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Old 12-16-2010, 09:37 AM   #1
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Replacing outlet - no ground wire


Need to replace an existing outlet on a 15amp circuit. The cabling is AC wired around 1964. I looked in the box and found the following.
One black wire connected to the outlet.
One neutral wire connected to the outlet.
One white and black wire connected via a wire nut.
Tab not broken.
No ground wire to outlet.
This is an outlet controlled by a switch.

Should I create a pigtail ground wire and connect it to one of the two screws in the back of the metal box where the AC cables are clamped to the box? The bottom clamp is empty (no AC cable coming in) but can I still use that clamp to secure the ground wire? Do I even need the ground wire with AC?

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Old 12-16-2010, 10:11 AM   #2
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Replacing outlet - no ground wire


You need to check if the box is even grounded. If just hook the wire there it doesnt mean its grounded. If you have a volt meter touch the red probe to the black wire then the other to the box if it reads 120 then the box is grounded.

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Old 12-16-2010, 11:48 AM   #3
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Replacing outlet - no ground wire


I did the test and the reading was roughly 124.6 volts when I touched red probe to the hot wire and the black probe to the box.
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Old 12-16-2010, 11:49 AM   #4
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Replacing outlet - no ground wire


Quote:
Originally Posted by clydesdale View Post
Need to replace an existing outlet on a 15amp circuit. The cabling is AC wired around 1964. I looked in the box and found the following.
One black wire connected to the outlet.
One neutral wire connected to the outlet.
One white and black wire connected via a wire nut.
Tab not broken.
No ground wire to outlet.
This is an outlet controlled by a switch.

Should I create a pigtail ground wire and connect it to one of the two screws in the back of the metal box where the AC cables are clamped to the box? The bottom clamp is empty (no AC cable coming in) but can I still use that clamp to secure the ground wire? Do I even need the ground wire with AC?
Do you have conduit to go along with this metal box? If you have conduit the conduit can be used as the ground. However if the conduit has lost its integrity it may not be safe alone as the ground.
Checking to ground (example above) does give you an indication as to the presence of a ground. If it is indeed a grounded system using the conduit as the ground you MUST install a grounding jumper from the box (not from the cable screw) but to the threaded 10/32" hole available to the receptacle ground.
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Old 12-16-2010, 01:31 PM   #5
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Replacing outlet - no ground wire


No conduit other than the AC cable going into the box. Looks like there are two threaded holes drilled in each side of the box I assume any one of those holes would work fine. Based on reading of 124.6 volts I assume the metal box is grounded.

So then a few more questions. 1) I guess the code was different back in the day when this work was done as it was a 3-prong outlet but no ground wire from outlet to box. 2) Will any metal 10/32" screw be okay to attach the ground wire to the metal box (from the receptacle ground terminal)? 3) I measured the voltage from the unused metal cable clamp in the bottom of the box and at was the same 124.6 volts as the box. Why not use the metal cable clamp if it has the screw and it tightly secured to the metal box?

Last edited by clydesdale; 12-16-2010 at 01:50 PM.
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Old 12-16-2010, 02:48 PM   #6
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Replacing outlet - no ground wire


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I guess the code was different back in the day when this work was done as it was a 3-prong outlet but no ground wire from outlet to box.
Yours would not be the first that had someone violated code by replace a two-prong outlet with an ungrounded three-prong outlet. Many have done this to avoid having to use those little adapters. The fact that it was done does not guarantee compliance with code "back in the day".
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Old 12-16-2010, 03:46 PM   #7
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Replacing outlet - no ground wire


As per 406.3(D)
  1. 406.3(D)(3)(a) it is acceptable to replace a 2 prong receptacle(non grounding type receptacle) with another 2 prong receptacle.
  2. 406.3(D)(3)(b) it is acceptable to replace said 2 prong receptacle with a GFCI receptacle and no ground wire needs to be connected to that GFCI.
  3. 406.3(D)(3)(c) you can replace the receptacle with a 3 prong grounding type without having to connect a ground wire to that receptacle if the receptacle is fed by a GFCI (ex. Change out the breaker for that circuit to a GFCI.
So what i suggest you do, since you did confirm you have a ground at that box is to get either a grounding clip or a ground screw. Get a grounding screw if you have a spare threaded hole in the box, most likely an unused cable support inside the box's hole will be the right size, or like JV said you can drill and tap a hole for the ground screw. but the screw size is 10-24 standard size not 10-32. If you do not have a spare hole or care to drill and tap a hole, you can use a ground clip and use it how displayed in the picture below, but make sure the part sticking out on the bottom is bent over obviously so as not to interfere with the device or the cover and connect a three prong outlet. that will be the proper way.

Hope that helps!!

Last edited by SGC622; 12-16-2010 at 03:53 PM.
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Old 11-02-2011, 08:31 PM   #8
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Replacing outlet - no ground wire


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If you have a volt meter touch the red probe to the black wire then the other to the box if it reads 120 then the box is grounded.
What do I set the dial to before putting the RED on the hot cable, and the black on the box/housing? I want to see if my outlet box/housing is grounded, like above, but I have no idea how to set the multimeter I just bought. There is no reference to AC or DC on the dial. ???

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Old 11-02-2011, 08:35 PM   #9
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Replacing outlet - no ground wire


The V~ is AC volts. Set it to 250.
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Old 11-02-2011, 08:40 PM   #10
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Replacing outlet - no ground wire


I touch the red to the hot wire, correct?
And the black to the housing to see if it's grounded?
If it is, then the circuit is closed, and it will show a current of 220, correct?
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Old 11-02-2011, 08:44 PM   #11
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Replacing outlet - no ground wire


It would read 120, if you are in the US.
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Old 11-02-2011, 08:46 PM   #12
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Replacing outlet - no ground wire


And if it's not grounded, it will read nothing, correct?
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Old 11-02-2011, 08:56 PM   #13
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Replacing outlet - no ground wire


Wait, do I turn off the circuit breaker to do this? Do I turn it back on only once stuff is disassembled, and I am ready to do the test?
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Old 11-02-2011, 08:56 PM   #14
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Replacing outlet - no ground wire


Yes, however, if your box is attached to old metallic wiring it will show 120v-but you do not have a good ground.

Also your meter is only CAT II, do not try and use it in a panel. Receptacles and such only.
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Old 11-02-2011, 08:57 PM   #15
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Replacing outlet - no ground wire


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Yes, however, if your box is attached to old metallic wiring it will show 120v-but you do not have a good ground.

Also your meter is only CAT II, do not try and use it in a panel. Receptacles and such only.
The 2nd sentence, I am only using it in my electrical wall socket. I am in an apt, so I have no idea about any panels. If CAT II is for wall sockets, what do you need for house panels?

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