Exposed, outdoor-rated intrinsically safe wire or cable

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IntrinsicSafety

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Hi all,

I'm a design engineer, not an electrician. Due to a bizarre set of circumstances, I've run into a wiring question I can't answer. I thought if anyone knew, they'd probably be here.

The application is an intrinsically safe cable.

I already know that NFPA 70 allows any ordloc wiring method for IS. This does not help me much since I am not familiar with the exact details of what is allowed and not allowed for all of the various kinds of wiring methods.

So I need to know if there are any NEC-compliant wires/cables that meet the following:

- Small (about 18 AWG max)
- Carrying one or more intrinsically safe circuits (< 6V, < 3A total for all circuits)
- Listed to be installed outdoors (wet locations, exposed to sunlight)
- Installed on a metallic wall (like a storage tank)
- Allowed to be installed exposed (no raceway, conduit, struts, channels, etc.); and
- Does not have a metallic jacket or metal armor.

The cable will be limited to about 6m (20') total and can be installed so that it is supported at just about whatever interval is necessary.

As an example, I looked at Class 2 and Class 3 cables. These would be fine except there are (seemingly) none listed for use in wet locations.


If this cable does not exist, I would appreciate any information on the next best options. Metal-jacketed cable would be a last-resort option.


I'd rather not get into why I need this, because I expect knowing the context would only confuse the issue further. Suffice to say that I'm being pushed into this by a certifications agency.

Any assistance greatly appreciated. Thanks!
 
IntrinsicSafety said:
Hi all,

I'm a design engineer, not an electrician. Due to a bizarre set of circumstances, I've run into a wiring question I can't answer. I thought if anyone knew, they'd probably be here.

The application is an intrinsically safe cable.

I already know that NFPA 70 allows any ordloc wiring method for IS. This does not help me much since I am not familiar with the exact details of what is allowed and not allowed for all of the various kinds of wiring methods.

So I need to know if there are any NEC-compliant wires/cables that meet the following:

- Small (about 18 AWG max)
- Carrying one or more intrinsically safe circuits (< 6V, < 3A total for all circuits)
- Listed to be installed outdoors (wet locations, exposed to sunlight)
- Installed on a metallic wall (like a storage tank)
- Allowed to be installed exposed (no raceway, conduit, struts, channels, etc.); and
- Does not have a metallic jacket or metal armor.

The cable will be limited to about 6m (20') total and can be installed so that it is supported at just about whatever interval is necessary.

As an example, I looked at Class 2 and Class 3 cables. These would be fine except there are (seemingly) none listed for use in wet locations.


If this cable does not exist, I would appreciate any information on the next best options. Metal-jacketed cable would be a last-resort option.


I'd rather not get into why I need this, because I expect knowing the context would only confuse the issue further. Suffice to say that I'm being pushed into this by a certifications agency.

Any assistance greatly appreciated. Thanks!
Click to expand...

TC, TC-ER, or PLTC might do the trick. The only issue would be support. What are you proposing in that regard?
 
We'll figure something out based on the support requirements for the wire.

Adding tie points of some kind to the wall may work. If we have to add short lengths of open channel (or something) for support purposes, we may be able to make that work. A closed raceway where we have to run the cable in one end and out the other (like conduit) will not work. It's an installation thing.

All I know about TC and PLTC comes from the Div 2 wiring requirements, which says "including installation in cable tray systems" (or similar). In my ignorance, I don't know if this means TC/PLTC must always to be installed in cable trays, has to be installed in trays only for Div 2, or can be installed without cable trays.

However, if they can be installed outside of a tray/raceway, then those types might do fine. Is that the case? Thanks!
 
IntrinsicSafety said:
We'll figure something out based on the support requirements for the wire.

Adding tie points of some kind to the wall may work. If we have to add short lengths of open channel (or something) for support purposes, we may be able to make that work. A closed raceway where we have to run the cable in one end and out the other (like conduit) will not work. It's an installation thing.

All I know about TC and PLTC comes from the Div 2 wiring requirements, which says "including installation in cable tray systems" (or similar). In my ignorance, I don't know if this means TC/PLTC must always to be installed in cable trays, has to be installed in trays only for Div 2, or can be installed without cable trays.

However, if they can be installed outside of a tray/raceway, then those types might do fine. Is that the case? Thanks!
Click to expand...

Check out the NEC, 2014 edition at 336.10 Uses Permitted. Section (4) allows it to be supported by a messenger wire. Can you do that? If you can, also make sure that it's listed for exposure to sunlight.
 
Hi Bob,

It's an NEC application.

