Column as Conduit??? 1

[tolind]

I'm trying to use a building column as a conduit. It's an 8x8 steel tube and the underground conduit would terminate into it. Is this ok? Do I have to have another conduit running inside to shield?? Is there anywhere in the NEC that comments on this?

 

[mpparent]

I believe you would need an approved raceway, ie EMT, GRC, etc. I would point to NEC 300.37.

Mike

 

[weh3]

All definitions of conduit in the NEC refer to "listed" equipment, referring to suitability for a particular purpose. One exception is underground directionally bored conduit, which has only to be acceptable to the authority having jurisdiction (cite ?).

I went through this when a client wanted to use stainless steel pipe as conduit. Stainless steel pipe is pretty much the same as stainless steel conduit, but it doesn't have a UL label as conduit, and it is about 100x cheaper.

It may not make any difference to anyone else, but if some accident happens twenty years from now, and if some lawyer finds out that you used a non-listed wiring method, even if that had nothing to do with the accident, then your retirement is down the drain. Be safe and stick with exposed rigid metal. It's not pretty, but it's safe.

William

 

[tolind]

What about hiding the conduit inside the column? That would take care of the conduit issue and it would still be vandel resistant.

 

[weh3]

If it is acceptable to the AHJ, then I don't know of any prohibition agains running a conduit inside a column. Conduits are concealed behind walls and ceilings and encased in concrete all the time. Vandal resistant? Is this a maximum security prison?

William

 

[rbalex]

The “real” NEC limit is placed on the conductors not the “raceway.” See the NEC definition of “raceway” which includes, but isn’t limited to, all the conduit forms is Chapter 3. See also Section 310.13 and it’s limitations applied to conductors listed in Tables 310.13, 310.61, 310.62, 310.63, and 310.64.

Other conductors, say those in Art 725, and not listed in Tables 310.13, 310.61, 310.62, 310.63, and 310.64, may possibly be used in the tube without additional requirements. Since I don’t know the full scope of your applications this is the best info I can give at the moment.

 

[rbalex]

I'd add that bonding between the UG and AG portions of the run will likely be an issue. I'd have a qualified EE look at the full application. After you determine you can or can't use the steel tube other issues such as conductor derating will come into play.

BTW "listing" is not part of the definition of most Chapter 3 raceways - although most are, in fact, listed. The steel tube could be an "identified raceway" per 300.37. "Identified" simply means "Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement." Most Authorities Having Jurisdiction (AHJ) prefer to see "listed" materials but it is NOT a general NEC requirement.

 

[dpc]

You could use metal-clad (MC) cable without any raceway, provided you could find a way to support it if the vertical distance is excessive.

 

[mpparent]

rbalex,

I would argue that the steel tube is not recognized as a raceway. I do agree it does not need to be listed, only approved by the AHJ. I would seriously doubt that any code inspector would allow that installation.

tolind,

If you were to route pipe like GRC, etc. in the steel tube that would satisfy the code and you would have no problem as far as the routing goes. I assume your steel tube is like a "shell" for a steel column, ie a architectural element.

Mike

 

[rbalex]

Depending on how dearly you hold on to "...designed expressly...” what was originally described is definitely a "raceway." Since I am an AHJ, I a may have accepted it, I would want to know the full and final installation application before I summarily rejected it.

 

[mc5w]

weh3,

There is no such thing as UL listed stainless steel conduit. I talked with some buddies of mine who do million dollar and larger industrial jobs in food plants about this issue. They say that any kind of stainless steel, bronze, brass, or copper conduit is only available as National Sanitation Foundation listed pipe.

The NSF listing for stainless steel pipe requires greater internal smoothness than the UL listing for conduit. In a food plant it is more important that electrical conduits be listed by NSF because they need to be cleanable. The primary purpose of requiring UL listed conduit is to keep people from using umgalvanized steel gas pipe or pipe that has an unreasonable weld bead inside.

How I got into asking my buddies over at E.F. Lea Electric is that we got stuck with installing an obsolete 120 volt underwater swimming pool light in a health care facility. According to an electrician who works for Litehouse Pools any underwater light that is nor fiber optic is a DINOSAUR!

 

[mc5w]

Ummm, I meant to write ungalvanized, not umgalvanized.

 

[tolind]

Good Discussion.

The application is for lights a city canopy for an alleyway, not attached to any buildings.
Steel tube is a structural member and the city is, and always has been, worry about teenage kids vandelizing the construction. Due to this my idea was to run the wiring underground, thru the column footing, then up the column to the beam. Poke thru the beam and power lights as necessary. From what I have gathered here, and put on the drawings, it is necessary, or at least a good idea, to run a conduit inside of the column. In hindsight it would probably be much easier for installation and maintenance.

 

[weh3]

mc5w,

No stainless steel conduit? Try

http://www.calpipe.com.

A phone conversation with their standards people (a couple months ago on an actual project) suggested that stainless steel conduit is not just pipe, and that to get the label as conduit is an involved process.

Regards,
William