Industrial GFCIs are finally here


How to apply industrial GFCIs

Industrial GFCIs can be used on equipment subject to washdown cleaning, process equipment that handles wet material, such as large pumps, mixers, wet saws; equipment that comes into frequent contact with workers, such as arc welding stations; and portable electric equipment used outdoors, where long power cords and less robust temporary connections may be exposed to rain and moisture.

Industrial GFCIs may be integrated by the equipment OEM or panel builder, or they may be installed in an electrical cabinet such as a motor control center. They are also available with their own enclosures, for mounting to the side of a machine or a wall.

The wiring is simple: attach source power on one side and the load on the other side (See Figure 4). No wiring to a circuit breaker is required because the GFCI internal interrupting mechanism can interrupt power on its own. In addition, there may be signal wiring for optional alarm communication.

Industrial GFCI connection diagram. Courtesy: Littelfuse

Some models are equipped with built-in overcurrent protection (fuse), which allows for a high interrupting rating (50 kA in some cases). This protects the internal contactor from damage and doesn’t require the user to install a current limiting device upstream of the industrial GFCI. Some models also offer undervoltage, brownout, and chatter detection. 

GFCI Standards and Classes

UL Standards

  • UL 943 – This Standard applies to Class A, single- and three-phase GFCIs intended for protection of personnel, for use only in grounded neutral systems in accordance with the National Electrical Code (NEC), ANSI/NFPA 70, the Canadian Electrical Code, C22.1 (CEC), and Electrical Installations (Use), NOM-001-SEDE. These devices are intended for use on alternating current (AC) circuits of 120 V, 208Y/120 V, 120/240 V, 127 V, or 220Y/127 V, 60 Hz circuits.
  • UL943C – These requirements cover ground-fault circuit interrupters intended for use in one of the following applications:
    • Where the voltage to ground is greater than 150 V and equipment grounding or double insulation is required by the National Electrical Code or ANSI/NFPA 70.
    • Where the voltage to ground is 150 V or less and equipment grounding or double-insulation is provided, but the use of a Class A ground-fault circuit interrupter is not practical.
  • UL 1053 and UL 943 both apply to EGFPDs.

GFCI Classes

  • CLASS A – A GFCI that will interrupt the circuit to the load when the ground-fault current is 6 mA or more but not when the ground-fault current is 4 mA or less.
  • CLASS B – A GFCI that will interrupt the circuit to the load when the ground-fault current exceeds 20 mA. Used only with swimming pool underwater lighting fixtures installed prior to local adoption of the 1965 edition of the NEC.
  • CLASS C – A GFCI that is intended to be used in circuits with no conductor over 300 VAC to ground where reliable equipment grounding or double insulation is provided.
  • CLASS D – A GFCI that is intended to be used in circuits with one or more conductors over 300 V to ground, and with specially sized, reliable grounding, to provide a low impedance path so that the voltage across the body during a fault does not exceed 150 V.
  • CLASS E – A GFCI that is intended to be used in circuits with one or more conductors over 300 V to ground but with conventional equipment grounding provided for the protected equipment in the system or double insulation. These ground-fault circuit interrupters respond rapidly to open the circuit before the magnitude and duration of the current flowing through the body reach the threshold for ventricular fibrillation. 


Ground-fault circuit interrupters for industrial use have finally become available. One hopes that their wide adoption will help to reduce the number of electrical shock fatalities by a substantial number. 


1. IEEE White Paper, “The Effects of System Grounding, Bus Insulation and Probability on Arc Flash Hazard Reduction–the Missing Links,” by Nelson, Billman, and Bowen, 2012.

See articles on electrical safety and arc flash below.

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