Why does a dimmer cause a microwave to buzz...?

Discussion in 'Electricians' Talk' started by syholl, Jan 19, 2007.

  1. syholl

    syholl New Member

    Fitted a 1000 watt dimmer to control a customers ceiling lights, 550 watts in total of 50 watt 12v downlights. When the dimmer is turned down the microwave buzzes. The lighting circuit and kitchen ring have all been tested, all fine, excellent readings for Zs, ring continuity, insulation etc... The dimmer hardly buzzes at all..!!!

    I took the microwave and plugged it in to the old part of the house, which is fed from a different fuseboard in a different part of the house, and it still did it. This has been happening for about a month now, and today the customer phoned to say her microwave has packed up. Its a few years old, so is this just a coincidence, or has the dimmer somehow caused the microwave to blow...? Also, on the same point, the house is a TT system, and when i check for PFC, i get a reading of 4amps every time. Not had anything like that before... why the hell is it only 4 amps...?
  2. fooman

    fooman New Member

    is this a windup :^O
  3. syholl

    syholl New Member

    I wish it was, its got me puzzled...!! I've had buzzing dimmers before, and even a buzzing consumer unit once, caused by the dimmer, but never a buzzing appliance...!!
  4. X

    X New Member

    Sounds like a mains filter would of sorted the problem.... or maybe even a humble capacitor.

    However, if the dimmmer was causing the problem... then a different make of dimmer (one with better filtering) would of been a idea.
  5. syholl

    syholl New Member

    Could this have caused the microwave to stop working though...? Just worried that she is going to buy another microwave and it might do the same thing...
  6. fooman

    fooman New Member

    still cannot see how the microwave is buzzing ? was this when it was just in standby mode ?
  7. JP.

    JP. Screwfix Select

    If that ain't a wind up...I dunno what is.... dimmer making a microwave buzz how is that possible? but then again maybe it is....if something is out of phase.
  8. JP.

    JP. Screwfix Select

    Sounds like the magnetron was going down....hence the susceptibility to buzz.....the final outcome is as stated....packed up microwave.
  9. syholl

    syholl New Member

    Itse definitely not a wind up, i just couldn't figure it out.... It was buzzing whilst not being used (standby if you like..)
  10. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Soundwaves and a very sensitive thin foil type part in the microwave somewhere.

    Look, it's appears a crazy suggestion(before the FOOL comes in to say it),

    but hey, it's as reasonable as any other.

    It would not be outside the realms of possibility that the frequency of the dimmer could be picked up by that type of part in the microwave.

    Maybe the microwave had a disintegrating part to start with anyway, and this part was picking up the frequency.

    Mr. HandyAndy - really
  11. MJA

    MJA New Member

    Suggest removing the dimmer from the microwave :):)
  12. MJA

    MJA New Member

    On a more serious note, 4 amps PFC on a TT system would suggest a very high (in excess of 200 ohms) electrode resistance. You need to test it and post the result on here.
  13. syholl

    syholl New Member

    Can't rememer off the top of my head what the earth electrode reading was, but i did a quick retest of Zs yesterday on the ring, and it was 63 ohms..
  14. jimmythemap

    jimmythemap New Member

    What make is the Microwave ?
    and what age is it ?

    and does it only happen on Full Power
  15. devil's advocate

    devil's advocate New Member

    Hi syholl.

    I suspect the interference transmitted by the dimmer (and they all give out some) highlighted a weakness in this particular oven - possibly a failing filtering capacitor.

    Did the dimmer cause this oven to fail? Possibly, but only because this oven was suffering a weakness in the first place. I'd be astonished if a new oven would suffer the same fate.

    Worth contacting the manufacturer of the oven - and switch?

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