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Non-Incendive Circuit - ESD Pushbutton

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    Non-Incendive Circuit - ESD Pushbutton

    Hi, I have a doubt about the code and if I am allowed or not to install a general purpose enclosure with an emergency shutdown (ESD) push button in a C1/D2.
    I am looking at 501.150...

    501.150 Signaling, Alarm, Remote-Control,
    and Communications Systems.


    (B) Class I, Division 2. In Class I, Division 2 locations, signaling, alarm, remote-control, and communications systems shall comply with 501.150(B)(1) through (B)(4).

    (1) Contacts. Switches, circuit breakers, and make-and-break contacts of pushbuttons, relays, alarm bells, and horns shall have enclosures identified for Class I, Division 1 locations in accordance with 501.105(A).
    Exception: General-purpose enclosures shall be permitted if current-interrupting contacts are one of the following:

    (1) Immersed in oil
    (2) Enclosed within a chamber hermetically sealed against
    the entrance of gases or vapors
    (3) In nonincendive circuits
    (4) Part of a listed nonincendive component



    So this circuit is a non-incendive circuit, with this in mind, I should be allowed to use a general purpose enclosure with an ESD push button? Also I would not need a seal (probably just for the boundary) since I do not have an explosion proof enclosure.

    What confuses me is 501.115...

    501.115 Switches, Circuit Breakers, Motor Controllers,
    and Fuses.


    (B) Class I, Division 2. Switches, circuit breakers, motor controllers, and fuses in Class I, Division 2 locations shall comply with 501.115(B)(1) through (B)(4).

    (1) Type Required. Circuit breakers, motor controllers, and switches intended to interrupt current in the normal performance of the function for which they are installed shall be provided with enclosures identified for Class I, Division 1 locations in accordance with 501.105(A), unless general-purpose enclosures are provided and any of the following apply:

    (1) The interruption of current occurs within a chamber hermetically sealed against the entrance of gases and vapors.
    (2) The current make-and-break contacts are oil-immersed and of the general-purpose type having a 50-mm (2-in.) minimum immersion for power contacts and a 25-mm (1-in.) minimum immersion for control contacts.
    (3) The interruption of current occurs within an enclosure, identified for the location, and marked “Leads Factory Sealed,” or “Factory Sealed,” or “Seal not Required,” or equivalent.
    (4) The device is a solid state, switching control without contacts, where the surface temperature does not exceed 80 percent of the autoignition temperature in degrees Celsius of the gas or vapor involved.


    So the above is also talking about enclosures but does not list the non-incendive exception.... Is this "enclosure" different from the above "enclosure"? I think 501.115 is talking about the encasing of the switch itself correct? Not the actual enclosure as in junction box, panel, etc...


    So if I understand correctly, I would be allowed to install a general purpose enclosure, with no end seal... And inside an ESD pushhbutton contact, which I would be able to use one of the exceptions of 501.115 for C1/D2 . In other words, a hermetically sealed pushbutton would be ok.
    If I install a regular pushbutton with the non-incendive circuit, I would need to install per 501.105(A) which mentions having explosion proof, purged or pressurized.

    Thanks in advance...
    Yogi

    #2
    I believe your answer is in Section 501.10(B)(3).

    Basically, a nonincendive system in Class I, Division 2 can be installed as if it were in an unclassified location. The additional relevant conditions are that it be installed per a control diagram AND any boundary be sealed per Section 501.15(B)(2).

    A side note: It is very difficult to achieve a nonincendive motor circuit as applied to Section 501.150; however, its control circuit may very well be nonincendive.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2017 NEC unless otherwise noted.

    Comment


      #3
      Thanks Bob, although 501.10 (B)(3) talks about wiring methods which is not really the question at hand. Or am I not seeing something relevant there?
      Yes, so boundary would have a seal (non explosion proof), max 10ft on either side.

      Thanks for the side note, this would not be for a motor circuit... It's an input to a PLC for an emergency stop.

      My doubt still lingers in which I am wondering if I can install a regular (non-classified) pushbutton on a general purpose enclosure, with this being a non-incendive circuit.

      Thanks !
      Yogi

      Comment


        #4
        I understand your concern - so you can either trust me and basically treat NI for Class I, Division 2 as you would IS for Division 1 which gets a whole Article for itself in Article 504 OR you can get a copy of ANSI/ISA 12.12.01 which is referenced in various nonincendive definitions in Article 100. Since ANSI/ISA 12.12.01 is ANSI sanctioned it is FedOSHA (and most StateOSHAs) enforceable. I no longer have a copy.
        "Bob"
        Robert B. Alexander, P.E.
        Answers based on 2017 NEC unless otherwise noted.

        Comment


          #5
          Oh ok... I'll take a look at 504 then.
          Thanks!
          Yogi

          Comment


            #6
            That's fine - remember the rules are only similar, not identical.
            "Bob"
            Robert B. Alexander, P.E.
            Answers based on 2017 NEC unless otherwise noted.

            Comment

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