grounding a weatherproof metallic box

[al21can]

Is it permissible to take a grounding conductor entering a metallic weatherproof box, strip a section of the conductor to wrap around the pinch type grounding screw typically found in weatherproof metallic boxes such as bell boxes while leaving a tail of 6-8 inches outside the box to make-up under a wire nut with the other grounding conductors entering the box? would not this be a better bond since the grounding conductor entering the box is continuously bonded to the box by wrapping it around the ground screw first?

[ July 13, 2005, 06:44 PM: Message edited by: al21can ]

 

[infinity]

Re: grounding a weatherproof metallic box

If you connect the equipment grounding conductor to the box you would not need to connect it to the device, if the device were of the self grounding type or if you removed the insulted washers that hold the 6/32 screws to the device. Removing the washers allows for metal to metal contact and would provide a sufficient ground path without the need for the additional conductor.

 

[benaround]

Re: grounding a weatherproof metallic box

I'm having trouble with this self grounding theory. In my opinion you would need a self grounding box to ground a recpt from a box.Self grounding recpt. will ground a box not the other way around imo also 250.148 seem to support that theory.

frank

 

[infinity]

Re: grounding a weatherproof metallic box

Frank,

Metallic boxes must be grounded and cannot depend on the device to ground them. On the other hand a self grounding receptacle can be installed in a grounded metal box without the need for an additional conductor. Take a look at 250.148(B).

 

[benaround]

Re: grounding a weatherproof metallic box

Infinity,

It just seems like a waste of protection to bring an EGC all the way to the recpts. and then not connect it to the grounding terminal just to save a minute or two at the most.

But,unfortunattly UL seems to think it's ok,I've spent the last hour trying to find some backup from UL but It's me who has to back up.

frank

 

[al21can]

Re: grounding a weatherproof metallic box

I understand that metallic boxes need to be grounded but my question is: May I wrap the supply grounding conductor 3/4 of the way around the screw provided I leave enough slack to satisfy 300.14 and still leave a long enough tail to bond with another grounding conductor entering the box?

 

[hbiss]

Re: grounding a weatherproof metallic box

To answer your original question yes that will be fine, otherwise put a pigtail under the screw. I find that sometimes that is easier than wrapping the supply around that screw especially when you are on the top of a ladder installing floodlights. Put the pigtail in the box while you are on the ground.

-Hal

 

[al21can]

Re: grounding a weatherproof metallic box

Thanks for the answers. The reason I brought this topic up was because I had an incident in which we were finishing up some one else's work. The round weatherproof boxes mounted on the exterior trusses did not have pigtails in them.. I instructed the crew to take the supply ground which were left pretty long and just wrap it around the screw leaving a tail to make up with the other grounding conductor entering the box. However, one individual said it was illegal and refused to do it, got down from the ladder and wasted 20 minutes looking for a scrap piece of green AWG 12 to make a pigtail. He then explained that he had just been ingformed by Mike Holt himself in a recent e-mail that this procedure was not permissible pursuant to 300.14 although exibit 314.3 in the NEC Handbook illustrates this very same procedure.
The reason for 300.14 if I am not mistaken is to leave enough wire in the box to work with, thus, by wrapping the equipment grounding conductor around the grounding screw 3/4 ways and leaving a tail does not shorten the wire, it actually keeps the wire longer than if it would be cut to make-up with a pigtail. Furthermore, the bonding in the box would be of a continuous one as well with less splices.

 

[hbiss]

Re: grounding a weatherproof metallic box

Why would this be any different than NM cable and a metallic box? That's the way most of us do it.

-Hal

 

[al21can]

Re: grounding a weatherproof metallic box

Hal,
exactly my point. I have been doing commercial work for a little bit over 15 years and never had an inspector tell me I couldn't do this. I try to keep up with the code as best as I can. However, the individual who challenged me on it is one of those guys that just took his exam and is full of code interpretations. I will always give someone the benefit of the doubt. But what made me curious about his interpretation is that he claims to have gotten his interpretation directly from a Mike Holt seminar. Even after I showed him the illustrated example (314.3) in the 2002 NEC Handbook permitting for such, he then claimed that Mike Holt said the illustration was wrong as well. I wonder if this guy is just a wacko or did he actually get this interpretation from Mike and if so I wonder why Mike Holt would give such an interpretation.

[ July 17, 2005, 05:59 PM: Message edited by: al21can ]

 

[celtic]

Re: grounding a weatherproof metallic box

Originally posted by al21can:
However, one individual said it was illegal and refused to do it...

One individual might need to start looking for new employment.

I have no problem with someone questioning my "opinion" of the code - BUT, refusing to do it...I don't think so.
If this individual wanted to "debate" the issue on his own time, that's fine...in the meantime, just do it.

Until you sign the checks - you do as I say.

...which brings us back to the post about the boss telling an electrician to do something that was obviously wrong (southernboys?).

If it turned out I was wrong, I would STILL be footing the bill to make the correction...if it turned out I was right ~ consider it a lesson learned (learnt? - spell check like both spellings LOL).

 

[celtic]

Re: grounding a weatherproof metallic box

Originally posted by al21can:
However, the individual who challenged me on it is one of those guys that just took his exam and is full of code interpretations.

I was thinking just that thought as I wrote my post.

 

[al21can]

Re: grounding a weatherproof metallic box

Celtic,
I agree, If I were signing the checks he would have been looking for a new job. But he just made leadman with the company I work for and although I was in charge of this particular clean up project, I couldn't send him packing. This is the south, good ole boy territory! and I am a transplanted Jersey guy

 

[iwire]

Re: grounding a weatherproof metallic box

Never Mind

[ July 17, 2005, 07:07 PM: Message edited by: iwire ]

 

[magoo66]

Re: grounding a weatherproof metallic box

Stranded or solid?

 

[romeo]

Re: grounding a weatherproof metallic box

If the wire is solid I don't see a violation because the wire is not cut and there is 6" of wire left for working with. I also agree with benaround.
romeo

 

[LarryFine]

Re: grounding a weatherproof metallic box

I also agree. After all, this is a connection not likely to ever be disturbed.

It is possible to get a decent attachment with stranded wire on a screw if you hold the hook closed with needle-nose pliers while tightening the screw.

One of my employees swears that twisting the strands "left-handed" helps keep the strands together; I haven't had the chance to try it since he mentioned it.