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Thread: Seal-off at explosion-proof motor?

  1. #1
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    Seal-off at explosion-proof motor?

    My understanding of seal-offs is that they are required at hazardous location boundaries, and where needed to isolate potentially arcing components (like switches). If an electric motor is rated as explosion-proof, I don't believe it requires a seal-off where the conduit enters the junction box housing the wiring splices. Is this correct?

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    Quote Originally Posted by Jon456 View Post
    ... Is this correct?
    Conditionally.

    See 501.15 for the specifics... but as an example, if the [raceway, cable] entry to the peckerhead is 2" or larger, seals are required. And for clarity, that assumes there will be splices in the peckerhead.
    I'll never get there. No matter where I go, I'm always here.

  3. #3
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    Quote Originally Posted by Smart $ View Post
    Conditionally.

    See 501.15 for the specifics... but as an example, if the [raceway, cable] entry to the peckerhead is 2" or larger, seals are required. And for clarity, that assumes there will be splices in the peckerhead.
    I have read about the seal-off requirement on conduit 2" or larger. Sorry for not mentioning that this is 1/2" rigid metallic conduit.

    Other than certain particular people, I have no idea what a peckerhead is.

  4. #4
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    The "formal" term is motor terminal housing (Section 430.12) but motor terminal box or junction box are probably more common and perfectly acceptable.

    You also failed to mention whether the motor was required to be explosionproof. Simply because it is explosionproof does not necessarily require it to be sealed in Division 2. Most three-phase motors in Division 2 are not required to be explosionproof and most single-phase motors in Division 2 are required to be.

    Most explosionproof motors have a factory seal installed between the motor terminal housing and the main motor enclosure. Such motors will have a marking on the terminal housing stating it is factory sealed or something similar. The 2 inch entry seal applies only to Division 1.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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    Quote Originally Posted by rbalex View Post
    The "formal" term is motor terminal housing (Section 430.12) but motor terminal box or junction box are probably more common and perfectly acceptable.

    You also failed to mention whether the motor was required to be explosionproof. Simply because it is explosionproof does not necessarily require it to be sealed in Division 2. Most three-phase motors in Division 2 are not required to be explosionproof and most single-phase motors in Division 2 are required to be.

    Most explosionproof motors have a factory seal installed between the motor terminal housing and the main motor enclosure. Such motors will have a marking on the terminal housing stating it is factory sealed or something similar. The 2 inch entry seal applies only to Division 1.
    Thank you again for your elucidation.

    The motor is single-phase, 240VAC; it is in a Class 1 Division 2 area. It does have a factory seal between the motor terminal housing and the main motor enclosure.

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    Quote Originally Posted by Jon456 View Post
    Thank you again for your elucidation.

    The motor is single-phase, 240VAC; it is in a Class 1 Division 2 area. It does have a factory seal between the motor terminal housing and the main motor enclosure.
    So what is your conclusion: seal required or not?
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    Quote Originally Posted by Jon456 View Post

    Other than certain particular people, I have no idea what a peckerhead is.
    Your decade on the Forum has enlightened you, I assume
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    Quote Originally Posted by Smart $ View Post
    So what is your conclusion: seal required or not?
    I conclude that no seal-off is required at the motor terminal box. However, there will be a seal-off within 18" of the explosion-proof switch that energizes the motor. And there will be a seal-off on the conduit bringing power to the equipment pad where that conduit exits the Class 1 Div 2 boundary.

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    Quote Originally Posted by augie47 View Post
    Your decade on the Forum has enlightened you, I assume
    Both enlightened, and humbled.

  10. #10
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    Quote Originally Posted by Jon456 View Post
    I conclude that no seal-off is required at the motor terminal box. However, there will be a seal-off within 18" of the explosion-proof switch that energizes the motor. And there will be a seal-off on the conduit bringing power to the equipment pad where that conduit exits the Class 1 Div 2 boundary.
    Sounds good to me.
    I'll never get there. No matter where I go, I'm always here.


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