Adding Ground Wire to 2 gang metal switch box

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Old 05-30-11, 07:20 PM
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Exclamation Adding Ground Wire to 2 gang metal switch box

Hi everyone,

I have a older home in southern California that uses old romex type (round with black covering) wiring without a ground wire. I opened drywall and ran new 14/3 NM Romex from a Broan Fan/Light bathroom fixture to a 2 gang metal switch box and connected #14/2 NM Romex into the switch with power. I would like to ground this new metal switch box. I noticed a bare copper wire that is twisted and held on with a locking nut and bolt in the back inside of an existing old switch next to my new 2 gang metal box.

I have a couple of questions. Can I use a scrap bare #14 copper wire and wrap it around that existing bare copper wire I see on the old switch box to act as a ground for my new 2 gang metal box? If so, how can I do this using a regular green grounding screw? I always see illustrations in electrical books that show a screw attached to the back inside of a switch box. But am not sure how it holds in place since all the holes in the switch box have no threading on them to turn the grounding screw. Also, how can I tell if attaching a bare grounding copper wire to an existing ground I found behind a switch will act as a conductor to return power to the grounding rod?

It seems like my home is connected with a single bare copper wire that is ran throughout the house to the other outlets and switches. Any advice will help thanks!
 
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Old 05-30-11, 07:25 PM
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The ground rod plays no part in the proper operation or grounding of your system. Electrode like rod are for high voltage events like lightning.

You would need to test the suspected ground wire with a test meter or you could visually trace it. It would need to originate in the panel or at an accessible part of your grounding system.
 
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Old 05-31-11, 07:01 AM
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If that copper wire is a good ground, you need to attach your other wires to it with a wire nut. If you have no threaded holes in the box for a grounding screw, use a grounding clip.
 
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Old 05-31-11, 08:58 AM
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Originally Posted by dtnoob View Post
Can I use a scrap bare #14 copper wire and wrap it around that existing bare copper wire I see on the old switch box to act as a ground for my new 2 gang metal box?

If so, how can I do this using a regular green grounding screw?

... all the holes in the switch box have no threading on them to turn the grounding screw.
1. What is the existing scrap bare #14 attached to now?

2. As already mentioned, for old boxes without tapped holes in the back, you can use a clip. That is easiest. Or, you can drill a hole in the back of the box with a #21 drill and tap it for 10-32. You can get a #21 drill and 10-32 tap "for cheap" at the big box, etc.
 
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Old 07-07-11, 12:17 AM
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Hi everyone, thanks for your replies and useful information! Right now, there is old switch box located next to the new 2 gang metal switch box. I had cut out dry wall behind the new 2 gang switch box and can see to my right a old switch box that controls lighting in the bedroom. That old switch box has a big bolt attached behind the box with what seems to be a #12 or #14 bare copper wire wrapped around the threads and tightened with a lock nut.

I was wondering if that is a ground wire that I can splice into to ground my new 2 gang metal switch box? My home is old and so I noticed that all metal switch and receptacle boxes have that single bare ground copper wire that is wrapped around these big bolts behind the metal boxes with the copper then wrapped a couple of times and extending and continuing on to the next metal box. What is the purpose of that?

Is this common in old houses since there were no ground wire in old NM cable wiring?
 
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Old 07-07-11, 12:21 AM
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Originally Posted by ArgMeMatey View Post
1. What is the existing scrap bare #14 attached to now?

2. As already mentioned, for old boxes without tapped holes in the back, you can use a clip. That is easiest. Or, you can drill a hole in the back of the box with a #21 drill and tap it for 10-32. You can get a #21 drill and 10-32 tap "for cheap" at the big box, etc.
The existing #14 bare copper wire is wrapped around a big bolt and tightened with a lock nut behind a old metal switch box. That same bare copper wire is just attached to that box but I do see it running up into the attic. I was wondering if I can splice a new #14 bare copper wire to it to act as a proper ground to my new 2 gang metal switch box?
 
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Old 07-07-11, 12:33 AM
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Originally Posted by pcboss View Post
The ground rod plays no part in the proper operation or grounding of your system. Electrode like rod are for high voltage events like lightning.

