About ground attached to metal junction box

[Danny Daniels]

I intend to replace four two-slot receptacles in the kitchen with GFCI protected three-slot receptacles in order to meet minimal code requirements for kitchen counter outlets. The old receptacles being replaced are enclosed inside metal junction boxes with copper ground wire attached via screw at the back of each box.

Due to the fact that the metal junction boxes are grounded, and since I will be using the original wiring to make connections, will this have any impact, either negative or positive, when I replace the old receptacles with three-slot receptacles? The new receptacles will be protected by the GFCI that will be installed at the beginning of the circuit. My thinking is that since the metal boxes are grounded it should be a plus; and the new receptacles will offer added personal protection via the GFCI (even though there will be no equipment ground).

Or is there some other aspect of "grounding" that I need to take into consideration for this project? Tks.

 

[Reach4]

My thinking is that since the metal boxes are grounded it should be a plus; and the new receptacles will offer added personal protection via the GFCI (even though there will be no equipment ground).

The metal boxes are grounded by a bare or green wire that runs back to the breaker box? I think that would constitute an equipment ground.

 

[Sponsor]

 

[Jadnashua]

IF the ground wire is part of the supply cable, yes, you can safely utilize a grounded receptacle. Otherwise, it is legal to put in a GFCI and label it with the included sticker that says something like "GFCI Protected, No Equipment Ground" - that's true for any receptacles supplied by the load side of that GFCI as well. Except when using conduit and a dedicated ground wire, just grounding the box to the receptacle does not constitute a ground...corrosion, etc., often makes that connection mostly useless.

The house I grew up in used BX, but without the modern ground wire. They relied on that as the ground. Actually measured it, and it was all rusted and a high resistance. Rather than tearing up the plaster walls, I replaced things with GFCI and grounded receptacles with the labels.

The ground wire is a safety feature to provide an alternate path to trip the circuit breaker or blow the fuse...if there's no fault, it essentially does nothing. Well, if you have a surge suppressor, it helps provide a path to divert that surge.

 

[Danny Daniels]

IF the ground wire is part of the supply cable, yes, you can safely utilize a grounded receptacle. Otherwise, it is legal to put in a GFCI and label it with the included sticker that says something like "GFCI Protected, No Equipment Ground" - that's true for any receptacles supplied by the load side of that GFCI as well. Except when using conduit and a dedicated ground wire, just grounding the box to the receptacle does not constitute a ground...corrosion, etc., often makes that connection mostly useless.

The house I grew up in used BX, but without the modern ground wire. They relied on that as the ground. Actually measured it, and it was all rusted and a high resistance. Rather than tearing up the plaster walls, I replaced things with GFCI and grounded receptacles with the labels.

The ground wire is a safety feature to provide an alternate path to trip the circuit breaker or blow the fuse...if there's no fault, it essentially does nothing. Well, if you have a surge suppressor, it helps provide a path to divert that surge.

 

[Danny Daniels]

Thanks to both of you. Just out of curiousity I re-checked each new outlet again with a 3-prong tester and it indicates all the wire connections are still correct on each (no open ground, etc.). So I guess my technical question (as a DIYer with a thirst for additional knowledge) is this. Since I am not utilizing the ground screw for anything on each of the new receptacles, then what is providing the ground path? Just the simple fact that there is a metal on metal connection at the point the receptacle itself is screwed into the metal box and the original copper ground attached to the screw on the box serves to continue this path back to the panel??

I don't want to take up a lot of time asking technical questions, but just trying to get a simple visual as to what is happening behind the scenes "groundwise" with my new 3-prong outlets. But since they are all working as they should, I am satisfied.

And one last related code question, should anyone know the answer : My next project is to upgrade 5 original 2-prong receptacles in the den, some of which are faded, cracked, etc. but otherwise working fine. If initial testing indicates that the old outlets are properly grounded, then can I just replace with new 2-prong receptacles, which are still on the market? I know somewhere in code it states that if older electrical circuits are altered in any way, then the circuit must be upgraded to meet current code. Does this apply if I am just replacing old receptacles with new ones. Or will I be required to go the GFCI route as I did on the kitchen circuit and replace all the 2-prong with 3-prong?

 

[Reach4]

Since I am not utilizing the ground screw for anything on each of the new receptacles, then what is providing the ground path? Just the simple fact that there is a metal on metal connection at the point the receptacle itself is screwed into the metal box and the original copper ground attached to the screw on the box serves to continue this path back to the panel??

Yes.

I don't know what the pieces that the mounting screws pass through on the outlet are called. Let's call that xxxx. I know they are not tabs or ears, because those are the pieces that are intended to be broken off of the xxxx for some installations.

In the case of EMT conduit, the conduit forms the ground conductor. No green or bare wire needed. Then the metal xxxx and screw on the outlet continue the ground.

Some xxxx have a little brass contact that improves the connection to a metal faceplate for better grounding of the faceplate.

 

[Danny Daniels]

Thanks, that is helpful and pretty much what I thought was the case.

 

[Jadnashua]

When new, yes, EMT can provide a decent ground path. That's not necessarily true on day two or later. EMT is steel...it rusts. But, steel has more resistance than copper so there may be a voltage drop should the ground ever be needed. That might be enough to prevent a GFCI from tripping.

If you look at a receptacle from the back, you'll typically see that the attachments to the box are part of the same metal band that the ground screw is attached to. That, too, can rust. A copper wire under the brass screw is a better ground. Not everyone screws them down tight, and they can loosen a bit on their own with thermal cycling, not counting corrosion if in a damp area. Whenever I run EMT, I include an actual ground conductor and rely on it only to protect the wiring from damage, not as a ground path.

 

[Cacher_Chick]

If a box is metal, it is required that a ground wire pigtail be in place between the box and the receptacle if you are installing receptacles that accept a ground pin. If the boxes have no ground connection back to the panel, you must use a GFCI that is labeled "no equipment ground", or you can install a replacement 2-blade receptacle.

 

[ImOld]

If a box is metal, it is required that a ground wire pigtail be in place between the box and the receptacle

Unless the receptacle is self-grounding as many are.

Nickel-plated brass, one piece mounting strap with integral ground contact, for superior ground path