Gounding Screw

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Re: Gounding Screw

Originally posted by romeo:
I still think that a screw designed to hold a box clamp does not have the surface equal to a grounding screw.
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I agree, it does not.

But it is still larger than the conductor it secures.

It does not make a difference if the screw head is 1/4" or 2" across, the conductor does not touch any more of the screw.

The NEC does not prohibit it from being used for used for grounding and I accept it. However the NEC may have had a blonde moment when it was allowed.
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Or maybe they simply refuse to make a rule without proof that a new rule is needed. :)
 
Re: Gounding Screw

Here are a couple of photos.

Is one screw really doing a better job than the other at bonding the EGC to the box?

GroundscrewB.jpg


GroundscrewD.jpg
 
Re: Gounding Screw

These two photos do a good job of showing what I mentioned before. That it would be hard for someone, even a "new" someone, to not be able to discern what the termination in those boxes is for.

Bob
I would like for you to accompany me on my next few jobsite visits to help me take pictures. :D
 
Re: Gounding Screw

I am still trying to find something bout threads... I remember something about a certain amount of threads need to be into the metal. That is why ground screws have such fine threads.
 
Re: Gounding Screw

Originally posted by Shockedby277v:
I am still trying to find something bout threads... I remember something about a certain amount of threads need to be into the metal. That is why ground screws have such fine threads.
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The threads are the threads. A 10-32 green bonding screw has the same number of threads per inch as the 10-32 clamp screw in Bob's photo. You may be thinking about the comparison between a machine screw and a sheet metal screw. A #10 pan head sheetmetal screw would have very few threads engaged with the metal of the box when compared to the machine screw.
 
Re: Gounding Screw

yes but if you drilled and threaded a 1/4 - 20 to use for grounding it won't have as many threads touching the metal of the box. One of my classes I took, I wanna say it was 3 full threads but the closest thing I can find is 314.40 (D). 314.40(D) would allow a 1/4-20 , the way I read it.

[ January 29, 2006, 08:45 PM: Message edited by: Shockedby277v ]
 
Re: Gounding Screw

Originally posted by Shockedby277v:
yes but if you drilled and threaded a 1/4 - 20 to use for grounding it won't have as many threads touching the metal of the box. One of my classes I took, I wanna say it was 3 full threads but the closest thing I can find is 314.40 (D). 314.40(D) would allow a 1/4-20 , the way I read it.
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I see your point about the 1/4-20 having less threads but I can't find where it's supported by the NEC. 250.8 states that sheet metal screws can not be used, but I see no prohibition for a 1/4-20 or any other machine screw threaded into the metal box.
 
Re: Gounding Screw

Originally posted by infinity:
I see your point about the 1/4-20 having less threads but I can't find where it's supported by the NEC.
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Don has brought this up before, it might be from UL or the Sores book.

There is a required or preferred amount of threads in contact with the enclosure.

FWIW I use a nut on any screw or bolt larger than a 10-32 when fastening to an enclosure.
 
Re: Gounding Screw

Originally posted by Shockedby277v:
yes but if you drilled and threaded a 1/4 - 20 to use for grounding it won't have as many threads touching the metal of the box.
Click to expand...
Looks like this "thread" :D has taken another turn.
 
Re: Gounding Screw

From Mark Ode's Jan 2006 ECM Magizine article:

"Wrapping the equipment-grounding conductor around an NM cable clamp screw in an NM box or around the 8/32 screw for the plaster ring or box cover are common methods used in the field, but are not acceptable in accordance with either Sections 250.8 or 250.148(A). A grounding screw or some other listed grounding device must be used."

I emailed him about this article. I presented some info to him and I will await his response.
 
Re: Gounding Screw

Originally posted by pierre:
From Mark Ode's Jan 2006 ECM Magizine article:

"Wrapping the equipment-grounding conductor around an NM cable clamp screw in an NM box or around the 8/32 screw for the plaster ring or box cover are common methods used in the field, but are not acceptable in accordance with either Sections 250.8 or 250.148(A). A grounding screw or some other listed grounding device must be used."
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Possibly he is talking about using the nm cable clamp screw without removing the cable clamp, which I've seen frequently.
 
Re: Gounding Screw

I hadn't checked in on this thread since page 1. I was wondering what the controversy was, so I just read it through.

It never ceases to amaze me how furious something as humble as a little ground screw can make us. :( )
 
Re: Gounding Screw

Originally posted by pierre:
From Mark Ode's Jan 2006 ECM Magizine article:

"Wrapping the equipment-grounding conductor around an NM cable clamp screw in an NM box or around the 8/32 screw for the plaster ring or box cover are common methods used in the field, but are not acceptable in accordance with either Sections 250.8 or 250.148(A). A grounding screw or some other listed grounding device must be used."

I emailed him about this article. I presented some info to him and I will await his response.
Click to expand...
He's probably talking about using the clamp with NM and wrapping the EGC around the screw.

