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Thread: Switch Gauge in Class I Div 2

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    Switch Gauge in Class I Div 2

    I'm looking into retrofitting a natural gas compression skid for Class I Div 2 and I need to clear up some doubts I have about an existing switch gauge on the skid.

    Here's the current gauge(it's the SDB500, not the XP model): http://www.fwmurphy.com/uploaded/doc.../pdfs/7543.pdf

    I checked with the manufacturer and the current gauge is not listed for CID2. Being that this gauge has an internal switch, I believe it qualifies as a switch under 501.105(B)(2) and does not meet any of the exceptions. Is this correct? If so, I'll be replacing it with the XP model and it seems that I'll also need a conduit seal between the gauge and the skid's terminal box.

    For context:
    The switch gauge sends a shutdown signal to the control panel via a 12VDC signal. The control panel will be mounted in an unclassified area. All conduit on the skid is threaded steel and the enclosure for the wiring terminals on the skid will be NEMA 4 as it isn't required to be XP.

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    potentially you could make the circuit to the existing switch an intrinsically safe circuit and thus not need to replace the switch. it is not a real difficult thing to do. there are some rules to follow but they are fairly straightforward.
    Bob

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    That had certainly crossed my mind. Depending on the cost differential, it's my other option. I'm not, however, familiar with any specific requirements for the control drawing if I go the IS route. Should it be a typical control drawing, specifically labeling the IS components?

    I would also need a separate enclosure for the IS barriers, correct?

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    Quote Originally Posted by STucker View Post
    That had certainly crossed my mind. Depending on the cost differential, it's my other option. I'm not, however, familiar with any specific requirements for the control drawing if I go the IS route. Should it be a typical control drawing, specifically labeling the IS components?

    I would also need a separate enclosure for the IS barriers, correct?
    • Your first analysis was correct.
    • IS barriers alone will not make an IS system. See Section 504.10(A).
    • You don't necessarily need a separate IS enclosure - but the barriers will most likely need to be in an unclassified location to begin with. (That will probably show up when Section 504.10(A) is satisfied)
    • IS is rarely economically justified unless it is part of the initial overall facility design.
    • IS rules aren't nearly as simple as some believe. See ANSI/ISA-RP 12.06.01
    • I am modestly (meaning not too) concerned about the CSA listing of the explosionproof version. Just make sure it is listed to a NRTL standard. It most likely will be.
    Last edited by rbalex; 03-07-18 at 03:41 PM.

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    I just had another thought concerning conduit seals. A piece of explosion proof equipment, such as a gauge, is connected to another piece of equipment that's not required to be XP, but is class rated(CID2). Is a conduit seal needed between the XP equipment and the equipment that is solely class rated, or would a seal only be needed where the it connected to the Junction box?

    Referring to 501.15(A)(1)- I suppose the real question I'm asking is: "Is the XP gauge considered an enclosure?"

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    Quote Originally Posted by STucker View Post
    I just had another thought concerning conduit seals. A piece of explosion proof equipment, such as a gauge, is connected to another piece of equipment that's not required to be XP, but is class rated(CID2). Is a conduit seal needed between the XP equipment and the equipment that is solely class rated, or would a seal only be needed where the it connected to the Junction box?

    Referring to 501.15(A)(1)- I suppose the real question I'm asking is: "Is the XP gauge considered an enclosure?"
    Enclosure is a defined term. [Article 100]. Your first analysis was correct.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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