# Adding ground screw



## n0c7 (Oct 7, 2008)

I ran into a handful of octagon light boxes that have 14/2 and 14/3 running to them and I need to add an additional ground screw(both bonding wires were cut after wrapped around box ground screws). For a quick fix, I want to avoid extending the grounds and use a self-tapper. I've recently been told that a self-tapping screw will not cut it as most do not penetrate adleast 2 threads into the metal. What kind of screws are you guys using out there for these situations? This is a CEC question but I believe the same rules to bonding applies at the moment(or very similar).


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## 480sparky (Sep 20, 2007)

Can you use a ground clip?


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## n0c7 (Oct 7, 2008)

480sparky said:


> Can you use a ground clip?
> 
> I've never worked with those. Do they just rely on the box being grounded and connect a spare piece of copper through them? Would it pose a problem in a light fixture scenario causing it not to sit flush? When reading the NEC and condensed CEC I didn't see them as an option at the time.


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## 480sparky (Sep 20, 2007)

Most fixtures have a recess on the 'top' or 'back', so clearance isn't an issue. If the box is metal, it's either grounded through a ground wire or a metal raceway. Grounding a metal box is required anyway.


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## n0c7 (Oct 7, 2008)

480sparky said:


> Most fixtures have a recess on the 'top' or 'back', so clearance isn't an issue. If the box is metal, it's either grounded through a ground wire or a metal raceway. Grounding a metal box is required anyway.


Yeah, I see your logic. I just seem to feel that an additional screw for the fixture wire would be more effective, I would be worried those clips could come loose. Can't knock it until I try it though. Are they up to code?


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## 480sparky (Sep 20, 2007)

n0c7 said:


> Yeah, I see your logic. I just seem to feel that an additional screw for the fixture wire would be more effective, I would be worried those clips could come loose. Can't knock it until I try it though. Are they up to code?


AFAIK, they're UL listed. Just check the box/package when you buy them. They're pretty good at grabbing since they have 'teeth' on them that make it hard to pull back off.


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## n0c7 (Oct 7, 2008)

Thanks for the heads up on that. I'll have to check with our inspector on them. As for the additional screw, any suggestions on which type?


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## Bkessler (Feb 14, 2007)

Buy a package of self tapping machine screws, it the self tapping sheet metal screw that are illegal for this application.


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## n0c7 (Oct 7, 2008)

Bkessler said:


> Buy a package of self tapping machine screws, it the self tapping sheet metal screw that are illegal for this application.


Any specific rules on how many threads, size, etc? The NEC is a bit generic on stating "two or more threads".


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## Bkessler (Feb 14, 2007)

I have a bag of 10-32 self tapping screws. I don't know where they came from.


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## dowmace (Jan 16, 2008)

I usually drill and tap for a 10-32 Ground screw, I believe that is the correct way to do it. Most inspectors here will fail you if you use ANY self tapping screw.


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## Adam12 (May 28, 2008)

Sheet metal scews are the only screws not permitted. Therefore a wood screw or even a drywall screw would be legal, but not recommended. Your best bet would be to take Kesslers advice.

Why arent self tappers legal? They hold better than any ground clip Ive ever used.


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## paul d. (Jul 13, 2008)

what EXACTLY does the NEC book say about it?


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## dowmace (Jan 16, 2008)

Adam12 said:


> Sheet metal scews are the only screws not permitted. Therefore a wood screw or even a drywall screw would be legal, but not recommended. Your best bet would be to take Kesslers advice.
> 
> Why arent self tappers legal? They hold better than any ground clip Ive ever used.


A self tapping screw can loosen over time I believe is the reason, I know that I've put some in sheet metal to strap conduit and then a week later I can come buy and wiggle the screw out.


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## Adam12 (May 28, 2008)

paul d. said:


> what EXACTLY does the NEC book say about it?


250.8
Blah.........blah...........blah........Sheet metal screws cannot be used to connect grounding or bonding conductors or connection devices to enclosures.


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## n0c7 (Oct 7, 2008)

paul d. said:


> what EXACTLY does the NEC book say about it?


I don't have a copy, but from my research, not sure if this is still valid, this is what it says:


*250.8 Connection of Grounding and Bonding Equipment.
(A) Permitted Methods.​*Grounding conductors and bonding
jumpers shall be connected by one of the following
means:
(1) Listed pressure connectors
(2) Terminal bars
(3) Pressure connectors listed as grounding and bonding
equipment
(4) Exothermic welding process
(5) Machine screw-type fasteners that engage not less than
two threads or are secured with a nut
(6) Thread-forming machine screws that engage not less
than two threads in the enclosure
(7) Connections that are part of a listed assembly
(8) Other listed means *

(B) Methods Not Permitted. *Connection devices or fittings
that depend solely on solder shall not be used.


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## n0c7 (Oct 7, 2008)

dowmace said:


> A self tapping screw can loosen over time I believe is the reason, I know that I've put some in sheet metal to strap conduit and then a week later I can come buy and wiggle the screw out.


I've seen some of the factory grounding screws in boxes come loose, go figure! I've never had any of my sheet metal screws for steel stud framing installations come loose.  But I do agree that they can come loose if they don't grab into the material very well.


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## n0c7 (Oct 7, 2008)

dowmace said:


> I usually drill and tap for a 10-32 Ground screw, I believe that is the correct way to do it. Most inspectors here will fail you if you use ANY self tapping screw.


The inspectors in town here don't give a rats ass. They spend more time on their cell phones then looking at your wiring. With our recent economic boom and the amount of homes that came up, I won't be surprised when I hear a 1/4 of them burned down.

