Tubing used as Conduit? 1

[timmer656]

We are designing a new product that goes on a fire truck. My boss likes the look of a stainless steel braid and wants to use Teflon hose with a stainless braid as the electrical conduit. I told him I didn't like it, mainly because it's plumbing, but I don't actually have a technical reason. I couldn't find anything in the NEC against it. The only thing I can imagine as a problem may be the flammability of the Teflon, if it's a problem. We have some samples of the type you buy out of McMaster-Carr. I've been looking on the internet for stainless steel conduit and have found some, but it's fairly costly.

Does anyone know if there is some code against using tubing for conduit?

 

[peebee]

On a fire truck? NEC would not apply, NEC 90.2 specifically excludes vehicles other than RV's and mobile homes. I have no idea if there's any legal authority who oversees electrical installations on vehicles. My guess is that you can install whatever you please.

In a building, rather than a vehicle, NEC & UL would usually apply. NEC 344.6 requires that Rigid Metallic Conduit be listed, and 352.6 requires that Rigid Nonmetallic Conduit be listed. Teflon pipe is not UL listed for use as conduit. And I'm like 99% sure that there's no listed stainless steel conduit either -- verify that whatver you've seen on the net is really listed as conduit, I betcha that it's not. If its not, it would be a code violation.

There's no code reason that you couldn't use listed conduit and then decorate it any way you please.

 

[pablo02]

Without knowing any of the details about your application, I can't address whether or not the NEC would apply (I would assume it does if your application involves a generator of any sort)... however, the DOT regs will most likely apply, you should review those also. The NEC does not permit "plumbing" in leau of conduit, but I can't point you to the verse that applies... also, you should review any other applicable NFPA codes and standards that deal with mobile fire equipment, etc...

 

[jlhmaint]

I don't think i would use it.

I saw this on an electrical forum i frequent they may be able to get you what you are looking for not sure of the prices

http://www.plastibond.com/

you could also look into what it would cost to have some conduit crome plated if it could be done would last and isn't expensive.

 

[Comcokid]

Running vehicle wiring through stainless braid/teflon tubing probably provides better protection than the typical vehicle with corrugated vinyl and/or taped-wrapped harnessing (which burns very well in an electrical fire!). Certainly, this is more expense and labor, but may add to the cosmetic appearance.

Stainless tubing in sizes similar to conduit can be obtained from Marmon/Keystone (

http://www.marmonkeystone.com)

and other tubing suppliers. Type 304 is good for general work, and 316 for cosmetic appearance. Just be sure to use a stainless wire brush if you polish it - otherwise you'll deposit iron particles which will make your stainless appear to rust!

There are few governmental regs that apply to vehicle wiring, mostly industry practices or SAE guidelines. Having previously worked within the vehicle industry, I realize a major driving factor is glitter and cost and not performance and endurance.

 

[peebee]

Pablo02:

Regarding your statement that "I would assume [the NEC applies] if your application involves a generator of any sort":

I've already given a code reference (NEC 90.2) that specifically excludes vehicles (with exceptions for RV's) from the scope of the NEC. There's nothing else I can locate anywhere in the code that indicates that it would cover this application. There's nothing in NEC 90 that indicates that NEC applies just because there's a generator. Please justify your statement.

 

[60hzhmmm]

peebee, I agree, though there is some mention of grounding of vehicle generators.

 

[pablo02]

after reading your post, I agree with you in that timmer656 application is not covered as I understand the application -- however, section 250-32 (NEC 2002) does refer to portable and mobile mounted generators (but does not seem to cover the discussion item)..

 

[timmer656]

There is no generator involved with this application. I am only connecting two small DC motors to a junction box that houses the control boards.
I have been searching through the SAE standards to find one that pertains to wiring practices on trucks. Any ideas?
I appreciate Comcokid's remark about the driving factor being "glitter". This is going on a firetruck and it needs to have the perception of being very rugged. It does of course have to be very waterproof too.
Thank you for all your comments.

