I am looking to see what the pros/cons and if it is a good idea to swap out old 2 prong receptacles (that are connected to old knob & tube wiring) with dual AFCI/GFCI receptacles or swap them out with just GFCI ones.

  • 1
    What make and model is your breaker panel? Apr 1, 2023 at 22:46
  • Hi! I have a mix of knob/tube and new wire. Basically the upstairs is knob/tube and downstairs is not. I got a couple of estimates to replace knob/tube 25k-30k. Looking at the gfci or afci or both as a more cost effective solution. The electrical box is updated Siemens G2020B1100 Apr 1, 2023 at 22:51
  • Yeah -- you're good to go to whack AFCIs in then Apr 2, 2023 at 14:03

3 Answers 3


I would guess that an accidental short circuit that sparks enough to start a fire is more likely in aging knob-and-tube wiring than in modern wiring. That's the scenario AFCI is intended to protect you against.

GFCI protects you against electrocuting yourself if the safety ground isn't there or doesn't do what it's supposed to do.

You can get combined AFCI/GFCI breakers. Or you can get an AFCI breaker and install GFCI outlets where desired, which may be less expensive (especially if a GFCI outlet can be used to protect downstream outlets rather than needing a GFCI at each location, but gods only know whether you can achieve that if you have K&T).

  • Is there a concern when "installing GFCI breakers" that any work on the installation may cause aged rubber insulation on the wires to fall off? I know K&T should still work without any insulation on the wires - but that means you only need one more thing to go wrong. Apr 3, 2023 at 8:25
  • @MartinBonnersupportsMonica: As always, intelligent evaluation is needed as you go.
    – keshlam
    Apr 3, 2023 at 12:31

GFCI and AFCI have almost the same name, but so does methanol and ethanol :) The first one is deadly to drink, the next one is fun!

You are saying that you want the wire in the walls protected. AFCI is pretty good at that, being an arc fault detector.

However, you aim to place the AFCI at the end of the wires instead of at the beginning. That's like having TSA make people go through metal detectors as they get off the airplane LOL.

The GFCI is a totally different deal. As a ground fault detector, it does a pretty good job protecting humans from shocks by appliances if it is at the receptacle.

Thus an AFCI won't help your situation unless it's at the breaker or at a receptacle immediately after the breaker (and wired to protect the rest of the circuit, which by the way is a thing that both AFCI and GFCI can do; most people don't know that).

  • Since the reset function for xFCI will be at the outlet/breaker itself, keep a diagram or labels indicating where the reset switch is for each outlet protected by something upstream rather than local.
    – Armand
    Apr 2, 2023 at 16:10

You should, if possible, protect your k&t wiring with dual function circuit breakers not outlets. GFCI and/or AFCI outlets will protect your wiring partially or not at all depending on where and how you install them. Combination breakers will protect against various in-wall failures throughout their circuits.

  • Thanks for the comment! Does this follow code? I am assuming it is okay to install regular 3 prong receptacles and add “no ground” “afci/gfci protected” labels on the outlets. Also, is there any potential problems with these dual breakers with knob and tube? Apr 4, 2023 at 2:26
  • Please see a more thorough and more authoritative answer here
    – jay613
    Apr 5, 2023 at 21:18

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