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Smoke detectors and dimmers

Northern Spark

I've noticed in domestic smoke and heat detector's instructions it is stating that dimmers must not be on the same circuit.

Is this because of the noise that can be imposed?

Is it likely to result in an alarm not detecting a fire?

Parents
  • 0

    It is indeed due to conducted emissions from the dimmers, which slice the square mains cycle to give the dimming effect,

    Arguably it is an admission both that the filtering standards for permitted noise getting out of dimmers allow noise that is too high, and that the standards for filtering for immunity to  noise getting into smoke alarms are inadequate.

    Sadly there will be layouts in some buildings where being on another circuit in the same CU does not significantly protect against such effects and additional filtering would be a better solution. Bur a sentence in the instructions passing the buck is cheaper for the manufacturers.

    Without seeing the test results we do not know if the smoke alarms are blinded and do not sound, or are triggered to false alarm, in the presence of mains borne interference, but we can be pretty sure they do not perform to spec, or it would not have been mentioned at all.

    Mike.

Reply
  • 0

    It is indeed due to conducted emissions from the dimmers, which slice the square mains cycle to give the dimming effect,

    Arguably it is an admission both that the filtering standards for permitted noise getting out of dimmers allow noise that is too high, and that the standards for filtering for immunity to  noise getting into smoke alarms are inadequate.

    Sadly there will be layouts in some buildings where being on another circuit in the same CU does not significantly protect against such effects and additional filtering would be a better solution. Bur a sentence in the instructions passing the buck is cheaper for the manufacturers.

    Without seeing the test results we do not know if the smoke alarms are blinded and do not sound, or are triggered to false alarm, in the presence of mains borne interference, but we can be pretty sure they do not perform to spec, or it would not have been mentioned at all.

    Mike.

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