Author Tom Kelly
Many people just take for granted that something is just going to work, and in many cases assume that it will work forever. One such device that does not get enough attention is the Ground Fault Circuit Interrupter (GFCI). Simply put, a GFCI is a protective device that compares the current flowing on the hot and neutral wires of the circuit and will “trip” to disconnect power to the circuit if a small imbalance of current is detected. The imbalance of current is an indication of a dangerous alternate path for the current to flow from a damaged line cord or a fault inside an appliance and constitutes a shock hazard to a person.
The most common two types of GFCI devices found in residential and commercial construction are the GFCI receptacle and the GFCI circuit breaker. All types of GFCI devices are defined by the Underwriters Laboratory (UL) Standard 943. This UL standard lists the conditions that the protective device must operate at including disconnecting power when the current imbalance reaches 6 milliamperes. The standard also requires doing so within 25 milliseconds of when the condition occurs to prevent a shock hazard.
Figure 1: A typical Ground Fault Circuit Interrupter (GFCI) Receptacle.
Figure 2: GFCI Circuit Breaker.
The National Electric Code (NEC) is the standard which guides electrical installations in the United States. This standard is revised every three years to incorporate new technologies and best practices to improve the safety of electrical systems and installations. Article 210 of the NEC, currently titled “Branch Circuits”, contains requirements for providing a GFCI protection to circuits installed in various locations in a building. In general, this type of protection is required in what can be considered “wet areas” exposing an occupant to water while using an appliance, such as kitchens, bathrooms, and laundry areas. Due to the type and location of the circuit, a receptacle or circuit breaker may be used to meet the requirement including one key element in section 210.8 stating that the “ground-fault-circuit-interrupter shall be installed in a readily accessible location”. The requirements for GFCIs were first introduced in 1971.
Why is it important that these devices be readily accessible? Because they need to be tested regularly to ensure that they are operating correctly and will be functional to prevent a shock hazard. And how often is “regularly”? The UL943 Standard requires in paragraph 39.2.10 that the manufacturer of these devices provide instruction that state that these devices are to be tested monthly. Testing of these devices is simply a matter of pressing a button labelled “TEST” on the receptacle or circuit breaker. The test function simulates an imbalanced current flow and trips the device. If the receptacle or circuit breaker does not trip or if the device will not reset after a test, then it is defective and needs to be replaced.
So the question is, have you tested every GFCI device in your house? Monthly? The committee for the UL943 Standard didn’t think so either and made a change to the standard that effective on June 29, 2015, required the GFCI device to be self-testing. This change is part of the continuous improvement of using technology to improve safety. However, it does not mean that you shouldn’t test GFCIs yourself. Go ahead… push the test button.
Figure 3: “Test Monthly” molded on the face of a GFCI receptacle.
Tom Kelly has a Bachelor of Science in Electrical Engineering and a Master of Science in Electrical Engineering from Florida Atlantic University, Boca Raton, Florida, along with a Master of Business Administration with emphasis in strategic leadership from Winthrop University, Rock Hill, South Carolina. Tom’s 25-year career in electrical engineering includes forensic engineering investigations involving industrial electrical accidents, electrical equipment failure analysis, control system failures, robotics and automation components, and scope of damage assessments. He has conducted investigations for fires, arc flash incidents, electrocution and electric shock accidents and lightning strike evaluations.
