Grounding Question fro old house w/ 2 prong outlets

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Old 01-27-08, 11:11 AM
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Grounding Question fro old house w/ 2 prong outlets

Hello - question for you, I live in a house built in the 1950s, and the previous homeowner had replaced some of the 2 prong outlets w/3 prong outlets. The home inspector mentioned to us at the time we bought that the rest could also be replaced.

When I went to replace the outlets I noticed the the wires coming into the boxes do not include ground wire. I went back and checked the ones that were already replaces and it is the same, just black and white wires, no ground.

Question - could it be that the metal electrical boxes are grounded? My electrical tester - a 3 prong tester with a series of light combinations is not showing a ground error on these outlets.

I am puzzled because this tester is not showing an error, and there is no ground wire at all in the box.

2nd Q - is it ok to take a piece of ground wire and go from the receptecal, to the metal box?
 

Last edited by smitchell169; 01-27-08 at 11:12 AM. Reason: forgot to add something
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Old 01-27-08, 11:40 AM
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a metal box should be grounded although if installed improperly it could possibly not be so.

What is used to connect the various boxes together. Is there metal conduit? NM cable (Romex), BX (AC cable)?

Metal conduit is acceptable as a ground conducotr (EGC) but anything else needs more explanation to know for sure if it is correct.

One thing you need to be sure of; the neutral and the ground must not be connected together in anyplace other than the main panel. Some "electricians" do this believing it is correct but it is actually illegal and unsafe.
 
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Old 01-27-08, 11:49 AM
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If you feel comfortable doing it remove the cover from your breaker panel. Do you have cloth or plastic cables coming in? Are there bare copper wires attached to the neutral (or ground if present) bar? If so then the ground wires may have been fastened at the "Romex" clamps of the receptacle boxes.

Or you may be able to see evidence of AC (BX) cable.
 
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Old 01-27-08, 11:54 AM
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Not all metal boxes are grounded. My house, built in the 50s had no grounds except in the kitchen. Plastic boxes were not used then, so all the boxes are metal.

What type of wiring do you have? Metal conduit? Cloth covered NM cables?
 
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Old 01-27-08, 11:58 AM
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all metal boxes SHOULD be grounded. If they were to become energized, the screw holding the trimplate on also becomes energized, which is never a good thing.

I would have to look back more code cycles than I have books for but I cannot imagine a metal box ever being allowed to be not grounded.

regardless, it was never safe to not have it grounded.
 
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Old 01-27-08, 12:31 PM
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Updated information

the panel that I have is newer. IT was replaced by the previous owner as well.

The woring coming out of it is ROMEX looking - white flat, wide wiring. In looking at a nearby junction box in a closet, I saw both this white looking flat wire, and a BLACK rough looking wire set going in. I opened the junction box and it looks like the black wire set has a Black, Red and Ground coming into the juntion box.

Now back to the outlet boxes in the rooms - the boxes are metal, only have White and Black wires coming in and going out.

I can not see the back of the box, it is in the wall. So someone asked if the ground was connected to the back of the box, not sure how I tell that?

If there is indeed a ground wire attached to the back of the metal box (and if I can fugure that out), should I attach a Ground wire from the receptacle to the inside of the box?

Is this a safe way to replace 2 pronged with 3 pronged outlets?
 
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Old 01-27-08, 12:40 PM
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I have seen installers cut the ground wire just as it comes in to the box and is clamped in the clamp.

If the tester shows a ground, I would suspect this is what was done. You would have to look very closely at where the cable enters the box but yo umay still not see it.

This is presuming the black rough looking cable (old style NM) has a ground conductor in it.

If the boxes are grounded, then yes, you can run a pigtail from the recep ground screw to the box itself.

btw; the bak of the box would not be the outside, it would be the back of the inside of the box. It would be visible from looking in to the box.

If there is not actually a grond conductor, then no, you do not replace the 2 prong receps with 3 prong receps. You would need to replace with GFCI receps (although those do have 3 prongs)
 
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Old 01-27-08, 12:42 PM
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The ground wire is probably wrapped around the wire then clamped in place by the romex connector. It was common back then . I'd leave it and install self grounders.
 
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Old 01-27-08, 12:46 PM
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Follow Up

So, botht the wiring types in the house seem to have a bare copper wire, so I will assume that those are the only two types in the house.

Question - If the bare copper wire is attached the clamp, and I can not see it to verify but the Tester is not indicating a ground error, I should be ok?

Follow Up Q - why would the tester in this case not show an error? There are only white and black wires going to the receptacle. There is currently NO ground wire going from the receptacles to the screw inside the metal box. I would think that this wire would need to be present at least, for the outlet to be grounded.

Am I missing something?

Is there a difference in leaving it AS-is (NO GROUND WIRES connect but no errors on the tester)
versus
Connecting a wire for the green receptacle screw to the box screw?
 
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Old 01-27-08, 12:52 PM
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the yoke of the recep is most probably providing you with the ground reading. While it does provide that continuity, unless the receps are rated as "self grounding" it is not acceptable to utilize that at "THE" grounding connection. A tail would still need to be installed, or, if you are changning receps, you could buy "self grounding" style receps.
 
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Old 01-27-08, 04:53 PM
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nap,

I agree that a ground is a good thing, and of course code now requires circuits and boxes to be grounded.

But in the late 1950s not all NM cable had a ground. Some varieties consisted of two wires, a white and a black. Other varieties had a smaller size ground wire.

They wires thousands of homes with metal boxes (plastic boxes did not exist) with no ground. These homes were wired legally and are still legal today, as long as renovations requiring updating have not been done.

When someone talks about older houses and two prong plugs, nothing should be assumed regarding grounding of the boxes.
 
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Old 01-27-08, 05:39 PM
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Problem solved

I do indeed have all "self-grounding" receptacles, and since my tester is showing no ground errors, I think I am all set and more importantly safe.

I did not realize that the self grounding receptacles run the ground to the box through the recept screws. I could not figure out how the thing was being grounded and started to think that my tester was malfunctioning.

So if I replaced the 2 prong outlets with 3 prong ones and using the self grounding outlets to run the ground to the box, which is grounded from the outside of the box.

Thanks for the help and peace of mind.
 
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