# how to groud mc in a plastic box



## StokesWorks (Dec 24, 2018)

Ok, I'm looking for a way to ground mc cable sheathing in a plastic box. Code allows metal conduit to enter a plastic box, however the crux of the matter is grounding the metal sheathing as there is no way. Is there any 1/2 grounding bushings that anyone knows about that would work for this purpose? I would like to cut in a plastic box with a metal faceplate with knock out, and 90 degree connector to give the MC cable a clean, flush finish. I guess maybe the solution is to give up on the plastic box and cut in a metal box. Can anyone think of a good way to junction 1/2" mc cable in a plastic box and connect it to a ground? Thanks in advance. Cheers!


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## HackWork (Oct 2, 2009)

https://www.homedepot.com/p/1-2-in-Rigid-Insulated-Metallic-Grounding-Bushing-2-Pack-29521/100164273


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## telsa (May 22, 2015)

Generally, it's not cost effective to fuss with MC into PVC.

Just stay with a nice deep, metallic cut-in box.


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## HackWork (Oct 2, 2009)

telsa said:


> Generally, it's not cost effective to fuss with MC into PVC.
> 
> Just stay with a nice deep, metallic cut-in box.


Metal cut-in boxes are too small for the hole cut out for a plastic box. Plus it’s a lot more work to switch boxes.


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## A Little Short (Nov 11, 2010)

HackWork said:


> Metal cut-in boxes are too small for the hole cut out for a plastic box. Plus it’s a lot more work to switch boxes.



Doesn't sound/read like OP has cut the hole yet.


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## Dennis Alwon (May 9, 2009)

Where does the mc originate? If it originates from a grounded enclosure it is grounded. however, 314.3 requires this...



> 314.3 Nonmetallic Boxes. Nonmetallic boxes shall be permitted
> only with open wiring on insulators, concealed knob-and tube
> wiring, cabled wiring methods with entirely nonmetallic
> sheaths, flexible cords, and nonmetallic raceways.
> ...


You can drill a hole and use an mc connector then use a bonding bushing


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## HackWork (Oct 2, 2009)

A Little Short said:


> Doesn't sound/read like OP has cut the hole yet.


I was taking it as he has an existing plastic box. But you are probably right in that he is cutting it in new.

If he is cutting it in new, why even consider plastic? I use plastic any time that I can, but in this situation metal wins.


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## MTW (Aug 28, 2013)




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## manchestersparky (Mar 25, 2007)

HackWork said:


> https://www.homedepot.com/p/1-2-in-Rigid-Insulated-Metallic-Grounding-Bushing-2-Pack-29521/100164273





Dennis Alwon said:


> Where does the mc originate? If it originates from a grounded enclosure it is grounded. however, 314.3 requires this...
> 
> 
> 
> You can drill a hole and use an mc connector then use a bonding bushing


Good luck getting a bond bushing on an MC connector . Keep in mind the MC connector is listed to be used with a locknut, so not using the locknut and just using the metal bond bushing is technically incorrect...……...


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## Dennis Alwon (May 9, 2009)

manchestersparky said:


> Good luck getting a bond bushing on an MC connector . Keep in mind the MC connector is listed to be used with a locknut, so not using the locknut and just using the metal bond bushing is technically incorrect...……...


IMO The locknuts has no function as it is a plastic box. The bushing is more than adequate to hold the connector and bond it. I believe a metal bushing is adequate instead of a locknut and this section to support that thought in a backwards way.



300.4 (G) said:


> Conduit bushings constructed wholly of insulating material
> shall not be used to secure a fitting or raceway.


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## macmikeman (Jan 23, 2007)

There is a bunch of Carlon boxes that have this printed on them, I've seen it before. "Non Metallic Cable's Only".


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## Bird dog (Oct 27, 2015)

manchestersparky said:


> Good luck getting a bond bushing on an MC connector . Keep in mind the MC connector is listed to be used with a locknut, so not using the locknut and just using the metal bond bushing is technically incorrect...……...


Do they make grounding locknuts in 1/2"?


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## MechanicalDVR (Dec 29, 2007)

Dennis Alwon said:


> IMO The locknuts has no function as it is a plastic box. The bushing is more than adequate to hold the connector and bond it. I believe a metal bushing is adequate instead of a locknut and this section to support that thought in a backwards way.


