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Thread: Flourescent Light w/Motion Switch

  1. #1
    DIY Junior Member MoMan's Avatar
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    Question Flourescent Light w/Motion Switch

    I have installed a Utilitech fluorescent fixture (with two 38w tubes) into my garage ceiling. And I'm using an existing motion detector switch.
    This new light glows when in the motion detect mode (the old one did not) yet it works fine, coming on full when motion is detected.
    Is there a safety issue here? Will this 'glow' cause my ballast to go out sooner?
    Why did the old one not glow, yet the new one does? The new one seems to be a newer energy saving model.

    I'm mostly concerned with safety and life of fixture. Thanks.

  2. #2
    Plumber jimbo's Avatar
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    Bad things are about to happen.

    Fluorescent bulbs are not compatible with many simple control devices like motion sensors and photocells.

    If you want motion control, you need to buy a more sophisticated vacancy or occupancy sensor switch which specifically is says compatible with fluorescent bulbs.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Many motion sensors remain powered by being inline with the load and expect the load to be something like a lightbulb. Yours apparantly does and is seeing the ballast transformer as a load and running current through it to power itself. There are some that do not connect and use the load to complete the circuit, and use a relay to power the load when motion is sensed. this can be done with SS, but it must be designed for it and generally, would require access to both the hot AND neutral to function.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member MoMan's Avatar
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    Quote Originally Posted by jimbo View Post
    Bad things are about to happen.

    Fluorescent bulbs are not compatible with many simple control devices like motion sensors and photocells.

    If you want motion control, you need to buy a more sophisticated vacancy or occupancy sensor switch which specifically is says compatible with fluorescent bulbs.


    "Bad things?" Like what? The motion sensor is working even if it is not as it is supposed to be.
    Please address the safety and ballast question. Thank you.
    MoMan

  5. #5
    Plumber jimbo's Avatar
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    I can't say if "safety" i.e. fire is an issue. But you will experience short bulb life, possibly short ballast life.
    When a manufacturer says "don't do it" they usually have good reason for that.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    If the motion sensor isn't using something like a relay to turn the lamps on/off, it is constantly supplying a small voltage to the ballast so that it can power itself, IOW, it's in series with the load and the load is completing the circuit...no complete circuit, no power to make the motion sensor work. That's why I said a better choice for this is a motion sensor that has an available neutral so it doesn't need the load to complete the circuit. When the load is not getting the full voltage and has constant low voltage being applied, it can result is short life, increased heat, and potentially a fire. Also, some motion sensors, even when they are tripped, without a relay, act like an in-line load, which reduces the voltage to the device. Now, they are designed, when on, to minimize their internal voltage drop, but it's never a true short like an on/off switch is. A relay acts as an on/off switch. Unless the fixture and the motion sensor are designed to work together, short life and extra heat and problems can occur.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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