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Old 02-17-2008, 08:53 PM   #1
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Grounding outlet to armored cable - fine?


My house is almost entirely two-prong electrical outlets. So I want to replace them with three-prong grounded outlets. I got a bunch of new outlets from the store and some copper wire to use as the ground wire, because when I took an old outlet out of the wall, I didn't see any already existing ground wire behind it. So I installed the outlet and grounded it with the copper wire wrapped and taped tightly around the armored cable (looks like this: http://images.orgill.com/200x200/3340163.jpg) that contains the electrical wires running from the circuit breaker. I've read in several places that it is okay to ground the outlets to these armored cables. I also bought an outlet tester and when I plug it in it says it's correctly wired and grounded and it seems to be functioning fine. So is this okay?

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Old 02-17-2008, 08:57 PM   #2
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Grounding outlet to armored cable - fine?


Umm, yeah, next time ask before you do...

The box is already grounded by the cable clamp, so as long as all the connectors are tight back to the panel your good to go, what you did is no good...

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Old 02-17-2008, 09:08 PM   #3
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Grounding outlet to armored cable - fine?


What Chris said.
Untaped and unwrap the wire the wire from the sheath and reinstall it in the clamp snugly. Run a pigtail from the receptacle's ground screw to either a green ground screw in the back of the box (most old boxes to not have a tapped hole for these) so you might have to use a grounding clip on the front edge of the box. Both of these are available at any hardware store.
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Old 02-17-2008, 09:17 PM   #4
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Grounding outlet to armored cable - fine?


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Originally Posted by junkcollector View Post
What Chris said.
Untaped and unwrap the wire the wire from the sheath and reinstall it in the clamp snugly. Run a pigtail from the receptacle's ground screw to either a green ground screw in the back of the box (most old boxes to not have a tapped hole for these) so you might have to use a grounding clip on the front edge of the box. Both of these are available at any hardware store.
Or just buy self grounding receptacles...
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Old 02-17-2008, 09:41 PM   #5
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Grounding outlet to armored cable - fine?


If the box is already grounded, can't I just attach the copper ground wire I screwed to the receptacle to the side of the box with electrical tape? Isn't this essentially the same as screwing it down in the back (I don't believe there was a screw hole anyway)? I did plug the outlet tester I had into one of those three-prong to two-prong adapters and then into the two-prong outlet and it indicated there was no ground, but the ground light turned on when I touched the adapter's ground wire to the box. If there's a simpler way to do it, I'll surely do so with the other outlets, but is there any reason why having it grounded to the cable isn't alright?
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Old 02-17-2008, 09:58 PM   #6
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Grounding outlet to armored cable - fine?


I have to ask..how did you get access the the metal cable to wrap your ground wire around it? Usually the cable does not extend into the box. Are you removing the metal boxes to do this?
Maybe your boxes have internal clamps (some have this feature) and your able to get access to it that way?

Go to lowes and get some ground clips like this ..below. all you need is a screw driver to clip the ground wire and green clamp to the box edge.

Last edited by Stubbie; 02-17-2008 at 10:02 PM.
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Old 02-17-2008, 10:10 PM   #7
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Grounding outlet to armored cable - fine?


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If the box is already grounded, can't I just attach the copper ground wire I screwed to the receptacle to the side of the box with electrical tape? Isn't this essentially the same as screwing it down in the back (I don't believe there was a screw hole anyway)? I did plug the outlet tester I had into one of those three-prong to two-prong adapters and then into the two-prong outlet and it indicated there was no ground, but the ground light turned on when I touched the adapter's ground wire to the box. If there's a simpler way to do it, I'll surely do so with the other outlets, but is there any reason why having it grounded to the cable isn't alright?
It sounds like you are yanking our chains. Attach the wire to the side of the box with electrical tape? No. Attaching the wire to the cable sheath? No. Like Stubbie said, you should not even have access to the cable if the box is properly installed.

What you can do if there is no tapped hole for a ground screw is to use the screw from the unused cable clamp, if there is one. If you have cables coming in from only the top or bottom, use the hole for the clamp on the opposite side to attach a wire. This hole is already tapped for a 10-32 screw, and may even still have a clamp and screw on it.

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Old 02-18-2008, 12:31 PM   #8
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Grounding outlet to armored cable - fine?


hey, so i checked other outlets in the house, and most do seem to have the clamp you're talking about, as well as not having the armored wire exposed. this one in particular that we wired first did have the wire exposed, and no clamp. the rest of the outlets i'll ground with the clamp, but i would just like to know if there is any danger in keeping the one grounded to the armored wire. like, will i start an electrical fire?
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Old 02-18-2008, 03:07 PM   #9
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Grounding outlet to armored cable - fine?


