Why do MCB's buzz?

[La Poste]

A mate of mine has quite a few 12v low voltage down lighters installed on a 6 Amp MCB BS60898 Contactum brand.

When he switches the load up IE he switches the dimmers of the lights to full power the MCB buzzes like mad, in fact the buzzing increases at the same rate as the power is increased, both in equal measure.

I have looked at loose connections on the buzz bar etc but everything is tight.

Does anyone have an opinion as to why the MCB is buzzing so much?

It really is quite noticeable.

Thanks.

 

[egginyourface]

Its normal, especially if theres dimmers all over the place

 

[La Poste]

Thanks mate.

Any idea why the dimmers create this buzzing sound?

 

[topquark]

Possibly coz they're overloaded or cheaper quality (often triac based). Check the rating of the dimmer (often around either 250W or 400W) versus the load it's being used to control.

Are you sure it's the dimmer and not the lamp. Check the type of lamp and ensure it's a dimmable type (not all are) that's appropriate for the dimmer type.

 

[La Poste]

To be honest everything is buzzing.

Including the fuse board, not really noticeably the dimmer switches but most certainly from the lights.

Once you hit a certain level on the dimmer switch the whole thing seems to buzz from the fuse board right along to the lamps.

I would get a head ache if I stood in that room for too long.

 

[egginyourface]

There is an explanation why this happens and im sure someone on here will be able to provide it. I remember looking for the same answer myself a while back

I find it happens when the house has lots of spot lights and dimmers in every room.

 

[topquark]

How many lamps is the dimmer controlling (is it single way?) and what type of lamp are they? I would try and exchange the lamp for a different type (old incandescent firstly) and see if you can prove that it's either the lamp, dimmer or combination of the two first.

 

[topquark]

There is an explanation why this happens and im sure someone on here will be able to provide it. I remember looking for the same answer myself a while back

I find it happens when the house has lots of spot lights and dimmers in every room.

May be down to a capacitance problem, but can be a number of things (easily eliminated before reaching that conclusion).

 

[Guest112]

dimmers are variable resistors and affect the current flowing through them causing them to buzz but as for the board does it still buzz if you turn off a different breaker? just thinking that ive seen boards before when all breakers are on buzzing like mad turn any breaker off which reduced the load slightly and reduced the buzzing significantly, (just wondering wether its the breaker itself buzzing or the board itself)??

 

[ipf]

Possibly coz they're overloaded or cheaper quality (often triac based). Check the rating of the dimmer (often around either 250W or 400W) versus the load it's being used to control.

Are you sure it's the dimmer and not the lamp. Check the type of lamp and ensure it's a dimmable type (not all are) that's appropriate for the dimmer type.

Similar problem a couple of weeks ago. Some expert ( female interior designer) advised and provided a complete change of lamps to energy saving, non dimmable. 2 main fittings with (5 lamps each) in the lounge were dimmer controlled. Strangely enough, later on I found a wasps nest in the loft. Plenty buzzing upstairs and down.

 

[Marvo]

The MCB is probably buzzing because it's close to its tripping threshold. Poor power factor and harmonics on a circuit load can also cause the MCB to buzz even if the current through it is less than its rated value.

The dimmer buzzing is probably either because it's cheap and poor quality or because it's running over its full load ability.

If the transformers are buzzing it's probably mechanical action between the laminations if they're wirewound. If they're electronic then it most likely 'cheap n' nasty' syndrome again or they're not designed to be dimmed or the wrong type of dimmer is being used (leading/trailing edge).

If the lamps are buzzing they're probably not compatible with the dimmer or the transformer.

All that said, the last buzzing control panel I investigated was caused by a massive wasps nest so it's always a good idea to keep your wits about you.

 

[Guest112]

i opened a db once and found the beginning of a nest thought i was the only one lol

 

[MarkieSparkie]

MCBs contain mechanical parts. Normally the supply is a nice smooth 50 or 60Hz sine wave and the designer of the MCB has ensured that the mechanical parts are not resonant at multiple and sub-multiples of the basic supply frequency. However, when fast switching electronics (e.g. dimmers) are introduced the supply waveform is distorted far from a sine wave and harmonics are generated on the fast rising/falling edges that are not related to the basic supply frequency, this can in some unfortunate cases resonate the MCB mechanical mechanism causing an intense buzzing noise.

 

[spark 68]

However, when fast switching electronics (e.g. dimmers) are introduced the supply waveform is distorted far from a sine wave

As others have said, if the dimmers are of 'cheap and nasty' construction (poor filtering), and/or overloaded, the triacs switching (read: chopping) the sine wave up, causes what is known as 'magnetostriction' (vibrations) in some of the mechanical devices (MCB's, laminations of trannys etc...etc.).

 

[La Poste]

I think the circuit is heavily loaded and it's some sort of resonance.

I think it's something to do with the chopping motion of the dimmers, there are a lot of them attached to many lights.

The circuit at full load pulls 8.04 Amps on a 6 Amp breaker, the higher the Ampage the louder the buzzing.

I mean are tools to analyse resonance really expensive?

Just out of curiosity.

Thanks.