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I'm wondering how combos of AFCI & GFCI protection on breakers and outlets affect overall circuit safety & performance. What I mean is, how do different combinations of GFCI and/or AFCI protection relate when applied on a circuit breaker and/or an outlet?

Some combinations I've heard/thought of already are as follows, but I'm not sure how the different protection methods and redundancy between the same kinds of protection can help or hurt one another. The items in bold are the ones in particular I'd like to learn more about. How does the combination of safety devices interact with one another? Assume the circuit is grounded (e.g. connected via NM 14/2 with ground wire hooked up properly throughout.

  • regular breaker with overcurrent protection + regular outlet
  • reg breaker + GFCI outlet
  • GFCI breaker + GFCI outlet
  • AFCI breaker + GFCI outlet
  • AFCI & GFCI combo breaker + GFCI outlet
  • AFCI & GFCI combo breaker + regular outlet
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Definitions

GFCI is intended to protect humans against severe shock or electrocution.

AFCI protects structures (and their human occupants) against fire.

AFCI detects if there is an open arc on a circuit and de-energizes the circuit. Electrical arcs can start fires easily if they hit the wrong material.

GFCI detects a current differential on the "hot" and "neutral" wires. In a functioning circuit, both wires carry exactly the same current. If there is a difference in current between the wires, it means current is leaking somewhere else. The "somewhere else" could be through you and cause injury or death.

GFCI breaker + GFCI outlet

This is pointless, or at least overkill. GFCI's can fail, but the electrical code doesn't require you to wire up redundant GFCI's in series. The GFCI breaker protects the entire branch circuit. Likewise, one GFCI receptacle on a branch circuit can protect all of the downstream receptacles if wired correctly.

Do test your GFCI's from time to time to ensure that they are still functioning correctly.

AFCI breaker + GFCI outlet

This will protect against fire (the AFCI will trip if there is an open arc), and it will also protect against severe human shock/electrocution. This is a fine combination and combines positive attributes of both types of protection.

AFCI & GFCI combo breaker + GFCI outlet

As in the GFCI breaker/GFCI outlet scenario, the GFCI outlet is redundant and thus unnecessary to meet code requirements.

EDIT

Tester01 makes a good point about the possibility of getting shocked before a GFCI trips. You may get bit, but a properly functioning GFCI should trip within 25ms (0.025 seconds), at a voltage differential between 4 mA to 6 mA. Most people can feel electric shock starting around 1 mA, and it's a relatively mild to uncomfortable sensation up to 10 mA, after which it becomes painful. 10 mA is also the threshold where involuntary muscular contractions become strong enough that you may not be able to let go of the thing that is shocking you, and the current starts to become lethal between 75 mA where breathing becomes so difficult that it stops, and 200 mA. In any event, a properly-functioning GFCI should cut the current completely before you are permanently damaged.

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    GFCI doesn't necessarily protect against shock, but should protect against electrocution.
    – Tester101
    Jan 21, 2018 at 20:07
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    That's fair! Still, just for reference, a properly functioning GFCI should trip within 25ms (0.025 seconds), with a voltage differential of only 4 to 6 milliamps. So it should protect against very painful and/or prolonged shock as well.
    – Craig Tullis
    Jan 21, 2018 at 20:17
  • The differential is measured between input & output. A person accidentally completing a normal circuit between the input & output won't trip the GFCI, not matter what as there is no differential imbalance.
    – Kris
    Jun 10, 2018 at 12:56
  • @Kris That’s true. However; it takes a little effort to pull that off. You would have to, for example, stick a knife in both slots in a receptacle at the same instant AND not be grounded to anything else. In other words, you’d have to be insulated well enough that touching the hot alone would not shock you. Or grab both the hot and neutral bare wires in an outlet at the same time and not be grounded to anything else, for example. It isn’t impossible, but it isn’t very likely. It’s easier said than done. ;-)
    – Craig Tullis
    Jun 10, 2018 at 16:48
  • @Craig ~ very true. Never thought about it in that perspective. Thanks
    – Kris
    Jun 10, 2018 at 23:24
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Overcurrent, GFCI, and AFCI are not receptacles. They are devices which provide zones of protection downstream of them. You can get standalone devices which do each of those thingss separately:

  • a circuit breaker (overcurrent only)
  • a GFCI deadface (GFCI only)
  • an AFCI deadface (AFCI only)

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Some of them are sold as "combination devices" that do more than one thing.

  • A combination overcurrent circuit breaker and also GFCI
  • A combination overcurrent circuit breaker and also AFCI
  • A combination overcurrent circuit breaker and also GFCI and AFCI
  • A combination GFCI and receptacle
  • A combination AFCI and receptacle
  • A combination GFCI and AFCI and receptacle (really)

However an AFCI receptacle is fairly pointless, as the purpose of AFCI is to protect wiring and splices from arcing, and putting it at the receptacle means the wiring is not in the zone of protection.

You can nest zones of protection. For instance a combination overcurrent+AFCI breaker, feeding a combination GFCI+receptacle in turn feeding other loads. The entire circuit is overcurrent and AFCI protected, but only part is GFCI protected.

Nesting the same type of protection is a total waste of resources. Essentially you're playing a "Yo Dawg" joke on yourself.

Yo dawg, I heard you like GFCIs

So I put a GFCI on your GFCI

So you can trip while you trip

And that's just what'll happen, you'll get a puzzle maze of tripping GFCIs that will be hard to properly reset. It's a support nightmare, hours of frustration and a pointless electrician call.

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