It is possible if you have a fault any air gaps between that wrapped wire and the armor of the cable will likely arc when the fault current is imposed on the connection. . The ground wire does not carry current unless you have a short to ground or some other fault occurs at the electrical box or another electrical box or the appliance plugged into the receptacle. A continuous fault current path must be in place through out the branch circuit ie box to box to box etc... Any break in that path and you lose your fault current path and the breaker will not trip. In your case the metal of the cable is used as the grounding path from box to box fixture to fixture and so on... back to the main panel neutral/ground bar. A break in that path due to a poorly made connection to the armor of the cable will prevent a breaker from tripping. Though your test light may show a good ground this is not a reliable connection by wrapping the armor of the conduit with a ground wire. If your cables are clamped properly inside the box this bonds the box to the cable but does not bond a metal receptacle yoke to the box. This must be done with an approved method. One being a grounding clip and connecting a jumper fastened to the box edge and then to the green screw on the metal yoke of the receptacle as shown previously. Or a self grounding type receptacle. to better understand this concept look at the image I've posted. The green line is the armored cable in your case and there may be any number of switch boxes and receptacle boxes and light fixture boxes along that green line. Any connection or bonding point along that line that comes apart or is so poor that it behaves like a broken connection will 'open' the green path and fault current has no way to complete a circuit path and your circuit breaker will not trip alerting you to the fact that a fault has occurred on the branch circuit. Instead all the metal before the opened point in the fault path will come to line voltage and pose a shock hazard and possible fire hazard.
Attached Thumbnails
Grounding outlet to armored cable - fine?-bonding-diagram.jpg  

Last edited by Stubbie; 02-18-2008 at 07:36 PM.
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Old 02-18-2008, 04:51 PM   #10
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Grounding outlet to armored cable - fine?


Whereas it is possible for the lengths of armored cable, armor as the ground, to not make that good a grounding connection as they are clamped to the various outlet boxes in the daisy chain, and whereas it is permissible to run a ground wire just approximating the route of the outlet box(es) it serves back to the panel, ...

... why is it not permissible to run a ground wire back to the panel, bonded to each receptacle and box it serves, and taped to the outside of the armored cables going from one outlet box to the next?

Last edited by AllanJ; 02-18-2008 at 04:53 PM.
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Old 02-18-2008, 06:05 PM   #11
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Grounding outlet to armored cable - fine?


Quote:
Originally Posted by voltage2 View Post
hey, so i checked other outlets in the house, and most do seem to have the clamp you're talking about, as well as not having the armored wire exposed. this one in particular that we wired first did have the wire exposed, and no clamp. the rest of the outlets i'll ground with the clamp, but i would just like to know if there is any danger in keeping the one grounded to the armored wire. like, will i start an electrical fire?
You might just start a fire. A wire wrapped around the cable sheath isn't a secure mechanical connection. If something shorts, there is a possibility of an arc between the wire and sheath, due to poor contact. This arc can cause combustible material to ignite.

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Old 02-18-2008, 08:01 PM   #12
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Grounding outlet to armored cable - fine?


The only correct way to get three prong receptacles with this method is to install GFCI receptacles. Remember the ground wires purpose is to protect people from shock by causing the circuit breaker to trip and shut off power. A GFCI wii not trip the breaker but it will stop the flow of current and save a life
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Old 02-18-2008, 09:42 PM   #13
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Originally Posted by wire_twister View Post
The only correct way to get three prong receptacles with this method is to install GFCI receptacles. Remember the ground wires purpose is to protect people from shock by causing the circuit breaker to trip and shut off power. A GFCI wii not trip the breaker but it will stop the flow of current and save a life
You are right that a GFCI will allow 3-prong receptacles to be used, I think it is always better to have a real ground. AC cable, if properly installed, is a grounding conductor. I think that is the original intent of the post.

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Old 02-18-2008, 10:46 PM   #14
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Grounding outlet to armored cable - fine?


Quote:
Originally Posted by voltage2 View Post
If the box is already grounded, can't I just attach the copper ground wire I screwed to the receptacle to the side of the box with electrical tape? Isn't this essentially the same as screwing it down in the back


I think tape does a better job than a screw any day.

Planes all over the world are held together with multiple layers of duct tape - so you know it's the way to go.
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Old 02-18-2008, 11:03 PM   #15
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Grounding outlet to armored cable - fine?


Gee I'll call that number right away, please delete your post it is disrupting the thread.

Yes that is how we have understood this. If it is BX cable (the real stuff) not allowed for grounding it will not have the internal bonding (shunt) wire in it. BX that was manufactured in the 1940's had a bonding wire in it and is allowed for grounding. This house would have to be very old to have BX installed in it. I would say if would be real odd for a home built after 1955 to have BX without the shunt wire in it and not AC. If you did find BX it would have been a contractor using up old stock.

The first image is both styles of the original BX cabling. One without the bonding wire and the other with it.



this image is comparing BX with the bonding strip to mc (middle) and ac (bottom).



Last edited by Stubbie; 02-18-2008 at 11:07 PM.
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