Just to clarify, it seems to me what the OP was looking to do was atttach the mc to a metal cover plate and ground the mc jacket, not try and enter the box with an mc connector.


"plastic box with a metal faceplate with knock out, and 90 degree connector to give the MC cable a clean, flush finish"


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## HackWork (Oct 2, 2009)

manchestersparky said:


> Good luck getting a bond bushing on an MC connector . Keep in mind the MC connector is listed to be used with a locknut, so not using the locknut and just using the metal bond bushing is technically incorrect...……...


Why not use the locknut and bonding bushing?


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## frenchelectrican (Mar 15, 2007)

Bird dog said:


> Do they make grounding locknuts in 1/2"?


Yuh but not super common afaik .,, but yes you can order it.


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## telsa (May 22, 2015)

*Thomas & Betts 3650 1/2" Grounding Wedge*

Also consider a grounding wedge. 

For the cheap-skates in our trade.:smile:

Fair warning: most dudes have never seen them, particularly counter monkeys.


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## Bird dog (Oct 27, 2015)

telsa said:


> *Thomas & Betts 3650 1/2" Grounding Wedge*
> 
> Also consider a grounding wedge.
> 
> ...


 Walmart online has it...
https://www.walmart.com/ip/Thomas-B...MI45iV4by83wIVRLXACh17bgfHEAYYAiABEgLna_D_BwE


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## HackWork (Oct 2, 2009)

Maybe I am missing something.

Why not just use the bonding bushing that I linked to in the first reply? Less than $5 for 2 of them.

Whatever that is that telsa posted costs a lot more than that.


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## MTW (Aug 28, 2013)

HackWork said:


> Maybe I am missing something.
> 
> Why not just use the bonding bushing that I linked to in the first reply? Less than $5 for 2 of them.
> 
> Whatever that is that telsa posted costs a lot more than that.


Not to mention readily available at HD if needed in a pinch. I doubt a grounding wedge is readily available particularly since telsa rightly pointed out that counter monkeys don't even know what they are.


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## jelhill (Nov 11, 2018)

I probably could count on one hand or less the number of time I ran MC into a plastic box. Even though it is legal when you bond correctly... it still seems weird. Oh well, that’s what you get with old school guys.


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## HackWork (Oct 2, 2009)

MTW said:


> Not to mention readily available at HD if needed in a pinch. I doubt a grounding wedge is readily available particularly since telsa rightly pointed out that counter monkeys don't even know what they are.


Or, even easier, if he is installing the box himself why not just install a metal box and be done with it?


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## CTshockhazard (Aug 28, 2009)

*Don't ask how I know...*

Always keep the grounding wedge in the back of your mind, the extra cost can be well worth not having to disconnect and reterminate. :wink:


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## splatz (May 23, 2015)

CTshockhazard said:


> Always keep the grounding wedge in the back of your mind, the extra cost can be well worth not having to disconnect and reterminate. :wink:


Good point, and it's probably a good thing to order a couple in common sizes and keep them around, rather than know about them but not be able to get them when you need them.


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## MechanicalDVR (Dec 29, 2007)

Bird dog said:


> Walmart online has it...
> https://www.walmart.com/ip/Thomas-B...MI45iV4by83wIVRLXACh17bgfHEAYYAiABEgLna_D_BwE


That seems expensive for Walmart!


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## MechanicalDVR (Dec 29, 2007)

MTW said:


> Not to mention readily available at HD if needed in a pinch. I doubt a grounding wedge is readily available particularly since telsa rightly pointed out that counter monkeys don't even know what they are.


Forget counter monkeys, have you ever come across one in the field?


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## MTW (Aug 28, 2013)

HackWork said:


> Or, even easier, if he is installing the box himself why not just install a metal box and be done with it?


Yeah, MC cable and metal boxes always go together. I can't ever remember a need to install MC in a plastic box, ever. :no:


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## MechanicalDVR (Dec 29, 2007)

MTW said:


> Yeah, MC cable and metal boxes always go together. I can't ever remember a need to install MC in a plastic box, ever. :no:


I'm not a plastic box fan in general so adding mc or conduit to one is not in my wheelhouse as a good practice.


