Ground-Fault Circuit Interrupters (GFCIs)

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Ground-Fault Circuit Interrupters (GFCIs)

By Diane M. Calabrese / Published August 2016



Most of us have experienced an electric shock, if only the little jolt of static electricity generated by friction when we walked on a rug in our stocking feet. Electric shock associated with tools is a much more serious matter.

Burns and heart failure can result from electric shock. Initial injuries can be compounded if the individual receiving the shock is on a ladder or a lift and the shock contributes to a fall. For some individuals, even a small amount of electric current can lead to heart fibrillation and death.

Protecting those who use electric tools from shock has long been a goal of industry and safety regulators. Consequently, there are requirements for electric tools.

In the United States and elsewhere, the requirements include that an electric tool have a three-wire cord with a ground and be plugged into a grounded receptacle, be double insulated, or be powered by a low-voltage isolation transformer. A three-wire cord has two current-carrying conductors and a grounding conductor. Double-insulated tools have an internal layer of insulation to isolate the external housing of the tool.

The grounding conductor is designed to speed the path of electric current—create a low-resistance path—to the earth, so that it will not build up and cause electric shock. The same electromotive force (voltage, or difference in electric potential, which is measured in volts) that enables work to be done can cause havoc (shock, electrocution) if there is a short (short circuit) that disrupts the desired path of current.

When a ground is working properly, the voltage will not build up to a dangerous level because it will follow the grounding path. The OSHA [Occupational Safety & Health Administration] construction standard requires two types of grounds. They are a system or service ground and an equipment ground.

In system or service ground, the wire called a neutral conductor is grounded at the transformer and at the service entrance to the building. It protects machines, tools, and insulation against damage. The equipment ground is designed to enhance protection to workers if some event (breach) causes the metal on the tool to become energized.

Here’s the rub: Grounding protocols can be followed scrupulously, as they should be, and there can still be a danger. If there is a break in a grounding system, an equipment user might not know it until it’s too late (i.e., when a shock occurs.) Enter the ground-fault circuit interrupter (GFCI). The GFCI is designed to take over if there is a breach in grounding.

A ground fault is a break in the low-resistance, or grounding, path from a tool or an electrical system. If such a break occurs, the electric current may take another path, which could be through the body of the equipment user. That is, unless a GFCI is in place.

The GFCI can detect changes in the amount of current along the circuit. If there is a difference of five milliamperes, for instance, the GFCI responds by shutting off the electric power. [The trip point for the cutoff mechanism varies with the type of equipment from about four to six milliamperes.] The entire detection and the shutoff sequence occurs in as little as 1/40 second.

The GFCI cannot protect against everything. Although it is still possible to get a shock with a functioning GFCI, the jolt would be unlikely to be lethal or cause much harm.

In addition to mitigating incidents of bodily harm, the GFCI also protects against fires, overheating, and destruction of wire insulation. Of course, the GFCI does not protect in certain situations, such as holding two hot wires or contacting an overhead power line.

Types of GFCI include a receptacle type, a portable type, and a cord-connected type. Any new electrical outlet installed in a home by a licensed, code-compliant contractor will have a GFCI. Small appliances, such as space heaters, now have a GFCI in the cord, so the GFCI is a familiar device.

OSHA regulations for the use and identification of grounded and grounding conductors are outlined in section 1926.404 of Safety and Health Regulations for Construction (1926 in Standards 29 CFR). According to the section, approved GFCIs must be fitted to all 120-volt, single-phase 15- and 20-ampere receptacle outlets for construction sites that are not a part of the permanent wiring of the building. (An alternative is participation in an assured equipment grounding conductor program, AEGCP).

Any tool in service experiences wear. Insulation may break under certain ambient conditions, a wire may fray or become exposed, and so on. The GFCI adds a layer of protection from electric shock. It should always be part of full protection. Full protection consists of layers that include following the manufacturer’s guide to using the tool, choosing double-insulated tools and equipment, inspecting a tool before using it, and taking a tool out of circulation (and applying a warning tag) if it has a defect.

Q&A On GFCIs and Pressure Washers

Cleaner Times (CT) put questions about GFCIs in the pressure washer industry to Barry Milstead, sales manager, electrical safety products at Tower Manufacturing Corporation in Providence, RI.

CT: How would you characterize the way GFCIs were integrated into equipment in the pressure washer industry?

Milstead: GFCIs were integrated into the pressure washer industry by UL as a result of ‘accidents’ in the field. [UL is the global independent safety science company that offers expertise and brings together stakeholders across commercial, industrial, and consumer interests.]

Electric pressure washers were originally manufactured with a 10-foot power cord. Due to the portability of the equipment, ten feet didn’t allow the required distance to reach most applications. Twenty-five-foot extension cords were being added to the power cords to allow users the mobility they needed. The problem then became a long cord (electricity), lying in a wet environment, and being used by people—the three ingredients for shock and electrocution.

The pressure washer equipment was not and is not inherently dangerous. The extension cord and the connection to the power cord were the problem points. Two things occurred: One, the power cord was lengthened to 35 feet—the original 10 feet for the old power cord and the 25-foot extension cord. And, two, a GFCI was added to protect the users from a possibly damaged power cord and also the machine.

CT: What’s the greatest misunderstanding about the function of the GFCI?

Milstead: Originally, people didn’t know what the device on the power cord actually did. After these many years, people have been exposed to GFCIs in their homes, workplaces, and on various pieces of equipment/appliances. We no longer get many inquiries as to what a GFCI is or why it is used. They may not know how it works, but they recognize what it does.

CT: In 2016, how probable is it that a GFCI will fail?

Milstead: Our records indicate an approximately one-tenth of one percent failure rate from manufacturing defects. These are normally caught when they are tested upon attachment to a piece of equipment. Field failures are normally due to abuse of the GFCI, not from a manufacturing defect, though that can possibly happen due to a component failure. Keep in mind that a GFCI is a piece of electronics and should be treated as such.

CT: How can the end user of a pressure washer/or service technician be certain that a GFCI is working properly?

Milstead: By UL standard (UL943), a GFCI must contain a test and reset button. To test the unit, a person presses the test button, which simulates a ground fault. The GFCI should disconnect the power traveling through the GFCI to the ‘load’ by breaking the contacts open. The person then presses the reset button which then ‘resets’ the contacts and allows the power to again flow to the ‘load.’ This, of course, is done with the GFCI plugged into the power source and with a ‘load’ attached and in the ‘on’ position. The test will turn off the ‘load’ and the reset will turn the ‘load’ on again. If the GFCI is not working or has failed, the ‘load’ will not perform as described. 

CT: Are there other questions you receive that we didn’t cover here? 

Milstead: We get lots of questions, but most are related to trip levels—a nominal 4mA [milliamperes]—and nuisance tripping.

Safety First

In 2014, 4,679 U.S. workers were killed on the job. Just over 20 percent (349) were killed in construction. Among the deaths in construction, those from falls predominated (349), but electrocutions (74) and struck by an object (73) were second and third. Given some falls probably were triggered by electric shock, the importance of taking all precautions to reduce its incidence, including universal application of GFCIs, is apparent.