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Thread: Exposed, outdoor-rated intrinsically safe wire or cable

  1. #1
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    Exposed, outdoor-rated intrinsically safe wire or cable

    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!

  2. #2
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    Quote Originally Posted by IntrinsicSafety View Post
    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!
    TC, TC-ER, or PLTC might do the trick. The only issue would be support. What are you proposing in that regard?

  3. #3
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    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!

  4. #4
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    Quote Originally Posted by IntrinsicSafety View Post
    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!
    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.

  5. #5
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    Quote Originally Posted by gadfly56 View Post
    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.
    That's an idea. Pretty sure we can't do that, but I can look into it further. Thanks!

  6. #6
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    You might also consider Article 727.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  7. #7
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    I noticed you are in Canada. Several TECK forms should also be acceptable.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  8. #8
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    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.

  9. #9
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    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.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  10. #10
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    Quote Originally Posted by rbalex View Post
    BTW you are probably also aware, but cable tray is NOT considered a raceway in the NEC as it is by the CEC.
    I did not know that, thanks!

    Quote Originally Posted by rbalex View Post
    Section 727.4 lists several acceptable installation methods.
    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!

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