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Thread: Another Emergency Lighting Thread

  1. #11
    Join Date
    Jul 2007
    Posts
    356
    emerg. lights are going to be powered by an emerg. panel circuit. The over-ride relay is only to override the switch position of the emerg. fixtures, that's it. So, they are powered by an emerg. circuit, but the relay has a normal ckt wired to it only to sense loss of normal power.

    So if you've lost power to a certain area of emerg. fixtures you've lost your emergency circuit.

    Am I wrong?

  2. #12
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    5,438
    Quote Originally Posted by IMFOTP View Post
    Say you're an owner of a building/campus with 500+ emergency fixtures, would you rather have 500+ battery packs to maintain or one genset/transfer switch. The expense of replacing battery packs every, idk, 5years can add up. Secondly, with a genset, you can expect full light output from emergency fixtures (battery packs typically don't run fixtures at full light output), hopefully reducing the sheer number needed.

    Generally speaking, emergency fixtures will have a device that senses the presence of normal power, when the normal power circuit is lost the device bypasses the switch state and says, turn on. If you loose power on any branch circuit feeding lighting, the emergency fixtures in that area would override the switch state and turn on, as they are powered by an emergency circuit. The emergency circuit is fed from a transfer switch (transfer switch is fed by normal power and backed up by genset). Transfer switch tells genset to turn on when normal feed is lost.

    That's a quick and dirty explanation, I'd suggest a google search.
    Having maintained a hotel with that many emergency lights and exit signs, I can say that doing the required monthly checks does not take that long, and if there are failures, they can be replaced for a much lower cost than maintaining an emergency generator. I'll also worked at one such hotel that had an emergency generator versus battery backup lights, that generator was eventually mothballed and battery backup lights installed. a hotel or School maintenance man can easily work on/change an emergency light out with another $15 unit, not so much with a legally required emergency generator.
    Electricians do it until it Hertz!

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