Putting it under the 4/S screw was the way I was originally taught. :p
 
Re: Gounding Screw

Bob I must admit that the bonding termination on the clamp screw shown in the picture was very well done. Looks like you or I did it. ( just a little humor)There is nothing wrong with that termination,but they are not always done that well. IMO the larger head surface of a grounding screw provides a better connection even for those less careful.

romeo
 
Re: Gounding Screw

One of my classes I took, I wanna say it was 3 full threads ...
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If that is true, then a 10-32 is not suitable for use with standard boxes. They only provide ~2 threads in the box material.
Don
 
Re: Gounding Screw

Here is what I posted on another forum about a year and a half ago.
Guys,
It appears that I'm wrong on this issue. CMP5 addressed this in the '99ROC. It is still not completely clear as I don't think that the "green" screws are listed devices for grounding and if they are not, then the only choice would be the push-on grounding clip.

quote:
--------------------------------------------------------------------------------
5- 42 - (250-8): Reject
SUBMITTER: Don Ganiere, Ottawa, IL
COMMENT ON PROPOSAL NO: 5-71
RECOMMENDATION: The proposal should be accepted in principle. Add new text: " Machine screws and bolts shall be permitted to secure listed pressure connectors and solid conductors ".
SUBSTANTIATION: Machine screws and bolts are used to secure pressure connectors and solid connectors. A machine screw is not a listed means and use of machine screws would be a violation. New wording should be added: "Machine screws and bolts shall be permitted to secure listed pressure connectors and solid conductors".
PANEL ACTION: Reject.
PANEL STATEMENT: The use of a machine screw to secure a listed pressure connector must be installed in accordance with the manufacturers. instruction. Section 110-14(a) does not permit the connection of a solid conductor with an ordinary machine screw.
NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE: 16
VOTE ON PANEL ACTION:
AFFIRMATIVE: 14
NEGATIVE: 2
EXPLANATION OF NEGATIVE:
DOBROWSKY: The comment should be accepted in principle and the proposed additional text revised as follows: "Machine screws identified for the purpose shall be permitted to secure 10 AWG or smaller conductors." This concept is permitted as described in Section 110.14(A). Forming a loop in a 14 AWG through 10 AWG solid conductor and securing it with a screw in compliance with Section 110.14(A) should be acceptable in Section 250.8.
HAMMEL: The comment should be accepted in principle and the proposed additional text revised as follows: "Machine screws identified for the purpose shall be permitted to secure 10AWG or smaller conductors." This concept is permitted as described in Section 110.14(A).
Forming a loop in a 14AWG through 10AWG solid conductor and securing it with a screw in compliance with Section 110.14(A) should be acceptable in Section 250.8.
___________________
--------------------------------------------------------------------------------


Don
Click to expand...
As far as I know the the "green" box screws are not listed for grounding so the only code compliant method of terminating the EGC is the push on clip.
 
Re: Gounding Screw

Here is my Email to Mark Ode, and his response. I am always impressed by how fast I get a response from Mark.


Pierre: No, there are no UL listed ground screws but there are listed ground screw and green wire assemblies and listed ground clips. Go figure, huh. Using a round shouldered NM cable clamp screw seems to be a common practice in some parts of the country. I have seen people wrap the equipment grounding conductor around the screw without even removing the NM clamp from the screw. I have seen others remove the NM clamp and reinsert the screw with the equipment grounding conductor wrapped around it.

Section 250.8 requires grounding conductors and bonding jumpers to be connected by exothermic welding, listed pressure connectors, listed clamps or other listed means. In Section 250.148(C), a connection shall be made between the one or more equipment grounding conductors and a metal box by means of a grounding screw that shall be used for no other purpose or a listed grounding device. Section 250.8 requires a listed means and 250.148 permits a ground screw or a listed grounding device. These two sections seem to be in conflict with each other. I will see if there was anything introduced for the 2008 NEC process that would permit me to address this issue for the 2008 NEC. Good luck with your class. Mark
"Pierre Belarge"

"Pierre Belarge"
01/30/2006 07:32 AM


To
"Mark C. Ode"
cc



Subject
Equipment Ground Screw



Hello Mark,

You mention in your ECM article, Jan 2006, that:

"Wrapping the equipment-grounding conductor around an NM cable clamp screw in an NM box or around the 8/32 screw for the plaster ring or box cover are common methods used in the field, but are not acceptable in accordance with either Sections 250.8 or 250.148 A. A grounding screw or some other listed grounding device must be used. "


250.8 mentions Sheet Metal Screws. 250.148 C says, "... by means of a grounding screw that shall be used for no other purpose or a listed device."

I do not see this as saying a "listed" ground screw.

My understanding is that there are no listed grounding screws manufactured as of today. Is this true?


If so, then using a cable clamp screw as long as it is not used for any other purpose would seem to be acceptable. Does UL have any more information that would be helpful here? I am presenting a Grounding and Bonding seminar on Saturday, and I would love some better direction on this topic.

Thanks again Mark,

Pierre Belarge
Electrical Training Solutions


I edited this to remove the email addresses

[ January 30, 2006, 05:01 PM: Message edited by: pierre ]
 
Re: Gounding Screw

This post is long enough, but Don:
"Machine screws and bolts" they are not bolts, they are hex head cap screws. When I was in the navy we had to get hardware from the Federal supply catalog, bolts were listed under cap screws, hex head.

I don't know when (at what size) a machine screw grows up to become a hex head cap screw. Maybe thats why your code proposal failed.
It would be interesting to see if 250.8 is changed. The language is too specific.
 
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