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Old 09-11-2007, 05:34 PM   #1
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Default Using metal junction box screw for grounding?

I have read several articles that say its acceptable to use the screw that comes with the metal box for grounding. The two silver ones usually used to attach a fixture. As long as that screw is only used for that purpose and none other.
Now the NEC says you must use a green hexagonal screw as the grounding screw for the metal box. It never talks about using other screws already attached.
Safety wise, everything is grounded. But would this pass inspection? Thoughts?
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Old 09-11-2007, 06:22 PM   #2
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If you use the screw that comes with it, how will you secure the cover, plaster ring, fixture, etc? If you use it to connect the EGC, you can't use it for anything else.

I just use a green, hex head 10/32. You know, a ground screw. Why give an inspector something to fuss over?
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Old 09-11-2007, 06:30 PM   #3
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Lets say your putting up a ceiling flourescent light where you use toggle bolts.
Then you can use the junction screw as a grounding screw because its not used for the fixture support.

Rare occasions would this be used anyway.
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Old 09-11-2007, 07:04 PM   #4
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Quote:
Originally Posted by shocking View Post
Now the NEC says you must use a green hexagonal screw as the grounding screw for the metal box.
Wanna tell us where you got this erroneous information from.....
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Old 09-11-2007, 07:10 PM   #5
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Quote:
Originally Posted by Speedy Petey View Post
Wanna tell us where you got this erroneous information from.....
I was waiting for someone to ask that.

It has to be green and hexagonal on receptacles, but the NEC doesn't happen to say that about box bonding screws.
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Old 09-11-2007, 07:23 PM   #6
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I figured I'd throw out the NEC reference.

250.148(C) Metal Boxes.
A connection shall be made between the one or more EGCs and a metal box by means of a grounding screw that shall be used for no other purpose or a listed grounding device.
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Old 09-11-2007, 08:10 PM   #7
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My mistake Speedy...it says the screw that you use must be that. E.g. Dont use a self tapping metal screw for grounding.

So it looks like the screw that comes already with the metal boxes may be used for grounding, as long as they are used for no other purpose.
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Old 09-11-2007, 10:24 PM   #8
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So it looks like the screw that comes already with the metal boxes may be used for grounding, as long as they are used for no other purpose

That may happen 1 out of 50 times you use a metal J-box?

get some 10/32 screws and use the threaded hole and use the cover screws for that, covers.
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Old 09-11-2007, 10:59 PM   #9
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Quote:
Originally Posted by jbfan View Post
That may happen 1 out of 50 times you use a metal J-box?
Y'think that much?
In almost 20 years I don't think I've done this once.


I agree. EVERY metal device or fixture box has a threaded 10/32 hole. Use it.
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Old 09-12-2007, 08:30 AM   #10
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Quote:
Originally Posted by Speedy Petey View Post
Y'think that much?
In almost 20 years I don't think I've done this once.


I agree. EVERY metal device or fixture box has a threaded 10/32 hole. Use it.

I had to come up with some kind of number.
1 in a million did not sound encouraging
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Old 09-14-2007, 12:38 AM   #11
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Quote:
Originally Posted by shocking View Post
My mistake Speedy...it says the screw that you use must be that. E.g. Dont use a self tapping metal screw for grounding.
I've been known to do this from time to time, is this prohibited by the NEC?

Thanks
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Old 09-14-2007, 12:42 AM   #12
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Quote:
Originally Posted by Reddy Kilowatt View Post
I've been known to do this from time to time, is this prohibited by the NEC?

Thanks
Yeah, there's a prohibition against sheet metal screws for grounding. Oddly, there's no prohibition against worse stuff like wood screws, drywall screws, railroad spilkes, nails, etc.
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Old 09-14-2007, 02:29 PM   #13
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Quote:
Oddly, there's no prohibition against worse stuff like wood screws, drywall screws, railroad spilkes, nails, etc.
250.8 has been changed to eliminate this problem in the 2008 NEC.

Here is the new wording in that section:

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.

Chris

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Old 09-14-2007, 02:37 PM   #14
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Wow...

(6) Thread-forming machine screws that engage not less
than two threads in the enclosure

So I guess Im wrong again... we are allowed to use self tapping screws from now on...

We can use anything we want now for that matter....
what if you use electrical tape to secure the ground to boxes... lol... j/k
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Old 09-14-2007, 02:43 PM   #15
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NO. A "Thread-forming machine screw" is NOT a self tapping screw.
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Old 09-14-2007, 04:17 PM   #16
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The typical self tapping screw will not meet the 2 threads fully engaged part of that requirment.

Here is a pitcure of a thread forming screw.



Chris
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Old 09-14-2007, 05:32 PM   #17
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Quote:
Originally Posted by raider1 View Post
250.8 has been changed to eliminate this problem in the 2008 NEC.
That's good news.

A self drilling machine screw will work now too.
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Old 09-21-2007, 10:15 AM   #18
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What is a
"6) Thread-forming machine screws that engage not less
than two threads in the enclosure"

"thread-forming machine screw"...I am not sure that I have ever heard that term before.
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Old 09-21-2007, 11:38 AM   #19
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Quote:
Originally Posted by Pierre Belarge View Post
What is a
"6) Thread-forming machine screws that engage not less
than two threads in the enclosure"

"thread-forming machine screw"...I am not sure that I have ever heard that term before.
Pierre,

The picture that I posted is of a thread-forming ground screw. The threads of the screw are designed to cut and form threads in the metal that they are being screwed into.

Chris
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Old 10-03-2007, 08:51 PM   #20
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I have sadly seen the EGC pinched between the cover and the box before.
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