How the GFCI work's and how to install

Submitted by JodyBabiash on Thu, 03/10/2011 - 08:55.

Ground-Fault Circuit Interrupters (GFCIs)

by Nick Gromicko and Ethan Ward

What is a GFCI?

A ground-fault circuit interrupter, or GFCI, is a device used in electrical wiring to disconnect a circuit when unbalanced current is detected between an energized conductor and a neutral return conductor. Such an imbalance is sometimes caused by current "leaking" through a person who is simultaneously in contact with a ground and an energized part of the circuit, which could result in lethal shock.

GFCIs are designed to provide protection in such a situation, unlike standard circuit breakers, which guard against overloads, short circuits and ground faults.

It is estimated that about 300 deaths by electrocution occur every year, so the use of GFCIs has been adopted in new construction, and recommended as an upgrade in older construction, in order to mitigate the possibility of injury or fatality from electric shock.

History

The first high-sensitivity system for detecting current leaking to ground was developed by Henri Rubin in 1955 for use in South African mines. This cold-cathode system had a tripping sensitivity of 250 mA (milliamperes), and was soon followed by an upgraded design that allowed for adjustable trip-sensitivity from 12.5 to 17.5 mA. The extremely rapid tripping after earth leakage-detection caused the circuit to de-energize before electric shock could drive a person's heart into ventricular fibrillation, which is usually the specific cause of death attributed to electric shock.

Charles Dalziel first developed a transistorized version of the ground-fault circuit interrupter in 1961. Through the 1970s, most GFCIs were of the circuit-breaker type. This version of the GFCI was prone to frequent false trips due to poor alternating-current characteristics of 120-volt insulations. Especially in circuits with long cable runs, current leaking along the conductors’ insulation could be high enough that breakers tended to trip at the slightest imbalance.

Since the early 1980s, ground-fault circuit interrupters have been built into outlet receptacles, and advances in design in both receptacle and breaker types have improved reliability while reducing instances of "false trips," known as nuisance-tripping.

NEC Requirements for GFCIs

The National Electrical Code (NEC) has included recommendations and requirements for GFCIs in some form since 1968, when it first allowed for GFCIs as a method of protection for underwater swimming pool lights. Throughout the 1970s, GFCI installation requirements were gradually added for 120-volt receptacles in areas prone to possible water contact, including bathrooms, garages, and any receptacles located outdoors.

The 1980s saw additional requirements implemented. During this period, kitchens and basements were added as areas that were required to have GFCIs, as well as boat houses, commercial garages, and indoor pools and spas. New requirements during the '90s included crawlspaces, wet bars and rooftops. Elevator machine rooms, car tops and pits were also included at this time. In 1996, GFCIs were mandated for all temporary wiring for construction, remodeling, maintenance, repair, demolition and similar activities and, in 1999, the NEC extended GFCI requirements to carnivals, circuses and fairs.

Watch this small video on how they work