By Vincent Plank, CSP
Safety Management Group
We’ve all seen ground-fault circuit interrupters or GFCIs at home near sinks in the bathroom and kitchen; but what exactly does a GFCI do, how does it work and where are they required?
OSHA defines a GFCI as a device for the protection of personnel that functions to deenergize a circuit or portion thereof 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 layman’s terms, a GFCI is an automatic device that protects people from serious electrical shock in the event of a ground-fault.
GFCIs work through an internal sensor that detects changes or imbalances in 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 current to shut off electricity to protect people from receiving a dangerous shock. GFCIs can trip in as little as 1/40 of a second! Due to their design, GFCIs can also protect against fires and overheating.
GFCIs are not designed to protect people from line contact hazards (i.e. a person with a hot and a neutral wire in each hand).
Is there a difference between a GFCI and a circuit breaker? A circuit breaker is an overcurrent device that closes the circuit within a predetermined overload, whereas a GFCI detects leakage current.
There are several types of GFCIs. All are designed to provide ground-fault protection; the primary difference is their application.
1. Receptacle type GFCIs are commonly found in the general industry, residential and commercial industry. This type of GFCI is typically designed as a dual configuration and is relatively inexpensive to purchase. An additional benefit of receptacle type GFCIs is the possibility to provide ground-fault protection for additional non-GFCI receptacles connected in circuit series. For proper protection the GFCI must be used as the first circuit to provide “downstream” protection.
2. Portable type GFCIs are moveable by design. This type is typically plugged into a non-GFCI outlet or can be connected with a cord and plug design. Some portable type GFCIs can be used in outdoor environments. These will be 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 will disconnect power to the outlets if any supply conductor is open.
3. Cord-connected GFCIs are designed to protect the cord and all equipment connected. Similar to the portable type, it features a no-voltage release device which will disconnect power if any supply conductor is open.
4. Circuit-breaker type GFCIs are designed to function as a standard circuit breaker and provide ground-fault protection. This type can protect an entire branch circuit.
5. Permanently mounted type GFCIs are installed in an enclosure and are permanently wired to the supply. These are commonly utilized around commercial swimming pools and other comparable wet locations.
There are two classes of GFCIs. Class A devices are designed to trip when current flow, in other than normal path, is 6 milliamperes or greater. The parameters are 5 milliamperes plus/minus 1 milliampere. Class B devices are designed to trip when current flow, in other than the normal path, is 20 milliamperes or greater. Class B devices are designed for use 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. To test GFCIs, turn on the tool or appliance connected to the GFCI and press the TEST button, the tool should immediately turn off. If it does not, there is a wiring problem or a GFCI failure, either problem 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 a period time, GFCIs can wear due to certain use of appliances or tools. When GFCIs trip on a regular basis, it is time to be replaced. In residential applications, Underwriters Laboratories estimated that the expected useful life of GFCIS is about 40 years.
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 permanent wiring of the structure and are in use by employees. This requirement is found in 1926.404(b)(1). Portable generators are commonly used on construction sites and also require the use of GFCIs.
In the 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 to ground-fault hazards. There are also GFCI requirements for construction-like activities in the 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. These requirements can be found in 1910.304(b)(3).
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 expose wires. GFCIs are required to be present in several settings. These include: 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.
Demystifying the Ground Fault Circuit Interrupter
