Grounding Question

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  #1  
Old 09-29-18, 12:32 PM
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Grounding Question

If I'm installing a GFCI type receptacle in a metal box using NM Cable do I need to attach a separate ground wire from the receptacle to the metal box? Or is the NM cable's bare wire attaching to the receptacles green screw adequate, considering the receptacle itself contacts the metal box? I've come across conflicting information.
Is there any downside to attaching a separate ground wire to the metal box?

If I should connect a separate ground wire to the metal box via a green screw can I connect it to the same green screw of the receptacle as the NM bare wire gets connected to (share the same screw) or should I use a pigtail connecting a separate wire from the box to the separate wire from the NM cable to a separate bare wire connected to the grounding screw of the receptacle?

The pigtail set up seems to just to add more wires/box fill to the situation.

Thanks
 
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  #2  
Old 09-29-18, 04:41 PM
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You have to run ground wire to metal junction box. If your ground wire is long enough, all you need to do is loop it around ground screw in the junction box and attach end of the wire to the receptacle.
If it is not long enough you can run pigtail and join ground wires with wire nut or twist and crimp.

If your receptacle is self grounding type (it has brass clip on mounting screw hole), then you don't have to run ground wire to the receptacle when installed on grounded metal junction box.

Is there any downside to attaching a separate ground wire to the metal box?
There is no downside and you have to attache it to meet the code.
 
  #3  
Old 09-29-18, 07:53 PM
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Thanks for the reply.

If you could please clarify - there is a brass clip on one of the mounting screw holes so based on what you wrote the receptacle is self grounding. So that obviates a need to run a ground wire from receptacle to a grounded metal junction box but how do I know if the metal box is grounded? Does the fact that the self grounded receptacle touches the metal box ground it? So in that scenario there should be no need for ANY grounding screw or ANY wire attached directly to the metal junction box? The NM Cable bare wire attached to the grounding screw of the self grounding receptacle should be adequate?
 
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Old 09-29-18, 08:17 PM
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how do I know if the metal box is grounded?
By checking if ground wire is attached to the junction box or metal conduit is used.

So in that scenario there should be no need for ANY grounding screw or ANY wire attached directly to the metal junction box?
The metal junction box needs to be grounded no matter what. Self grounding means the receptacle or switch will get grounded to the junction box. Not the other way around.


Receptacles or switches are not always fully tightened to the junction box due to variation in depth the junction box is installed.
Therefore, screw alone is does not always provide positive path to ground. Self grounding receptacles or switches has brass clip that clamps down on the screw and that makes sure it has positive path to ground.


The NM Cable bare wire attached to the grounding screw of the self grounding receptacle should be adequate?
No.

Metal junction boxes are always grounded regardless of presents of receptacle or switch. That is to prevent electric shock in case something gets loose or damaged inside junction box and bare hot wire touches metal junction box. Without ground wire attached to the junction box, someone touching the junction box can get electric shock. If it is grounded, it will trip the breaker instead.
 
  #5  
Old 09-30-18, 06:14 AM
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Thanks for all the answers. I will attach a wire and grounding screw to the metal box-receptacle
 
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