Grounding Armored Cable In a Subpanel

[Ditch Doc]

Hi all,

I am currently wiring up my workshop. I have done a fair amount of electrical work in the past with Romex, but this is my first large project using armored cable.

I have the main panel on the outside of the building and this is feeding a 200 amp subpanel on the inside through a section of PVC conduit. I understand that typically I would need to separate the neutrals and grounds and remove the bonding screw in the subpanel. But in this case, I am using armored cable that does not have a green conductor, only the bonding wire, so there will not be a ground bus. If I remove the bonding screw from the subpanel, how is the ground maintained back to the main panel? Would I need to run a separate ground line and ground rods for the sub panel? Other people have suggested that I bond the two panels together with a ground wire, but this seems like it would be the same thing as leaving the bonding screw in place... or would it?

Just trying to do this the safely.


Thanks!
Doc

 

[pattenp]

Are you saying you used armored cable to feed the subpanel?

 

[Ditch Doc]

Are you saying you used armored cable to feed the subpanel?

I have 3/0 THHN running from the main panel to the subpanel, then armored cable going from the subpanel to the lights and receptacles.

 

[Norcal]

I have 3/0 THHN running from the main panel to the subpanel, then armored cable going from the subpanel to the lights and receptacles.

Is it armored cable, AC, or metal clad, MC, ? They are 2 different materials and what is sold at big box stores is usually MC. Do you have a grounding conductor between the main & subpanel, or just 3-wires?

 

[teamextreme]

I think you're confusing us by mixing discussions of armored cable (for branch circuits) and the feed to the subanel (in PVC). Yes, you absolutely need to run a ground wire to the subpanel from the main panel, as well as removing the bonding screw and adding ground rods.

 

[Ditch Doc]

Is it armored cable, AC, or metal clad, MC, ? They are 2 different materials and what is sold at big box stores is usually MC. Do you have a grounding conductor between the main & subpanel, or just 3-wires?

Steel armored cable (AC), 12/2. Two conductors and the bonding wire. I have not installed a grounding conductor between the panels, but that was one of the questions I had about how to do this. If I need to install a grounding conductor to bond the boxes together, would bare copper be appropriate?

I think you're confusing us by mixing discussions of armored cable (for branch circuits) and the feed to the subanel (in PVC). Yes, you absolutely need to run a ground wire to the subpanel from the main panel, as well as removing the bonding screw and adding ground rods.

Ok, so bond the boxes together with a conductor. I can do that. I am assuming that just having the ground rods for the main panel will be sufficient and I do not need to add a separate set of rods for the subpanel? If I understand correctly, adding a second set of ground rods while the boxes are bonded may result in a ground loop.

 

[pistolpete1313]

For the grounding for the sub panel, thhn based upon the sub panel breaker size

Sent from my Pixel using The Garage Journal mobile app

 

[grounded-b]

Ok, so bond the boxes together with a conductor. I can do that. I am assuming that just having the ground rods for the main panel will be sufficient and I do not need to add a separate set of rods for the subpanel? If I understand correctly, adding a second set of ground rods while the boxes are bonded may result in a ground loop.

Is the sub-panel in a detached building? If so, then you will need to run a separate grounding conductor, remove the neutral bond screw AND drive two ground rods. A ground loop will not be created. Also, a main disconnect is required in your sub-panel. These are all NEC required.

If it is not a separate building then ground rods and a main disconnect are NOT required. The grounding conductor and removal of neutral bond, still is required.

Steve

 

[pattenp]

I'm getting from you that the main panel and the subpanel are on/in the same building. What feeds the main panel on the outside of the workshop? Is it fed off a panel from a separate building? I'm not sure that your main panel on the workshop is not also a subpanel.

 

[Norcal]

The only only place that the neutral and grounding conductors are bonded together is at the main, after that they must be separate, it was allowed in the past to run 3-wire feeds to outbuildings but is no longer allowed.

 

[alfredeneuman]

Once you run the grounding (bonding) wire to the panel.....
To properly terminate the AC is easy.
Strip the armor, cut off the bond wire, put the insulating bushing into the remaining armor, and use an AC cable connector. The connector is listed for grounding.
That's it. You're done.

 

[wyliesdiesels]

Hi all,

I am currently wiring up my workshop. I have done a fair amount of electrical work in the past with Romex, but this is my first large project using armored cable.

I have the main panel on the outside of the building and this is feeding a 200 amp subpanel on the inside through a section of PVC conduit. I understand that typically I would need to separate the neutrals and grounds and remove the bonding screw in the subpanel. But in this case, I am using armored cable that does not have a green conductor, only the bonding wire, so there will not be a ground bus. If I remove the bonding screw from the subpanel, how is the ground maintained back to the main panel? Would I need to run a separate ground line and ground rods for the sub panel? Other people have suggested that I bond the two panels together with a ground wire, but this seems like it would be the same thing as leaving the bonding screw in place... or would it?

