edge of laundry, wet bar or utility sink , Article 210-8(A)(7)
GFCI Receptacles differ physically from regular duplex receptacles in that they are a great deal larger so you need to be sure that there is enough room in the device box to install one. As a rule they will fit but there are situation where the original electrician used a shallow device box instead of a standard depth box and in that case you would have to remove the old box and install a standard depth box but that’s a topic for another DIY Electrician’s Guide. The electrical connections on a GFCI Receptacle also differ. On the back of a GFCI Receptacle you will find two sets of terminals, one set is marked “Line” and the other set is marked “Load.” When installing a GFCI Receptacle, the conductors bringing power into the first device box is connected to the line side of the GFCI Receptacle. The conductors feeding all the receptacles downstream from the GFCI Receptacle is connected to the load terminals. The green grounding screw on the GFCI Receptacle is connected to the circuit’s grounding conductor just as with any other receptacle. Connecting the feed conductors to the line side and the downstream receptacles to the load side is very important because if you reverse the connection the GFCI will not function properly if at all. Okay, let’s begin our project.
1. Turn off the CB protecting the receptacle circuit that you will be working on. If you aren’t sure which breaker controls the circuit use your circuit breaker locator (See The DIY electrician’s guide to replacing receptacles. This guide will also give you valuable information on making pigtail splices, etc) to locate the proper breaker. Once you’ve located the proper breaker and turned it off, use your non-contact voltage detector to make sure that the circuit is actually safe to work on.
2. Remove all the old receptacles from their device boxes and separate the wires. Make sure that none of the wires touch one another or the metal device box.
3. In this step you will be working with energized conductors so be very careful. Turn the CB back on for a moment so you can determine which conductors bringing power from the breaker panel. You could use your digital multimeter for this task but your non-contact voltage detector will do the job and it will be safer for you. Simply bring the tester near each black insulated conductor until it indicates the presence of voltage, that’s the set of conductors coming from the panel and they are the conductors that you will connect to the line side of the GFCI Receptacle. All the other conductors in the box will connect to the load side of the GFCI.
4. Fixing the position of those conductors firmly in your mind’s eye, turn the breaker off again.
5. Install the GFCI Receptacle in the first device box and then reinstall all the receptacles downstream from it. Remember what I said in The DIY electrician’s guide to replacing receptacles about the use of pigtail splices and the proper way to connect conductors to screw terminals.
6. After all the receptacles are back in place and their covers are in place, turn the CB back on.
7. On the front of the GFCI Receptacle there are two buttons, one marked “test,” the other marked “reset.” On some GFCI Receptacles there will also be a light that indicates when the GFCI has tripped open. If this light is lit when you first turn the breaker on, press the reset button. The light should go out and stay out.
8. Using your Digital Multimeter check for voltage at the GFCI Receptacle and at all the receptacles downstream from it. They should all be live with nominal 110-Volts. If the GFCI is live but the other aren’t, turn off the CB and check to see if you reversed the connections, line and load, on the GFCI. Most likely that will be your problem.
9. If the GFCI Receptacle and all the other downstream receptacles check good, push the “test” button to trip the GFCI open and then test again. This time all the receptacles including the GFCI Receptacle should be dead.
