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Mounting Components on a Type Z Purged Enclosure

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    Mounting Components on a Type Z Purged Enclosure

    I have an enclosure residing in a CID2 area that I would like to apply Type Z pressurization to so that I can mount GP components inside the enclosure. I know inside the enclosure, general purpose components can be used.

    I have a touchscreen monitor that is itself rated for Class I Div 2. I want to mount the CID2 touchscreen on the purged enclosure. The enclosure will have a cut-out, and the touchscreen will be installed directly through the cutout on the enclosure door.

    Should I be concerned about pressurization effects on the touchscreen? Does the touchscreen need to be rated for the pressurization?
    Time is of the essence, and I am low on essence. ~ Graham Hill

    #2
    As long as you maintain proper pressure, your proposal is acceptable.
    [COLOR=black]"Bob"[/COLOR]
    Robert B. Alexander, P.E.
    Answers based on 2017 NEC unless otherwise noted.

    Comment


      #3
      Thank you for the response. My concern is if the Type Z pressurization can damage the touchscreen. Should the screen have a specific rating for the pressurization?
      Time is of the essence, and I am low on essence. ~ Graham Hill

      Comment


        #4
        Originally posted by fifty60 View Post
        Thank you for the response. My concern is if the Type Z pressurization can damage the touchscreen. Should the screen have a specific rating for the pressurization?
        Why don't you ask your whole question at the beginning? I don't believe I will attempt to answer any more of your questions in the future until you have had the opportunity to run some other responder around the garden first. In any case, the pressure differential for Type Z is fairly low and a "pressure rated" touch screen is unnecessary.
        [COLOR=black]"Bob"[/COLOR]
        Robert B. Alexander, P.E.
        Answers based on 2017 NEC unless otherwise noted.

        Comment


          #5
          Originally posted by rbalex View Post
          Why don't you ask your whole question at the beginning? I don't believe I will attempt to answer any more of your questions in the future until you have had the opportunity to run some other responder around the garden first. In any case, the pressure differential for Type Z is fairly low and a "pressure rated" touch screen is unnecessary.
          I asked this very question of AB once about Panelview terminals maybe 15 years ago. They came back with a list of model numbers that they felt were suitable for use in pressurized enclosures and some that were definitely not suitable. The product manager told me if it was not on the list it had not been verified one way or the other. There did not seem to be any discernible pattern of what was OK and what was not to me.
          Bob

          Comment


            #6
            Originally posted by petersonra View Post
            I asked this very question of AB once about Panelview terminals maybe 15 years ago. They came back with a list of model numbers that they felt were suitable for use in pressurized enclosures and some that were definitely not suitable. The product manager told me if it was not on the list it had not been verified one way or the other. There did not seem to be any discernible pattern of what was OK and what was not to me.
            Were all the units in question otherwise suitable for Class I, Division 2? Even those AB thought were “definitely not suitable”?
            [COLOR=black]"Bob"[/COLOR]
            Robert B. Alexander, P.E.
            Answers based on 2017 NEC unless otherwise noted.

            Comment


              #7
              Originally posted by rbalex View Post
              Were all the units in question otherwise suitable for Class I, Division 2? Even those AB thought were “definitely not suitable”?
              i.e., for purged/pressurized service.
              [COLOR=black]"Bob"[/COLOR]
              Robert B. Alexander, P.E.
              Answers based on 2017 NEC unless otherwise noted.

              Comment


                #8
                There is a big difference between being OK for use in a pressurized environment (with or without any additional hazardous location properties) and being used as part of the wall of the pressurized enclosure rather than mounted within it.
                It sounds like you are proposing the latter, and I can see potential objections on mechanical grounds.

                Comment


                  #9
                  As I understood it from talking to the product manager the issue was that some of the panelview terminals had membrane keyboards that the internal pressure would pull apart and some of them had touch screen overlays that had the same problem. Those were the ones that I said they referred to as definitely not suitable for pressurized environment. I think they were all rated for class 1 div 2 though but it was a long time ago and I don't specifically remember. Could be putting them in a separate unpressurized box and they would have been fine.
                  Bob

                  Comment


                    #10
                    Originally posted by petersonra View Post
                    As I understood it from talking to the product manager the issue was that some of the panelview terminals had membrane keyboards that the internal pressure would pull apart and some of them had touch screen overlays that had the same problem. Those were the ones that I said they referred to as definitely not suitable for pressurized environment. I think they were all rated for class 1 div 2 though but it was a long time ago and I don't specifically remember. Could be putting them in a separate unpressurized box and they would have been fine.
                    Well, that confirms one of our more common clichés, “When in doubt confirm with the manufacture.” However, I am curious what Section 500.7 protection technique the manufacturer used to aquire a Class I, Division 2 rating. Almost any one other than IS or NI that would be likely would also be likely to be robust enough to handle a modest pressure differential. And requiring IS or NI wouldn’t need a Class I, Division 2 rating in the first place.

                    While I’m not quite the fan of NFPA 496 that you are, I’ve never come across this particular restriction in over 50 years.

                    Unlike purging, NFPA 496 only requires a positive pressure be maintained for a Type Z pressurized enclosure and no specific flow rate is required.
                    [COLOR=black]"Bob"[/COLOR]
                    Robert B. Alexander, P.E.
                    Answers based on 2017 NEC unless otherwise noted.

                    Comment


                      #11
                      it wouldn't have created any hazard to pressurize the box one of the panel views was in that was deemed unsuitable for pressurization. Either the keyboard or the touch screen would have just eventually failed but presumably not in some way that would cause some hazard.

                      in fact now that I think about it they actually had some terminals that were specifically stated suitable for pressurization.
                      Bob

                      Comment


                        #12
                        Originally posted by petersonra View Post
                        it wouldn't have created any hazard to pressurize the box one of the panel views was in that was deemed unsuitable for pressurization. Either the keyboard or the touch screen would have just eventually failed but presumably not in some way that would cause some hazard.

                        in fact now that I think about it they actually had some terminals that were specifically stated suitable for pressurization.
                        That sounds reasonable. The truth is, while our control systems or electrical engineers may have specified a Type Z system, in my experience, we would have left it up to the panel fabricator to select the touchscreen and not worried about it. Unlike many current CSI type specs, unless there was a specific need, we rarely specified a brand or catalog number, only a performance requirement.
                        [COLOR=black]"Bob"[/COLOR]
                        Robert B. Alexander, P.E.
                        Answers based on 2017 NEC unless otherwise noted.

                        Comment


                          #13
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                          Bob

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                            #14
                            Originally posted by fifty60 View Post
                            Thank you for the response. My concern is if the Type Z pressurization can damage the touchscreen. Should the screen have a specific rating for the pressurization?
                            I have over 30 installations with HMI touch screens (various mfgr's) and have had zero issues w/ pressure on the panel, nor keeping a purge to meet the purge kit requirements. I think you'll be fine. If you're running anything over a few ounces of pressure/psi, you've got other issues you need to take care of.

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