 

[buzzp]

NEC code does not apply. As mentioned, SAE will apply as well as DOT specs. Most DOT specs refer to SAE documents. I used to know them. However they have slipped my mind. Check out

http://www.sae.org.

When I did 12VDC systems I did not ever use protective covers for ground connections. I always used a wire ran to one point on the chassis that connected to the vehicles battery ground. This included any ground on the vehicle. Chassis grounds were avoided if possible (except for one point where all grounds terminated too and then ran to battery ground). This helped with several problems with digital equipment (ground noise).
I agree with your concern. All of our conduits were not visible (ran along frame). What stops you from using regular conduit with braid on it instead of teflon tubing (probably cheaper too)? There is also colored sleeves that could be slipped over the conduit.
If you are manufacturing trucks from bare chassis you better be using SAE guidelines because you are supposed to be putting your sticker on that says so per DOT regulations. Granted, where I worked that just put the sticker on and called it good with no regard to SAE or DOT specifications. The fine is $5000 per offense (not per truck). Just something to think about. I believe Cummins website has some good downloads on wiring practices(not SAE docs).
Don't think your comnpany is alone. I think there are many issues with manufacturers of specialty industrial vehicles not following guidelines like they should.

 

[peebee]

What voltage are you talking about? 12 or 24vdc? Not that I'd be able to give you any better an answer if you told me, just curious.

Maybe you should check out the automotive engineering forums here on eng-tips.

If you get an answer somewhere, please post it here, thanks.

 

[busbar]

For "show", MIL type-E or -EE PTFE-jacketed silver-plated copper wire in the raceway may go well. …in lotsa' bright colors.

 

[timmer656]

For most applications the voltage will be 12VDC. When we sell this particular product in Europe, it will be 24VDC. The part we are designing is only 1 component that goes on a fire truck, we do not build the actual fire truck.
I'm am still checking on the appropriate SAE standards to follow.

 

[Heydave]

I would recommend a return ground conductor within your assembly and not count on the conduit for ground. The mechanical stresses at connection points could cause arcing. Teflon should not be a fire problem as it was first used for fire safety after the Apollo fire that killed several astronauts. Be wary of silicons used as sealents as they may actually react with tin found in soldered joints and connectors causing them to fail earlier. Teflon with a stainless braid may be about the best thing available for durability but treat the electrical circuits seperately.

 

[ScottyUK]

If you get Telfon (PTFE) hot enough it decomposes into, I think, hydrofluoric acid. PTFE is good for high temperature work, but becomes dangerous if heated to very high temperatures.

I seem to recall some problem in areas where PTFE machining was carried out, where the dust decomposed on the ends of cigarettes and entered the smoker's lungs as hydrofluoric acid. Pleasant.

 

[BJC]

timmer656
There's a forum on this site called:

SAE (Automotive) Code Issues Forum

IIF somebody there dosen't we should go back to horses and buggys.

 

[resqcapt19]

You might look at NFPA 1901, Standard for Automotive Fire Apparatus. A Draft cope of that standard is online at

http://www.nfpa.org/Codes/NFPA_Codes_and_Standards/List_of_NFPA_documents/NFPA_1901.asp

Chapter 13 covers the low voltage electrical and Chapter 23 cover line voltage.
"23.2.2 Conformance with the National Electrical Code®.
23.2.2.1 All components, equipment, and installation procedures shall conform to NFPA 70, National Electrical Code, except where superseded by the requirements of this chapter.
23.2.2.2 Where the requirements of this chapter differ from those in the NFPA 70, National Electrical Code, the requirements in this chapter shall apply.
23.2.3* When available, line voltage electrical system equipment and materials included on the apparatus shall be listed and used only in the manner for which they have been listed."

Don

 

[peebee]

Well, hows about that?

Red star for Mr. Don.