receptacle with AC cable

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  #1  
Old 05-12-06, 10:26 AM
magicalpig
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receptacle with AC cable

I was attempting to rewire a reverse-polarized GFCI receptacle in my garage the other day. It was my first project, and a chance to see how well I understood all that I've been reading about in wiring books for the last few months. I came across something unexpected though.

The cable running to the metal box is armor clad (I don't know if it's technically BX, so let's just call it AC; it has just 2 conductors and no grounding wire). It appears to be properly clamped to the box at the entry hole. What struck me as weird was that the bottom tab on the GFCI was bent back to make contact with the green grounding screw on the GFCI. The tab I'm talking about is the metal plate that attaches the receptacle to the box.

I'm a little bit confused about what the intent was of the person who did this. Securing the receptacle to the box with screws grounds it, correct? But code also requires a pigtail from the receptacle's grounding screw to the box? This person (hopefully not a trained electrician) was too lazy to make the pigtail ?

An additional question: If it is the case that the pigtail is needed, but the box does not have any screw to attach to?,
what do I do? Is there some kind of clamp I put on the box?

Thanks all
 
  #2  
Old 05-12-06, 10:31 AM
R
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Metal boxes have a threaded hole in the back where a ground screw can be attached.
 
  #3  
Old 05-12-06, 10:44 AM
magicalpig
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Was I right that the tab was bent simply to avoid having to make this connection you speak of? Is that connection required? (I'll certainly do it, if only for the practice of stripping and securing wires)

Another thing that I'm trying to figure out right now regarding this same box, next to the GFCI is a light switch (it used to interrupt the neutral until I corrected it!) The screws that attach the switch to the box are insulated by a red bushing. What is that for? Does having that present prevent the switch from being groudned??
 
  #4  
Old 05-12-06, 10:48 AM
J
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The metal plate that holds the receptacles to the box is called a "yoke".

Screwing the yoke directly to the metal box is permitted to serve as ground. I still rin a ground wire from the receptical's ground screw to the box. If the screws that hold the yoke down are loose, you may not have a truly effective ground. Adding the ground wire is just a little added safety.

However, where I use romex (Type NM) most of the time, the ground wire is provided, and I take two 8" pieces of bare copper wire, wirenut them to the incoming ground, one goes on the metal box, the other to the receptacle's green screw. This is actually called a pigtail. A single wire from one point to another is not called a pigtail.

Your metal clad cable of course does not have a ground wire. The metal cladding is the ground. All you would need is a green or bare wire from the receptacle's green screw to a new screw you provide in the metal box.

There is ordinarily a small raised "bump" inside a metal box. It has a pre-tapped hole in it to be used for a ground screw, but many of them do not come with the screw. You need a self-tapping screw. And it has to be marked green. The NEC does not permit sheet metal screws for grounding and bonding.

Hope that helps.

~ Juice
 
  #5  
Old 05-12-06, 10:52 AM
J
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I think the guy who bent that tab back was just lazy.

The red bushing is just there to hold the screw in place so it doesn't fall on the floor when installing or removing the receptacle for servicing. It does not isolate the yoke from grounding to the box, because the head of the screw makes contact with the yoke, and when the screw is threaded into the box that completes the ground.
 
  #6  
Old 05-12-06, 11:59 AM
magicalpig
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Originally Posted by JuiceHead
It does not isolate the yoke from grounding to the box, because the head of the screw makes contact with the yoke, and when the screw is threaded into the box that completes the ground.
OH yes, of course.
*magicalpig slaps his head*
 
 

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