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## HackWork (Oct 2, 2009)

MechanicalDVR said:


> I'm not a plastic box fan in general so adding mc or conduit to one is not in my wheelhouse as a good practice.


I could see if he had an existing plastic box somewhere and he needed to bring an MC whip out of it, such as hardwiring a garbage disposal.

But if you’re installing the box yourself, there’s no reason not to use metal. And that’s coming from me who never uses metal by choice.


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## MechanicalDVR (Dec 29, 2007)

HackWork said:


> *I could see if he had an existing plastic box somewhere and he needed to bring an MC whip out of it*, such as hardwiring a garbage disposal.
> 
> But if you’re installing the box yourself, there’s no reason not to use metal. And that’s coming from me who never uses metal by choice.


What you first mention is what he is looking to do, not sure what he's looking to feed with the MC.


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## Bird dog (Oct 27, 2015)

MechanicalDVR said:


> That seems expensive for Walmart!


It's another company on Walmart.com.


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## Going_Commando (Oct 1, 2011)

It's going to be easier just cutting in a metal box, throw some madison straps on it, amd going from there. Or going into the back of a shallow 4 square. What's this for, anyway? A water heater or something? I used to fight with connectors going into blank plates, but said to hell with it and just surface mount boxes now. If anything its cheaper than cutting in a metal box and easier to install.


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## HackWork (Oct 2, 2009)

Going_Commando said:


> It's going to be easier just cutting in a metal box, throw some madison straps on it, amd going from there. Or going into the back of a shallow 4 square. What's this for, anyway? A water heater or something? I used to fight with connectors going into blank plates, but said to hell with it and just surface mount boxes now. If anything its cheaper than cutting in a metal box and easier to install.


They make 1900 boxes with a one gang cut out on the back of them. They are excellent for what you mentioned. I use them all the time now.


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## MechanicalDVR (Dec 29, 2007)

Bird dog said:


> It's another company on Walmart.com.


I didn't notice that.

I've had great luck a couple times with Walmart's site getting 250' rolls of 12/2 and 14/3 for like half price of HDepot when they were being clearanced out.

I used to watch their site often for good buys.


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## MTW (Aug 28, 2013)

HackWork said:


> They make 1900 boxes with a one gang cut out on the back of them. They are excellent for what you mentioned. I use them all the time now.


$3.75 at the local supplier here, I keep a few on the truck. I don't use them that often but when I do they are a lifesaver.


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## Bird dog (Oct 27, 2015)

MechanicalDVR said:


> I didn't notice that.
> 
> I've had great luck a couple times with Walmart's site getting 250' rolls of 12/2 and 14/3 for like half price of HDepot when they were being clearanced out.
> 
> I used to watch their site often for good buys.


Good idea for romex because sometimes it's a loss leader. People will call around for the cheapest romex, so, cut the romex price & possibly bring more business in the door.


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## MechanicalDVR (Dec 29, 2007)

Bird dog said:


> Good idea for romex because sometimes it's a loss leader. People will call around for the cheapest romex, so, cut the romex price & possibly bring more business in the door.


Once I paid like $21 for 250' rolls of 12/2, I got all they had left at the time.


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## telsa (May 22, 2015)

HackWork said:


> They make 1900 boxes with a one gang cut out on the back of them. They are excellent for what you mentioned. I use them all the time now.


Known as an Extension Ring. (versus Box Extension)

While the term of art seems odd, do keep in mind that it mounts directly to a mud ring -- not a junction box. So, it's the ring that's being extended.

One should expect that these terms are conflated by apprentices and journeyman, alike... that is, they've got both terms reversed.


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## HackWork (Oct 2, 2009)

telsa said:


> Known as an Extension Ring. (versus Box Extension)
> 
> While the term of art seems odd, do keep in mind that it mounts directly to a mud ring -- not a junction box. So, it's the ring that's being extended.
> 
> One should expect that these terms are conflated by apprentices and journeyman, alike... that is, they've got both terms reversed.


I don't know what you are saying, but I do know that they aren't only mounted to mud rings. They are mounted to any single gang box.