Just trying to do this the safely.


Thanks!
Doc

Youre creating a whole lot of confusion here by mixing up the discussion on your branch feeder and branch circuits.

Lets start with your branch feeder, then we can get to your branch circuits.

You obviously are a bit confused on grounding and bonding and dont know what youre doing.

You shouldve started by reading some of the posts on the electrical FAQ thread, specifically #3. This wouldve answered all your questions without needing to type one word.

https://www.garagejournal.com/forum/showthread.php?t=356460

So, you need a 4-wire feeder between your main panel and the subpanel. The bonding screw MUST be removed. This is important because with the bonding screw in place, you are creating potential for shock. The main service panel is the ONLY place that neutral and ground should be bonded. You already alluded to this but then confused the discussion when you brought up the armored cable. The branch circuit wiring has nothing to do with the bonding.

You also need to make sure you also have an equipment ground bar(one that is listed and labeled for your panel) bolted to the panel enclosure. Move all grounds currently on the neutral bar, over to this bar. Neutrals should NOT be terminated on this bar.

then you asked how the ground would be maintained back to the main panel. In answer to that, the EGC that you're missing would be doing that.

The AC cable would be bonded to ground via the panel enclosure.

Ok, so bond the boxes together with a conductor. I can do that. I am assuming that just having the ground rods for the main panel will be sufficient and I do not need to add a separate set of rods for the subpanel? If I understand correctly, adding a second set of ground rods while the boxes are bonded may result in a ground loop.

yes bond the boxes together.

The ground rods are for lightening suppression among other things. They are only needed on one panel in each structure.

Adding a second set of ground rods will not create a ground loop which has absolutely nothing to do with any of this. you could add as many rods as you want and it wouldnt create issues....

I think the issue here is you dont understand the difference between equipment grounding conductors and grounding electrodes. They are different animals and you dont want to confuse the two. On that note, I'm going to point you back to my electrical FAQ thread again and post #4, where i talk about the difference between the two:

https://www.garagejournal.com/forum/showthread.php?t=356460

 

[Ditch Doc]

Okay, the third inspector I talked to was able to give me a definitive answer. I'll post it here in case someone else runs into this. Obviously, this pertains to my local jurisdiction. Your mileage may vary.

Since there is no actual ground conductors in the circuits and everything is grounded through the armor back to the subpanel itself, I would need to bond the main panel and the subpanel together using a bare 4ga conductor. With this, I would not need to add additional ground rods. Just have to make sure the ones I install are at least 6ft apart.

Thank you all for your help and your patience... except wyliesdiesels... your response, sir, was simply condescending and arrogant. Other than that, it is nice to be involved in a community that is patient and supportive.

 

[mike93lx]

Thank you all for your help and your patience... except wyliesdiesels... your response, sir, was simply condescending and arrogant. Other than that, it is nice to be involved in a community that is patient and supportive.

You might be best to find a new forum if you thought that post wasn't helpful. That was years of experience spoonfed to someone that doesn't know what he is doing, for free

 

[teamextreme]

You still have not answered the question on building configuration and it's not clear what you have. You stated your "main" panel and "subpanel" are on opposite sides of the same wall (and therefore building). Is this the only building on the property, or is this a detached building fed from a house, etc?
If this is a detached building with both "main" (in which case you shouldn't use that term, as it confuses things due to being technically inaccurate) and "subpanel", then your inspector is WRONG and ground rods ARE required. There is no exception for not installing ground rods (or a ufer ground) at a detached building. Local codes can supplement NEC, but they can't detract from it.
Come to think of it, if it's the only building, then you actually still need ground rods since the main service would still need them as well.

 

[teamextreme]

You still have not answered the question on building configuration and it's not clear what you have. You stated your "main" panel and "subpanel" are on opposite sides of the same wall (and therefore building). Is this the only building on the property, or is this a detached building fed from a house, etc?
If this is a detached building with both "main" (in which case you shouldn't use that term, as it confuses things due to being technically inaccurate) and "subpanel", then your inspector is WRONG and ground rods ARE required. There is no exception for not installing ground rods (or a ufer ground) at a detached building. Local codes can supplement NEC, but they can't detract from it.
Come to think of it, if it's the only building, then you actually still need ground rods since the main service would still need them as well.

 

[AntonLargiader]

Ditchdoc,
You have it all wrong about Wylie. AFAICT you selected an inappropriate wire to work with (lacking a ground) and he was trying to walk you through that from the beginning. You're probably better off working with someone in person, as you are probably doing with your third inspector.

