Results 1 to 8 of 8

Thread: Shunt Trip Breakers/Elevators

  1. #1
    Join Date
    Oct 2010
    Posts
    3

    Question Shunt Trip Breakers/Elevators

    As an Elevator Inspector I have come across a common practice having the shunt trip breaker installed in the machine room and it being utilized as the elevator disconnect. NEC 620.51(B) requires the "power supply" to be opened prior to application of water. And based on the single line drawing figure 620.13 it can be presumed that the power supply originates from a MDP outside an elevator machine room. It is my concern that with the shunt breaker inside the room there is still a shock hazzard present in the room on the line side, which could electrically charge the conduit etc... additionally the code doesn't indicate a NEMA-4 enclosure requirement. And after all the disconnect in the room is only a means of opening the "power supply" and not the source of power. Your thoughts please. Thanks Jim

  2. #2
    Join Date
    Feb 2003
    Location
    N.C.
    Posts
    15,189
    Quote Originally Posted by JKBenson View Post
    NEC 620.51(B) requires the "power supply" to be opened prior to application of water.
    Per the 2011 NEC (because that is what I'm looking at right now) the actual wording is

    (B) Operation. No provision shall be made to open or
    close this disconnecting means from any other part of the
    premises. If sprinklers are installed in hoistways, machine
    rooms, control rooms, machinery spaces, or control spaces,
    the disconnecting means shall be permitted to automatically
    open the power supply to the affected elevator(s) prior to
    the application of water. No provision shall be made to
    automatically close this disconnecting means. Power shall
    only be restored by manual means.
    which specifically allows the disconnecting means that incorporates the shunt trip mechanism to be the automatic disconnecting means under sprinkler activation.

    Roger
    Moderator

  3. #3
    Join Date
    Oct 2010
    Posts
    3

    Shunt Breaker/Elevator

    I read it as a two part reference with normal disconnecting operation to be performed in the machine room however the method of inducing shunt trip is through devices which do send a signial to a different part of the premises via a fire panel and yes I agree that the disconnecting means shall be automatic, but I guess I should clarify my position. I believe the intent of the wording "power supply" is that upon receiving the signial to shunt via the heat detector hopefully after recall that the main line power be removed from the room which is supported by FPN at the end of section B indicating reducing shock hazards. With that being said should the shunt breaker be located outside of the machine room?

  4. #4
    Join Date
    Jun 2003
    Posts
    5,619
    All the conduit and the disconnect enclosure would all be grounded, so I don't really see any shock hazzard.

    There also wouldn't typically be anyone in the equipment room if the sprinkler in that room went off anyway.

    And we don't have to shut off power in any other parts of the buidling, before the sprinklers go off, so I really don't see why we would need to in the elevator equipment room.

    Steve

  5. #5
    Join Date
    Jan 2007
    Posts
    1,129
    This is an interesting point.
    I always thought the purpose of the shunt trip was to remove the power from the controller before the water was applied, but, it seems as though the pupose of it is to remove the power from the elevator so no one can use it.

    If the intent was to remove the power before water was applied,to keep things from shorting out or someone getting shocked, you would have to disable the power to all the electrical devices in that area.

    What is the true purpose of the shunt trip?

  6. #6
    Join Date
    Nov 2007
    Location
    Louisville, KY
    Posts
    389
    I can't remember where I read it, but once I read the purpose of the shunt trip is to prevent water from getting on the elevator braking system and causing an elevator free fall. This does not explain why you would need it on a hydraulic elevator.

  7. #7
    Join Date
    Jun 2003
    Posts
    5,619
    Quote Originally Posted by dhalleron View Post
    I can't remember where I read it, but once I read the purpose of the shunt trip is to prevent water from getting on the elevator braking system and causing an elevator free fall. This does not explain why you would need it on a hydraulic elevator.

    Yes, I think I've heard that also. But I think the general idea is to just shut down power to the elevator so nobody can use it after any part of it has been compromised by the application of water.

    I don't think the idea it to shut off all power to the equipment rooms. We often have electrical rooms with main switchgear, panels, etc. that are sprinklered. And there isn't any requirement to shut off power to those areas before the sprinklers go off. Just like there is no requirement to shut off lights and receptacles in an occupied area before the sprinklers go off.

    I think its pretty much assumed that when the sprinklers go off, people will leave the area (most people don't like to be showered with stinky sprinkler water, and the fire alarm is going off too) until trained personel come in for firefighting or for damage repair and cleanup.

    Steve

  8. #8
    Join Date
    Oct 2010
    Posts
    3

    Shunt Trip/Elevators

    Shunt tripping elevators has been a sticking point with many of my fellow Inspectors here in Pennsylvania, and the elevator mechanics. The intent is that after recall to the effected machine room or hoistway is to remove main power prior to water and that the flashing fire hat in the car is to alert Fire Fighters of the potential of the power being disconnected. I receive many questions from the mechanics why the branch circuits aren't shunted and my answer is that the device sending the shunt signial just may be a head that went bad or that someone damaged it and that we wouldn't want to turn the lights out on the passengers they would already be upset from the abrupt stop ( there may be another reasons). And with hydraulic elevators there is the concern for the flash point of the oil. And true the water in the system really stinks...

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •