Receptacle grounding in a commercial building

[beggsmoore]

Hello,
I want to verify the grounding of a receptacle in a commercial application. The receptacle is to be installed in a metal 4X4 box with a metal cover. The raceway is EMT. It looks like, in the NEC, that the EMT can be used as the the ground and all I need is a bonding jumper from the receptacle grounding terminal to the metal box. It would seem to me that if the integrity of the EMT where ever violated then, a separate grounding conductor should be used. I think I like the idea of both a bonding jumper and a separate grounding conductor but I would like to know the NEC requirement.

 

[ryan_618]

Re: Receptacle grounding in a commercial building

I think you have summed up the NEC requirement pretty well, to tell you the truth.

 

[charlie tuna]

Re: Receptacle grounding in a commercial building

if you like the idea of a separate ground wire to the receptacle you will ask for a "dedicated grounded receptacle"..

 

[russ]

Re: Receptacle grounding in a commercial building

250.146

Generally with metal conduit and metal boxes a bonding jumper is not required.

Feel free to put them in.

 

[dereckbc]

Re: Receptacle grounding in a commercial building

250.118 sums up what can be used for a EGC. You can use EMT, a conductor, or both. Best design practice is to use both.

 

[beggsmoore]

Re: Receptacle grounding in a commercial building

Thanks to all!!

 

[hurk27]

Re: Receptacle grounding in a commercial building

By Russ: 250.146

Generally with metal conduit and metal boxes a bonding jumper is not required.

Feel free to put them in.

This is not what I was told.

406.10 tell us "The connection of the receptacle grounding terminal shall comply with 250.146."

250.146 tells us:
An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a grounded box unless grounded as in 250.146(A) through (D).

(A) allows no bond wire when box is mounted on the surface, and the receptacle has direct metal-to-metal contact between the device yoke and the box shall be permitted to ground the receptacle to the box.
Unless the receptacle is mounted on the cover. as in a garvin cover.

(B) allows no bond wire when the receptacle is self grounding type.

But if the box is flush mount and the receptacle is not a self grounding type then there has to be a bond wire installed.

 

[russ]

Re: Receptacle grounding in a commercial building

Wayne:

I only said generally not always
Maybe it's not as common in other areas as it is around here, but I don't often see the receptacles that aren't self grounding.
When installed flush mount with the self grounding spring, clip, or what ever they call it.
No bond wire required.
If mounted on a steel surface mounted plate and receptacle is bolted to the plate with screws and nuts, the bond is not required.

 

[ryan_618]

Re: Receptacle grounding in a commercial building

Originally posted by russ:
If mounted on a steel surface mounted plate and receptacle is bolted to the plate with screws and nuts, the bond is not required.

Good evening Russ. Could you please describe to me what a "surface mounted plate" is? Do you mean a zero rise plaster (mud) ring?

If the box is surface mounted, and the receptacle is attached to the cover (faceplate), then the box and the cover combination must be listed for grounding.

I have never seen such listing, has anyone here?

 

[russ]

Re: Receptacle grounding in a commercial building

The steel plate I'm talking about is the kind you put on a 4" square when the box is surface mounted.
Three screws hold the receptacle.
One is the uasual one inthe center the other two are nuts and bolts with serated washers. they install where the 6/32 normally go.

http://www.garvinindustries.com/box_covers_exposed.htm

 

[ryan_618]

Re: Receptacle grounding in a commercial building

Thanks Russ.

These covers do require a bonding jumper though, unless spefically listed for grounding as a combination with the box. 250.146(A)

 

[russ]

Re: Receptacle grounding in a commercial building

Iv'e always taken these to be aproved for bonding because everything is bolted together.
I look for proof and will post what I come up with.

 

[don_resqcapt19]

Re: Receptacle grounding in a commercial building

Russ,
As far as I know none of those cover and box combinations are listed for grounding the receptacle without a bonding jumper. The intent of the extra screws holding the receptacle was to secure the receptacle, not to improve the grounding connection.
Don

 

[tom baker]

Re: Receptacle grounding in a commercial building

A raised cover required a bonding jumper. A SG receptacle does not when mounted in a flush type cover where the 6/32 screws provide a bonding path.

The most diabolical covers made are the ones with the clips that are part of the receptacle opening, that you break off. I like the ones with 6-32 kep nuts, but gosh those nuts are tiny.

But go to site about 10 years old with raised covers secured by the one center screw and you'll see why the code was changed.

 

[hurk27]

Re: Receptacle grounding in a commercial building

Tom are you saying that a SG receptacle doesn't have to be bonded if mounted to a flush cover? Because of the 6-32 screws?

"250.146(A) says that only when the strap is in direct metal-to-metal contact between the device yoke and the box shall be permitted to ground the receptacle to the box."
Notice the key word's here is device yoke and box there is nothing that say's anything about screws.

Many times in a flush mount the yoke never contacts the box as the building surface holds it away from making this needed contact. and in this case the only permitted grounding other than a bond wire is the self grounding type receptacle that has the brass clip that puts pressure against the screw. As per 250.146(B)

 

[russ]

Re: Receptacle grounding in a commercial building

The UL white book (RTRT) refers you to article 250.146(B) when using self grounding receptacles.
This allows you to use the support screw for grounding.
I cant find any thing on the surface mount covers I talked about earlier, but I think you could use the same theory for using these covers with out a bonding jumper, as long as the receptacle was self grounding.
All covers Mud rings, Blanks, extension ring are excepted, anchored with the 8/32s. the only argument would be the 6/32s holding the device to the cover. That should be eliminated with the use of the self grounding receptacles. Or is it, as I thought, removed because the receptacle strap is mounted directly to the metal cover with the nuts and bolts. Then the cover is mounted to the box like any other cover used

[ February 06, 2004, 10:13 AM: Message edited by: russ ]

 

[electricman2]

Re: Receptacle grounding in a commercial building

I hope Russ is right, I just got through installing some 4 squares with cover mounted receptacles. Don't tell me I have to go back and put in bonding jumpers.

 

[caosesvida]

Re: Receptacle grounding in a commercial building

I always use a ground wire in emt. I have seen too many loose connections and missing pieces bent and broken emt.

 

[eprice]

Re: Receptacle grounding in a commercial building

250.146 requires a bonding jumper unless one or more of (A) through (D) can be used. (C) and (D) don't seem to apply here. (B) requires a device listed for the purpose. Per the last sentence of (A), that one doesn't apply to cover-mounted receptacles unless the box and cover combination are listed as providing satisfactory ground continuity. Like Don, I have not seen a combination that is so listed

 

[hurk27]

Re: Receptacle grounding in a commercial building

Around here if the receptacle is mounted to anything other than directly to a box where the yoke is in direct contact with the box it get's a jumper. Metal box's that apply without a jumper are handy box's surface mounted masonary box's (they look like a 1900 but with screw ears for installing devices) The inspectors here say that even the 8/32 are not listed for grounding. and over the years I have seen where they will work loose on plaster rings even inbedded in plaster.
If the box is flush mount they require a jumper as the building surface will keep the yoke from contacting the box. (of course not if it is a self grounding type)