Quicky - ground screw in metal junction box

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  #1  
Old 03-04-03, 07:03 AM
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Quicky - ground screw in metal junction box

Quick (stupid) question:

I have (2) 12/2 NM-B wires going into a large metal junction box in my basement where they will be connected to (2) 12/2 NM-B wires going to the SEP (each gets 20A breaker). Basically the JB is just to extend the wires (didn't measure...).

The metal box I bought didn't have a ground screw, and I couldn't find one that fit the holes in the box. So, does it need to be grounded?

I assume _yes_ since it is a metal box, but I looked at one of the other JBs in the basement and didn't see that is was grounded either...

TIA

Tony
 
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  #2  
Old 03-04-03, 07:46 AM
hotarc
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Yes it should be grounded. If you can't find the right sized green grounding screw, you can use one of those slide-on grounding clips that goes over the edge of the box. It is a somewhat inferior method to an actual grounding screw, but it does work. The other boxes in your basement might be utilizing these clips and you just didn't notice.
 
  #3  
Old 03-04-03, 09:03 AM
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There will only be one hole in the back of the box suitable for a ground screw. It is the smaller threaded hole and will accept a 10-24 screw. You can buy a small pack of green ground screws at any hardware store that will fit it. Any 10-24 will work, but you are supposed to paint the head green (by code).

Some goobers wrap the ground around one of the mounting screws which works perfectly well, provided the mounting screw never works loose. Not code compliant of course so forget I even mentioned it. You could always drive a self tapping screw into the back of the box to connect your ground wire if you can't find a 10-24.

If the box is not grounded and a live conductor comes into contact with the box, the breaker will not trip and the box will be live. If you are standing on a damp and/or concrete floor and touch the box you will realize the importance of grounding.
 
  #4  
Old 03-04-03, 12:27 PM
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My favorite Grounding technique for Grounding metal outlet-boxes with a Grounding wire is done using 1/4" fender-washers 1-1/4 " in diameter. I remove a 1/2 KO and assemble together 3 fender-washers and a 1/4' nut and bolt. 2 of the washers are inside the box and one washer on the outside. You loop the Ground wire around the bolt between the 2 washers inside the box and then "crunch" the washers and the Ground wire together by tighting the nut & bolt which results in the Ground wire being compressed between 2 washers which are compressed against the metal of the box. Now it sez in Art 250---
 
  #5  
Old 03-04-03, 12:34 PM
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There was only one tapped hole, and it was pretty big - definitely bigger than other grounding screws I've seen. I need to stop at the Depot anyhow, so I will pickup something that will work.

Thanks for the replies.
 
  #6  
Old 03-04-03, 06:30 PM
P Michael
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The hole in the back of the box is tapped for 10-32, not 10-24.

In one of its few coherent moments, the dear Code states: "Sheet-metal screws shall not be used to connect grounding conductors to enclosures." [250-113]
Dottie makes a fine 10-32 ground screw #1032TC which is a machine screw with little cutting slots on the tip so it can thread itself. This happens to fit in one of those side holes of the metal box.

~Peter
 
  #7  
Old 03-04-03, 07:13 PM
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Yes, no drillers to attach grounds. I am GUILTY here on a couple of these. I did buy a whole box of ground screws the other day, but that is another matter. I am one of those goobers that often used to twist the wires together and jamb under a screw where I can in Jboxes and some light fixture boxes. I never do it in recepts where equipment gets plugged in though. Am also guilty of using tek screws (not in panels) to hook grounds to equipment on occasion but really try to make sure they are solid and not to really light sheet metal.
 
  #8  
Old 03-05-03, 06:45 AM
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10-32 fit just fine - took me forever to find them in HD though!
 
  #9  
Old 03-05-03, 09:13 AM
Sparksone42
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Should you run into this problem again. You can always use a grounding clip. These little gems can be used on any metal box and you don't need a ground screw hole for them, they satisfy all applicable code articles and cost about the same as a box of ground screws.

I have one question in regard to PATTABA's method of grounding, haven't you ever been turned down on an inspection due to the fact that your method, not only violates code but, leaves all of those boxes that you ground using that method open, most likely, to a combustible? Just curious.....


Sparksone42
 
  #10  
Old 03-05-03, 09:48 AM
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PATTBAA's method does not leave an open box - for instance on a 4" square junction box he would use a knockout on the side of the box and install a blank 4" square cover to close the box. Although his method appears electrically sound and safe, although not necessarily code compliant, it seems to be a lot more trouble than using a simple ground screw.
 
  #11  
Old 03-05-03, 10:25 AM
Sparksone42
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Technically, Yes, Pattaba's method does in fact leave that box open. The opening that I am refering to is where the bolt and the fender washers are used in the knockout.

Let me say here that I agree that the ground may, in fact, be better than using a grounding screw given the fact that there is more metal to metal contact. However, there are two inherent problems with this method that would keep you from passing an inspection here.

