Grounding Screw Sizes & Types


I recently opened up an old electrical box with a weak ground. To fix the ground problem I wanted to connect a ground wire to a green grounding screw into the box.
However, the old box doesn't have any holes for 8-32 sized screws, but only for the larger holes (for mounting?).
Questions:
A) Is there any reason why I cannot screw the grounding wire into one of the larger holes in the box?
B) What size screws fit the larger holes?
C) Would any normal screw metal type work?
Thank you.
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If you are sure the box is grounded, then you can drill a hole and run a self-tapping screw into it.
I'd doubt that the box is grounded, based on what you posted.
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Charles Schuler wrote:

I agree. If it were grounded, there's little chance the ground would be "weak," because the outlet's ground would already be connected to the box via its mounting screws.
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redbrickhat wrote:

hmm. don't know exactly what you're talking about but i'll assume maybe an house whole panel? If so, go to your local electrical supply shop and get a grounding Bus strip. Attach it good to the panel and attached a direct ground from the outside to this bus strip also. attaching a single ground to a box that you do not even know if it is grounded to start with, is not a good idea.
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Standard box grounding screw is 10/32

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Not sure I understand... Why is the ground "weak"? And why do you believe this will fix it?

Code requires that the screw holding the grounding wire may not be used for any other purpose. So if the hole you're proposing to use is already in use for mounting the box, or attaching a cable clamp, then the answer is no. Otherwise, yes.
Also no reason (given the appropriate tools) why you couldn't drill and tap a new hole for standard 8-32 grounding screws.

Usually 10-32.

No -- you want a screw with a pan head, round head, or washer head. Flat head and oval head will not hold the wire securely.
You'll find that something with a Phillips or Robertson (square drive) head is easier to install than a slotted head.
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Doug Miller (alphageek at milmac dot com)
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On Mon, 11 Dec 2006 01:46:02 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

This always gets me. Lets say I always mount a box to a stud or joist with 2 sheet metal screws. So I put in my two mounting sheet metal type screws, but then add a 3rd sheet metal screw with a small washer on the end to become the ground. Now this is actually only intended to be a ground, but it is also going into the wood, thus holding the box more securely. I didnt need a 3rd screw for holding the box, it just happens to also go into the stud. I always wondered how the code would view that????
Generally I always use the green screws made for that purpose, but sometimes on old work using the sheet metal screw is the only option without ripping the house apart. You really cant tap threads in the box with wood behind it.
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wrote:

Code would view that as a violation -- mostly because it's not making secure contact with the box. There's a *reason* they supply boxes with holes that are tapped for machine screws, you know...

What's stopping you from using a grounding clip? That's Code-compliant.

Sure you can. I've done it many times. Just drill your pilot hole into the wood, too. Tap the metal, and you wind up tapping the wood behind it too. So what?
What's stopping you from using a grounding clip? That's Code-compliant.
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can't drill and tap the back of the box?
wood's not going to stop a drill or a tap.
I wonder if self-drilling screws are acceptable, they're certainly convenient.
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I'm pretty sure they won't pass code - or the local inspector.
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And why would that be? Got a Code cite for that?
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Doug Miller wrote: x

(2002) NEC 250.8 Connection of Grounding and Bonding Equipment. ".......Sheet metal screws shall not be used to connect grounding conductors to enclosures."
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But "they" make grounding screws that are "self-taping" but aren't sheet metal screws.
Indeed, sheet metal screws will likely not penetrate the steel in a typical J-box. But the true self-drilling/self-tapping screws will do the job. When you finish you have a tapped hole and a screw that fits and even is "green". You can removing the self-tapping/self-drilling screw, if your wish, and replace it with a regular machine screw (green or not). I don't see why you would want to unless you have lots of machine screws but only one self-tapping screw.
OR you can get the proper sized drill and a tap (and a tap wrench). Either way you end up with a machine screw ready tapped hole.
According to my electricial friendly, the screw doesn't really have to be green.

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John Gilmer wrote:

That depends on the local code. A lot of places will fail any ground screw that isn't green.
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wrote:

IMHO:
I'm not there, so I can only tell you what I've done. I've used ground clips where I could not use a secure ground screw. A quick search in google for "Solid Conductor Grounding Clips" should help. I believe they are for sale at your local lowes and home depot. Check and follow directions.
later,
tom @ www.Consolidated-Loans.info
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