I am renovating an old home(90 years) that my wife and I just purchased. The electrical system in the house is outdated - some of the outlets appear to be knob and tube but most are the brass and silver; forgive me if this is incorrect info, I honestly know very little.

To the point - We do not have grounded outlets and I started replacing the 2 prong outlets with 3 prong outlets (without installing the ground). I realized this is a bad idea and decided to start researching. I am a little confused because I hear opposing arguments on whether or not the GFCI outlets are able to compensate, to some degree, for the inability to short circuit on demand.

I have read that the GFCI are good for nothing more than water running into the outlet whereas the actual ground would short circuit if there was a problem with too much electric output or metal coming into contact.

My question is: Could I replace the 2 prong outlets with GFCI and call it good, or should I be installing a ground? I prefer not to overhaul and install a ground but please tell me if this is a terrible idea or not.

Thanks in advance😀

-- UPDATE --

I see that some of the outlets are encased with a metal rectangular box and was wondering if I could ground the outlet(s) by running a bare copper wire to the metal rectangle box back to the ground screw on the outlet?

Pictures requested:

The Older Looking Outlet The Older Looking Outlet

The Newer Looking Outlet The Newer Looking Outlet

On "The Newer Looking Outlet" above, you are not able to see it in the photograph but there is a green screw for grounding; it is on the bottom left hand side

  • Can you get us photos of the insides of the boxes? May 15, 2016 at 19:31
  • 1
    You say "some of the outlets appear to be knob and tube"; how can you tell? Are you sure there's knob and tube wiring involved? May 16, 2016 at 2:49
  • I crawled up into the Attic but it was difficult because all of the old insulation and mold etc... I wasn't able to locate a knob anywhere but I hardly checked. I am going to throw a long sleeve with gloves and a mask tomorrow and check again.
    – aguertin
    May 16, 2016 at 4:13

3 Answers 3


Replace the outlets with GFCIs -- the operation of a GFCI in no way depends on the presence of the equipment grounding wire. You'll have to use the "No Equipment Ground" sticker that comes with them, by the way.

P.S. on the metal boxes -- since it sounds like your house is a mix of K&T and other wiring techniques (perhaps NM additions), you cannot ground to the boxes -- that technique only works if your house was wired with BX/AC, MC, or metallic conduit (RMC/IMC/EMT).

(Confirming that you have K&T and NM mixed in your house, based on your photos, by the way -- I also do not see a ground wire on the NM, but the angle of the photo makes it hard to tell.)

  • So GFCI will be able to compensate for not having it grounded? That is awesome if that is the case! I did just realize that some of the outlets have a metal casing around them so maybe I could just run copper wire to that for a ground?
    – aguertin
    May 15, 2016 at 19:03
  • A GFCI outlet, properly installed will basically eliminate all shock/electracution hazard, with or without a ground connected. However, the lack of a ground may still cause problems for some desktop computers, surge protectors and such. For these types of devices, you may be better off rewiring to get a good ground.
    – DoxyLover
    May 15, 2016 at 22:12
  • The NM does not have a ground, you are correct (though I am not entirely sure what "NM" stands for). On the outlets themselves (the blue colored on second photo), there is a green screw for grounding on the bottom left of it.
    – aguertin
    May 15, 2016 at 23:55
  • 1
    NM = non-metallic cable (called "Romex" as a genericized trademark) May 15, 2016 at 23:57
  • 3
    Agree with @ThreePhaseEel, but the simple fact that your house isn't a pure / untouched K+T system would scare me if it was my place. Intact K+T is actually pretty good; it's when people have messed with it over intervening years that it gets ugly. Strongly suggest you have someone that knows about this stuff to look over visible parts of the wiring. May 16, 2016 at 1:17

Consider what happens when you have a "class 1" metal cased appliance and a wire comes loose and touches the case.

The best case is when you have both grounding and a GFCI, the GFCI will quickly trip disconnecting the faulty appliance from the aupply.

If you have grounding but no GFCI then the outcome depends on the impedance of the fault path. If it's a low impedance path then the fuse/breaker will blow/trip quickly disconnecting the fault. If it's a high impedance path then the fuse/breaker will remain intact but the grounding will keep the voltage on the metal case to a low level.

If you have a GFCI but no grounding then the case will become live. If/when you touch the case and a significant current flows through you then the GFCI will trip. Hopefully it will trip fast enough to save you.

If you have no grounding and no GFCI then the case will become live and there will be nothing to stop the current flowing through your body.

So GFCI with no grounding is better than no GFCI and no grounding but it's still less than ideal.

Pragmatically the regulators can't really force people to rewire and they know people will find ways of connecting class 1 appliances to unearthed circuits (cheater plugs, cutting off the earth pin, extension cords). So they allow fitting of 3-pin GFCI-protected outlets to existing circuits.


if you have knob and tube anything, it all has to come out and be replaced with modern 2 conductor and ground wiring. this can be done at lot more inexpensively than most people think, but you need to know what you are doing, and judging by your own comments, its probably time to get a licensed electrician.

  • Not necessarily.... May 15, 2016 at 18:58
  • I hope that isn't the case because I really can't afford it right now. Good news is there is only 1 outlet that appears to be using it so far... the only reason I believed it to be k&t is because of how the wires looked compared to all the others in the room. When I took the cover of it looked like two old ass copper wires with no color coordination at all. Thanks for your help btw
    – aguertin
    May 15, 2016 at 19:04
  • 1
    you may be misunderstanding what knob and tube is - check and make sure. knob and tube is a fire waiting to happen. May 15, 2016 at 19:08
  • 3
    The fire risk from K&T is caused by improper building insulation that allows the wiring to overheat and ignite nearby combustibles, along with the spectre of overfusing or bypassed fuses. (There are other issues with K&T in buildings, such as haphazard junctions to NM that is put in later and excess magnetic fields caused by the "go wherever" neutral routing of the K&T era, though....) May 15, 2016 at 19:32
  • 2
    I have a 1930 home that was partly rewred with a new panel in the late 90's. Some of the original knob and tube was left in and this was legal in the U.S. I have removed most of the in wall and all of the runs in the attic, using old work boxes in the walls and NMB. I do plan to replace the last few runs so I can have blown insulation to the walls. The old hard drawn copper was is really good shape and all of the insulators were in good shape I did not have to do the upgrade but wanted to so the house will be safe with the insulation upgrade.
    – Ed Beal
    May 15, 2016 at 19:58

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