Unfortunately, I don't understand Article 727. I spent some hours trying to figure it out and got lost in all the cross-referencing. Plus I was unable to figure out if cable trays were required or not, etc.
 
Trays are not required. Section 727.4 lists several acceptable installation methods. It does have some securing/support issues as all cables do, but 6' intervals shouldn't be a problem from your OP. ("The cable will be limited to about 6m (20') total and can be installed so that it is supported at just about whatever interval is necessary." [Sections 727.4(4) & (5)] BTW, Section 727.4(4) is very much like a TECK cable and 727.4(5) needs the further identification as ITC-ER.

BTW you are probably also aware, but cable tray is NOT considered a raceway in the NEC as it is by the CEC.
 
rbalex said:
BTW you are probably also aware, but cable tray is NOT considered a raceway in the NEC as it is by the CEC.
Click to expand...

I did not know that, thanks! :D

rbalex said:
Section 727.4 lists several acceptable installation methods.
Click to expand...

:? 727.4 deals with ITC cable. I can't find a reference to PLTC cable with respect to 727.4 - what am I missing?

I also saw this:

"(D) Industrial Establishments. In industrial establishments
where the conditions of maintenance and supervision
ensure that only qualified persons service the installation,
Type PLTC cable shall be permitted in accordance with
either (1) or (2):

(1) Where the cable is not subject to physical damage,
Type PLTC cable that complies with the crush and impact
requirements of Type MC cable and is identified as
PLTC-ER for such use shall be permitted to be exposed
between the cable tray and the utilization equipment or
device. The cable shall be continuously supported and
protected against physical damage using mechanical
protection such as dedicated struts, angles, or channels.
The cable shall be supported and secured at intervals
not exceeding 1.8 m (6 ft).

(2) Type PLTC cable, with a metallic sheath or armor in
accordance with 725.179(E), shall be permitted to be
installed exposed. The cable shall be continuously supported
and protected against physical damage using
mechanical protection such as dedicated struts, angles,
or channels. The cable shall be secured at intervals not
exceeding 1.8 m (6 ft)."

To me, this reads that PLTC has to be installed protected or armored. Neither suits my application. How is it that it's allowed to be installed exposed, without trays? Thanks!
 
I started to write an essay and long history lesson - I'm just too tired to do that. I'm simplifying this as much as I can.

Basically, start in Sections 725.125, 127, and 130. You might also review the definitions of Class 2 Circuits and Class 3 Circuits. The key element to defining Class 2 Circuits and 3 Circuits is the power supply, not the wiring method. Cables and wiring methods listed in Section 715.135 and following are simply permissible alternates to those in Chapter 3 for Class 2 and 3 Circuits

A brief history. Article 727 was written specifically to avoid most of the crap in Article 725; especially several dubious separation requirements. Type ITC isn't Type PLTC although it is conceivable a given cable may have a dual identification.

"Protected against physical damage" is such a broad concept that it's almost impossible to clearly define what is and what isn't. Depending on the traffic it is exposed to, RMC wiring may still be exposed to physical damage; whereas lighter wring methods may be fine by an isolated location.
 
Bob: Articles 725 and 727 are currently impenetrable to me; I lack the necessary background. I especially don't see how 727 applies when "ITC is not PLTC". I'll just have to take your word for it.

nec_addicted: Thanks for the suggestion! Hopefully we can make something work.
 
IntrinsicSafety said:
Bob: Articles 725 and 727 are currently impenetrable to me; I lack the necessary background. I especially don't see how 727 applies when "ITC is not PLTC". I'll just have to take your word for it..
Click to expand...
Sorry, so I will be blunt. For your application, Type ITC installed per Section 727.4(4) or (5) will work; Type PLTC installed per Section 725.135(J) will work; OR Type TC installed per Section 336.10(7) will work.

IntrinsicSafety said:
...
nec_addicted: Thanks for the suggestion! Hopefully we can make something work.
Click to expand...
This is a reason I usually avoid Intrinsically Safe (IS) systems if I can. By the time all the bells have been rung, all the whistles have been blown, and all the hoops have been jumped through, IS is rarely cost effective after the additional requirements of Sections 504.10, 50, 60, and 70 have been addressed just to avoid Sections 501.10(A) or (B) - and honestly, it isn't that much safer as the link to the control.com thread attests.
 
Hi Bob,

Thanks for being blunt, I appreciate it. :) The information is very helpful, thanks!

I wouldn't give this project much weight when judging intrinsic safety vs. other applications. This one is off-the-charts bizarre.

I kind of like IS, but that's just me. It's not always the best thing but sometimes you don't really have an option.

Thanks again!
 
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