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Old 09-29-2012, 10:48 PM   #1
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Old switch and recepticle boxes


My location is Hamilton Ont. Canada.
I have recently purchased a new ( old ) house, it has 2 prong outlets thru out the house. The house was built in the late 50's or early 60's. No electrical updates had being done, so all was original as built.

I have had an electrician update the service and panel to 200A ( old service was 100A with fuses ). I will be doing the rewiring of the rest of the house, Yes I did get the permits.

The wiring ( cloth/paper/plastic 14Ga ) has a ground wire in it, the problem is with the metal boxes.
There are no ground screws and no threaded holes in the boxes ( there are some holes 3 or 4 but they are not tapped for screws). The ground wire is either cut short as the wire enters the box or is wrapped around the wire retaining screw or the wire retaining plate, which does not provide for a safe ground.

These boxes are in the plaster walls and I would rather not have to rip them all out. So my question is can I tap the existing holes and put in a ground screw ( what size ? std ground screw are too small for the existing holes ) or use a self tapping screw ?

Or do I have to replace all the boxes with modern ones, which I am hoping to avoid, but if there is no other way then I will make lots of new holes in the walls.

Thanks in advance for any reply's.

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Old 09-29-2012, 11:15 PM   #2
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You should be able to tap holes for grounding screws. Most use #10x32 threads.

Or, you should be able to use push-on grounding clips. No holes needed.


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Old 09-29-2012, 11:35 PM   #3
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I also own a house from 1960's and my electrical boxes are grounded the way you describe them.

Heck, plastic boxes don't have grounds so I think it is perfectly ok to ground to the wire retaining screws.

If ground from the wire is too short, I would wrap a new bare wire to that screw than pigtail it using a wire nut.

Good luck
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Old 09-30-2012, 01:56 AM   #4
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Plastic boxes aren't widespread in Canada. Maybe in brand new builds they may have them but for the most part we are strictly metal here in ontario. Those clips look like a nifty solution, ill need to see if we can get em up here.
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Last edited by andrew79; 09-30-2012 at 01:59 AM.
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Old 09-30-2012, 05:00 AM   #5
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Quote:
Originally Posted by allthumbsdiy View Post
I also own a house from 1960's and my electrical boxes are grounded the way you describe them.

Heck, plastic boxes don't have grounds so I think it is perfectly ok to ground to the wire retaining screws.

If ground from the wire is too short, I would wrap a new bare wire to that screw than pigtail it using a wire nut.

Good luck
NOT, Ground screw or clip required. You also need to be able to extend the the ground to the switch or receptacle grounding screw.

BTW I could not find those grounding clips on the Home Depot Canada web site but try an electrical supply house. Here is the info from the USA home Depot site:
http://www.homedepot.com/h_d1/N-5yc1...1#.UGgXLK6s--I
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Old 09-30-2012, 07:35 AM   #6
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Originally Posted by allthumbsdiy View Post
Heck, plastic boxes don't have grounds so I think it is perfectly ok to ground to the wire retaining screws.
Plastic boxes are non conductive so they don't need a ground. The code requires the screw used for grounding to have no other purpose.
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Old 09-30-2012, 10:14 AM   #7
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Old switch and recepticle boxes


Ok...this is part question....part comment....

Plastic boxes don't need a ground....just the receptical...

Metal boxes must have the ground attached to them as well as the receptical?

On a personal note....it just seems common sense to me that if you have something metal...with wires in it...it should be grounded....
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Old 09-30-2012, 10:23 AM   #8
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Originally Posted by ddawg16 View Post

Metal boxes must have the ground attached to them as well as the receptical?
Metal boxes must always have the EGC attached.

Self grounding recs connected to a bonded metal box do not require that the EGC be attached, although I always do.

Regular recs, with the plastic washers removed, with direct metal strap/yoke contact with a surface mounted bonded metal box do not require the EGC attached, again-I still do.

Last edited by Code05; 09-30-2012 at 10:30 AM.
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Old 09-30-2012, 10:51 AM   #9
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Quote:
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Metal boxes must always have the EGC attached.

Self grounding recs connected to a bonded metal box do not require that the EGC be attached, although I always do.

^^ This I was aware of.

Regular recs, with the plastic washers removed, with direct metal strap/yoke contact with a surface mounted bonded metal box do not require the EGC attached, again-I still do.

^^ This is a new one on me. Always learn something new on this board.




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Old 09-30-2012, 11:02 AM   #10
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When multiple cables enter a box, you will also need to connect their ground wires together; just twisting is not good enough. I'm not sure whether you can tap separate holes for each to be screwed to the (metal) box if the wires are too short to reach each other. (Two wires cannot go under one screw)
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Last edited by AllanJ; 09-30-2012 at 11:05 AM.
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Old 09-30-2012, 11:02 AM   #11
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So Code, I was aware of those, but could someone explain to me the difference between a surface mounted box and a metal flush mounted box? Assuming the metal device strap is is contact with the box.
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Old 09-30-2012, 11:03 AM   #12
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A surface mounted box is wholly outside the wall, i.e. its back is screwed onto the wall.
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Old 09-30-2012, 11:07 AM   #13
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The flush mounted box could be recessed and the bonding would only be through the screw contact to the yoke instead of the entire yoke in intimate contact with the surface mounted cover.
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Old 09-30-2012, 11:12 AM   #14
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Quote:
Originally Posted by k_buz View Post
So Code, I was aware of those, but could someone explain to me the difference between a surface mounted box and a metal flush mounted box? Assuming the metal device strap is is contact with the box.
I see no exemptions in 250.146 for the non attachment of an EGC for a bonded metal flush mounted box and regular receptacle despite direct metal to metal contact.
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Old 09-30-2012, 11:19 AM   #15
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Quote:
Originally Posted by Jim Port View Post
The flush mounted box could be recessed and the bonding would only be through the screw contact to the yoke instead of the entire yoke in intimate contact with the surface mounted cover.
However, there is no stipulation for a metal raised surface cover as I assume you are referencing here. My point being, what is the difference between mounting a 4 SQ box on the the face of the drywall, install a plaster ring and a plastic receptacle cover (which I read as legal) VS installing the same setup inside a wall?

In fact...

"This provision shall not apply to cover-mounted receptacles unless the box and cover combination are listed as providing satisfactory ground continuity between the box and the receptacle."

Quote:
Originally Posted by Code05 View Post
I see no exemptions in 250.146 for the non attachment of an EGC for a bonded metal flush mounted box and regular receptacle despite direct metal to metal contact.
I understand that, but my question is why? (assuming the metal box is completely flush with the drywall/finished surface)

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Last edited by k_buz; 09-30-2012 at 11:21 AM.
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