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My house was built in 1949 and some of my outlets look like this guy while others run updated Romex into plastic boxes. With the wires coming through the conduit in the plaster, are these grounded outlets? I was going to replace the outlets and want to make sure I understand what is going on with these before I do. Thanks!

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    The receptacle is not grounded, but the box may be. – Tester101 Mar 21 '16 at 16:16
  • If so, wouldn't the receptacle would be grounded when screwed tight into the box? That's how it works in industrial work where the outlet bottoms out on an all-metal box. – Harper - Reinstate Monica Mar 21 '16 at 22:17
  • By chance do you live in a condominium? – Kris Mar 22 '16 at 11:11
  • @WolfHarper only if the receptacle is the "self-grounding" type. That one is not. Notice the plastic screw-keepers on the screws. Self-grounding receptacles have a metal or wire clip on one screw on the yoke. A self grounding receptacle is normally specified in industrial work. The cheap receptacles at the box stores are not self-grounding. So, even if the box is grounded, without an EGC jumper, this receptacle is not up to Code for equipment grounding. – ArchonOSX Mar 23 '16 at 10:37
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Back in 1949 when your house was built, the code of the time allowed the metal shielding of the BX cable to be used as a ground. Over time these connections degrade from corrosion, and the grounding could eventually fail. Oftentimes, when a home is renovated to use non-metallic wiring (NM), the ground to existing BX cable can also become disconnected. This is likely the case with your house.

There still is a possibility that the ground is intact, but it is unlikely. You can test this with an inexpensive outlet tester like pictured below. These typically run around $10, and are a good investment. In your case, you would probably see that this outlet has an open ground. Make sure that the outlet is properly secured to the box before you test it.

Outlet Tester

If you find that the outlet is not grounded, you should avoid using it until you can have that part of your home rewired.

  • Would I be able to install a GFCI to rectify this for the time being? If so, would I just ground the GFCI to the box? I would assume this wouldn't protect any surging so it would not be safe to plug a stereo into it, but it would make plugging a lamp into a safe bet? – junta Mar 21 '16 at 19:48
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    I believe that you can install a GFCI in place, but it would not make the outlet grounded. An outlet like this should be properly labeled with a sticker that says no equipment ground. I believe some GFCIs come with the sticker in the box. A long term solution would be to upgrade the electrical system. – Jason Hutchinson Mar 21 '16 at 20:23
  • Last question then and I know this isn't a very good one. But any idea on very roughly how much this could cost for an electrician to rewire? On the circuit there are 3 outlets and a switch and the length is probably around 60feet from the panel outside to the outlets. I know there could be obviously a lot of variables, but I am trying to wrap my head around what kind of job this is before I got through the hassle of calling an electrician out to take a look at it. Thanks again! – junta Mar 21 '16 at 23:03
  • @junta the cost is going to depend on what's under that floor. If it's a crawl space/unfinished basement/etc where the electrician can get easy access, it will take much less time than if he has to fish the wires all 60' back to the box. You will be paying by the hour (plus material), and the going rate in your neighborhood will be different than just about anybody else's rate who might be here to answer. – FreeMan Mar 22 '16 at 17:54
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This is a picture postcard application for a GFCI outlet. Attach it to the black and white wires without ground. That is code legal for this type of situation, but the outlet should be labeled "no equipment grounding conductor". At that point you can plug 3-prong appliances into it. The GFCI provides much of the protection of the ground. This doesn't satisfy every appliance, but it is, at least, not unsafe.

I an skeptical that this is actually grounded because I see both conductors disappearing into a 1/2" hole, and with all the debris on the bottom of the box, I don't see the normal hardware I'd expect to see from the conduit joiner or the BX clamp. An unguarded knockout hole is a real problem. It may look ok now, but when you put the outlet back in and tighten it down, it could pinch and damage the conductor.

This is not 1949 work. The outlet is grounded and worse, has those vile "back stabs". That introduces the real possibility that the wire-run is a retrofit also, in which case, maybe it is practical to pull new cable the same way.

Those 3-light outlet testers are neat, but keep in mind they can trip GFCI's. The hot-ground yellow lamp is, by nature, a ground fault. (so is the neutral-ground red lamp, but the GFCI is unlikely to detect that one.)

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    The 3-light tester pictured below will not normally trip a GFCI, I've used a similar one to that on many GFCI outlets, and purchased a second one that has a specific GFCI test button that will trip the GFCI. – Johnny Mar 21 '16 at 23:13
  • But even with the GFCI upgrade, will a surge protector protect electronics plugged into the outlet? Thanks for the info. – junta Mar 21 '16 at 23:26
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    @junta -- a surge protector absorbs surges and will still work without an equipment ground. – ThreePhaseEel Mar 22 '16 at 0:18
  • From my experience, that looks like a 1900 box with 1/2 plaster ring. And 1/2" grounded EMT – Kris Mar 22 '16 at 11:11
  • I do a lot of EMT. I thought it was a 2x4 1-gang steel box set horizontal, and I expected to see the locknut or at least the threads coming up from the connector. Is there another way that was fastened back then? Chase nipple maybe? homedepot.com/p/1-2-in-Rigid-Chase-Conduit-Nipple-2-Pack-20701/… – Harper - Reinstate Monica Mar 22 '16 at 21:49
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They don't appear to be. Wiring didn't usually contain ground conductors during that era. Unless you have grounded conduit and either a pigtail from the box or a self-grounding outlet, it is not grounded.

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