Virginia Tech®home

Ground-Fault Circuit-Interrupters

Electrical Safety Quick Links


Ground-Fault Circuit-Interrupters Overview

In most cases, proper insulation and effective grounding prevent injury from electrical wiring systems or equipment. However, there are instances when these methods do not provide the degree of protection required. Ground-fault circuit interrupters (GFCI) are designed to protect people from electrical shock. They are not overcurrent devices like fuses or circuit breakers. GFCIs sense an imbalance in current flow over the normal path. If the current flowing differs more than 5 milliamperes between the hot and neutral wires, the GFCI will open the circuit in approximately 1/40 of a second, greatly reducing the likelihood of a serious shock to any person in the circuit. The GFCI "assumes" that the leaking current on the circuit is flowing in an abnormal path (i.e. ground fault), which could be you.


Types of Ground-Fault Circuit-Interrupters

There are three basic types of GFCIs:

  • Circuit-Breaker GFCIs: These GFCIs function as a standard circuit breaker with the additional functions of a GFCI. They are direct replacements for standard circuit breakers of the same rating.
  • Receptacle GFCIs: One or more receptacle outlets are protected by the GFCI because GFCIs protect the circuit "downstream" from its location in the system.
  • Portable GFCIs: "Pigtails" are designed to be easily transported from one location to another, such as use with extension cords, power tools, and equipment.

GFCIs Required Use

GFCIs must be used in the following situations:

  • Wet or damp locations where water could possibly enter the housing of power tools or equipment and shock the person in contact with it;
  • Construction sites; and/or
  • Renovation projects.

Some examples of where GFCIs would provide additional protection include:

  • When using double-insulated hand tools in wet/damp locations where water could possibly enter the tool housing and cause a shock.
  • Using extension cords with portable equipment, which are often exposed to physical damage.

Ground-Fault Circuit-Interrupters Maintenance

GFCIs have a built-in test circuit, which imposes an artificial ground fault on the load circuit to assure the protection is still functioning properly. You should follow the manufacturer's instructions for testing the device being used. The tests should be performed on a regular basis.

  • Monthly for permanently wired devices, such as the circuit breaker or receptacle types.
  • Prior to use for temporary portable types, such as "pigtails."

Contact Information

Robin McCall-Miller, Occupational Safety Program Manager