How to attach the green ground screw?

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  #1  
Old 07-10-14, 08:00 PM
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How to attach the green ground screw?

This old house is all EMT and metal boxes but most of the receptacles are not grounded.

In this case this box has no hole for the ground screw. What is the best way to attach the ground screw? Drill my own hole (which seems to take forever), use clips?

 
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Old 07-10-14, 08:06 PM
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Those are mud boxes set in cement. Tough to drill the metal/cement combo. Tough to get clips on unless you chisel a little of the cement.

Looks like that box has room to drill but most are probably not like that.
 
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Old 07-10-14, 08:14 PM
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Is it OK to use a smaller sheet metal screw and screw into the "slot" in the middle of that knock out hole?
 
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Old 07-10-14, 08:33 PM
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Is it OK to use a smaller sheet metal screw and screw into the "slot" in the middle of that knock out hole?
No, you cannot use a sheet metal screw for grounding.
 
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Old 07-10-14, 08:36 PM
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OK care to explain why a sheet metal screw is no good? I thought it's just a matter of connecting metal to metal?

Does it have to do with the coarse-ness of the threads? A machine screw would be good but sheet metal screw is bad? Or more to do with sheet metal screws are more tapered?
 
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Old 07-10-14, 08:40 PM
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The code requires at least 2 threads in contact with the box. Sheet metal screws will not meet this requirement. There are drill and tap bits made in one piece that will work if there is room behind the box.
 
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Old 07-10-14, 08:43 PM
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The NEC requires a machine thread. My best guess is a sheet metal screw can easily be stripped and doesn't provide sufficient contact with the metal box.
 
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Old 07-10-14, 08:59 PM
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You need a set of these:
SAE Drill/Tap/Deburr Bit Set

They work very well to drill and tap in one operation. Use the 10-32 drill/tap.
Other companies make, them but these are the best deal I have found.
 
  #9  
Old 07-10-14, 09:10 PM
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Why not just use spec grade receptacles? No green screw needed as EMT and metal boxes.
 
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Old 07-10-14, 09:15 PM
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Couldn't he use a grounding bushing?

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  #11  
Old 07-10-14, 09:21 PM
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Good idea Ray but the receptacle may hit it.
 
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Old 07-11-14, 04:51 AM
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No need for taps, sheet metal screws or grounding bushings. Your raceway is your EGC. Use a self grounding outlet and your done.

Not in this case, but in a pinch you could also consider a grounding clip if you had space to slide it onto the box.

Don't let that tap get lost though, even though you have a metallic raceway, there are times when you might need to add a bonding jumper to the box.
 
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Old 07-11-14, 06:31 PM
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Self grounding device...Duh!
 
  #14  
Old 07-12-14, 09:13 PM
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I went to a local Harbor Freight and bought the bit set Tolyn Ironhand recommended. Worked great! Thanks!
 
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Old 07-13-14, 07:50 AM
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Glad to hear it worked out for you.
 
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