quick question on grounding J-boxes

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Old 03-25-06, 05:34 PM
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quick question on grounding J-boxes

A silly question...

When attaching a j-box to a joist, where the back of the box is where it's attached, how do you attach the grounding screw? If you attach the box first, the screw will not be able to penetrate the wood because it's a sheet metal screw. It is proper to attach the grounding screw/wire prior to installing the box, then screw the box in tight?

It's the little things that I'm sure are going to get to me...

Thanks all !
 
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Old 03-25-06, 05:53 PM
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Test fit the box, mark the stud thru the 10-32 hole.

Drill suitable depth at the marked spot.

Mount box.

I've also done this after box mounting, carefully, with a slightly smaller bit. But then make sure you have a tap in case you mess up the threads.
 
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Old 03-25-06, 05:58 PM
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This metal box you can ground after installation. Do not use the pre drilled hole, used for mounting.

Use a self tapping screw, go thru the box, so as the screw is threaded into the metal box.
 
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Old 03-25-06, 06:34 PM
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Originally Posted by lectriclee
Do not use the pre drilled hole, used for mounting.
??

We're talking about the green screw.

This is something annoying about metal boxes.

I put the screw in place, and strike it to make a mark on the wood.
Then I drill directly on the wood. Or if I'm not drilling anything else, I just run in a screw to make a hole.

I recommend against drilling through any threaded hole.
If you compromise the threads, then you compromise the ground.
 
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Old 03-25-06, 07:02 PM
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Correction.
In any metal box you purchase, (forgive me I lost my micrometer) There are 2 sets of holes one is larger than the other. The larger hole is typicaly used for mounting the box, To wood-metal what ever the medium.The smaller hole is typicaly Pre-drilled at the factory to a 10/24,10/32 screw tap.; If you go to your local supplier you will be able to find these screws, They are green in color. Or you can just install a SELF tapping screw thru the metal box (not a predrilled hole). And paint it permanately green.
 
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Old 03-25-06, 07:44 PM
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Originally Posted by bolide
??

I recommend against drilling through any threaded hole.
If you compromise the threads, then you compromise the ground.
Good point. I think my memory was faulty: When I had to drill and tap old boxes that were already in place and mounted flush against framing on the back, I drilled a hole through the metal with the #21 drill (The size for 10-32 I think) and went deeper into the wood. Then I tapped the hole for 10-32.

Regarding the self-tapping self-painted green screws ... I though the screws had to be rated or listed for grounding.

Can't you also use a clip over the edge of the box, too, in most cases?
 
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Old 03-25-06, 07:51 PM
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Originally Posted by lectriclee
Correction.
In any metal box you purchase, (forgive me I lost my micrometer) There are 2 sets of holes one is larger than the other. The larger hole is typicaly used for mounting the box, To wood-metal what ever the medium.The smaller hole is typicaly Pre-drilled at the factory to a 10/24,10/32 screw tap.; If you go to your local supplier you will be able to find these screws, They are green in color. Or you can just install a SELF tapping screw thru the metal box (not a predrilled hole). And paint it permanately green.
just curious, why would it matter if you used a self-tapping screw thru one of the pre-drilled holes? You'd still be hitting the metal of the box. Seems much harder to screw thru the metal box.

Also, is it code to have the screw colored green?

It seems to me that you could also just attached the grounding wire to one of the mounting screws. Again, touching metal and now the box is flush and secure.

I'm sure there is probably a reason against doing this. Just my thinking.
 
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Old 03-25-06, 08:06 PM
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Yes it must be green. If you use a self tap thru a pre-drilled hole... Now thats not self tapped is it. And if it was easy, Don't you think everyone would do it?
Seriously----If you ground to the mounting screw, you do not have a proper mechanical connection.
If the screw hole is tapped you have a secure mechanical connection to the box.
Too many people do not understand the importance of the ground in an electrical system.
Too much to go into now. NEC-ART 250 (good reading, if your loosing sleep).
 
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Old 03-25-06, 08:13 PM
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Originally Posted by lectriclee
Yes it must be green. If you use a self tap thru a pre-drilled hole... Now thats not self tapped is it. And if it was easy, Don't you think everyone would do it?
Seriously----If you ground to the mounting screw, you do not have a proper mechanical connection.
If the screw hole is tapped you have a secure mechanical connection to the box.
Too many people do not understand the importance of the ground in an electrical system.
Too much to go into now. NEC-ART 250 (good reading, if your loosing sleep).

