What Does GFCI Mean, and What Do They Do?
When working with electrical circuits, a normal operation consists of the same amount of current flowing from line to load and returning from load to line. Ground fault hazards occur when the low-resistance ground path from a tool or electrical system becomes temporarily interrupted or breaks completely. When this occurs, leakage current doesn't return through the intended path, leaking to the ground instead.
Ground fault conditions can occur through the exposure of connectors and tools to excessive moisture. Because electrical current always seeks the quickest path complete a circuit, someone operating a tool or working with an appliance can inadvertently become an alternative path to ground. At a minimum, the resulting electrical shock could cause an individual to damage the component or appliance that they're working on; the worst-case scenario, however, is serious injury or even death.
Ground-Fault Circuit Interrupters
Exposure to as little as 18 milliamperes of current can kill a worker, causing chest muscles to contract to the point where breathing ceases or the heart stops pumping. Designed as a fast-acting circuit breaker, a Ground-Fault Circuit Interrupter (or GCFI, for short) compares the amount of line current flowing to equipment with the amount of load current flowing from equipment along the circuit conductors. A GCFI will shut down electrical circuit in a fraction of a second if it detects a minimum of 5 milliamperes of leakage flowing from the circuit to ground, preventing electric shocks.
In contrast to a traditional circuit breaker, which shuts down a circuit if an overload condition occurs, a GCFI only shuts down circuit operation if there is current leakage. As a result, protection from ground fault interruptions doesn't cover every possible electrical hazard. Instead, GCFIs limit the duration of an electrical shock endured by an individual. In other words, a GCFI protects only against electrical shock, fires, overheating, and degradation of wire insulation caused by a ground fault.
OSHA’s GCFI Standards for the Construction Industry
Employers should ensure that all electrical power tools are equipped with GCFI protection. OSHA standards specify guidelines for the use of ground fault circuit interrupters at construction sites, covering the type of protection as well as minimum requirements for use. For example, any job site using 120 volt, single-phase, 15 or 20 ampere electrical outlets not connected to the permanent wiring of an occupied building or structure must utilize GCFI protection.
OSHA also requires that employers implement an Assured Equipment Ground Conductor Program (AEGCP) at each job site. In basic terms, the AEGCP ensures that workers follow important best practices, such as visually inspecting any equipment connected by a cord and plug as well as cord sets for possible damage. Workers also cannot use spliced cords or attempt to interchange receptacles or cords intended for different voltages, frequencies, or types of current. The OSHA specifies that employers and workers should tag damaged or defective equipment and remove the equipment from use until fully repaired.
Types of GCFI Protection
Permanent GCFI receptacles fit into a standard outlet box and protect against ground faults when a device plugs into the receptacle; a permanent GCFI receptacle can also protect other outlets in branch circuits. Portable GCFI protection consists of extension cords which use GCFI protection, offering the advantage of easy movement from one job location to another. Both types include test and reset buttons.