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My upstairs office has 3-prong outlets, but according to my surge suppressor, they are not grounded. I took one of the sockets off to inspect how it was wired, and it seems to have a ground wire connected to it.

My house was built in the late 1960s. Is it conceivable that all 3 sockets are "bad" with respect to their ground wires? Or is it more likely that the ground wires are not actually grounded? Would it be worth my time to replace one to see if the problem is fixed?

Short of running a copper wire from downstairs up through my window, I don't have a convenient path to ground from the office, if the copper in the wall isn't grounded. I'm running into occasional instability on my UPS because of the lack of ground.

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Have you looked at this Question, or this Question? Try searching electrical ground. –  Tester101 Apr 16 '12 at 20:16
have you checked the other end of the wire at the breaker panel? –  Borzio Apr 17 '12 at 4:54
And keep in mind that power outlets are typically daisy chained from box to box -- any point along the chain could cause your loss of ground. –  Borzio Apr 17 '12 at 4:55
Does your UPS report other outlets as OK? What does one of these tell you? –  Brock Adams Apr 17 '12 at 7:43

1 Answer 1

up vote 9 down vote accepted

It is extremely unlikely that all three receptacles all have bad grounds. Not impossible, but unlikely.

The most likely scenario is that your home was built before grounding became required by code (1962, plus however long it took for your state/municipality to adopt it), and then someone renovating after that time put in 14/2 Romex with a bare ground for the outlets, but then found that the supply wire from the panel didn't have a ground and didn't bother to replace that wire. So, the ground is either shorted to the neutral or left open.

The other likely scenario is that there is a discontinuity in the ground between these three outlets and the supply wire. The necessary wires exist, but whoever last messed with your home's electrical didn't connect them properly.

An outlet tester, and a more thorough inspection of the wiring, can tell you. Head to Home Depot, Lowe's, Ace, whatever, and pick up a 3-prong GFCI outlet tester:

enter image description here

Plug it into all of the outlets on each receptacle; ideally, you should see the two amber lamps light, but that's unlikely if the surge protector doesn't detect a proper ground path. What's more likely is that you'll see only the middle lamp light, indicating an "open ground".

Unfortunately, because the neutral and ground are supposed to be continuous (they both tie directly to the neutral bus strip in the service panel), there isn't a really good way to detect a neutral-to-ground short or swap without opening up all the outlet boxes; a 3-lamp tester will read "correct", and a multimeter will read continuity between neutral and ground no matter whether they're correct, swapped or shorted. However, this scenario is very unlikely in your case, as the surge protector should read "grounded" if the ground pin has continuity.

With the symptoms confirmed (hopefully), turn off the breaker (or pull the fuse) for this circuit, and open up all the outlet boxes. Verify that all of the wire bundles coming into each of the outlet boxes have a bare ground wire, which is twisted together with any other bare wires in the box, and is also connected to the outlet's grounding terminal (it is also acceptable, if the outlet box is metal, for the wires to be screwed into the box itself; the outlet will then be grounded through its chassis and the mounting screws. If the box is a resin or thermoplastic, the ground screw of the outlet chassis must be used).

If that doesn't indicate the cause of the problem, you will need to determine which of the various wire bundles is fed directly fro the panel. This is generally done by disconnecting all the black wires from all the outlets, then turning the power back on and VERY CAREFULLY probing each one with a non-contact voltage tester, like this:

enter image description here

The black wire that lights up is the one fed most directly from the panel; however, it may not be the actual wire run from the panel itself, as there could be something further "upstream". The usual culprit is the switch for the lights, especially in older homes (newer NEC code encourages lights and outlets to be on different circuits, by encouraging calculation of demand load based on separate lighting and appliance branch components, so you're not fumbling around in the dark if your hair dryer shorts out). If your NCVT lights up on anything else that you know is "dead" when the power to this circuit is off, turn the circuit back off and pull those things out of their boxes to inspect those wires. Check for the existence of ground wires, whether they're properly continuous with all other grounds, and with all black wires disconnected, whether any black wire still lights up with the power on.

If the trunk that seems to be the main power feed does have a ground, use a multimeter to measure the ohms between the neutral (white) and bare (ground). It should be zero. If it isn't, the ground is probably not properly connected to the neutral bus strip at the panel; this is where you call in a qualified electrician, because the rails in a fusebox or breaker panel can kill you instantly with one wrong move. If the ground doesn't exist in that supply wire, that's the problem; you'll need to run a new length of grounded Romex to the panel, or alternately run a green-jacketed ground wire to another box with a known good ground (I THINK this is acceptable; an electrician can verify). Understand that if you have a fusebox and the electrician has to open it up, he may insist on replacing it with a breaker panel in order to bring everything he's touching up to current code.

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If an electrician has to replace anything, everything upstream of it has to be brought up to code as well. –  Brad Gilbert Apr 18 '12 at 14:48
@BradGilbert: If ground wiring was unavailable, could an electrician install a GFCI and label the outlets as "No Equipment Ground" without having to fix the upstream wiring? –  supercat Nov 16 at 22:43
@supercat I would assume so. –  Brad Gilbert Nov 17 at 0:37
@BradGilbert - I would not. If a licensed electrician touches any part of a home wiring installation, everything upstream of that must be brought up to code. So, given that a GFCI requires a ground in order to function, the electrician must create a suitable ground path for at least that one receptacle. Merely labeling the outlet as being ungrounded is not kosher; the label can be removed or fade over time and then the information is lost. –  KeithS Nov 17 at 17:01

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