1. You can't have that box open to any combustible, this grounding method would classify as leaving an opening to a combustible. The only permissible method of closing a knockout, as we all know, is to either use an approved connector for cable or pipe or a knockout seal. The fact that you would definitely tighten the bolt and nut combo and apparently close the opening would not fly with inspectors here.

2. This method of grounding also nullifies the UL listing of the box. Again, those that do this for a living should well know that all of the equipment that we install must be UL listed and labeled and installed according to those listings. This is mandated by the NEC.

I am not trying to start a fight here, I just want those that are asking for advice to get the best, most correct, information they can get. Being an electrcial contractor myself I try to give the most correct, that includes politically correct, information I can give.

Just my opinion...

Sparksone42
 
  #12  
Old 03-05-03, 10:57 AM
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I'm not disagreeing with code relevance and passing inspections. I will say that I have passed the usage of 1/4" fender washers with 1/4" bolt/nuts as knockout fillers many times. If you want to get technical about open boxes, what about all the extra screw holes on the back of boxes that aren't used? Even if mounted to a wood structure we're not required to fill those holes. What about the "cracks" on the sides of gangable boxes? What about the gaps that remain beside a piece of romex in a romex connector?

I agree that his grounding method would have a much more difficult time passing an inspection than would my knockout sealing method which is practically identical. I believe I stated that his method, in my opinion, was "electrically sound and safe although not necessarily code compliant", in much the same manner as using a threaded 10-32 to ground a wire to the back of the box without painting the head green.
 
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Old 03-05-03, 12:38 PM
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I resort to this hybrid Grounding method as a exigency when the outlet-box is fastened to a wood or masony surface which impedes the use of the tap on "wall" side of the box.Compare looping the Ground-wire under the head of a 10/32" machine-screw with looping the wire under two 1-1/4" diameter washers.
 
  #14  
Old 03-05-03, 02:29 PM
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I always mark the ground tap location and drill a hole behind the box before mounting, especially on masonry surfaces where I have a drill and masonry bit out already. On wood surfaces where if I'm using a drill it usually has a driver bit instead of a twist bit, I usually align the box (if on a 2-by) so the ground tap is not over the wood. If mounting to a flat wood service, I mount the box with two tapping screws and then drive a third one about half way into the ground tap hole. I remove the screw, and then the ground screw will seat without a problem.
 
  #15  
Old 03-06-03, 11:50 AM
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Posted by sparksone42:

"2. This method of grounding also nullifies the UL listing of the box. Again, those that do this for a living should well know that all of the equipment that we install must be UL listed and labeled and installed according to those listings. This is mandated by the NEC."

A good example of the above, which I passed by many inspectors before being turned down:

Many panelboxes have a neutral bar on each side of the panel which are connected to each other with a rigid metal strap. When using the box as a main panel, a bonding screw connects one of the bars to the metal can. To use the box as a subpanel, a seperate ground bar must be installed to the metal can and the bonding screw is not used so that the ground and neutral will remain seperated all the way back to the service main. Instead of buying the 10 dollar ground bar, I would install the bonding screw AND remove the metal strap, thereby creating a seperate neutral and ground bar. I tried to run this installation by the wrong inspector as he turned it down because I was not using the box according to the UL listing. In my mind, it was a safe and sound installation, but did not meet the code requirements (installed according to 3rd party listing specifications).
 
  #16  
Old 03-06-03, 01:57 PM
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Buy a green grounding screw/w a 6" length of green insulated wire (pigtail). There is supposed to be a hole in the metal box strictly for connecting the grounding screw to the box.
 
  #17  
Old 03-06-03, 02:25 PM
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10-32 worked like a charm.

JB is now grounded and I made the connections to the breakers last night. Only took 10 minutes and I didn't electrocute myself.

Next step is installing all the receps and switchs and hope all my circuits work out!

cheers
 
  #18  
Old 03-06-03, 09:03 PM
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mcjunk. I recently installed a subpanel, and the main panel was installed the way you stated. took the jumper from one netural to the next off and put the bonding screw in. House is only 6 months old, and in one of the toughest coounty in the state for inspections, so it had to pass. Often thought about doing that to save that 10 dollars. Glad I went ahead and installed the ground bar.
 
  #19  
Old 03-07-03, 07:04 AM
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jb, not quite sure I understand. Are you saying that the main panel (where the main service disconnect is located) has a seperate neutral and ground with the neutral not bonded to the grounding system itself? The "jumper" between the two neutral bars AND the bonding screw should all be in place at your main service disconnect. Once you leave there all neutrals and grounds should remain seperate which it sounds like you have done properly at the sub-panel you installed.

Apologize if I misunderstood your situation.
 
  #20  
Old 03-07-03, 02:23 PM
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this a main lug panel with the disconnect on the outside next to the meter, and yes they are bonded there. sorry to be confusing
 
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Old 01-18-13, 01:48 PM
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I am locking this thread and moving the new reply. See: http://www.doityourself.com/forum/el...ml#post2058570
 
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