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Thread: Class 2 circuit separation in UL508A control panels

  1. #1
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    Class 2 circuit separation in UL508A control panels

    HI everybody. I am a controls engineer at a company that makes palletizing equipment. We are a UL listed panel shop and do our control panels in house for our equipment. My question is the separation of different circuits in a control panel. In our control panel we have a class 2 power supply supplying power for a SICK safety controller and power to various safety sensors and other devices. Some of our assembly technicians have been running some of the 120VAC power wires with the class 2 circuit and safety wires in the wireway. As far as I am aware this isn't allowed. I have been always told to keep theses separate from each other. I have told the techs not to run the ac power wires with the class 2 and safety circuits, but they fight me on this because of what the UL508A guide says in it.
    I know under UL508A in section 29.5 it only mentions that wires need to have the same insulation ratings to be run together and not separated. I have looked around and only been able to find references to article 725 about separating Class 2 circuits from power circuits. I have a couple of questions. Does NEC Article 725 apply to UL508A control panels? Are there any other articles, codes or rules that would apply to the separation class 2 circuits in UL508A control panels? If so does anyone know what they are? Thanks.

    -Jeremy

  2. #2
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    I have installed many UL508A control panels, several hundred. The NEC does not apply to the internal wiring done by the panel shop.
    I used to see dividers in the wiring duct, but lately all the class 2 and 120 V are in the same duct. The rules change on the load side of the terminals.
    But I am not familar with safety wiring, may be a specific procedure/listing for that, much as for IS wiring.
    And to repleat the NEC does not apply to the internal wiring. Our AHJs open the panel door, see the 508A label, sign the permit and life is good
    Moderator-Washington State
    Ancora Imparo

  3. #3
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    Does 409.3 require you to follow the requirements of Article 725 or does UL508A supercede Article 409?

    409.3 Other Articles. In addition to the requirements of
    Article 409, industrial control panels that contain branch
    circuits for specific loads or components, or are for control
    of specific types of equipment addressed in other articles of
    this Code, shall be constructed and installed in accordance
    with the applicable requirements from the specific articles
    in Table 409.3.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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