Receptacle grounding in a commercial building

[fishin' electrician]

Re: Receptacle grounding in a commercial building

Would a steel, old work box be considered "mounted on the surface" or "flush mounted"?

 

[speedypetey]

Re: Receptacle grounding in a commercial building

Fish, yes an old work metal box is approved for metal to metal grounding.

Russ, an "industrial cover", "raised cover" whatever you want to call it is not approved for grounding and needs a bonding jumper. With these covers there is no metal to metal contact between the yoke and the box. It's between the yoke and the cover so a bond is required.
It's in the handbook. Mine's at the shop, anyone have a cut from the handbook on this article. It's quite clear.

 

[pierre]

Re: Receptacle grounding in a commercial building

If you mean by 'old work metal box', a cut-in gem box, one that is installed in a wall after the finish has already been installed, a bonding jumper is required. It is not considered a surface mounted box (refer to Mike Holt's vol. 1 Understanding the NEC p.206).

Pierre

 

[speedypetey]

Re: Receptacle grounding in a commercial building

Pierre, I was under the impression that a gem box where the mounting ears are flush with the surface was considered a flush box.
250.146(B) says this box in conjunction with a grounding yoke receptacle requires no jumper.
Am I mistaken?

[ February 08, 2004, 07:36 PM: Message edited by: speedypetey ]

 

[pierre]

Re: Receptacle grounding in a commercial building

SpeedyPetey
.146(B) is the subsection that permits the selfgrounding receptacle types. My comment is based on .146(A) Surface Mounted Box.

Pierre

 

[hurk27]

Re: Receptacle grounding in a commercial building

Speedy the question I would have is, Is the yoke of the device contacting the box, or is it contacting the plaster strap on the box? If the latter, a bonding jumper would be needed. The plaster strap is held to the box by screws that are not listed for grounding. and most of these gain-able old work box's this strap can not be adjusted to allow for the yoke of the device to make direct contact with the box. which is the only method that I see the NEC allows with out having to have a bonding jumper or a self grounding device.

 

[russ]

Re: Receptacle grounding in a commercial building

Wayne:

To say the 8/32 screws are not approved for grounding just is not going to fly.
All these parts are conductive materials and they are solidly bonded together.
They create the low impedance path required by code, and are legal.
Otherwise your saying anything using bolts that are steel are not a legal, grounding electrical connection.
We better start welding all 4" blanks and pull box covers.
Also don't bolt the ground bar into the panel,
I could list an awful lot of stuff we join together with some type of bolting.

[ February 09, 2004, 09:29 AM: Message edited by: russ ]

 

[speedypetey]

Re: Receptacle grounding in a commercial building

Hurk, most every gem I have seen can be adjusted so the box and plaster ears are flush. This way the yoke contacts both. As long as the box is flush with the surface.
I usually do install a jumper, this is just how I read this section.

 

[hurk27]

Re: Receptacle grounding in a commercial building

All I know is what I read and what I read is 250.146 requires a bonding jumper first. then if it meets (A) through (D) It is not needed.

(A)To be exempt from the bonding wire (A) say's direct metal-to-metal contact between the device yoke and the box is what is required. now it will allow if both the cover and the box combination (together) is listed for grounding then a jumper is not required.(I have not seen one listed)

(B) Only allows Contact Devices or Yokes (self grounding devices) to be used in flush type box's there is nothing else in (B) that say's other wise. There is nothing in this section that say's anything about the size of the screw or how many. And it even doesn't give the allowance if the yoke can be made to contact the box as in (A) It just say's that other than self grounding type device's a bonding wire is needed if the box is flush mount.

Yes it is true that the screws would make contact and would allow for a ground fault to trip the breaker But after a few years would this connection still be that good? remember fault current can be very high for a few cycles. and it doesn't take much to have a loose connection that will blow open instead of triping the breaker. I had a 1900 box with a raised cover (garvin) that when a drill shorted out caused a arc large enough to start a fire in some papers in a trash can underneath it. even though the cover looked secure there was enough crosion between the two metal connection's to allow the high fault current to arc instead of tripping the breaker.

[ February 10, 2004, 12:34 AM: Message edited by: hurk27 ]

 

[cripple]

Re: Receptacle grounding in a commercial building

beggsmoore read the following Section in the NEC, which I feel will have you the answer you may be looking for.

250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes.
Where circuit conductors are spliced within a box, or terminated on equipment within or supported by a box, any separate equipment grounding conductors associated with those circuit conductors shall be spliced or joined within the box or to the box with devices suitable for the use. Connections depending solely on solder shall not be used. Splices shall be made in accordance with 110.14(B) except that insulation shall not be required. The arrangement of grounding connections shall be such that the disconnection or the removal of a receptacle, luminaire (fixture), or other device fed from the box will not interfere with or interrupt the grounding continuity.

