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#76212 - 01/01/01 10:18 AM Grounding wire for sub panel
gto6t7 Offline
Member

Registered: 12/16/00
Posts: 30
Loc: Machias, ME
I have a customer that has a 200A main panel and he has a 100A sub going to his attached barn. The cable going to the barn is a #2 SE cable three wire, copper. I told him since the barn is not seperate from the house the feeder should be 4 wire. He agrees to this and understands the sub needs to have the neutral buss isolated and a ground buss installed. His question to me was, can a single conductor be run along side the SE cable to provide the ground. I have not been able to find any information that clearly shows this can not be done. After two days of searching through the Code I am at a loss to find something to show the customer why the SE cable should be replaced instead of his proposed solution. Your comments are welcome.

Thanks
Dave T.



[This message has been edited by gto6t7 (edited 01-01-2001).]

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#76213 - 01/01/01 05:49 PM Re: Grounding wire for sub panel
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
I'm always finding sub-panels like that myself. The key word you have me caught up on is "attached".I can't see an out in 250-24......I've seen installations such as you suggest, the grounding conductor tie wrapped along the se cable, then the SE bare conductor isolated with tape. I'd like to read a code justification too....

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#76214 - 01/02/01 09:38 AM Re: Grounding wire for sub panel
Tom Offline
Member

Registered: 01/01/01
Posts: 1069
Loc: Shinnston, WV USA
Article 300 can be considered the "MIscellaneous" section of the NEC. If I know it's in the code & can't find it, I turn to Article 300.

In this instance, take a look at 300-3(b) which applies to the equipment ground being inside the cable. None of the sections cited in 300-3(b)(2) apply to this installation.

[This message has been edited by Tom (edited 01-02-2001).]
_________________________
Few things are harder to put up with than the annoyance of a good example.

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#76215 - 01/02/01 03:09 PM Re: Grounding wire for sub panel
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
Thanks Tom;
So if this were a "branch circuit" or "nongrounding receptacle" the grounding conductor could be run outside of the cable or raceway.

Or if this was a detached barn, one could use the existing SEU, create a grounding electrode & conductor and bond it all together.....


So Dave, I guess you gotta either have just a branch circuit, or saw off the barn...

I do see a lot of this, and have heard inspectors use the term "existing" , usually depending on the amount of changes happening.

It's too bad there can't be a compromise as you've pointed out in Art 250 for larger scenario's....maybe a GFPE ??? or change that "attached" word....

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#76216 - 01/03/01 12:15 AM Re: Grounding wire for sub panel
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
First off, if the cable is not installed in a raceway, and is direct burial, then you could not just add an equipment grounding conductor and bury it. The conductor would, of course, need to be rated for direct burial. If it is not underground or direct burial and not in a raceway, this would not comply to the requirements for cables in the NEC [I do not recall the article, but it's been a subject here and there in several forums over the past year, plus as I remember, it allows for only branch circuits that are being "upgraded" which have existing 2 wire non-metallic sheathed cable to have the eq. grounding conductor run externally].

However, if you have the cable running through conduit that is continuous from the main service panel to the sub panel, you could run an equipment grounding conductor through that conduit with the cable, provided you have ample room .
It's kind of a revolving situation to clarify it in the NEC, but as long as they all occupy the same RACEWAY, it should be compliant.


** Don, Bennie and Rick: - let me know how you guys would feel on this interpretation!!


To me, it seems that it would have been less expensive to use #2 THHN / THWN cu, than to install the SE cable, however I am biased by the fact that I rarely touch Romex or any non-metallic sheathed cable - so I am not sure if there is a cost difference or not.

Anyhow, try to stay away from using the methods described in 250-24 [deriving a new grounding electrode system and bonding the grounded conductor to it in remote buildings from a common AC service], as it should only be done for certain circumstances. I know that this statement will generate lots of flames, but it should not be done in liew of running an equipment grounding conductor.

If there is any metallic conduits or other types of piping that interconnects the two buildings, along with any concrete that contains REBAR that interconnects the two buildings, you may not use 250-24.
Personally, I would only use this method on very remote buildings, like 1,000 feet away remote! That is where this method becomes an advantage.

So to sum it up, install a ground bond if you used conduit as described above. Otherwise, replace the cable with one that has an insulated grounding conductor [4 wire]. You could [more like should ] consult the Building Department / Electrical Inspector for that city/county and find out what they have to say about the whole thing.
Do stay away from direct burial of a single conductor for a ground bond. This is a very critical conductor! more critical than the grounding electrode system! You can have major hazards [no relation to Toy Story ] if the bond is insufficiently continuous and there is a ground fault off the sub panel.

If the cable is not run underground, maybe the AHJ will allow you to just simply add an equipment grounding conductor - attached to the cable's exterior - instead of replacing the entire cable. This would be the first logical step to take after getting suggestions from this forum, plus be the final determination for the installation. I have a hard time answering code related questions like this one, in which the installation's compliance is an issue rather than the installation it's self. This is when the Inspectors are called into the picture!

It would sure make things like this easier if the person at the Home Improvement Centers would explain to the customer when not to use a 3 wire cable, but that makes too much sense I guess .

I am not sure if the owner purchased this cable themselves or if the cable was something convenient.

There seems to be an ever increasing number of questions relating to this type of installation - mostly an underground, or direct burial sub feed - where the person wants to use 3 wire cable. I usually do not reply to these threads, in hopes that another member can better tackle the question, but your's got my interest. Also I want to see what the Inspectors in the group have to say about the situation and apply it to future postings.

Comments are welcome [AKA - let the flames begin ].


Hope this was helpful.

Scott. "S.E.T."
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#76217 - 01/03/01 04:59 AM Re: Grounding wire for sub panel
Bill Addiss Offline
Member

Registered: 10/07/00
Posts: 4196
Loc: NY, USA
Scott,

No Flames here, I'm on the Fence watching this one. I know the one side has to do with convenience at this point and want to see how that balances with safety factors. This scenario would produce a Covered neutral not an Insulated one - unless the new wire was used as the Neutral and that would violate something else, right?

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#76218 - 01/03/01 05:27 AM Re: Grounding wire for sub panel
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Scott,
I don't think the word "not" belongs in the second sentence of your post, other than that I think you are right on with the answers. As far as the cost goes, I think that conduit and wire would be about 15 to 20% more than the SE cable.
If I was the inspector (given that this ins an existing installation and there is no way to force the owner to bring it into compliance with the code) I would allow the installation of a forth conductor run with the SE cable, as long as it is not in an area subjected to physical damage. Even though this is a code violation, it would be better than what is there now.
Don(resqcapt19)
_________________________
Don(resqcapt19)

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#76219 - 01/03/01 08:37 AM Re: Grounding wire for sub panel
gto6t7 Offline
Member

Registered: 12/16/00
Posts: 30
Loc: Machias, ME
I have decided to run a ground wire along side the SE cable. As Don said there is no way to force the customer to change to a 4 wire cable. The Code gets close to this situation when it states it is permitted to run the equipment bonding jumper outside of the raceway for up to 6 feet per Article 250-102(e) but this situation is not a bonding jumper. Article 250-24((a)(5) shows the sub panel, as wired, to not be in compliance. Article 250-142(b) is of no help because of the building being attached. So leaving the sub panel as it is would be further from compliance than running the single conductor along side the SE cable.


Thanks for the comments.
Dave T.



[This message has been edited by gto6t7 (edited 01-03-2001).]

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