enter image description here

1940s era house with two-wire electrical. I'd like to install AFCI/GFCI throughout the house for fire-protection and for the third prong.

-> Kitchen and bathroom already have GFCI outlets.
-> Outlet boxes are small-ish, so probably can't fit combo AFCI/GFCI outlet.
-> Plaster walls means new outlet boxes work would suck.
-> I've heard AFCI at the panel is better than at the outlet, to protect the run from the panel to the outlet.
-> I can't find a type BR breaker 20-amp/dual with AFCI that fits.
-> Can't afford a whole new electrical panel and electrician's fees.

Is it better to install AFCI or GFCI outlets? Primarily phone chargers, lamps, vac, air purifier, TV, etc.

  • old wiring suggests AFCI breakers to stop in-wall fires from failing wiring. GFCI can be added at the outlet, where in fact it does a (slightly) better job than at the breaker.
    – dandavis
    Commented Sep 7, 2023 at 18:23
  • thanks-- the problem is I don't think there exists an AFCI breaker that fits. In that case, is it advised to use the AFCI outlet?
    – adobedodo
    Commented Sep 7, 2023 at 18:27
  • 1
    Re: small old outlet boxes in plaster. You can get more volume by adding a box extension (not a "mud ring") that will look OK on a finished surrounding surface. I used such to install shallow GFCI-only outlets in the kitchen in tiled or stucco'd wall areas.
    – Armand
    Commented Sep 7, 2023 at 19:35
  • I've installed quite a number of new "old work" boxes in my plaster & lath walls. With some care, you can install them very nicely. Note that "some care" requires time & some fiddling to get them right.
    – FreeMan
    Commented Sep 8, 2023 at 12:06

1 Answer 1


You have the challenge of the tandems. (Which is a Google-nope, but won't be once Google indexes this page. Yay!)

Two big things have happened in the world of residential electricity in the past few decades. (Well, actually a lot more things have happened. But these two are relevant here.)

More Circuits

New homes require a lot more circuits than they used to. While old homes, generally, can get by with what they were built with - i.e., code doesn't require most changes to be retrofitted to existing houses - homes are often expanded, renovated or changed in ways that require new circuits. Some examples:

  • Full kitchen renovation - need to bring up to current code with at least two countertop receptacle circuits. Circuits often added for microwave ovens, dishwashers and disposals which are more common then they used to be.
  • Bathroom renovation - if additional receptacles are added and the only receptacles are on a shared circuit then you may need to add a new bathroom-only circuit. Circuits are often added for exhaust fans, heaters, towel warmers and other appliances.
  • Electric vehicle charging - didn't exist until a few years ago
  • Basement converted to a workshop - you can never have too many circuits in a good workshop!
  • HVAC upgrades

and many more. As a result, a 20 space panel (or even smaller in some older homes) can easily run out of space. Sometimes, especially if the old panel has fuses, the solution is to replace the panel with a larger one. Sometimes you can add a subpanel. But if the panel is in good shape and has tandem (a.k.a., twin or double-stuff) breakers available for it then that is often a great solution. Tandems don't work for everything, but where they work they can often avoid, or at least significantly delay, a panel replacement.


Arc-Fault Circuit Interrupters (AFCI) primarily protect against fires. They watch for telltale electrical noise that is caused by arcing. AFCIs started with bedrooms (because of concerns about similar problems with electric blankets) and gradually rolled out to most other rooms in the house except those that require GFCIs, though I think some rooms may now require both AFCI and GFCI.

Due to the way AFCI works, it is best done either together with the breaker (I call this AFCI/breaker) or as close to the panel as possible. I believe that where code requires AFCI, it normally has to be either AFCI/breaker or installed (a) at or before the first outlet (i.e., not: breaker, receptacle 1, AFCI, receptacle 2; even if the current code only requires AFCI because of the location of receptacle 2) and (b) with wires in metal conduit between the panel and the AFCI. That effectively means that unless you already use metal conduit anyway that the place for AFCI is either as AFCI/breaker or in a box next to the panel connected by a conduit nipple.

