Today, hundreds of millions of GFCIs are installed in
electrical systems in North America. A harmonized tri-national standard
defining Class A GFCIs was jointly issued by ANCE in Mexico as NMX J 520, CSA
in Canada as CSA C22.2, and by UL in the United States as UL 943 in 2008.
The standard describes Class A GFCIs as devices designed to
protect 95% of normal healthy adults by interrupting a circuit when a ground
fault current exceeds 6 milliamps. According to the standard, it must trip at 6
milliamps of leakage current and must not trip below 4 milliamps of leakage
current.
Since they are inverse-time devices, they react faster to
higher currents. Class B GFCIs were the original GFCIs with a minimum trip
current of 20 milliamps that were used in swimming pool lighting
circuits. They have long since been obsolete, but there are
still some installed and in use.
Since RCDs and earth leakage circuit breakers (ELCBs) have
higher trip currents, they do not meet the standard of a Class A GFCI in North
America. They are, however, considered personnel protection devices in some
other countries.
Since the development of GFCIs, the live production event
industry has been left to its own devices as to whether to use them or not. But
now the Entertainment Services and Technology Association (ESTA) is working on
BSR E1.19, Recommended Practice for the Use of Class A Ground-Fault Circuit
Interrupters (GFCIs) Intended for Personnel Protection in the Entertainment
Industry.
This recommended practice spells out when, where, and how to
use GFCIs in places of assembly, the production of film, video, and broadcast,
theatrical productions, carnivals, fairs, and similar events in North America.
It covers electrical services of 100 amps or less, 120–240
VAC single- and three-phase 60-Hz circuits where the voltage to ground does not
exceed 150 VAC. Note that since the voltage to ground in Europe is 230 VAC or
240 VAC, this standard specifically excludes those systems.
In brief, the standard calls for the use of GFCIs in any
outdoor, wet, or damp locations unless the circuit is for egress lighting, exit
lighting, or emergency lighting systems, or if tripping the GFCI could cause
injury.
Since the control circuit in a GFCI requires constant power,
the use of standard GFCIs on dimmed circuits is not allowed. There are, however, special GFCIs with a
separate non-dim input designed for use with certain dimmer racks.
There is another potential problem with using GFCIs in a
dimming circuit. In a conventional forward phase-control dimmer, the waveform
is altered by the switching action of the dimmer.
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