As for drilling and tapping, do you know of any 10-32's that are self tapping and just need to drill a pilot hole so you can avoid pulling out the tap/die set?


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## Adam12 (May 28, 2008)

n0c7 said:


> I've seen some of the factory grounding screws in boxes come loose, go figure! I've never had any of my sheet metal screws for steel stud framing installations come loose.  But I do agree that they can come loose if they don't grab into the material very well.


You can get them real tight when drilled into a J-box.


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## n0c7 (Oct 7, 2008)

dowmace said:


> I usually drill and tap for a 10-32 Ground screw, I believe that is the correct way to do it. Most inspectors here will fail you if you use ANY self tapping screw.


Tried that method on a spare box. The metal is way too thin and the ground screw just spins when it reaches the box. Would definitely feel sketchy about this method. How thick is the metal you're usually tapping in these situations?


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## dowmace (Jan 16, 2008)

n0c7 said:


> Tried that method on a spare box. The metal is way too thin and the ground screw just spins when it reaches the box. Would definitely feel sketchy about this method. How thick is the metal you're usually tapping in these situations?


Normal 1900 boxes and switch boxes, I couldn't tell you the gauge off hand. Have you tried landing a wire on the screw and then tightening it, when you have a wire under the screw it won't run out of threads before tightening down.


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## Pierre Belarge (Feb 3, 2007)

I was recently at a UL meeting. These meetings have been set up by UL to answer our questions as best as they can.

The sheet metal screw question was asked at the meeting. And yes, 2 threads minimum are required.

I am curious as to how one would prove 2 threads in a box that have been field tapped.


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## MDShunk (Jan 7, 2007)

Pierre Belarge said:


> I am curious as to how one would prove 2 threads in a box that have been field tapped.


By measurement. The inspector could easily take a micrometer to the box and measure the thread pitch of the screw, and do the math. In my opinion, it would be up to the inspector to determine that there isn't at least two threads engaged rather than me having to prove that there are. 

Having said that, you might find this interesting. Ever noticed that the ground screw hole in a 16 gauge pull box is swaged to allow more screw contact? That's for a reason. If you field tapped 16 gauge, which is .051" thick, and you installed a 10-32 ground screw (.03125" per thread), you wouldn't have 2 full threads engaged. A four square is much thicker, and would easily engage 2 threads if it was field tapped for a 10-32.


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## JamesINla (May 19, 2007)

This is what I use. Just drill a pilot and tap it to 10-32 and use a regular ground screw. I HATE finding self tappers inside any box.


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## flashmn (Mar 29, 2007)

250.8(A)(6) Thread forming Machine screws...... This is a self tapping screw. Not a TEK screw but a machine eg 10-32, 8-32, etc.


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## Pierre Belarge (Feb 3, 2007)

MDShunk said:


> By measurement. The inspector could easily take a micrometer to the box and measure the thread pitch of the screw, and do the math. In my opinion, it would be up to the inspector to determine that there isn't at least two threads engaged rather than me having to prove that there are.
> 
> Having said that, you might find this interesting. Ever noticed that the ground screw hole in a 16 gauge pull box is swaged to allow more screw contact? That's for a reason. If you field tapped 16 gauge, which is .051" thick, and you installed a 10-32 ground screw (.03125" per thread), you wouldn't have 2 full threads engaged. A four square is much thicker, and would easily engage 2 threads if it was field tapped for a 10-32.


 

Yes Marc, I forgot that I carry a micrometer in my inspection bag...please forgive me.

In my opinion, as an inspector, I look at bonding closer than any other portion of an electrical installation. If you were to depend on me to determine how many threads there were, it would not bode well for you. As you mentioned, the manufacturer uses a factory process to enable them to provide enough threads. I do not see the average installer able to do the same.


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## Nodoggie (Oct 17, 2008)

dowmace said:


> I usually drill and tap for a 10-32 Ground screw, I believe that is the correct way to do it. Most inspectors here will fail you if you use ANY self tapping screw.


This is the de facto correct method. 

The ground screw will not strip the metal if you: 1.) drill a hole slightly smaller first, and; 2.) tap with a "tri-tap" _by hand_. The entire operation should take under 60 seconds per box if the circuit is safed-off.


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## itsunclebill (Jan 16, 2007)

I carry a "drilltap" size 10-32. Drills, taps and reams in one step. They are about the price of a tap. Takes a bit of learning to keep from breaking them but once you get the hang of it they are fast.

The math is simple. 32 = threads per inch. Anything less than a 16th of an inch (.0625) (8 guage is just a bit thicker, and a common device/j-box material), won't have 2 full threads.


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## tam (Oct 21, 2008)

JamesINla said:


> This is what I use. Just drill a pilot and tap it to 10-32 and use a regular ground screw. I HATE finding self tappers inside any box.


why do you hate tap screws so much would it not be faster and more productive to just drill a screw once?

i usually use a self tap screw. but how about bonding it to the 8-32 screw on the box? is this not permissible?


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## william1978 (Sep 21, 2008)

tam said:


> i usually use a self tap screw. but how about bonding it to the 8-32 screw on the box? is this not permissible?


 Your kidding right?:wallbash::wallbash::wallbash:


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## tam (Oct 21, 2008)

no can you please explain to me, so you dont hurt your head on those bricks anymore? i am obviously not a professional electrician yet, but i do have some experience. and i wont be seeing my boss until this weekend.


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## william1978 (Sep 21, 2008)

250.148(c) says that 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, equipment listed for grounding, or a listed grounding device.


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## tam (Oct 21, 2008)

thank you for your help


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## william1978 (Sep 21, 2008)

tam said:


> thank you for your help


Sure thing, by the welcome to the forum.:thumbsup:


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