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Old 04-26-2008, 10:28 PM   #1
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replacing old outlets and switches


I am working on getting rid of those old painted over outlets and switches. I have that old wiring with the metal coil through the house. I was told that it is that metal that grounds the circuit and to run a wire to the back of the box for a ground. How can I check to see if the circuit is truly grounded, what kind of tester should I get? And also, do I need to add a ground wire to the new switches as well, or are they fine with just the two wires that are there. I did a couple outlets and switches already and they work, but I'd like to have them properly done, rather than "just good enough" If you know what I mean

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Old 04-27-2008, 12:51 AM   #2
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A receptacle tester can be bought at most hardware stores for less than $10. It just plugs in, and helps you determine if it is wired right and if it is properly grounded. They'll have three lights that light up in certain patterns to indicate what the problem is if there is a problem. They have prongs just like an extension cord or appliance cord does.

That tester will tell you if you have an equipment ground on a receptacle circuit or not, but you'll have to pigtail the receptacle's ground screw to a (green) screw on the box to test for ground.

I'm assuming you have metal boxes. Assuming your boxes are grounded, the switch is not required to be bonded since there is metal-to-metal continuity with the box. If you have plastic boxes, you have to bond the green screw on the switch to the equipment ground on the circuit. This way, in the event of a fault at the switch, the breaker will clear.

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Old 04-27-2008, 12:06 PM   #3
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Originally Posted by thekctermite View Post
I'm assuming you have metal boxes. Assuming your boxes are grounded, the switch is not required to be bonded since there is metal-to-metal continuity with the box. If you have plastic boxes, you have to bond the green screw on the switch to the equipment ground on the circuit. This way, in the event of a fault at the switch, the breaker will clear.

I do have the metal boxes, but if the metal to metal contact in the switch is enough to ground the switch why is it that I need to run a wire from the green screw on the outlet to the back of the box? I am just curious as to why the metal to metal contact isn't enough for the outlets as well. Also to be clear that I understand you right, the metal to metal contact that you are talking about is in the screws that hold the switch in place in the box, right?
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Old 04-27-2008, 12:57 PM   #4
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replacing old outlets and switches


Under certain circumstances, you don't need to run a ground wire from the receptacle to the box. Mike Holt has a good explanation at:http://www.mikeholt.com/newsletters....y&letterID=241

Depending on how old your wiring is, you may or may not have an effective ground path. Older BX cable did not have the thin metal grounding strip that is included in newer type AC cable. The armor of the older BX cable should not be used as an equipment grounding conductor.
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Old 04-27-2008, 01:03 PM   #5
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replacing old outlets and switches


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Originally Posted by Nailpounder View Post
I do have the metal boxes, but if the metal to metal contact in the switch is enough to ground the switch why is it that I need to run a wire from the green screw on the outlet to the back of the box? I am just curious as to why the metal to metal contact isn't enough for the outlets as well.
As long as the boxes and metal (which they are) and the cable has an integrated EGC (in your case the cable armor), then the receptacles do not need a separate EGC to the box (note: the receptacles must be the self-grounding type). When you buy recepts, they typically have the grounding screw since it will be used for type nm-b cable, i.e. the manufacturers do not want to make two different types of recepts depending on intended use.

On a side note, for exposed work boxes and covers, i.e. where the switch or recept is actually held by the cover itself and not the box, you do need to provide a bonding jumper between the switch/recept and box.

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Originally Posted by Nailpounder View Post
Also to be clear that I understand you right, the metal to metal contact that you are talking about is in the screws that hold the switch in place in the box, right?
You are correct. Self-grounding receptacles will have a brass strap over the top of the yoke. Is it via contact between this strap and the 6/32 mounting screws that the ground connection is made (the strap is designed to make good contact with the screw).
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Old 04-27-2008, 10:18 PM   #6
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Thanks a lot.
You guys have been very helpful. Now I have one more thing. I have purchased the tester, and 2 of the 4 outlets that I replaced test for a faulty ground. Two are good. Why is that if I wired them all the same, with a lead to the back of the box? Or is it time to call in a professional?
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Old 04-28-2008, 08:26 AM   #7
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Thanks a lot.
You guys have been very helpful. Now I have one more thing. I have purchased the tester, and 2 of the 4 outlets that I replaced test for a faulty ground. Two are good. Why is that if I wired them all the same, with a lead to the back of the box? Or is it time to call in a professional?
See the reply in post #4 (your cable armor may not be making good contact at some point in the run).
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Old 04-28-2008, 09:36 AM   #8
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Look at post 4 like Jimmy suggests. Matsukaze explains it. Some cable of the type you describe is not acceptable for use as a ground, and can actually be dangerous when carrying fault current. But this cable can fool a receptacle tester and an ohm meter into thinking a ground is present.

The way to check is to carefully check the armored cable. The type that is acceptable for use for grounding will have a thin aluminum strip inside the sheath, along with the wires. It is not connected to anything. Usually the electrician will simply cut it off, or will fold it back over the sheath before inserting the assembly into the cable clamp at the box.

If you do see that strip, make sure the cable box connectors are tight and clean to establish a good ground on those you are having problems with. If that strip is not present, you do not have an acceptable ground.

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