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Class I Div I, Low voltage cabinet installation (intrinsic safety)

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    Class I Div I, Low voltage cabinet installation (intrinsic safety)

    We are designing in a IOT device into a Class I Div I Zone 1 IIc T4 location. Because it's a wireless device using small antennas, it is preferred to use a non-metalic cabinet as we have done for standard commercial installations.

    The NEC requires metalic conduit as our 12V power is high enough in power to require protection. Highest voltage is 12VDC. We are designing our own I.S. barrier.

    Question: Can we attach metal conduit to a suitably rated non-metallic cabinet? If so, what fittings are available? It isn't explosion proof, but we just need to seal out water as it is an outdoor installation. The box will have a vent as there is a barometer inside.

    #2
    I must confess I have no idea what IOT means in the context of your post; however, the description of your application indicates you are designing utilization equipment [See Section 100 for the definition] that would be subject to Section 501.135(A) unless you could qualify it under Article 504. In either case, you will have issues with having your product identified (another defined term) for the location. A self-designed IS barrier is questionable.

    BTW the voltage level, as such, is irrelevant.

    All that said, IF you actually do qualify as an intrinsically safe system THEN you don't need to worry about metal conduit either.
    [COLOR=black]"Bob"[/COLOR]
    Robert B. Alexander, P.E.
    Answers based on 2017 NEC unless otherwise noted.

    Comment


      #3
      IOT/ Utilization Equipment

      Originally posted by rbalex View Post
      I must confess I have no idea what IOT means in the context of your post; however, the description of your application indicates you are designing utilization equipment [See Section 100 for the definition] that would be subject to Section 501.135(A) unless you could qualify it under Article 504. In either case, you will have issues with having your product identified (another defined term) for the location. A self-designed IS barrier is questionable.

      BTW the voltage level, as such, is irrelevant.

      All that said, IF you actually do qualify as an intrinsically safe system THEN you don't need to worry about metal conduit either.
      Thank you for the reply Bob. IOT stands for "Internet of Things". This is equipment to facilitate connection of modern sensors and controls to the internet (the cloud) for everything from personal electronics to industrial equipment. It seems we will be able to qualify under 501.135(A). The confusion about the conduit is that most "intrinsically safe" barriers are for wiring of sensors which are MUCH lower power than our device. Furthermore, you can't just run bare 12V wiring capable of carrying 1.5A as an accidental short will cause a spark which is capable of detonating a hazardous atmosphere. That is why I was asking about the conduit or MC-HL cable. Our device (I.S. barrier) will clamp transient voltages, and limit the current so temperature limit, T4 is never exceeded by any device in our box or the wiring. The fuse we are using will be an IS safe fuse.

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        #4
        Since you are not attempting to qualify under Article 504, you do not have an intrinsically safe application. Under Section 501.135(B) you still have the problem of identifying your product/application for Division 2 since it will kick you back to Section 501.115(B).

        While identified (as applied to equipment) [another Article 100 defined term] does not necessarily require listing or labeling, it can be a monumental task establishing its Suitability [see Section 500.8(A)] for Division 2. While you are at it read and absorb all of Section 500.8.
        [COLOR=black]"Bob"[/COLOR]
        Robert B. Alexander, P.E.
        Answers based on 2017 NEC unless otherwise noted.

        Comment


          #5
          Terminology / Article 500

          Got it. The terminology is taking some getting used to. Much of Article 500 is captured in UL 60079-0, and 60079-11 intrinsically safe systems which is what I have been diving into. Yes, it is some work, but what I'm using to when designing systems for Naval and Aerospace customers. Thanks for clarification on terminology and pointing to the paragraphs we need. We are doing a preliminary design review with our regulatory laboratory shortly to see how well our assumptions meet their requirements.

          Comment


            #6
            If your current "[COLOR=#000000]regulatory laboratory" [/COLOR]is an NRTL, you should have no problem.

            BTW the UL 60069 series, while referenced heavily in Articles 505 and 506 for NEC Zone equipment, is not generally a recognized basis for equipment in NEC Divisions. They don't mix and match too well without an extremely knowledgeable designer.
            [COLOR=black]"Bob"[/COLOR]
            Robert B. Alexander, P.E.
            Answers based on 2017 NEC unless otherwise noted.

            Comment

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