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Thread: NEC 500.7(K)

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    NEC 500.7(K)

    NEC figure 90.3 states chapters 1-4 are general and 5-7 modify chapters 1-7.

    NEC 500.7(K). Using that article. Does it nullify the requirements of 501.105(B) and 501.115(B)?

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    Quote Originally Posted by Kendrick K View Post
    NEC figure 90.3 states chapters 1-4 are general and 5-7 modify chapters 1-7.

    NEC 500.7(K). Using that article. Does it nullify the requirements of 501.105(B) and 501.115(B)?
    Not necessarily. Combustible Gas Detection Systems are a protection technique limited to the applications listed in Sections 500.7(K) (1),(2), and (3). If a location were protected properly under Section 500.7(K), then Sections 501.105(B) or 501.115(B) requirements would only be modified, not nullified. However, the strict limitations of the Subsections 500.7(K) make proper application unlikely.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2017 NEC unless otherwise noted.

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    Expanding on application.

    Quote Originally Posted by rbalex View Post
    Not necessarily. Combustible Gas Detection Systems are a protection technique limited to the applications listed in Sections 500.7(K) (1),(2), and (3). If a location were protected properly under Section 500.7(K), then Sections 501.105(B) or 501.115(B) requirements would only be modified, not nullified. However, the strict limitations of the Subsections 500.7(K) make proper application unlikely.
    Inside the bubbles of a C1D2 area on an outdoor gas compressor. I have Industrial Control panels for unclassified locations installed in gasketed boxes. Inside those panels I have NON C1D2 rated devices such as breakers, switches, fuses, drives, and power supplies.
    Would adding gas detection equipment inside the gasketed boxes and properly sealing the equipment off, the conduit and cable connections with sealing fittings and seal offs from the outside air be a proper way to mitigate the area inside the industrial control panel to unclassified?
    If so, how do we get around 501.105 and 501.115 stating the equipment and components must be listed for a C1D2 area?

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    Quote Originally Posted by Kendrick K View Post
    Inside the bubbles of a C1D2 area on an outdoor gas compressor. I have Industrial Control panels for unclassified locations installed in gasketed boxes. Inside those panels I have NON C1D2 rated devices such as breakers, switches, fuses, drives, and power supplies.
    Would adding gas detection equipment inside the gasketed boxes and properly sealing the equipment off, the conduit and cable connections with sealing fittings and seal offs from the outside air be a proper way to mitigate the area inside the industrial control panel to unclassified?
    If so, how do we get around 501.105 and 501.115 stating the equipment and components must be listed for a C1D2 area?
    As I mentioned in my earlier post, you are limited to applications listed in Sections 500.7(K)(1),(2), and (3). In my opinion, your description of the installation doesn’t fit any of them.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2017 NEC unless otherwise noted.

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    Clarifications.

    Quote Originally Posted by rbalex View Post
    As I mentioned in my earlier post, you are limited to applications listed in Sections 500.7(K)(1),(2), and (3). In my opinion, your description of the installation doesn’t fit any of them.
    500.7 (K)(3) is the application. Talking with a Nationally Recognized Testing Laboratory (NRTL) field rep yesterday for 508 listings. He got on the phone their hazardous locations person for 698 listing for hazardous locations. Granted stringent criteria is required. The NRTL going off of basic understanding that the panel is a 508 rated panel, installed in a 698 area, with approved gas detection inside the 508 panel to call the interior of that panel unclassified not having to meet the requirements of 698 (IE NEC articles 501.105 and 501.115).

    The question and concern I have is. How can you de-classify a C1 D2 area to unclassified? I have been of the understanding you cannot declassify an area completely just lower the division of classification. Granted the area is inside a gasketed box installed inside a C1 D2 area.

    Example of a C1 D2 area with a switch in a rigid system for lights. You open a the switch box to replace the bad switch, the interior is all sooty. What happens, over time gas does build up in those conduit and box systems, the switch creates a spark igniting those gases, the box, seal off and expansion plate on the switch box did its job not allowing the ignited gases out of the box and conduit system.

    But as stated by the NRTL the job of the gas detection equipment in the 508 listed panel is to kill power before ignitable concentrations of gases or vapors builds up. Thus creating an unclassified area. Requiring all conduit and cable entries to have boundary seals installed on the cabinet. Correct?

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    You and the NRTL must reread 500.7(K)(3) carefully. The equipment inside the panel must still be suitable for Class I, Division 2. You cannot “de-classify” a location with gas detection alone. In fact, if you understand the basic definition of Division 2 correctly [500.5(B)(2)(1), last clause] then gas detection means the location must be Division 2 as a minimum. Furthermore, once you detect the gas you are instantly in a Division 1 location.

    The NRTL is erroneously attempting to apply a purging/pressurizing philosophy [NFPA 496] where the protection technique actually does alter the classification.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2017 NEC unless otherwise noted.

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    Clarification 2

    Quote Originally Posted by rbalex View Post
    You and the NRTL must reread 500.7(K)(3) carefully. The equipment inside the panel must still be suitable for Class I, Division 2. You cannot “de-classify” a location with gas detection alone. In fact, if you understand the basic definition of Division 2 correctly [500.5(B)(2)(1), last clause] then gas detection means the location must be Division 2 as a minimum. Furthermore, once you detect the gas you are instantly in a Division 1 location.

    The NRTL is erroneously attempting to apply a purging/pressurizing philosophy [NFPA 496] where the protection technique actually does alter the classification.
    (Note: the NRTL stated that the restrictions of such an installation as is being attempted are rigid and not commonly used.)

    How does API RP 500 2012 edition 6.5.1 come into play? According to that section. Use of gas detection along with vapor tight construction of the structure or and I quote (Similar Area) can be used to declassify an area.

    The engineer of this project and its design which I am questioning with the NRTL and through this form as resources for information, is using (Similar Area) as substantiation to use gas detection equipment inside the 508 industrial control panels to not have to relocate what is by definition equipment in NEC 100 out of the C1 D2 area.

    Granted this engineer has stamped and signed the documentation for this design. But it does not mean its right. And I in good conscience am trying to understand the whole thing before power gets connected and the equipment is processing flammable gases. As anybody whos been around the Electrical Industry for any amount of time, the NEC sometimes is GREY as with 500.7(K) which references the API in informational note 2.

    Unless this post changes the thinking on my question. Your opinion from previous posts the devices inside the 508 industrial control panels need to be rated for C1 D2 or installed in an Explosion proof enclosure.

    Gas detection equipment does NOT even though API RP 500 6.5.1 states you can do it, declassify the inside of the of an area through use of gas detection equipment and vapor tight construction or (similar area).

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    API RP500 Section 6.5.1 contains clear applications for NEC Sections 500.7(K)(1)or(2). (For which it was originally written in the first place) Note, however, RP500 is a recommended practice, not a code in itself. While it says a location may be "designated" for a lower classification, it simply means a lower grade of construction is permitted within its application; it does not mean the location is reclassified.

    Edit add: See NEC, 2002 Edition for the original text of 500.7(K).
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2017 NEC unless otherwise noted.

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