 

[ryan_618]

Re: Receptacle grounding in a commercial building

Cripple: Your reference addresses the required bonding of the box, not the grounding of the receptacle outlet.

 

[websparky]

Re: Receptacle grounding in a commercial building

2002 NEC Handbook

Cover-mounted wiring devices, such as on 4-in. square covers, are not considered grounded. Section 250.146(A) does not apply to cover-mounted receptacles, such as the one illustrated in Exhibit 250.53. Box-cover and device combinations listed as providing grounding continuity are permitted.

Exhibit 250.53 An example of a cover-mounted receptacle attached to a surface box where a bonding jumper is required.

 

[russ]

Re: Receptacle grounding in a commercial building

Hi Dave:

I agree that the cover you've pictured, requires a jumper, because it is the type that uses the single center screw to hold the receptacle to the cover.
The type with the additional 2 screws and nuts I believe are adequately grounded with out the jumper.

 

[don_resqcapt19]

Re: Receptacle grounding in a commercial building

Russ,
The rule that required the additional screws to hold the receptacle to the cover have nothing to do with the grounding issue. I was the original submitter of the proposal that required these additional screws and the issue was the receptacle coming loose form the cover and creating a hazard when someone tried to plug in a cord.
Don

 

[russ]

Re: Receptacle grounding in a commercial building

OK Don:

I'm impressed, but not too surprised, you're a smart guy.

For now I think I'm losing this argument, but I'm not ready to concede, I will try to get more info to bolster my end.

 

[tom baker]

Re: Receptacle grounding in a commercial building

Don, I didn't know you were the submitter of that proposal. It was an appropiate change. However, there are still electricians that don't know what the clips provided with the cover are for.
I agree with Don a jumper is required.

 

[electricman2]

Re: Receptacle grounding in a commercial building

As I stated in an earlier post in this thread, I have a vested interest in this as I am in the process of installing some 4 squares with double duplex cover mounted receptacles. I asked my AHJ about it and he says he will require a bonding jumper citing 250.146(A). Also if I have 2 receptacles on the same cover, I will need 2 jumpers. So at least as far as I am concerned the argument is over because come inspection time they had better be there.

 

[Guest]

Re: Receptacle grounding in a commercial building

In our area all metal boxes have a ground pigtail to each device regardless as to whether the device is self gounding,in direst contact , or on a raised cover. All of oue inspectors hearabouts will tag it if not. The onle time they will not require box bonding is in pull boxes without splices.

 

[iwire]

Re: Receptacle grounding in a commercial building

Originally posted by joe stewart:
In our area all metal boxes have a ground pigtail to each device regardless as to whether the device is self gounding,in direst contact , or on a raised cover. All of oue inspectors hearabouts will tag it if not.

We put the pigtails on the self grounding outlets by choice but how can your inspectors fail it if you do not?

UL White Book

Self-grounding Receptacles ? Self-grounding receptacles have special integral means for establishing the grounding circuit between device yokes and (1) the grounded metallic flush-type boxes, or (2) the grounded nonmetallic flush device boxes employing a grounding strap and terminal; without the use of bonding jumpers as permitted by Section 250.146(B) (formerly Exception No. 2 to Section 250-74) of the NEC.

These devices are identified by the statement: ??This receptacle is Listed by Underwriters Laboratories Inc. and has a special pressure spring clip to establish the grounding circuit between device yokes and (1) the grounded metallic flush-type boxes, or (2) the grounded nonmetallic flush device boxes employing a grounding strap and terminal; without the use of bonding jumpers as permitted by Section 250.146(B) of the National Electrical Code?? (or equivalent wording) which may appear on the device or shipping carton.

250.146(B) Contact Devices or Yokes. Contact devices or yokes designed and listed for the purpose shall be permitted in conjunction with the supporting screws to establish the grounding circuit between the device yoke and flush-type boxes.

 

[don_resqcapt19]

Re: Receptacle grounding in a commercial building

Tom,
I submitted it the first time for the 89 code cycle. It was unanimously accepted in the TCR (now know as ROP) and unanimously rejected in the TCD (now known as ROC) after comments were made by some manufacturers. In the 92 code cycle, I resubmitted my proposal and 3 or 4 others submitted similar proposals. The proposal that was accepted for the 92 code was not as broad as I wanted because it only applied to receptacles installed in "raised covers". The current rule in 406.4(C) is very close to what I proposed in 89.
Don