[amw311]

Hi everyone, I'm working on wiring my shed for electric service and the inspector came out and mentioned that I needed to not only wire a ground to my outlets/switches, but I also had to wire a ground back to each box.

I'm a little confused on why. Once the ground is attached to the device, and then screwed into the box, that's bonding the 2 together, correct? Why would it be necessary to have a second ground wired from the device back to the box?

I should also mention that I'm using MC cable. I'm not sure if that's the reason for the double ground?

Thanks for your time!

 

[Oso954]

With metallic boxes and cables that are not grounding, you should screw the ground wire to the box first, then extend the ground to the device. That way the box remains grounded even when the device is removed.

 

[amw311]

Thanks Oso.

 

[rjniles]

Or ground the box and use self grounding devices. Or use plastic boxes.

 

[Know A Little]

Or ground the box and use self grounding devices. Or use plastic boxes.

With MC Cable??????

 

[rjniles]

With MC Cable??????

Missed that.

 

[Speedy Petey]

Hi everyone, I'm working on wiring my shed for electric service and the inspector came out and mentioned that I needed to not only wire a ground to my outlets/switches, but I also had to wire a ground back to each box.

I'm a little confused on why. Once the ground is attached to the device, and then screwed into the box, that's bonding the 2 together, correct? Why would it be necessary to have a second ground wired from the device back to the box?

I should also mention that I'm using MC cable. I'm not sure if that's the reason for the double ground?

Thanks for your time!

Ask him to clarify since this makes absolutely NO sense. Also, if he tries to stick by this absurd demand ask him for a code reference.

 

[rjniles]

Ask him to clarify since this makes absolutely NO sense. Also, if he tries to stick by this absurd demand ask him for a code reference.

Jim,

With MC cable wouldn't you need to ground the box as the metal sheath is isolated from the green insulated ground?

 

[Jim Port]

I think the ground needs to go to the box and the device. I agree with the inspector. The sheath of Mc is not the ground.

 

[rjniles]

I think the ground needs to go to the box and the device. I agree with the inspector. The sheath of Mc is not the ground.

I agree, the box (and the device) needs to be connected to the ground conductor.

Jim, sorry I addressed my last comment to you and it was SP who I intended.

 

[Syberia]

If you're using self grounding devices, you ground to the box only and the devices ground themselves by way of attachment. If you're not using self-grounding devices, there will still be a "path" to ground by way of the yoke, and verifiable on a meter, but it does not count for NEC purposes.

 

[amw311]

Is there a way to tell if the device is self grounding?

 

[rjniles]

It will say so on the packaging.


I of the yoke screws will have the copper tab show in this picture.

 

[Oso954]

If you're not using self-grounding devices, there will still be a "path" to ground by way of the yoke, and verifiable on a meter, but it does not count for NEC purposes.

That's because you don't know whether the meter path is yoke to box, or yoke, mounting screw, box. It's the path thru the screw that code is trying to prevent.

There is an allowable exception. However, I think the best advice is; if in doubt, always connect the ground wire to the box and the device. They might mention it, but they can't criticize it.

 

[Speedy Petey]

I think the ground needs to go to the box and the device. I agree with the inspector. The sheath of Mc is not the ground.

I got the impression he is asking for a second ground wire.
I certainly agree that both the box and receptacle must be grounded with MC cable.

 

[Jim Port]

I thought he was just asking for the box to be bonded to the ground instead of only going to the device.

 

[Luke M]

250.148(b)

Grounding Continuity. The arrangement of grounding
connections shall be such that the disconnection or the
removal of a receptacle, luminaire, or other device fed from
the box does not interfere with or interrupt the grounding
continuity.

 

[Know A Little]

Missed that.

I assumed you did...But I had to jump on it:vs_wave:

 

[amw311]

Thanks everyone! And thanks Luke for the code reference.

How does a self grounding receptacle still meet that requirement if removed from the box?

 

[Oso954]

How does a self grounding receptacle still meet that requirement if removed from the box?

The requirement is that your metal box remains grounded when you pull the device. That's what started this thread in the first place.