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Thread: 501.17 Process Sealing

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    501.17 Process Sealing

    If there is a pressure switch that meets the 504.2 definition of simple apparatus, and is connected to an Intrinsically Safe Isolator, does 501.17 apply in any way to this pressure switch.

    501.17 says "Process-connected electrical equipment that does not rely on a single process seal or is lested and marked "single seal" or "dual seal"" shall not be re required to be provided with an additional means of sealing..."

    Since the intrinsic isolator is used, then the process seal is not relied upon for protection. Or, would the intrinsic isolator and an extra means of process sealing need to be used per 501.17.

    It is a Class I Division 2 location...

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    Quote Originally Posted by fifty60 View Post
    If there is a pressure switch that meets the 504.2 definition of simple apparatus, and is connected to an Intrinsically Safe Isolator, does 501.17 apply in any way to this pressure switch.
    ...
    Yes, it still applies. Unlike the general purpose of seals described in Section 501.15 Informational Note No. 1, "[a] process seal is a device to prevent the migration of process fluids from the designed containment into the external electrical system." [Second sentence Section 501.17] Being an intrinsically safe, simple apparatus or not is irrelevant.

    Actually, the purpose even goes beyond that somewhat. It is to prevent the migration of process fluids (gas or liquid) from being transmitted to other parts of the facility through the electrical system.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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    504.20 lists the wiring requirements for IS systems. It says that methosds suitable for unclassified locations can be used, and directs to 504.70 for sealing. 504.70 mentions that 501.15, 502.15, 505.16, and 506.16 need to be followed, but does not mention 501.17.

    I think i am not fully understanding the intention of 501.17. It is not necessarilly referring to conduit seals, but the actual process seal on the equipment. But an acceptable method to satisfy 501.17 is a conduit or cable seal? Am I understanding that correctly?
    Time is of the essence, and I am low on essence. ~ Graham Hill

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    I'm going to suggest you memorize the last sentence of Section 90.1(A).

    Also read Section 504.3 carefully.

    Until 2011, Section 501.17 was largely reflected in Subsection 501.15(F)(3); i.e., it was part of Section 501.15 until 2011. In 2011 it was decided to expand it and give it its own Section to list suitable "process sealing" methods. Its omission from the list of cross-references in Section 504.70 was probably an oversight.

    It is important to understand Intrinsically Safe Systems are not some panacea for hazardous locations - it only deals with electrical ignition sources, not process fluid migrations. Any "trained person" wouldn't think about ignoring Section 501.17.

    Quote Originally Posted by fifty60 View Post
    ...
    I think i am not fully understanding the intention of 501.17. It is not necessarilly referring to conduit seals, but the actual process seal on the equipment. But an acceptable method to satisfy 501.17 is a conduit or cable seal? Am I understanding that correctly?
    It's one of several suitable methods.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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    For a float switch that is regarded as a passive component and a Simple Apparatus, and is wired to an intrinsically safe isolator, what would applying 501.17 (2) look like? Would I simply run a listed type MI cable from the IS isolator to the pressure switch?
    Time is of the essence, and I am low on essence. ~ Graham Hill

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    Quote Originally Posted by fifty60 View Post
    For a float switch that is regarded as a passive component and a Simple Apparatus, and is wired to an intrinsically safe isolator, what would applying 501.17 (2) look like? Would I simply run a listed type MI cable from the IS isolator to the pressure switch?
    I apologize for my tardy response.

    You need to ask what would it look like if you weren't enamored with IS; i.e., what are you doing, "... to prevent the migration of process fluids from the designed containment into the external electrical system?" "Intrinsically Safe" alone won't cut it.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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    to further rbalex's remark, you would install an approved seal at the transition of classification areas to physically prevent process vapors/fluids from commingling with the electrical system. this also serves as a physical barrier should there be an ignition in the classified space

    it might be helpful review why we install sealing devices and what happens if there is an explosion with or without seals. ECM article

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    What is meant by the "external electrical system"? Is it the electrical system in the non-hazardous area? What if the process connected equipment (a float switch for example) only has electrical wiring going to a Type Z purged enclosure located inside the Hazardous area?

    Would using MI cable between the float switch and where the wire terminates at the purged enclosure suffice to satisfy the process seal requirement?
    Time is of the essence, and I am low on essence. ~ Graham Hill

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    Quote Originally Posted by fifty60 View Post
    What is meant by the "external electrical system"? Is it the electrical system in the non-hazardous area? What if the process connected equipment (a float switch for example) only has electrical wiring going to a Type Z purged enclosure located inside the Hazardous area?
    In most cases I have seen, people put a seal at the pressurized enclosure where anything enters the enclosure just to avoid loss of the pressurizing gas, so no need to add another seal since it is already there.

    Quote Originally Posted by fifty60 View Post
    Would using MI cable between the float switch and where the wire terminates at the purged enclosure suffice to satisfy the process seal requirement?
    I think the MI cable would need to be sealed. I am not real familiar with MI cable but it appears to me to be basically a semi-flexible conduit and probably should be treated like any other raceway as far as sealing goes.

    Incidentally, I have seen at least one case where a designer put a junction box on the bottom of the pressurized enclosure so the external IS protected equipment could come in there and then used cord grips to run the cables from the junction box into the pressurized enclosure. Presumably the cord grip was considered an adequate seal. I don't know how Mr. Alexander would see that approach, but it seems adequate to me.
    Bob

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    Quote Originally Posted by fifty60 View Post
    What is meant by the "external electrical system"? Is it the electrical system in the non-hazardous area? What if the process connected equipment (a float switch for example) only has electrical wiring going to a Type Z purged enclosure located inside the Hazardous area?

    Would using MI cable between the float switch and where the wire terminates at the purged enclosure suffice to satisfy the process seal requirement?
    From Section 501.17: "... A process seal is a device to prevent the migration of process fluids from the designed containment into the external electrical system. ..." Most people would understand the "external electrical system" as the part that is beyond or outside of the "designed containment".

    With regard to MI cable you have read Section 501.17(2) - right?
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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