Ground-Fault Circuit Interrupters (GFCI) are primarily about life safety. They detect an imbalance between hot and neutral on a 120V circuit (most things), between the two hots on a 240V circuit (e.g., water heater), and between the two hots and neutral on a 120V/240V circuit (e.g., MWBC, some HVAC). From a safety standpoint, GFCI can be anywhere up to and including the point of use. However, GFCI/receptacles are currently (at least generally from what I have seen) only available for 120V receptacles. As a result, if you need to protect an MWBC or other 240V or 120V/240V circuits then you need to use a GFCI/breaker.

The Tandem + GFCI/AFCI problem

The problem is that almost all GFCI/breakers and AFCI/breakers are only available as full-size breakers. There are some Siemens tandem AFCI/breakers. I expect that other manufacturers will bring out tandem AFCI and/or GFCI breakers over time. But they aren't out there yet.

As a result, generally speaking if you have tandems in your panel then you can't swap them out for AFCI or GFCI. But all is not lost if you really want to add this protection.

GFCI can be installed as receptacles - familiar to most of us in kitchens and bathrooms - and also as deadfronts. A deadfront has no receptacle on it but has the TEST and RESET buttons and some indicator lights and can, as can a GFCI/receptacle, be wired up to protect other receptacles down the line. This will not work for MWBC or other 240V or 120V/240V circuits. The protection here is equal to that of a GFCI/breaker.

AFCI can be installed as receptacles or deadfronts. However, it must be wired up near the panel, as discussed above, in order to provide complete protection. This will not work for MWBC or other 240V or 120V/240V circuits. The protection here is equal to that of a GFCI/breaker.

And finally we get to the ground issue. Despite the name, a GFCI does not actually need a ground wire, and neither does an AFCI. Due to the way that a GFCI works, it can effectively provide protection equivalent to having a ground wire. How? If current would have gone to ground due to a problem, and there is no ground wire, the current won't go anywhere. No current flowing, no problem. But if that current finds a path to ground through a person then the current flow will no longer be balanced between hot and neutral, and the GFCI trips. Problem solved! As a result, using GFCI with a sticker that says "No equipment ground" is a code-compliant way to solve the ground problem. If the circuit requires (in a new installation at least) GFCI anyway then this definitely makes sense. But even if the circuit would not otherwise require GFCI protection, it can make sense because it allows you to install additional 3-prong receptacles on the load side of the GFCI, even though they don't have a ground wire, as long as you also put on the stickers.

As far as I know, installing AFCI (whether AFCI/breaker, AFCI/deadfront or AFCI/receptacle) does not provide "instead of a ground wire" protection. As I understand it, some AFCI/breakers provide limited GFCI functionality, but that is not at a level that really substitutes for a ground wire in the way that GFCI does.

  • Re: Ground. It is now legal to ADD a ground to an existing two-prong receptacle, as long as its electrical path eventually makes it back to the electrical panel that supplies the circuit. Iirc it is OK to first add ground, then replace the receptacle with a GFCI receptacle, but perhaps not in the reverse order.
    – Armand
    Commented Sep 7, 2023 at 19:31
  • Actually, either way would work: 1 - install GFCI/receptacle with "no ground" stickers, install ground, remove stickers; or 2 - install ground, install GFCI/receptacle. If it were me I wouldn't bother to retrofit ground except where GFCI/receptacle isn't really an option. In my own house I thought I might need to put in GFCI/receptacle in some rooms in order to solve the problems - and it turns out every existing 2-prong receptacle had a ground wire behind it ready and waiting! Commented Sep 7, 2023 at 19:35
  • 3
    There is one small case where a deadfront can work on a MWBC: if the MWBC splits to have two neutrals after some point in the circuit, you can put a GFCI deadfront there to protect the rest of that side of the MWBC. It's not a common way to wire a MWBC so I wouldn't expect to run in to it often.
    – KMJ
    Commented Sep 7, 2023 at 19:50
  • Your answers are becoming more and more Harperesque (and that's a good thing!). +1 However, the 2nd paragraph under AFCI could use a bit of formatting - I really got lost. Maybe my coffee just hasn't kicked in yet...
    – FreeMan
    Commented Sep 8, 2023 at 12:10

Your Answer

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

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