Stainless Rigid Metal Conduit vs. Stainless Tubing 3

[USAeng]

If we ever wanted to put a product in a Class 1 Div 1 or 2 Group D area and wanted to use a stainless tube instead of rigid metal conduit for a raceway... is this allowed?

I assume you have to use a rigid metal conduit, but our normal product which houses the wire for a sensor that is screwed on the end uses a 316 stainless tubing that holds up well for heat....

And not that anyone should know this off the top of their heads, but if you run a flex conduit approved for c1 div2 grp D to a nema 7 box... does there have to be a seal on the end of the conduit? or does a nema 7 box have some sort of built in seal already....

 

[jraef]

"Tubing" has no standing and therefore recognition as an electrical raceway unless specifically stated as such. But if you are only looking at running low voltage, i.e. intrinsically safe, signal wires then you don't absolutely need "conduit" so tubing would be for convenience and mechanical protection only and most likely OK. But if they are going between classified / non-classified areas, you will not find approved seals for "tubing" so the point would be moot.

Off the top of my head, you need a seal whenever something is coming from / to a non-hazardous area to / from a hazardous area. If the flex is coming from a NEMA 7 junction box that is in the hazardous area already and going to another NEMA 7 box in the same area, then I don't think you need a new seal off. But it's been a long time for me... better to check with others.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[USAeng]

thank you very much...

does anyone know what or who determines if something is "intrinsically safe" ?

I saw that when doing my research also, and do not know if there is a voltage/current threshold or if an inspector must make that determination? or?

 

[jraef]

It must be certified as such by whatever local authority you are subject to (this is an international forum). Assuming you are in the US or Canada (from your earlier NEMA reference), that would be UL and/or FM listing as "Intrinsically Safe". The voltage level that is considered non-incendiary is, I believe, 8VDC. But that means nothing really; either your device has been listed or it has not, you can't "wing it" just because it's low voltage.

If you are looking at signals that themselves are not IS, you can sometimes use what are called Intrinsically Safe Barriers or Zener Barriers at each end to make the wiring so.

Good place to start since it appears you are unfamiliar with the concept.

http://en.wikipedia.org/wiki/Intrinsic_safety

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[DRWeig]

If you can describe your product to us, you might get some more specific info...

Good on ya,

Goober Dave

 

[USAeng]

it is a flame rod that uses the fire in the furnace to complete the path to ground and then sends a signal to the control room that there is a flame...

normally we make the housing for the wire out of 316 stainless for a certain number of feet and then the actual flame rod screws on the end making the connection

I think I got pretty good answers here... but if you can think of anything else to add because of that, please do

Thanks a lot

 

[USAeng]

oh and the current travels out the tip of the flame rod, through the flame, then back into the stainless housing/wire race, and then into the frame of the boiler... we are talking utility boilers here

 

[DRWeig]

Thanks USAeng,

You're right, I have no good suggestions for you -- can't really picture the area.

I'm not a utility guy, but around most large boilers (such as in hosptitals or campus power plants), the area outside the boiler is not usually classified as hazardous. I'm left wondering what makes your area Class I Div 1 or 2?

Good on ya,

Goober Dave

 

[zappedagain]

IEC 60079 series defines explosive environment requirements. Intrinsically safe is defined by IEC 60079-11; it will tell you which other dash numbers you will need. By my research so far I understand that by meeting the IEC rules I'll meet the NFPA/UL rules.

NFPA Section 70 Article 500 (aka NFPA500?) defines the requirements for explosive environments. Section 500.7E defines Intrinsic Safety.

NFPA 504 defines Intrinsically Safe Systems


UL White Book (2008) defines explosive environments (references NFPA 70 Articles 505 and 506, ANSI/UL 913.


FM 3610 follows the IEC standards referenced above.

John D

 

[peebee]

Re. stainless steel tubing/conduit/raceway/etc -- To the best of my knowledge, there is no UL-listed stainless steel tubing/conduit/raceway available anywhere on the market, which would make it an automatic violation of NEC. My understanding is that when people say they've installed SS conduit, what they've really installed is SS water pipe. A key manufacturing difference between electrical conduit/tubing and pipe is that when the metal sheet into a tube shape and welded, electrical tubing/conduit undergoes the further step of removing any rough spots or welds from the inside of the tube. They may be left in place in SS water piping. Your AHJ may not be aware of any of this and may permit you to use SS pipe -- but you should be aware of the assoicated technical and liability issues.

My understanding of the availability of SS raceways may be obsolete, if SS raceways are indeed now available someone please correct me and provide additional info (perhaps a URL for a manufacturer's catalog cut).

I would generally recommend PVC-coated RGS or other similar alternates in such locations where you're currently considering SS conduit/tubing.

Re. jraef's statement that "Tubing has no standing and therefore recognition as an electrical raceway" -- assuming we're talking about Electrical Metallic Tubing (EMT), this *is* defined as a raceway by NEC 358.2, although code does make a distinction between EMT and conduit; EMT is *not* conduit. Other types of tubing (eg, water tubing), clearly are not listed by UL or recognized by NEC as a raceway.

 

[waross]

If your device is approved by any approvals agency then the change may require re-approval.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BJC]

There is stainless rigid conduit available.

http://www.gibsonstainless.com/

It's used in food processing plants all the time. There are also fittings ( LBs boxes etc).
The fittings are sometimes screwed and welded. The weld is to provide a smooth surface so no contanimation can hide. The places I have seen were steamed cleaned often.
Bring plenty of money.
Boiler fronts are not usually a classified area. After all there is a fire not far away.

 

[peebee]

Thanks for that link, BJC, red star for you.