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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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  • 0

    Hello Mike

    Thanks for your reply, as far as I know it has been a problem for quite a while, it looks like a quite old installation with halogen down lights changed to LED at some point. The dimmer switches in the lounge are standard MK grid dimmers not the LED version. Not sure what the dimmer switch in the dining room is looks like it might be BG or something like that. They are all standard traditional dimmers with no neutral connection.

    I agree about the meter and inaccurate readings but I was only really using it for comparisons and not looking for an accurate reading, the clip on ammeter is designed to do pretty much what it was using it for so I expect that to be pretty good (megger actually suggested using it in this way to identify circuits with high harmonic content). 

    It could well be spikes caused by failing smoothing/filtering capacitors that would have an effect on the entire circuit in a similar way to harmonics and the ammeter might have filtered the spikes when set to only look at 50/60Hz.

    I have agreed with the client to replace the lights with new KSR fittings as the existing ones look like they need replacing anyway (I’m not confident they are fire rated so will be happier with new ones!) also I have warned the customer that this may not fix the problem and to expect to replace the dimmer switches as well, this should hopefully cove it!

  • Former Community Member
    0 Former Community Member in reply to paul2884

    Hi Paul, it really sounds to me that something is miswired, have you confirmed the wiring is correct? 

  • 0 in reply to Former Community Member

    That was what i thought, but its all wired correctly and the supply is comming from the dining room then to the lounge, disconnecting the feed to the lounge switches results in all the lounge lights off but leaves the dining room lights on. whatever it is its affecting the dimmer switch/light upstream!

  • 0 in reply to paul2884

    Just a thought but some old Dimmer units cannot cope with dimming LEDs.  They work fine on Halogens with the larger load.
    A simple test is to switch over some the LED bulbs for Halogen (you can often get these in charity shops almost for free)

  • Former Community Member
    0 Former Community Member in reply to paul2884

    Thanks for the reply Paul.

Reply
  • Former Community Member
    0 Former Community Member in reply to paul2884

    Thanks for the reply Paul.

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