Editing Residual-current device (section)

==History and nomenclature==
The world's first high-sensitivity [[Earth_leakage_circuit_breaker|earth leakage protection system]] (i.e. a system capable of protecting people from the hazards of direct contact between a {{Not a typo|line}} conductor and earth), was a second-harmonic magnetic amplifier core-balance system, known as the magamp, developed in [[South Africa]] by [[Henri Rubin]]. Electrical hazards were of great concern in South African [[gold mine]]s, and Rubin, an engineer at the company C.J. Fuchs Electrical Industries of Alberton Johannesburg, initially developed a cold-cathode system in 1955 which operated at 525{{nbsp}}V and had a tripping sensitivity of 250{{nbsp}}mA. Prior to this, core balance earth leakage protection systems operated at sensitivities of about 10{{nbsp}}A.

The cold cathode system was installed in a number of gold mines and worked reliably. However, Rubin began working on a completely novel system with greatly improved sensitivity, and by early 1956, he had produced a prototype second-harmonic magnetic amplifier-type core balance system (South African Patent No. 2268/56 and Australian Patent No. 218360). The prototype magamp was rated at 220{{nbsp}}V, 60{{nbsp}}A and had an internally adjustable tripping sensitivity of 12.5–17.5{{nbsp}}mA. Very rapid tripping times were achieved through a novel design, and this combined with the high sensitivity was well within the safe current–time envelope for ventricular fibrillation determined by [[Charles Dalziel]] of the [[University of California, Berkeley]], United States, who had estimated electrical shock hazards in humans.  This system, with its associated circuit breaker, included overcurrent and short-circuit protection. In addition, the original prototype was able to trip at a lower sensitivity in the presence of an interrupted neutral, thus protecting against an important cause of electrical fire.

Following the accidental electrocution of a woman in a domestic accident at the Stilfontein gold mining village near [[Johannesburg]], a few hundred F.W.J. 20{{nbsp}}mA magamp earth leakage protection units were installed in the homes of the mining village during 1957 and 1958.  F.W.J. Electrical Industries, which later changed its name to FW Electrical Industries, continued to manufacture 20{{nbsp}}mA single phase and three phase magamp units.

At the time that he worked on the magamp, Rubin also considered using [[transistor]]s in this application, but concluded that the early transistors then available were too unreliable. However, with the advent of improved transistors, the company that he worked for and other companies later produced transistorized versions of earth leakage protection.

In 1961, Dalziel, working with Rucker Manufacturing Co., developed a transistorized device for earth leakage protection which became known as a ground fault circuit interrupter (GFCI), sometimes colloquially shortened to ground fault interrupter (GFI). This name for high-sensitivity earth leakage protection is still in common use in the United States.<ref>Charles F. Dalziel, Transistorized ground-fault interrupter reduces shock hazard,  IEEE Spectrum, January 1970
</ref><ref>The Professional Engineer, Official Journal of the Federation of Societies of Professional Engineers of South Africa, pp 67, Vol 6(2) 1977
</ref><ref>Earl W. Roberts, Overcurrents and Undercurrents – All about GFCIs: Electrical Safety Advances through Electronics, Mystic Publications, Mystic CT, 1996
</ref><ref>Edward L. Owen, Power System Grounding Part II: RCD & GFCI, IEEE Industry Applications Magazine, July/August 1996
</ref><ref>Forging ahead: South Africa’s Pioneering Engineers, G R Bozzoli, Witwatersrand University Press, 1997
</ref>

In the early 1970s most North American GFCI devices were of the circuit breaker type. GFCIs built into the outlet receptacle became commonplace beginning in the 1980s. The circuit breaker type, installed into a [[Electrical distribution panel|distribution panel]], suffered from accidental trips mainly caused by poor or inconsistent insulation on the wiring. False trips were frequent when insulation problems were compounded by long circuit lengths. So much current leaked along the length of the conductors' insulation that the breaker might trip with the slightest increase of current imbalance. The migration to outlet-receptacle–based protection in North American installations reduced the accidental trips and provided obvious verification that wet areas were under [[National Electrical Code|electrical-code]]–required protection. European installations continue to use primarily RCDs installed at the distribution board, which provides protection in case of damage to fixed wiring. In Europe socket-based RCDs are primarily used for retrofitting. <!-- The term [[earth leakage circuit breaker]] (ELCB) is also sometimes inaccurately applied to RCDs, but really 'ELCB' refers to a related but different device. RCDs were often formerly labeled as ELCBs, and the two have a lot in common, hence the devices are confused in many minds. -->