# securing ground lug in a disconnect



## telsa (May 22, 2015)

emahler said:


> looking for the code article that requires the ground lug in a disconnect be secured with a machine thread screw with at least 2 threads...
> 
> anyone know off the top of their head?


Learn something new every day.


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## don_resqcapt19 (Jul 18, 2010)

Take a look at 250.8.


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## emahler (Oct 13, 2011)

don_resqcapt19 said:


> Take a look at 250.8.


yep, i'd found it there...thanks...


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## RIVETER (Sep 26, 2009)

emahler said:


> looking for the code article that requires the ground lug in a disconnect be secured with a machine thread screw with at least 2 threads...
> 
> anyone know off the top of their head?


Three threads...10/32


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## Southeast Power (Jan 18, 2009)

So, @ 32 threads per inch...


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## freeagnt54 (Aug 6, 2008)

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RIVETER said:


> Three threads...10/32


Where does it say it needs to be a 10/32?


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## don_resqcapt19 (Jul 18, 2010)

RIVETER said:


> Three threads...10/32


Where does the 3 threads come from?


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## don_resqcapt19 (Jul 18, 2010)

freeagnt54 said:


> Where does it say it needs to be a 10/32?


It doesn't but the next standard machine screw size is 1/4-20 and you would have to have a thicker enclosure to have two threads. You only need 1/16" (about 15 gauge sheet metal) for two threads with a 10-32. You would need 1/10" (about 12 gauge sheet metal) for two threads with a 1/4-20.


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## bigdan1 (Jun 16, 2013)

I have always wondered why most ground bar kits come with 2 8/32 screws and I had one inspector tell me it had to be a 10/32 and marked green. He had me run across the street to a rite aid and put green nail polish on it. I was 18 or19 at the time so it made an impression. I guess.


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## freeagnt54 (Aug 6, 2008)

don_resqcapt19 said:


> It doesn't but the next standard machine screw size is 1/4-20 and you would have to have a thicker enclosure to have two threads. You only need 1/16" (about 15 gauge sheet metal) for two threads with a 10-32. You would need 1/10" (about 12 gauge sheet metal) for two threads with a 1/4-20.


What about a 6-32 or 8-32? Also you can use a nut on the back of a 1/4-20 if your material isn't thick enough.


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## Bad Electrician (May 20, 2014)

freeagnt54 said:


> What about a 6-32 or 8-32? Also you can use a nut on the back of a 1/4-20 if your material isn't thick enough.


Or a fine thread 1/4"X28


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## don_resqcapt19 (Jul 18, 2010)

freeagnt54 said:


> What about a 6-32 or 8-32? Also you can use a nut on the back of a 1/4-20 if your material isn't thick enough.


There is nothing magic about the 10-32 grounding screw...it is just what is commonly used. I don't like to see screws that are smaller than the hole in the lug used, but I am not aware of a requirement that says you must use a screw that matches the lug hole size.


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## don_resqcapt19 (Jul 18, 2010)

Bad Electrician said:


> Or a fine thread 1/4"X28


Still too few threads per inch for the typical electrical enclosure. They appear to be designed for use with grounding screws that have 32 threads per inch.

Also, in a number of cases the thickness of the enclosure is less than what would be required for the engagement of two threads, but the pre-punched holes are made so that they provide a raised lip on the back side of the hole and allows for the required two threads. If the hole has a raised lip on one side, this is the reason, and you would not be permitted to drill and tap your own holes for a ground screw in this type of enclosure.

Of course you can always use a nut as was suggested in an earlier post.


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## Bad Electrician (May 20, 2014)

don_resqcapt19 said:


> There is nothing magic about the 10-32 grounding screw...it is just what is commonly used. I don't like to see screws that are smaller than the hole in the lug used, but I am not aware of a requirement that says you must use a screw that matches the lug hole size.


Don I THINK I was told several years back from the UL white book this was a requirement for the listing I always match the hole to the hardware when possible but never verified this statement


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## Bad Electrician (May 20, 2014)

don_resqcapt19 said:


> There is nothing magic about the 10-32 grounding screw...it is just what is commonly used. I don't like to see screws that are smaller than the hole in the lug used, but I am not aware of a requirement that says you must use a screw that matches the lug hole size.


Don I THINK I was told several years back from the UL white book this was a requirement for the listing I always match the hole to the hardware when possible but never verified this statement


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## MDShunk (Jan 7, 2007)

Bad Electrician said:


> Don I THINK I was told several years back from the UL white book this was a requirement for the listing I always match the hole to the hardware when possible but never verified this statement


That's true. The exact language says, "... the maximum standard hardware diameter compatible with the hole or holes in the connector...".


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## Bad Electrician (May 20, 2014)

MDShunk said:


> That's true. The exact language says, "... the maximum standard hardware diameter compatible with the hole or holes in the connector...".


AND - I believe you are the one that told me that back then.