You would need to test the suspected ground wire with a test meter or you could visually trace it. It would need to originate in the panel or at an accessible part of your grounding system.
Hi pcboss, is there a specific type (name) of test meter that will allow me to test to see if its a true ground? If I use a test meter, how can I tell if it is a true ground that originates in the panel? Any advice will help. Thanks!
 
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Old 07-07-11, 08:18 AM
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Hi pcboss, is there a specific type (name) of test meter that will allow me to test to see if its a true ground? If I use a test meter, how can I tell if it is a true ground that originates in the panel? Any advice will help. Thanks!
You can use a two-lead lampholder with a 100-watt incandescent lamp. If the lamp lights at full brightness, you have a ground.
 
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Old 07-07-11, 09:17 AM
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Originally Posted by Justin Smith View Post
You can use a two-lead lampholder with a 100-watt incandescent lamp. If the lamp lights at full brightness, you have a ground.
Thanks Justin. How would I connect the 2 lead lamp holder to the existing copper wire? I am trying to visualize how to do it.
 
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Old 07-07-11, 09:24 AM
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With breaker off one side to hot (usually black or red) and other to ground. Turn on the breaker just long enough to test. This could in rare instances create a personnel hazard if someone should touch a grounded device during testing so be sure no one is near a device on the circuit while testing.
 
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Old 07-07-11, 11:20 AM
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Originally Posted by ray2047 View Post
With breaker off one side to hot (usually black or red) and other to ground. Turn on the breaker just long enough to test. This could in rare instances create a personnel hazard if someone should touch a grounded device during testing so be sure no one is near a device on the circuit while testing.
Hi Ray, are you referring to using the lamp socket lead(s) or wire? Or another device like volt meter?
 
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Old 07-07-11, 11:25 AM
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Two leads from a lamp socket with a bulb in it. Leads are wires.
 
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Old 07-07-11, 02:15 PM
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http://www.1000bulbs.com/product/831...-LH145WP.html- Most big box homecenters have these.

Connect the black to hot and the white to the ground wire. Be sure to have the breaker off when you do this.
 
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Old 07-07-11, 03:27 PM
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Justin you need to use a different URL. The one you included requires a sign-in.
 
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Old 07-07-11, 03:30 PM
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Dtnoob, you don't need anything fancy. Even a simple receptacle with two wires on it you can then plug a lamp into.
 
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Old 07-07-11, 04:06 PM
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Just tape up the receptacle real good so noone accidentally gets shocked.


Justin you need to use a different URL. The one you included requires a sign-in.
I don't know why. Try this: Pigtail Socket - No Hook | 1000Bulbs.com
 
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Old 07-07-11, 04:47 PM
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Yes, that URL worked and the lamp holder would be easier then a receptacle.
 
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Old 07-13-11, 01:26 AM
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Thanks for your suggestions everyone. I have other questions. I have multiple switch and outlets that have a bare copper wire attached to the metal box but wrapped around a big bolt with a big washer holding the wire in place. When I opened up my drywall, I can see that the metal boxes all have this bare copper wire attached to the back of the metal boxes and it continues on to the next.

Can someone explain the purpose of those bare copper wires attached to the back of my metal boxes held on with a bolt and washer? I know I have old NM electrical wiring in my home which did not have a bare copper wire for grounding. Any good explanation will help. Thanks!
 
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Old 07-13-11, 01:30 AM
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Originally Posted by ray2047 View Post
Two leads from a lamp socket with a bulb in it. Leads are wires.
Thanks for the ideas everyone. My goal is to check to see what the bare copper wire I see attached to the back of another metal switch box is. Also, to see if that bare copper wire can be used as a ground that leads back to my main circuit breaker panel.

What is the purpose again for using the lamp socket? How would this test the bare copper wire I see as a good ground? I just need some clarification. Thanks.
 
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Old 07-13-11, 05:58 AM
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It tests it under a heavier load then a multimeter would. Sometimes a light load will show it good but it will fail under a heavy load such as a short and not provide the level of protection needed. Also eliminates the possibility of a ghost voltage reading.
 
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