Ground Fault Circuit Interrupter (GFCI)

In case of ground faults on construction sites, GFCIs help reducing electrical accidents and injuries by shutting off electric power immediately.


Ground Fault Circuit Interrupters (GFCIs) constitute as engineering controls because they block electric current, caused by a ground fault, from moving through a worker’s body.  The Hierarchy of Control (HOC) is a well-known framework to evaluate the performance of safety solutions in Occupational Safety and Health (OSH) research (Wakefield et al. 2014). HOC consists of five levels of effectiveness: (1) Elimination, (2) Substitution, (3) Engineering Controls, (4) Administrative Controls, (5) Personal Protective Equipment; with elimination being the most effective. At the third level, engineering controls “use safeguarding technology to place a barrier to keep a hazard from reaching workers” (Zhao et al. 2015). Ground Fault Circuit Interrupters (GFCIs) constitute an engineering control solution because they block electric current caused by a ground fault from moving through a worker’s body.

While a standard way to ground receptacles is shown in figure 1, electrical devices plugged into outlets can cause electric shock, fires, and explosions in the event of a ground fault – an unintentional path between electrical sources to the ground. Ground faults usually occur as a result of insulation breakdown or when equipment is damaged or defective. If a worker provides a path to the ground for this current, he or she could be burned, severely shocked or electrocuted.


According to OSHA, “a Ground-Fault Circuit Interrupter (GFCI) is a fast-acting circuit breaker designed to shut off electric power in the event of a ground fault within as little as 1/40 of a second. It works by comparing the amount of current going to and returning from an equipment. When the amount going differs from the amount returning by approximately 5 milliamps, the GFCI interrupts the current.”

Fig 1. Grounding diagram for receptacles (Source:

GFCIs can significantly reduce ground fault hazards and are safe solutions for any outlet. Following are some features that can improve GFCIs’ performance and promote their application:

  • Designed to conduct an automatic internal test to confirm that the unit can respond to a ground fault
  • Auto-monitoring exceeds the Underwriters Laboratories (UL) requirements. Some GFCI testers and monitors are available in the market to ensure that such devices are working properly (See Ground Continuity Monitor and Testers solutions).
  • Status indicator light provides simple, intuitive feedback on power and protection status as well as indicating line/load reversal.
  • Patented lockout action prevents reset if GFCI is damaged.
  • Electronics are designed to minimize any false triggers.
  • Reduced depth makes it easier to install in any electrical box, even shallow ones.
  • Terminals allow for easy wiring options, both back- and side-wire capable.
  • External back wire clamps provide visual indication of proper wire seating.
  • Withstands high torque and resists wire pullout.
  • Provides standard brass self-grounding clip.
  • Trip threshold meets or exceeds UL requirements for tripping time.
  • Improved immunity to high-frequency noise reduces nuisance tripping.
  • Advanced electronics design provides superior resistance to electrical surges and over-voltages.

Fig 2. Different types of GFCI (Source: )


Portable GFCIs

Some outlets are not equipped with GFCIs and will not trip if they detect a ground fault. However, there are portable GFCIs that can fix that. The circuit will need to run through the portable GFCI before it reaches the electrical device, which makes it safer. The GFCI cord is a ground fault circuit interrupter that shuts off an electric circuit when the current flows along an unintended path, providing personal protection from ground faults and open neutral conditions. Included on the adapter is a manual reset button- Fig 3.


Fig 3. Portable GFCI (Source: )

Spider box

One way to supply electrical requirements safely, especially in construction sites, is to use a ‘spider box’. Spider box is a portable power distribution system equipped with built-in GFCI technology to keep workers safe from arcing hazards and weather-proof covers in case of wet conditions. UL (Underwriters Laboratories) listed spider box for both outdoor and indoor conditions. Wide variety of configurations (in terms of amps, voltage, and number of outlets) are available for either small or large companies.


Fig 4. Spider box (Source:

Risks Addressed:

Contact with electric current is a major cause of injury and death among construction workers (Janicak, 2008). Properly grounded equipment is not always the case in construction environment, thus, ground faults still remain a concern for electrical workers when using electrical devices. Main risks related to ground faults are:

  • Electrocution of the workers
  • Destruction of loads in the electrical systems
  • Risk of fire due to the fault current

GFCIs, if installed properly, can reduced these risks significantly by interrupting electric current before it reaches the operator’s body. These risks are more likely to occur on construction sites where finding GFCI outlets might be difficult at times. Thus, portable GFCIs and spider boxes might help significantly in these situations. While this solution reduces the risk of electric shock, the GFCI’s integrity should be tested regularly and before each operation.

How Risks are Reduced:

A GFCI outlet is sensitive equipment that can act fast to protect a worker from a deadly shock. It monitors for a current imbalance between the hot and neutral wires and breaks the circuit if this imbalance is confirmed. The GFCI is faster than a circuit breaker or a fuse.

Effects on Productivity:

The GFCI acts faster than a circuit breaker in protecting a worker from any injuries that might come with an electrical shock. It can improve productivity because it more quickly identifies any inappropriate fault current in the system that could delay work activities or even damage the equipment used.

Additional Considerations:

Administrative guidelines:

· The employer must provide GFCI on the construction sites – it is an OSHA requirement.

· On initial power-up, the GFCI is tested within 3 seconds.

· OSHA regulations indicate that receptacles (all 120-volt, single-phase 15- and 20-ampere) being used temporarily by employees on construction sites should have approved GFCIs. An ‘assured equipment grounding conductor program’ is also required to be implemented by the employer.

· Each equipment shall be inspected visually every day before using them.

· Various testers are available which are designed to inspect safety requirements of GFCIs such as correct wiring, open ground, reverse polarity, open hot, open neutral, and reversed hot/ground.


Behzad Esmaeili, Ph.D. - University of Nebraska- Lincoln
Pouya Gholizadeh - University of Nebraska- Lincoln
Sogand Hasanzadeh - University of Nebraska- Lincoln
Ana Clara Carvalho - University of Nebraska- Lincoln
Kendra Euscher - University of Nebraska- Lincoln


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