I am taking a National Electric Code safety class as part of an electrical maintenance certificate course. On one of my quizzes, it asks me to explain how a GFCI is to be installed and tested. I've carefully searched the NEC and have been unable to find anything about how GFCIs are to be installed. It explains where they are to be installed, but not how. This seems like a dumb question since GFCIs can be used in many applications such as circuit breakers and receptacles. Does anyone know what this is asking or if the NEC has any specifications on how GFCIs are to be installed?

Explain how a GFCI is to be installed and tested

  • Any Nation in articular?
    – Brian Drummond
    Sep 30, 2017 at 19:51
  • @BrianDrummond: Isn't the NEC US-specific?
    – Ignacio Vazquez-Abrams
    Sep 30, 2017 at 19:55
  • Mostly. It's used in a few places outside the U.S.
    – Daniel Wolfe
    Sep 30, 2017 at 19:59
  • @BrianDrummond United States
    – Daniel Wolfe
    Sep 30, 2017 at 20:00
  • NEC is not US law, it's a "model law" written by a nonprofit organization with the hopes that jurisdictions worldwide will adopt it as law. It has become Code-of-default anywhere 120/240-ish split-phase is used - writing an alternate Code is expensive (Chicago, Canada). Even in 230V-land it is respected, and if a Thailand agency questions your wiring, "I installed to NEC" is a pretty good defense. Mar 1, 2018 at 17:32

2 Answers 2


The NEC isn't the right place to look for this stuff

The reason you couldn't find anything that answered this question in the NEC is stated right up front in NEC 90.1(A) (quoting from the 2014 edition, italics mine, italicized text new in 2014):

90.1 Purpose.

(A) Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This Code is not intended as a design specification or an instruction manual for untrained persons.

Instead, you want to look at the installation instructions that the manufacturer provides for a given GFCI device. This is enshrined in NEC 110.3(B):

(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

However, I'm not sure if that's a sufficient answer for your quiz. If it's not, most receptacle and deadfront devices do install similarly -- your input conductors terminate on to the LINE-side screws (black/brass is hot and silver is neutral, as usual), while loads downstream of the box can either be fed from the LOAD terminals if they need protection or from pigtails off the LINE terminals if they don't. Grounding and pigtailing is the same as a standard receptacle otherwise. Breaker-type GFCIs install like a breaker, but have a pigtail or clip that attaches to the neutral bar, and then an extra lug for the load neutral to land on (if you try to wire the load neutral to the neutral bar, the GFCI won't ever reset as it won't be able to "see" the current returning back from the load).

As to testing? There's one correct answer, and that's to use the TEST button on the device. This creates a path from load-hot to line-neutral (or vice versa) through a current-limiting resistor that is a "controlled leak" for the GFCI to sense and trip on.

  • 1
    The quiz does specifically regard the National Electric Code, so in light of your post, the correct answer would probably be "according to the manufacturer's specifications." Sep 30, 2017 at 22:17
  • @DanielWolfe -- yeah, that's one possible answer, but I'm not sure what the quiz writer was intending. Either way, it's not exactly a good quiz question in the context of the quiz in question! Sep 30, 2017 at 22:33

This is addressed in NEC 110.3:

110.3(B). Listed or labeled equipment shall be installed and used in accordance with any instructions included with the listing or labeling.

Simply put, you must install a GFCI the way the manufacturer tells you to.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.