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Buzzing change over

lyledunn

A fairly loud buzzing noise has recently appeared in a 200A changeover switch. Everything checked for tightness. Assumption is that it is one of the coils but I am unsure if this is an issue of concern. 

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    Is there a sensing coil in series with the load ? If the waveform is the classic LED diode input one of  drawing almost no current at all except at the crests of the waves that can lead to a much sharper 'raspy' buzz (think heavy metal bass guitar waveform ) from inductors asked to pass that waveform  when compared to the gentle hippy trance hummmm of a sine wave. 
    Sometimes seen on MCBs and RCDs also.
    If it gets gentler when a few 3kW heaters are added in parallel that is all it is. If so it is not sinister, but it may indicate a poor waveform and a flag for possible power factor billing anomalies.. Longer term some low pass filtering may be worth considering but probably not a big issue.
    Mike.

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  • 0

    Is there a sensing coil in series with the load ? If the waveform is the classic LED diode input one of  drawing almost no current at all except at the crests of the waves that can lead to a much sharper 'raspy' buzz (think heavy metal bass guitar waveform ) from inductors asked to pass that waveform  when compared to the gentle hippy trance hummmm of a sine wave. 
    Sometimes seen on MCBs and RCDs also.
    If it gets gentler when a few 3kW heaters are added in parallel that is all it is. If so it is not sinister, but it may indicate a poor waveform and a flag for possible power factor billing anomalies.. Longer term some low pass filtering may be worth considering but probably not a big issue.
    Mike.

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