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Thread: Class I Div. 2 Gr. D Motor Enigma

  1. #1
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    Class I Div. 2 Gr. D Motor Enigma

    I'm working on installation specifications for a process skid provided by one of our vendors. The motor is in a Class I Div. 2 Gr. D location, and the nameplate identifies it for use in this location. However, the motor has several RTDs that were installed by the factory - and the motor nameplate also says "for safe area"! This is a WEG W22 series motor, and based on the part number I believe it was custom made by WEG for the vendor. In addition, the technical brochure does not show the "for safe area" designation on the motor nameplate template. The RTDs are to terminate in a nearby Class I Div. 2 enclosure with intrinsically safe I/O.

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    I'm having a hard time rectifying this with NEC 2017:

    501.125 Motors and Generators.
    (B) Class I, Division 2. In Class I, Division 2 locations, motors, generators, and other rotating electrical machinery shall comply with (1), (2), or (3). They shall also comply with (4) and (5), if applicable.
    (1) Be identified for Class I, Division 2 locations, or
    (2) Be identified for Class I, Division 1 locations where sliding contacts, centrifugal or other types of switching mechanism (including motor overcurrent, overloading, and overtemperature devices), or integral resistance devices, either while starting or while running, are employed, or
    (3) Be open or nonexplosionproof enclosed motors, such as squirrel-cage induction motors without brushes, switching mechanisms, or similar arc-producing devices that are not identified for use in a Class I, Division 2 location.

    To break it down into a few points:
    1. Does (1) take precedence over (2) here, since the nameplate indicates that it is listed for this area? But it could also be argued that the "for safe area" designation invalidates the classified area listing.
    2. Do manufacturer installed RTDs count as "integral resistance devices"? I can't seem to find a definition for what an "integral resistance device" might be. Would (2) still apply if said "integral resistance devices" are intrinsically safe?

    And the potential outcomes:
    1. The motor is acceptable for the location, including the RTDs. No conduit seals will be necessary beyond the boundary seal from the motor controller raceway (which is in an unclassified area)
    2. The motor is not acceptable, and is required to be rated CID1, and when the appropriate motor is obtained all of the necessary conduit seals for a CID1 application will be required.

    Outcome #2 could be very messy.

    It's also worth noting here that this is an agriculture project and there is technically no AHJ, beyond the owner's independent engineers. Despite this, we're dedicated to sticking to industry standards to avoid catastrophic outcomes or disputes with the owner.

    Any guidance here would be very helpful.
    Last edited by sym; 12-29-17 at 04:42 PM.

  2. #2
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    There is no order of precedence of Subsections unless it is specifically stated.

    Unless the RTDs are expected to generate temperatures in excess of the process material’s T-Code that creates the hazardous location, they can be ignored. This is especially true if they are part of an intrinsically safe system. However, they must be indicated in a manufacturer’s control drawing per Section 504.10(A).

    Section 501.125(B)(2) is basically looking for thermal overload devices.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
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    I appreciate the reply. My confusion stemmed from the definition of an "integral resistance device".

    Does the ability to ignore the RTDs stem from the application of the definition of a "simple apparatus" as laid out in 504.10(D)? Or am I overthinking it?

    In addition, does the "manufacturer" for the control drawing need to be the OEM (WEG in this case), or more simply the panel builder (or in this case, skid builder)?

    Edit: I found the definition for "control drawing" per Article 100. My interpretation is that the "manufacturer" would actually be the manufacturer of the intrinsically safe RTD input module (Siemens in this case), as they are the manufacturer of the "associated apparatus", given that we are able to consider the RTDs to be a "simple apparatus" as outlined above.

    I apologize if I'm being pedantic, but my intent here is to learn as much as I can during this project. This is my first major foray into classified area requirements.
    Last edited by sym; 12-29-17 at 09:49 PM.

  4. #4
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    Actually, since RTDs aren’t heat producers in themselves is the reason they can be ignored, simple apparatus or not.

    Your follow up understanding of control drawing is correct, the manufacturer that establishes that a system is intrinsically safe is responsible for creating the document.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  5. #5
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    Perfect. I believe we have connected all of the dots. Thanks again for your clarification.

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