Understanding Ground Fault Circuit Interrupters
By Vincent Plank, CSP
Safety Management Group
You’ve probably seen ground-fault circuit interrupters (GFCIs) at home near bathroom and kitchen sinks, but how exactly do they work and where are they required?
OSHA defines a GFCI as a device for the protection of personnel that can deenergize a circuit or portion of a circuit within an established period of time when a current to ground exceeds some predetermined value that is less than that required to operate the overcurrent device of the supply circuit. In simple terms, a GFCI is an automatic device that protects people from serious electrical shock in the event of a ground fault.
These devices work through an internal sensor capable of detecting changes or imbalances in the current going to and returning from the appliance or tool. When the sensor detects a change of approximately 5 milliamperes of current going to and returning from, the GFCI interrupts the flow of electricity to protect a dangerous shock from occurring in as little as 1/40 of a second. A GFCI’s design can also protect against fires and overheating. GFCIs are not designed to protect people from line contact hazards, such as when someone is holding both a hot and a neutral wire in their hands.
While circuit breakers and GFCIs both interrupt the flow of electricity, they serve different purposes. A circuit breaker is an overcurrent device that closes the circuit within a predetermined overload, while a GFCI detects leakage current.
There are several types of GFCIs. While all are designed to provide ground fault protection, their applications require different designs, as follows:
Receptacle-type GFCIs are commonly found in general industry, along with residential and commercial locations. Typically designed as a dual configuration, this type is relatively inexpensive. An additional benefit of is the possibility that it will provide ground-fault protection for additional non-GFCI receptacles connected in circuit series. The GFCI must be used as the first circuit to provide this “downstream” protection.
Portable-type GFCIs are moveable and are typically plugged into a non-GFCI outlet or connected with a cord and plug design. Some can be used in outdoor environments and are placed in enclosures appropriate for the environment. Certain types may be listed as rainproof for exposure to rain. The portable type also incorporates a no-voltage release device which disconnects power to the outlets if any supply conductors are open.
Cord-connected GFCIs protect the cord and all equipment connected to it. Like the portable type, they include a no-voltage release device which will disconnect power if any supply conductor is open.
Circuit breaker-type GFCIs are designed to function as a standard circuit breaker while providing ground-fault protection. This type can protect an entire branch circuit.
Permanently mounted-type GFCIs, normally installed in an enclosure and permanently wired to the supply, are commonly used around commercial swimming pools and similar wet locations.
There are two classes of GFCIs. Class A devices are designed to trip when abnormal current flow is 6 milliamperes or greater (the parameters are 5 milliamperes plus/minus 1 milliampere). Class B devices, designed to trip when abnormal current flow is 20 milliamperes or greater, are used on underwater swimming pool lighting installed prior to the adoption of the 1965 National Electrical Code.
GFCIs are designed with a built-in manual test and reset function. Permanent GFCIs should be tested at least monthly and portable GFCIs should be tested before use. Testing GFCIs is as simple as turning on the tool or appliance connected to the GFCI and pressing the TEST button. The tool should immediately turn off; if not, there is a wiring problem or a GFCI failure, either of which requires immediate attention. Pressing the RESET button will reestablish the electrical current to the circuit.
When a GFCI is tripped due to change in current, it must be manually reset. Once the GFCI has been reset, electrical power should be restored to the affected circuit. However, if the change in current remains, the GFCI will not reset. Over time, GFCIs can wear out and when they trip on a regular basis, they should be replaced. Underwriters Laboratories estimates the expected useful life of GFCIS at about 40 years in residential applications.
OSHA requires GFCIs on construction sites for all 120-volt, single-phase, 15- and 20-ampere receptacle outlets that are not a part of the structure’s permanent wiring and are being used by employees. Portable generators, commonly used on construction sites, also require the use of GFCIs.
In general industry, OSHA requires GFCIs for all 125-volt, single phase, 15- and 20-ampere receptacles installed in bathrooms or rooftops. These areas have the potential to expose employees to wet environments and a greater potential of ground fault hazards. There are also GFCI requirements for construction-like activities in general industry. These include certain maintenance, remodeling, or repair activities. When GFCI protection is required but not available for receptacles other than 125-volt, single-phase, 12-, 20-, and 30-ampere, the employer is required to implement an assured equipment grounding conductor program.
In summary, ground-fault protection is designed to protect employees from dangerous current that could result in electrical shock, electrical burns, fire, and death. Wear and tear on electric equipment can cause insulation break down, short circuits and exposed wires. GFCIs are required in several settings, including bathrooms; rooftops; temporary wiring for maintenance, remodeling, or repair; extension cords used for temporary electric power; and receptacles used for equipment in damp/wet locations.