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Thread: NFPA 79 Cables For 24V Internal Machine Wiring

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    NFPA 79 Cables For 24V Internal Machine Wiring

    I'm working on selecting cables for general 24V signals and I'm stuck determining what requirements makes sense and what is actually correct.

    Issues 1: AWM
    For the most part, AWM isn't accepted in NFPA 79 for most applications. But I found this:
    12.9.2 Appliance wiring material (AWM) shall be permitted under any of the following conditions.
    12.9.2(1) Where part of an assembly that has been identified for the indented use

    So if a website says their 3 conductor cables with molded ends are intended for sensors and valves are they ok to use? Are there other UL ratings that still need to be met?


    Issue 2: Cable routing and rating requirements
    If I'm selecting a multi-conductor cable to connect to a door switch or another panel but the cable gets routed along a machine frame does it need to be a -ER rating? It's technically exposed outside of a cable tray or conduit. Are there special cable ratings needed for this kind of installation?


    Issue 3:
    If a cable isn't rated for >300V then it can't be routed next to/with a cable that supplies 480 Volts to a device. Correct?
    This could make cable routing on a machine very cumbersome and/or cable selection very costly.

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    Quote Originally Posted by SD Dylan View Post
    I'm working on selecting cables for general 24V signals and I'm stuck determining what requirements makes sense and what is actually correct.

    Issues 1: AWM
    For the most part, AWM isn't accepted in NFPA 79 for most applications. But I found this:
    12.9.2 Appliance wiring material (AWM) shall be permitted under any of the following conditions.
    12.9.2(1) Where part of an assembly that has been identified for the indented use

    So if a website says their 3 conductor cables with molded ends are intended for sensors and valves are they ok to use? Are there other UL ratings that still need to be met?


    Issue 2: Cable routing and rating requirements
    If I'm selecting a multi-conductor cable to connect to a door switch or another panel but the cable gets routed along a machine frame does it need to be a -ER rating? It's technically exposed outside of a cable tray or conduit. Are there special cable ratings needed for this kind of installation?


    Issue 3:
    If a cable isn't rated for >300V then it can't be routed next to/with a cable that supplies 480 Volts to a device. Correct?
    This could make cable routing on a machine very cumbersome and/or cable selection very costly.
    Regarding AWM. Most single conductor AWM wire are dual rated as MTW. I think what this section is trying to do is allow the use of flexible bus bars that are insulated with AWM insulation.

    UL508a specifically allows the use of AWM inside of industrial control panels. That pretty much covers the idea that it is identified for the use.

    3.3.52* Identified (as applied to equipment). Recognizable as
    suitable for the specific purpose, function, use, environment, application,
    and so forth, where described in a particular code or
    standard requirement.
    IMO, a manufacturer who says their cable is suitable for a particular use is identifying it that way so is acceptable.

    I see no reason that an "-ER" rated cable would be required.

    There are plenty of cords and cables rated 600V.
    Bob

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