Stainless steel in class I div I

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nathanslc

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Can stainless steel conduit be used in a class I div I area? My interpretation of the code is no. Section 501.10(A) does not list stainless steel conduit as a method nor is stainless steel conduit UL listed as class I div I. Also, explosion proof devices are not made in stainless steel and there would be dissimilar metals between the conduit and explosion proof box. However, the code is vague on the use of stainless steel conduits in class I div I. Can someone please clarify or give my interpretation a confirming nod.

Thanks
 
nathanslc said:
Can stainless steel conduit be used in a class I div I area? My interpretation of the code is no. Section 501.10(A) does not list stainless steel conduit as a method nor is stainless steel conduit UL listed as class I div I. Also, explosion proof devices are not made in stainless steel and there would be dissimilar metals between the conduit and explosion proof box. However, the code is vague on the use of stainless steel conduits in class I div I. Can someone please clarify or give my interpretation a confirming nod.

Thanks
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The actual Art 501 requirement is only that it be threaded and metal, either RMC or IMC. The materials of construction are not specified. [See Section 501.10(A)(1)(a)]. Stainless steel is considered a nonferrous metal because it has virtually no magnetic properties. As RMC, it is recognized under Section 344.2 as Rigid Metal Conduit and is listed by UL under product Code DYWV.

Since it is nearly impossible to cast, stainless steel isn?t used in explosionproof enclosures; however more conventional metallic explosionproof enclosures are not generally prohibited from use with stainless steel raceways.
 
nathanslc said:
The owner is providing all stainless steel enclosures in the class I div I area. Is this a violation of the code?
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Not necessarily so, but most likely. The prime question would be; does the installation requires the use of XP listed equipment?(ex.: intrinsically safe circuits and equipment.) The other issue is if the enclosure is listed and labeled for the Class and Division or is the enclosure made safe by other emans for the location(Ex. by Bob Alexander: purged.)?
 
rbalex said:
Since it is nearly impossible to cast, stainless steel isn?t used in explosion proof enclosures; however more conventional metallic explosion proof enclosures are not generally prohibited from use with stainless steel raceways.
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Actually, Stainless Steel is no more difficult to cast than conventional cast iron, or sand cast brass/bronze. Investment and sand casting techniques have improved dramatically over the past 20 years, to where casting stainless steel is relatively easy and commonplace. You can easily purchase cast stainless plumbing pipe and valves and more recently, conduit and fittings. The real prohibition comes from cost. A cast stainless enclosure may cost up to 3x the equivalent in epoxy coated cast aluminum. The same holds true for Stainless rigid conduit vs standard galvanized rigid conduit.

Stainless conduit and fittings are becoming more common in food processing installations where previous PVC coated steel product has failed over time. The failures are due to the chemical detergents, hot water, and high pressure washing that occurs every day in these facilities. We know folks who manufacture Stainless conduit and fittings, and the best line they gave me for the success of their business was "Every time a cow dies, its good for us!"..

Getting back to the issue at hand, I know of no code or related UL issue that precludes the use of Stainless Steel specifically. As long as it passes the requirements by the related specifications (i.e. UL514B, UL6A, etc.) there should be no problems.

If an enclosure or fitting is listed as Class I or II, it will be specifically listed as such - no matter what the material it is. The products are tested in all versions of the materials offered. Explosion proof,Stainless enclosures are difficult to find because there is a very limited market for them and the cost to manufacture them would outweigh the overall corrosion benefits.


If stainless in hazardous locations is viewed as a no-no, FYI T&B carries hazardous location drain/breather fittings in Stainless Steel (ECD384-TB), so I don't think stainless material is a problem.

This is probably the reason why you don't see conduit bodies made out of Titanium or conduit fittings made out of oxygen-free, high-conductivity copper. High Cost and Low Demand.
 
Thanks for the information. I'll admit my knowledge about stainless is dated; especially with regard to casting.

My original response indicated stainless was in itself an acceptable material of construction for equipment in classified locations. However, with a few minor exceptions, such as the T&B drain and breather, stainless still doesn't lend itself well to constructing explosionproof enclosures. Of course, the simple cost of raw material plays a large part, but the difficulty of working with the raw material is a factor in the cost.

I wanted it clear that NEMA 4X boxes would not be acceptable in a Division 1 location solely on the basis that they were stainless.
 
LJSMITH1 said:
... A cast stainless enclosure may cost up to 3x the equivalent in epoxy coated cast aluminum. The same holds true for Stainless rigid conduit vs standard galvanized rigid conduit. ...
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I think your pricing may be on the low side. I priced out stainless 3/4" rigid conduit from a couple of suppliers a couple of years ago and it was at $17/foot. A coupling was $25. The client did not want to spend that much so we ending up using PVC coated rigid at less than $3/foot.
 
don_resqcapt19 said:
I think your pricing may be on the low side. I priced out stainless 3/4" rigid conduit from a couple of suppliers a couple of years ago and it was at $17/foot. A coupling was $25. The client did not want to spend that much so we ending up using PVC coated rigid at less than $3/foot.
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I said "cost" which is not what the price might be to a contractor.:grin: The overall price may be up to 10X of a comparable steel or aluminum product. Bing on the manufacturing side, I have nothing to do with what the guys in marketing and sales want to do with pricing ;) That's way out of my league!

Form a manufacturing perspective, the costs typically come down when the volumes go up. Since stainless is a fringe or niche product use, the volumes will always be low until demand increases.
 
rbalex said:
Thanks for the information. I'll admit my knowledge about stainless is dated; especially with regard to casting.

My original response indicated stainless was in itself an acceptable material of construction for equipment in classified locations. However, with a few minor exceptions, such as the T&B drain and breather, stainless still doesn't lend itself well to constructing explosionproof enclosures. Of course, the simple cost of raw material plays a large part, but the difficulty of working with the raw material is a factor in the cost.

I wanted it clear that NEMA 4X boxes would not be acceptable in a Division 1 location solely on the basis that they were stainless.
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Right. The NEMA 4X specification is primarily concerned with the construction of the enclosure, and the features included to prevent water intrusion. If the enclosure was stainless or PVC it wouldn't matter. The only thing that might get in the way of using stainless, is if the engineering specifications call for something else specifically (i.e. PVC, Epoxy coated Steel, etc.). Then you are locked into whatever is required.

Casting a stainless enclosure is essentally no different than casting a malleable iron enclosure. The main issue is the application and demand (and resulting high cost). There are not many applications (if at all) that would require a cast, stainless, explosion proof enclosure (or even a malleable iron version). The standard cast aluminum version is usually sufficient for 99.99% of the applications out there. If you just need a NEMA 4 enclosure in stainless, then fabricated (i.e. sheet metal) versions are available and acceptable.
 
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