The invention of and subsequent requirements for ground-fault circuit interrupters (GFCIs) has saved many lives. Many specific rules require GFCIs to be installed in many locations in wiring systems, and that number is increasing, as are the requirements for surge protective devices—but that story is for another time. 

The National Electrical Code requires GFCI installation, but it never directly addresses performance testing of GFCIs periodically after installation. Let’s explore how the NEC makes testing of GFCIs mandatory, and why. 

GFCIs are required because they provide protection against electrocution and minimize the severity of electric shock a person can receive, aligning directly with the purpose of the NEC in Section 90.2(A). Although there are no actual statistics available, data collected by the Consumer Product Safety Commission indicates that electrocutions in the United States have been decreasing since the introduction of GFCI requirements, specifically Class A GFCIs. 

Most industry and safety experts agree that GFCI protection has saved numerous lives and significantly reduced the number of shock injuries. Insulation breakdown or failure is often the cause of electrical shock to humans. A person who contacts an energized circuit can become a series path for current or the person can be in parallel with other fault current paths. If a person is in series contact with the circuit, all current can pass through the body from entry to exit points. People in parallel contact with the circuit will become a current path in combination with other current paths over which all the fault current will divide. The severity of shock a person receives is related to the length of time the current is present through the body, amount of current, path through the body, frequency of the current and size of the person. GFCIs operate at a low level of current. 

GFCIs and the NEC

“Ground-fault circuit interrupter” is defined in NEC Article 100. The informational note following the definition indicates that Class A GFCIs trip at 6 milliamperes (mA) or greater of ground-fault current and do not trip when the current to ground is less than 4 mA. 

Additional information about GFCIs is provided in UL 943, Standard for Ground-Fault Circuit Interrupters. See the online UL Product iQ for Electrical Equipment category KCXS. 

GFCI protection is available in a few forms, such as GFCI circuit breakers, outlet devices, portable cord sets, portable plug-in devices and more. All GFCI protective devices generally function the same way. The circuit breaker types of GFCI open the entire circuit if a ground fault occurs, while outlet types only open a portion of the circuit. 

The principles of operation for a GFCI device are simple. The circuit conductors are monitored internally by the GFCI-­sensing device for equal circuit current in both directions (supply and return). If the return current (on the neutral conductor) of the circuit becomes lower than the current present in the ungrounded conductor, there must be a fault-current path creating an imbalance or differential between them. When this imbalance reaches a 4- to 6-mA difference, the device opens. 

GFCI devices do not directly limit the level of current through the body during a contact event; instead, they reduce the amount of time the current is present. Extensive research about preventing human electrocution resulted in established current and time levels for Class A GFCI devices. GFCI protection monitors current in the complete electrical circuit for an imbalance; therefore, it can be used in grounded systems. 

SPGFCIs

Special purpose ground-fault circuit interrupters (SPGFCIs) were incorporated into the 2023 NEC and are defined in Article 100. The three different classifications are Class C, D or E. Each of these classifications and their respective functionalities are described in these definitions. All three classes trip at 20 mA or higher, rather than 6 mA as with a Class A device. Underwriters Laboratories’ Outline of Investigation 943C is referred to in each of the informational notes to the definitions of SPGFCIs. 

Testing GFCIs

The testing rules are not found as direct requirements in the code. The NEC requires GFCIs to be tested monthly to ensure proper operation and function; however, the mandate is addressed indirectly through product installation and use requirements, which is required under Section 110.3(B). Notice the word “use” in that rule, which is the trigger. 

Testing the GFCIs can reveal defective or inoperative products that must be replaced to maintain this vitally important protection. Test GFCIs monthly as required and take action if necessary to maintain proper protection.

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