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## B-Nabs (Jun 4, 2014)

telsa said:


> Known as an Extension Ring. (versus Box Extension)
> 
> While the term of art seems odd, do keep in mind that it mounts directly to a mud ring -- not a junction box. So, it's the ring that's being extended.
> 
> One should expect that these terms are conflated by apprentices and journeyman, alike... that is, they've got both terms reversed.


Nonsense. A similar box that mounts straight to a 4x4 is also called an extension ring. 

Sent from my SM-G920W8 using Tapatalk


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## CTshockhazard (Aug 28, 2009)

HackWork said:


> They make 1900 boxes with a one gang cut out on the back of them. They are excellent for what you mentioned. I use them all the time now.



Looks like you can maybe spin it 90 for 2g, will those holes hit?


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## CTshockhazard (Aug 28, 2009)

MechanicalDVR said:


> Once I paid like $21 for 250' rolls of 12/2, I got all they had left at the time.



Damn dude, I knew you were old but :devil3:


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## MTW (Aug 28, 2013)

MechanicalDVR said:


> Once I paid like $21 for 250' rolls of 12/2, I got all they had left at the time.


I remember when a coil of 14/2 was $15 and 12/2 was $21 at the Depot. Those were the days.


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## HackWork (Oct 2, 2009)

CTshockhazard said:


> Looks like you can maybe spin it 90 for 2g, will those holes hit?


Wow, you may be right, I never even thought of that. Both the Raco and Steel City have those same holes so maybe they do line up. I will check it out next time I am playing in the boxes bin.


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## MechanicalDVR (Dec 29, 2007)

CTshockhazard said:


> Damn dude, I knew you were old but :devil3:


LOL!

Wiseguy!


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## MechanicalDVR (Dec 29, 2007)

MTW said:


> I remember when a coil of 14/2 was $15 and 12/2 was $21 at the Depot. Those were the days.


Me too but this wasn't all that long ago. New old stock with white jacket.


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## telsa (May 22, 2015)

B-Nabs said:


> Nonsense. A similar box that mounts straight to a 4x4 is also called an extension ring.
> 
> Sent from my SM-G920W8 using Tapatalk


Here you've proved my point.

BTW, the terms, as I use them, come straight from the manufacturer's packaging.

&&&&&&&

As for Hax... he skipped past the fact that they DON'T mount to 4 square boxes.

They mate to 1gang mud-rings that are mounted to 4-squares...

That's how they got their name.

They also, obviously, will mount to 1gang old-work (GEM) boxes and handiboxes.

Folks, I didn't come up with the names.

The fact that they are crossed over ALL THE TIME is what I pointed out.

Next time, buy a full case. Then check the label. :biggrin::biggrin::biggrin::biggrin::biggrin:

I'd say that 80% of the time, they are crossed over. 

The box extension looks so 'ring like.'

While ring extensions certainly can be mounted to handiboxes -- you don't see a lot of that. Such a thing would look so weird, too.


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## HackWork (Oct 2, 2009)

Telsa, you are the only person who brought up mounting them to 1900 boxes. Everyone else is talking about mounting them to single gang boxes, and not mud rings like you keep saying.


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## MTW (Aug 28, 2013)

HackWork said:


> Telsa, you are the only person who brought up mounting them to 1900 boxes. Everyone else is talking about mounting them to single gang boxes, and not mud rings like you keep saying.


Hi Hacky. :vs_wave:


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## Gnome (Dec 25, 2013)

Bird dog said:


> Do they make grounding locknuts in 1/2"?


Yep. I end up with quite a few extra because they come with 3m heat trace termination kits but you don't need to use it when terminating in a metal box. Handy things to have around.


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## Gnome (Dec 25, 2013)

telsa said:


> *Thomas & Betts 3650 1/2" Grounding Wedge*
> 
> Also consider a grounding wedge.
> 
> ...


Most electricians haven't seen them because they are like C$8+ a piece. Only time I use them is fixing TECK cable coming into PVC where redoing the Terminations/Splices is going to take longer/cost more than the cost of the wedge.


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## awjelectric_co (Dec 16, 2018)

HackWork said:


> Metal cut-in boxes are too small for the hole cut out for a plastic box. Plus it’s a lot more work to switch boxes.


dont want to pull that maneuver on someones kitchen island


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