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Dimmer switch interference?

paul2884

Has anyone else experienced this with dimmer switches/lighting?

 I have just visited a house with problems with lighting in the dining room.

Symptoms.

The centre light in the dining room flickers/dims when the dimmer in the lounge is adjusted.

This sounded like someone had mixed up the switch wire and feed so I was expecting a simple fix but..

The supply comes from the dining room then on to the living room, when checking the voltage at the input to the dining room switch it was 241.7v and did not change when the dimmer in the lounge was adjusted BUT the output from the dining room switch changed from 160v to 177v dimming the lamps in the dining room when the lounge dimmer was adjusted!

I have checked the load on the lounge dimmer switch with my Megger clip on ammeter and used the 50/60Hz switch to check harmonics, it is clear there are a lot of harmonics on this output. Around 200mA at 50Hz and 370mA without the 50Hz filter. I have come to the conclusion that the harmonics are affecting the dining room dimmer, it is the first time I have had this issue, the dimmer switch at the far end of a circuit affecting the output (but not input) of a dimmer switch up stream of it! Clearly my Fluke volt meter is less affected by harmonics.

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    It sounds unlikely, but not totally incredible. some designs of dimmer, and some designs of lamp with switch more power supplies for that matter, manage to put several volts peak to peak of spikes onto the mains, high but of short duration, so a meter with a long averaging time does not see them.

    Are these dimmers with a loop through neutral or just in series with the lamps like a traditional switch would be ? What sort of lamps are being dimmed ?  Be very wary of what meters read on the sliced wave-forms out of dimmers - it is not like measuring a sine wave and that can confuse the meter internals.

    Has it always done it ? Filter capacitors in one or other dimmer  may be missing or defective. (foil type capacitors can reduce in value spectacularly over time a mains surges blow small holes in the foils, and then 'self heal' by burning back - I have cut open a few where the foils look more like a paper doily than a continuous conductive sheet.) Ideally if neutral is available at the dimmer some filtering capacitance is in order, but that may not be practical if there is no neutral or no space. If you swap the dimmers does the effect swap with them ? - i.e is it the dimmers that are source and victim, or the wiring layout...

    More info needed really.

    Mike

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  • 0

    It sounds unlikely, but not totally incredible. some designs of dimmer, and some designs of lamp with switch more power supplies for that matter, manage to put several volts peak to peak of spikes onto the mains, high but of short duration, so a meter with a long averaging time does not see them.

    Are these dimmers with a loop through neutral or just in series with the lamps like a traditional switch would be ? What sort of lamps are being dimmed ?  Be very wary of what meters read on the sliced wave-forms out of dimmers - it is not like measuring a sine wave and that can confuse the meter internals.

    Has it always done it ? Filter capacitors in one or other dimmer  may be missing or defective. (foil type capacitors can reduce in value spectacularly over time a mains surges blow small holes in the foils, and then 'self heal' by burning back - I have cut open a few where the foils look more like a paper doily than a continuous conductive sheet.) Ideally if neutral is available at the dimmer some filtering capacitance is in order, but that may not be practical if there is no neutral or no space. If you swap the dimmers does the effect swap with them ? - i.e is it the dimmers that are source and victim, or the wiring layout...

    More info needed really.

    Mike

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