Ground-fault circuit interrupter, special purpose. Class A GFCI protection is used on circuits of 150V or less to ground and 60A or less, single-phase and three-phase to protect receptacles and outlets. Class A GFCIs trip at 4-6 milliamperes (mA). They are the class that provides protection for personnel. Class C, D and E trip at 15-20 mA. Class C GFCIs are for use on circuits over 150V to ground with a maximum line-to-ground voltage of 300V. In addition, either double insulation or reliable equipment grounding must also be provided. They can be used on systems operating 480V line-to-line. Class D GFCIs are used on circuits with one or more conductors operating at over 300V to ground. They are required to have a larger-sized equipment grounding conductor to provide a low-impedance path to ground to ensure the voltage across a human body will not exceed 150V.
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