Ok, sounds like the most practical way is to mark it, pre-drill the hole, mount the box then attach the ground with the green screw.

Thanks all.
 
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Old 03-25-06, 08:24 PM
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PRE-DRILL & tap.....solid Mechanical connection.

The small hole is already tapped, HD has the green screws.
 
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Old 03-25-06, 08:27 PM
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Originally Posted by lectriclee
PRE-DRILL & tap.....solid Mechanical connection.

The small hole is already tapped, HD has the green screws.
Right, by pre-drill, I meant into the joist, not the box. Pre-drill a larger hole into the stud, behind the small tapped hole. Then screw the green grounding screw into the tapped hole.
 
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Old 03-25-06, 08:31 PM
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Right on Man !!!!
 
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Old 03-25-06, 08:53 PM
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Originally Posted by lectriclee
you can just install a SELF-tapping screw thru the metal box (not a predrilled hole).
Do you have a photo?

The steel boxes I used are too strong/thick for self-tapping screws.

Yes, I think the ground must be connected by a machine screw.
 
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Old 03-25-06, 08:58 PM
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Originally Posted by lectriclee
If you use a self-tap thru a pre-drilled hole... Now that's not self-tapped is it.
It's the only way it could work.

> And if it was easy, Don't you think everyone would do it?

How about if it were even permitted?

> If you ground to the mounting screw, you do not have a
> proper mechanical connection.

Diito if you use a self-tapping sheet metal screw.


> If the screw hole is tapped you have a secure mechanical connection to the box.

That's the reason.


> Too many people do not understand the importance of the ground

Technically, bonding.
The correct terminology is appearing more and more in the NEC.
 
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Old 03-25-06, 09:24 PM
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C'mon Bolide, You have never seen a self tapping screw that can go thru a standard box!?
And would you realy run out to the store to buy a green screw? On a T&M job maybe.
 
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Old 03-25-06, 10:29 PM
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Originally Posted by lectriclee
You have never seen a self-tapping screw that can go thru a standard box!?
Never had a reason. If I need a hole in steel, I drill it.


> would you really run out to the store to buy a green screw?

Not when I have a couple hundred with me.
 
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Old 03-26-06, 05:06 AM
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2005 NEC® 250.8 Connection of Grounding and Bonding Equipment.
Grounding conductors and bonding jumpers shall be connected by exothermic welding, listed pressure connectors, listed clamps, or other listed means. Connection devices or fittings that depend solely on solder shall not be used. Sheet metal screws shall not be used to connect grounding conductors or connection devices to enclosures

C'on guys, not using sheet metal screws is basic stuff. Ground screws HAVE to be drilled and tapped
 
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Old 03-26-06, 05:41 AM
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As itsunclebill has pointed out, the ground MUST be connected to the proper ground screw terminal. It cannot be attached to a screw used to mount the box, it cannot be soldered to the box.

Pre drill a hold into the wood behind the box where the ground screw will be located.
 
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Old 03-27-06, 10:40 AM
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I've also seen boxes (4" square, j-boxes, etc) with a small mound at the back of the box with the pre-tapped hole for the ground screw. The dimple (or mound) allows the ground screw to be attached and not interfere with the mounting of the box.

Granted, I don't do this everyday like many people here, but to me, that sounds like a good solution that sure beats drilling out the wood behind the box or tapping my own hole.

Just another option.
 
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Old 03-27-06, 11:04 AM
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Originally Posted by Zorfdt
I've also seen boxes (4" square, j-boxes, etc) with a small mound at the back of the box with the pre-tapped hole for the ground screw. The dimple (or mound) allows the ground screw to be attached and not interfere with the mounting of the box.

Granted, I don't do this everyday like many people here, but to me, that sounds like a good solution that sure beats drilling out the wood behind the box or tapping my own hole.

Just another option.
I've seen those as well, but only on switch boxes, not on J-Boxes. That would be a lot easier though.
 
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Old 03-27-06, 02:58 PM
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Glad I read this thread

I am needing to ground my 12 x 12 x 6 box. I was going to use a mounting screw until I read this even though I have read that section of the NEC. Just goes to show you that if you don't use it, you lose it. So I don't get why I would need to drill a larger hole behind the tapped hole. It seems like the wood would just "take" the metal threads, even if they are not meant for wood.

