Grounding Boxes

[LOW1]

Ontario is big on attaching a ground wire to the box that is used for a switch, lite etc.

Obviously connecting the ground wires is needed.

But what good does it do to also connect a ground to a metal box when that box is only attached to wood framing? Or if it’s a plastic box?

 

[75gmck25]

I believe US code also requires a ground wire to a metal box, but nothing if the box is plastic. I assume that the theory is that the metal box might accidentally come in contact with a hot wire that is not properly insulated, and you don't want to have a user contact a box that is live.

 

[Chuckster in NJ]

Hopefully this explains it in simple terms:
Grounding is the most "important thing" on any electrical system, so anything metallic like a metal box, switch back strap, receptacle back strap and ground screws that can become energized must be grounded……. "IF" a hot wire touches anything metallic the ground wire takes the voltage (to ground) and the breaker will trip instead of you taking the voltage and being shocked or worse electrocuted.
The only thing in a non-metallic plastic box that needs to be grounded is the switch, fixture or receptacle…… Basically any wire or screw that is colored green.

 

[mm08822]

Grounding a metallic box is to ensure if it became energized, it will quickly cause a fault current of sufficient size to trip the cb.

It's to prevent a waiting hazard from remaining present for the next unsuspecting person fiddling in the box. Even cover plate screws would become energized as part of this condition.

I dont think Ontario is wanting plastic boxes grounded. If they do, then I suggest you ask where you could find plastic jumpers and plastic ground screws to use.

Even when plastic boxes and plates are used, the yokes of each wiring device needs a ground wire connected to it.

 

[Chuckster in NJ]

I dont think Ontario is wanting plastic boxes grounded. If they do, they i suggest you ask where you could find plastic jumpers and plastic ground screws to use.

I had an electrical contractor call me and ask, "How do I ground the water pipes in a house that has all plastic pipe?"……… I told him to go to the supply house and ask for a non-metallic ground clamp so he did that and was very embarrassed.
He was really pissed off at me for giving him that answer and I told him I thought he was the one who was joking.

 

[sparky 1971]

I dont think Ontario is wanting plastic boxes grounded. If they do, then I suggest you ask where you could find plastic jumpers and plastic ground screws to use.

Even when plastic boxes and plates are used, the yokes of each wiring device needs a ground wire connected to it.

I may not be remembering correctly, but I swear that somewhere along the line I saw a plastic box that had a metal bar with a ground tail attached to it mounted to the inside. I didn't use it, but do remember wondering WTF good is that. Maybe it was a Canadian immigrant box ?

 

[sparky 1971]

I had an electrical contractor call me and ask, "How do I ground the water pipes in a house that has all plastic pipe?"……… I told him to go to the supply house and ask for a non-metallic ground clamp so he did that and was very embarrassed.
He was really pissed off at me for giving him that answer and I told him I thought he was the one who was joking.

I had a look at everything: electical, HVAC, plumbing, and framing in five minutes inspector fail me for not bonding the plastic water service. A phone call was all it took to get it straightened out.

 

[wyliesdiesels]

But what good does it do to also connect a ground to a metal box when that box is only attached to wood framing? Or if it’s a plastic box?

its to prevent the box from becoming energized so the wood framing attachment is moot

and code doesnt require a plastic box to be grounded. that makes no sense

 

[dscheidt]

I may not be remembering correctly, but I swear that somewhere along the line I saw a plastic box that had a metal bar with a ground tail attached to it mounted to the inside. I didn't use it, but do remember wondering WTF good is that. Maybe it was a Canadian immigrant box ?

I've seen boxes like that, too. It provides a place to tie all the grounds together, and allows the use of a self-grounding device, which makes trimming faster.

 

[mikedodge]

Unless it's changed the only thing in Canadian code for plastic boxes is it needs to be brought into it, not that it's connected to the box.

Here's a box that does have that grounding strip mentioned.

 

[Bert_]

You always have to ground a metal box.

If a metal box you often do not have to run a separate ground wire to the switch or outlet.

 

[dave*99]

You always have to ground a metal box.

If a metal box you often do not have to run a separate ground wire to the switch or outlet.

And a self grounding receptacle completes the detail