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Thread: Disconnecting means, CL1 DIV2 fixed electric space heater

  1. #1
    Join Date
    Nov 2017
    Location
    Denver, CO, USA
    Posts
    10

    Disconnecting means, CL1 DIV2 fixed electric space heater

    Greetings, my first post (moved from NEC, got zero responses):

    We have a CL1 DIV2 space with a 480V, 3-phase, ceiling mounted heater, which contains a 1/2HP 480V 3-ph fan motor. The heater was not ordered with the on-board disconnecting means (it is a 15 kW Ruffneck FX5-480-360-150-WT). NEC 2017 sections 424, 422 and 430 are all cross-referenced when you try to decode this.

    The heater branch circuit originates in a control panel outdoors, outside the hazardous area. The incoming 480V line to this panel hits a distribution block, then feeds the control transformer, a starter, and the correctly-sized, panel-mounted, 25A 3P breaker that serves this heater.

    My question is, may I put the disconnecting means outside the hazardous area to avoid the expensive explosion proof disconnect? Is there any chance this 25A breaker in the control panel can serve as the disconnecting means? My thinking is no, as below. I think the disconnect has to be within sight, and therefore explosion proof, but it's confusing.

    Since the unit does not have the on-board disconnect, and no supplementary O.C. protection, I think you end up at 424.19 (B) (2), which requires a disconnecting means within sight, or compliant with 424.19 (A) (2).

    Then 424.19 (A) (2) allows either (1), a disconnect within sight and compliant with 430 Part IX,

    Or (2) "Where a motor(s) of more than 1∕8 hp and the heater are provided with a single unit switch that complies with 422.34(A), (B), (C), or (D), the disconnecting means shall be permitted to be out of sight from the motor controller."

    But 422.34 (D "other occupancy") only applies if the disconnect (unit switch) is part of the appliance.

    It is like being led with an imaginary carrot, but I think the only remaining option is the XP disconnect, within sight. Anyone see anything else?

    Thanks, looking forward to being part of this community.

  2. #2
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
    Posts
    5,191
    I wish you had left this in the NEC forum because this forum does not speak to your situation other than selecting the disconnect’s enclosure.

    That said, you have basically analyzed your situation correctly. I wish it were otherwise for classified locations but, unfortunately, fundamental safety rules want disconnects “in sight” of the subject equipment. Unless it is “impracticable” (read that “damn near impossible”) to do otherwise, that is your case.

    Despite cautions, proper designs, and training to the contrary it is still very tempting to use a disconnecting means to shut down equipment in an emergency. That can be extremely dangerous in hazardous locations. (If it were necessary, I would want it far away and out of sight, if possible.) Section 430.102(B)(2)(a) Exception IN speaks vaguely to the subject.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
    Join Date
    Nov 2017
    Location
    Denver, CO, USA
    Posts
    10
    Thanks Bob, the only reason I moved it to the Classified Location section is because I got zero responses in NEC. It worked...

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