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#206584 - 07/19/12 05:24 AM Grounding metal building
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: NC
I have a 200 amp service install on a metal barn. After installing the service panel/meter and driving the 2 ground rods, will I need to run a #4 ground to the frame of the metal barn? The panel/meter will be attached to the barn. Just a quick question, I haven't had time to verify it with Code yet. Thanks for the input, Steve..

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#206585 - 07/19/12 09:20 AM Re: Grounding metal building [Re: sparkync]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
If the panelboard enclosure and the meter can are effectively bonded to the metal framing, I think you are done but the code says you use a jumper sized to 250.66

Metal buildings generally do not have sufficient ground contact to qualify as electrodes in 250(A)(2) so you are just bonding it. (J bolts are not usually considered enough to be a ufer)

Quote:

250.104(C) Structural Metal. Exposed structural metal that is interconnected to form a metal building frame and is not intentionally grounded and is likely to become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with Table 250.66 and installed in accordance with 250.64(A), (B), and (E). The points of attachment of the bonding jumper(s) shall be accessible.


Florida amended this to include all steel studs in internal or external framing but they say attaching metal boxes to each segment of interconnected stud constitutes a bond.
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#206586 - 07/19/12 12:45 PM Re: Grounding metal building [Re: gfretwell]
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: NC
Thanks Greg. I'm thinking to make sure I meet the requirements, I will run #4 bare solid down to the ground rod instead of #6, and run it through a copper ground lug screwed into the metal siding. This should meet the requirements since it's bonded to the grounding electroded conductor if I'm reading right.
Also I am required to put at least one light and one GFCI outlet in the barn. It looks like I should be able to use M/C cable if the cable meets 330.10 A-11. I know inside a barn would not be "wet" location, but for sure "moist" location. Only don't know for sure whether the cable I got at Lowes meets those conditions or not. Thanks

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#206587 - 07/19/12 01:39 PM Re: Grounding metal building [Re: sparkync]
renosteinke Offline
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Registered: 01/22/05
Posts: 5299
Loc: Blue Collar Country
I defy anyone to bring power to a metal building, and fail to have it bonded. Your usuall construction methods pretty much guarantee that there is not only a bond, but a very good one.

That said, Greg refers to an oddball situation that I, with my primarily commercial background, just never would have imagined.

I can't imagine anything but steel boxes used with 'light steel framing' studs, but it seems someone did. Where that person got the idea that nail-mounted plastic boxes and romex were suitable for use with that construction method is beyond my understanding. The end result was that a fault made the entire frame 'live,' just waiting for comone to act the role of the ground wire.

Barns can be another thing completely, and that is where you can see the difference between 'legal' and 'good design.'

I would tend to treat everything above head level as a 'dry' location, but I would also give some serious thought to corrosion issues. Both animal waste and fertilizer can create some pretty severely corrosive locations.

MC has two strikes against it: the connectors are 'dry location' only, and most has an aluminum jacket. Aluminum readily corrodes when exposed to alkalies, such as fertilizer.

Romex actually might be a better choice ... assuming that critters can't chew it, and you can call the location 'dry.'

If you have to mount anything to sheet metal (as opposed to the structural pieces), only toggles will work.


Edited by renosteinke (07/19/12 01:39 PM)

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#206591 - 07/19/12 04:17 PM Re: Grounding metal building [Re: sparkync]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
MC cable is usually going to be wet location rated but Reno points out an interesting thing about the connectors not being "wet". Usually when I see MC in a wet place they enter the bottom of the box so it will drain. You can always get a fight started about whether galvanized steel is more corrosion resistant than aluminum. I suppose it depends on where you are. Aluminum holds up better around salt water but PVC is the raceway of choice there.

The boxes they use on steel studs are PVC with a lip that they screw into the stud (not a nail up). The other kind have a metal bracket on the side that gets screwed into the stud, some of those now have a bonding lug that extends into the box so they can meet the Florida code.
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#206603 - 07/19/12 07:22 PM Re: Grounding metal building [Re: gfretwell]
sparkync Offline
Member

Registered: 10/17/02
Posts: 811
Loc: NC
I found out that there are not any metal studs. The outside of the building is metal but inside is wood studs.
How about UF cable for a wiring method as long as I protect the wires that are going horizontal with wood braces? I'm kind of being a little particular because this job will be in a county that I haven'nt done any work in, not that, that makes much difference, but I know some counties are more strict than others, plus this job is out in the boonies, and I want to make everything count while I'm there. Don't want to be turned down on something if I can help it.
The only thought I have about using UF cable with regular nail up boxes is, that I thought that inside a barn where there is no heat, may be considered a "moist" location, and if so, that regulates what kind of wire can be used and the switch would have to be rated for damp location possibly. I think this barn will mainly have a couple horses in it, and believe it or not, in the future may have a small living quarters which will dramatically change the wiring methods. I guess I need to think about the wiring down low so that the horses don't chew on anything...hmmm... may have to use emt. Thanks


Edited by sparkync (07/19/12 07:27 PM)

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#206607 - 07/19/12 07:58 PM Re: Grounding metal building [Re: sparkync]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
I think that in a barn, MC would be a good choice. It is tough enough that critters won't easily hurt it and damp is not a problem. You still have to support it somehow in horizontal runs if you are not following building finish, if for no other reason people will hang things from it.
I think I would just go up and over following the top plate.
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