 

[wyliesdiesels]

Some days i wonder why i even bother.

I can see that his inspector gave him all the right info(sarcasm)

Wonder why he even came on here if he’s not open to listening...

 

[Showkey]

Some times it’s in the delivery and the true hurts. Not everyone in the electrical gets a trophy.

Some don’t like to be called a stupid f*ck or “they are confused or don’t know what their doing”.

 

[alfredeneuman]

Ditchdoc,
AFAICT you selected an inappropriate wire to work with

It's not an inappropriate wire to work with. The bond strip has intimate contact with the armor and it just needs to be terminated properly.

The title was misleading though, he talked about neutral bonding screws and everything under the sun before he finally got around to asking about terminating the AC cable.

 

[Dh3256]

It's not an inappropriate wire to work with. The bond strip has intimate contact with the armor and it just needs to be terminated properly.

Using the armor as the EGC for AC cable is not recommended, it is not a reliable connection.

 

[alfredeneuman]

Using the armor as the EGC for AC cable is not recommended, it is not a reliable connection.

Where did hear that?

2017 NEC 320.108 Equipment Grounding Conductor. Type AC cable shall provide an adequate path for fault current as required by 250.4(A)(5) or (B)(4) to act as an equipment grounding
conductor.

 

[Dh3256]

2017 NEC 320.108 Equipment Grounding Conductor. Type AC cable shall provide an adequate path for fault current as required by 250.4(A)(5) or (B)(4) to act as an equipment grounding
conductor.

I did not say it was not to code, I said it is not a reliable connection.

It's now common knowledge in the industry - but was not when we first confirmed it through extensive testing when we were developing the AFCI. In the process of that development we learned a lot about residential wiring that was previously not known.

 

[AntonLargiader]

It's not an inappropriate wire to work with. The bond strip has intimate contact with the armor and it just needs to be terminated properly.....

I was remembering his first post where he made it sound like he was using this to feed the subpanel. But even in other places, I don't see why one wouldn't select a cable with a real ground in it if possible. Yes the armor counts as a ground, same as EMT does, but as you say it relies on the termination and I've sure seen lots of gapped EMT when it gets hit by forklifts or whatever.

 

[alfredeneuman]

I was remembering his first post where he made it sound like he was using this to feed the subpanel. But even in other places, ...... same as EMT does, but as you say it relies on the termination and I've sure seen lots of gapped EMT when it gets hit by forklifts or whatever.

If he had used it for a feeder then the termination would be the same as it is for a branch circuit.
AC cable has the same rules for protection from physical damage as NM cable, so I doubt you seen it damaged by any forklifts or whatever.

 

[alfredeneuman]

It's now common knowledge in the industry

What industry is that? I was a commercial electrician for 45+ years, and never heard that.
If you want to use rigid conduit for everything, that's OK too. It's just unnecessary.
(EDIT) Could it be you're thinking about BX, which didn't have the grounding strip?

 

[Dh3256]

What industry is that? I was a commercial electrician for 45+ years, and never heard that.

The "industry" I referenced is commercial and residential wiring. I'm really surprised you would be using AC without a separate ground wire commercially, that would not be approved in most placed in the East.


Next issue of NEC is supposed to clarify this issue.

 

[alfredeneuman]

If a separate ground wire was involved, it would be MC not AC.

Let's see if it's changed at all in the NEC 2020

 

[alfredeneuman]

The toughest Code in the US is the Chicago Electrical Code.
Even they allow it in certain circumstances.

(A) Existing Installations. Except where otherwise specified in this Code and where not subject to physical damage, listed Type AC cable with listed fittings and not exceeding 7.62 m (25 ft) in length between junction boxes shall be permitted to be installed for branch circuits in concealed work fished into existing walls, partitions, floors, or hard surface ceilings where other work does not require or include removal of the existing finished surface.

 

[Dh3256]

Except where otherwise specified in this Code and where not subject to physical damage

That's the key phrase....

 

[acer66]

Some days i wonder why i even bother.

Please do not give up, your input is highly valued.

 

[dogdog]

Some days i wonder why i even bother.

I can see that his inspector gave him all the right info(sarcasm)

Wonder why he even came on here if he’s not open to listening...

Because you are not saying what they wanted to hear.... No matter how right your answer is, if you didn't coated with candy and topped with flowers, you are one big bad meanie on the "Internet"....

 

[alfredeneuman]

That's the key phrase....

Elsewhere in the Chicago Code they permit physical damage, in length less than 6' (EDIT 6' or less) where flexibility is necessary. The NEC doesn't make that exception.

The NEC "protection from physical damage" rule is the same for NM, AC, and MC cables, Flexible Metal Conduit, and Liquidtight Flex.