I have already mounted my junction box, so I will buy a green screw and even a tap if necessary. Do they not make green (UL listed, I guess) self tapping screws for this situation? Could I use a self tapping screw as a substitute for a tap?
 
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Old 03-27-06, 03:25 PM
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Originally Posted by Tyger52
I don't get why I would need to drill a larger hole behind the tapped hole. It seems like the wood would just "take" the metal threads, even if they are not meant for wood.

Do they not make green (UL listed, I guess) self tapping screws for this situation? Could I use a self tapping screw as a substitute for a tap?
A larger hole makes it easier. I didn't really think about it until now, but when you drill the hole for tapping your drill size is roughly the size of the screw shaft _without_ threads. Your screw has threads on it, which makes it larger than the drill size, and the threads are not pitched to dig into wood efficiently. So it's a real torque job. I think you would be able "tap" the wood fairly easily, though.

I've used the self-tapping screws that come with aluminum weatherproof boxes. Maybe someone else has more info. It's a good idea.

If your 12x12x6 box is from Hoffmann, they make a grounding kit http://www.hoffmanonline.com/iHelps/...t.cfm?ID=9031B but that might be overkill. I have some of the same size boxes for low-voltage so I have grounded them but maybe not to NEC or NEMA standards.
 
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Old 03-27-06, 07:18 PM
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green shmeen

you don't have to have a green screw ...
It does have to be machine thread, 10-32 is common ground screw pitch
box mounted already?
drill box with #21 drill, into wood
tap with 10-32 tap - will clear wood
install ANY 10-32 screw
 
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Old 03-27-06, 07:54 PM
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Why the #@$% do you have to drill the wood? 99.9% of the building material is pine. Put a little muscle into it and the (green) screw sinks itself !! (through the 10/32 Pre threaded hole) It's not rocket science!
 
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Old 03-27-06, 08:04 PM
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Originally Posted by lectriclee
Why the #@$% do you have to drill the wood? 99.9% of the building material is pine. Put a little muscle into it and the (green) screw sinks itself !! (through the 10/32 Pre threaded hole) It's not rocket science!
sometimes if the wood is 50+ years old, it's a little hard.

I tried using a regular screwdriver, and couldn't get it.
 
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Old 03-27-06, 08:35 PM
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> install ANY 10-32 screw

How about any suitable 10-32 screw?

Green screws are different. The head is larger to hold the wire.
I'm sure there are many 10-32 screws which are not suitable for holding a ground wire.
 
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Old 03-28-06, 05:07 AM
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Originally Posted by bolide
> install ANY 10-32 screw

How about any suitable 10-32 screw?

Green screws are different. The head is larger to hold the wire.
I'm sure there are many 10-32 screws which are not suitable for holding a ground wire.
Amen. Uncle Bill's citation (above) says "listed".

Originally Posted by fuente
sometimes if the wood is 50+ years old, it's a little hard.

I tried using a regular screwdriver, and couldn't get it.
Ditto. I stripped a hole when I tried to play tough guy with my drill. I easily broke off a lag bolt in my old-growth framing even when pre-drilled and lubed like I'd done many times for new growth pine.
 
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Old 03-28-06, 05:08 PM
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the octogon boxes in my local hardware store ahve 2 screws in teh back of the box....iwas told are for grounding...they have big fat heads on them ..but are not green...? this green rule...is rule of thumb? or code? (ontario canada)

im no electrician but do dabble at my own stuff..have always had it inspected and never been told to get green screws?
 
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Old 03-28-06, 08:48 PM
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BEATEN To death, The code is the BARE MINIUM you must follow.
How many of the general readers here have a hundred green screws with them? How fine are the tolerances of most installs that the box cannot be out of wack by 1/8 of an inch? How hard is it, if the box is a touch out of wack, to place a driver of some sort onto the suspect screw and WACK it as to sink the screw and flush the box?
The trick here(no trick) Is to make sure that there is a mechanical ..solid..secure connection to the box, For a good BOND (ground).
As proffesionals we must follow rules, However we understand, what must be done,and why. and we do it! Because we all must sleep.
 
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