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## don_resqcapt19 (Jul 18, 2010)

MDShunk said:


> That's true. The exact language says, "... the maximum standard hardware diameter compatible with the hole or holes in the connector...".


Where does that come from?


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## MDShunk (Jan 7, 2007)

don_resqcapt19 said:


> Where does that come from?


UL468a or b. I forget which one.


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## RIVETER (Sep 26, 2009)

emahler said:


> looking for the code article that requires the ground lug in a disconnect be secured with a machine thread screw with at least 2 threads...
> 
> anyone know off the top of their head?


Three


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## don_resqcapt19 (Jul 18, 2010)

RIVETER said:


> Three


Please cite a rule that requires 3 threads for a grounding connection of the machine screw type.


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## don_resqcapt19 (Jul 18, 2010)

MDShunk said:


> UL468a or b. I forget which one.


But that is not something that most of us have access to. If that is the intent of the standard, then that information needs to appear in the white book. I don't seem to find it there, and don't recall seeing it in the instructions that are provided with the wire connectors.


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## MDShunk (Jan 7, 2007)

don_resqcapt19 said:


> But that is not something that most of us have access to. If that is the intent of the standard, then that information needs to appear in the white book. I don't seem to find it there, and don't recall seeing it in the instructions that are provided with the wire connectors.


Makes no difference if you have access to it or not. It's adopted by reference as part of Federal Law, strangely enough.


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## don_resqcapt19 (Jul 18, 2010)

MDShunk said:


> Makes no difference if you have access to it or not. It's adopted by reference as part of Federal Law, strangely enough.


But don't you think that would be (or should be) in the White Book?


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## MDShunk (Jan 7, 2007)

don_resqcapt19 said:


> But don't you think that would be (or should be) in the White Book?


Absolutely not. If every UL spec that applied to us as electricians was in the White Book, it would be like an encyclopedia set. Each UL spec that has the force of law is available online if you know how to search.


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## don_resqcapt19 (Jul 18, 2010)

MDShunk said:


> Absolutely not. If every UL spec that applied to us as electricians was in the White Book, it would be like an encyclopedia set. Each UL spec that has the force of law is available online if you know how to search.


How does a UL spec have the force of law as far as the local AHJ goes?

As far as I know there is no legal free access to the UL standards. I see that as the same issue as the same issue as in the 5th Circuit Court of Appeals case: Veeck vs Southern Building Code Congress.


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## telsa (May 22, 2015)

It strikes me as very odd that what figures to be a UL design spec has been folded into the NEC.

One would think that by installing only listed disconnects the purpose has been served. That this line item specification need not even be called out in the NEC.


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## MDShunk (Jan 7, 2007)

don_resqcapt19 said:


> How does a UL spec have the force of law as far as the local AHJ goes?
> 
> As far as I know there is no legal free access to the UL standards. I see that as the same issue as the same issue as in the 5th Circuit Court of Appeals case: Veeck vs Southern Building Code Congress.


How? Don't much care, myself. The question was asked, and I answered. It's doubtful any soul on this planet is enforcing model standards adopted by reference in the The Code Of Federal Regulations except, perhaps, on military bases. 

There is free legal access to UL standard that are adopted by reference in the CFR. They're on official United States Federal Government websites.


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## danhasenauer (Jun 10, 2009)

I keep a copy of CFR-29 in my office.

https://www.law.cornell.edu/cfr/text/29/part-1910/subpart-S


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## don_resqcapt19 (Jul 18, 2010)

MDShunk said:


> How? Don't much care, myself. The question was asked, and I answered. It's doubtful any soul on this planet is enforcing model standards adopted by reference in the The Code Of Federal Regulations except, perhaps, on military bases.
> 
> There is free legal access to UL standard that are adopted by reference in the CFR. They're on official United States Federal Government websites.


But those standards are not required for other than federal projects...they don't apply to most work.


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## macmikeman (Jan 23, 2007)

FWIW, any field guy knows he is getting a superior ground connection inside a modern cheap ass super thin sheet metal fluorescent light fixture using a self tapping button head tek screw than he is going to get with that crappy small head 8-32 green screw that came with the fixture. But all knowing code cmp members who live and work in Manhattan and have no idea about life outside that city made sure to never allow it to be done like that.


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## danhasenauer (Jun 10, 2009)

don_resqcapt19 said:


> But those standards are not required for other than federal projects...they don't apply to most work.


Uhm, no, OSHA goes by The Code Of Federal Regulations as well. A lot of the NEC has been made part of it. Do it the right way, once. No call-backs, no lawsuits.


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## don_resqcapt19 (Jul 18, 2010)

danhasenauer said:


> Uhm, no, OSHA goes by The Code Of Federal Regulations as well. A lot of the NEC has been made part of it. Do it the right way, once. No call-backs, no lawsuits.


There is a lot of work where the finished product has nothing to do with OSHA. If the rule is not cited in the OSHA regs, it does not apply even to the projects where OSHA applies.


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