MCB Loud buzzing noise

[Dazza1976]

Hi all, can anyone help please?

I installed 18 downlights today, in 2 rooms with 9 in each room. and ran them on a completely new circuit with a 6amp breaker. When turning on the lights there is a very loud buzzing sound coming from the mcb ??? Both switches are dimmers. I thought perhaps the mcb is too close to overload ?? when i tried replacing the dimmers with standard one way switches the buzzing stopped ??
Can anyone help please as the customer is adament they want dimmer switches, and im not happy leaving the job with the loud buzzing.


Thanks in advance.

 

[Darkwood]

Matter of interest what downlighters you running and to just eradicate the chances of a faulty mcb can you change it with a similar one in the board and last but not least what are your dimmers rated at?

 

[SirKit Breaker]

Are the downlighters suitable for a dimmer, what rating are the dimmers.

 

[gaffer]

I agree with sirkit check suitability of dimmers and stick your clampon on the circuit just out of interest.

 

[Steve1412]

Is the mcb yellow with black stripes...If so its supposed to buzz..its a bumble bee

Seriously though. Are the downlighters mains or LV..Not many LV trans are dimmable.

 

[lister]

Have you tried replacing the mcb, sounds like thats where the problems are, 18 spots at 50w 3.9 amps so not exactly overloaded.

 

[Spudnik]

Cheap transformers and cheap dimmers can sometimes cause the buzzing.

Even certain makes of CU.

I would agree about swapping out the MCB.

Certainly worth a try

 

[Benn]

I had this very same problem on thursday afternoon. Ill explain...

We have been working in sort of a old peoples home but they have there own flats. We were wiring new kitchens but got behind on the testing so just caught it up whilst we were snagging. Whilst at one persons flat he asked us if he could have a Flourescent flight up in the front room aswell as the Kitchen. No worries we put it up. Then went to test the lighting circuit which had another circuit in the same MCB (B type 6amp) and soon as we reconnected the cables back in the breaker and turned it on all we herd was buzzing from the mcb.

We put this down to the dimmer switch in the front room as when we changed it to a normal one way switch it didn't make the same sound.

 

[Dazza1976]

After listening to your advice and that of a guy i know who is a manager at a wholesalers with alot of contacts in techncial support, it appeared that the problem was down to the dimmer switches i was using. They were both MK rated at 500w.
However i was informed that when using transformers you need to go by the V/A rating and it appeared the ones i used were not suitable, and can only handle about 5 transformers per circuit.
So i upgraded these to Halolite ones rated at 800 V/a.
Hoping this would solve the problem i swiched the mcb and dimmers on, and still i had exactly the same problem. A loud buzzing at the mcb !!
I took into account what some of you have said, and tried changing the mcb, 2 different ones i tried and still the same loud buzzing ??? Just out of curiousity i decided to try it with a 10amp breaker, which is fine as i have wired the circuit in 1.5 mm, and guess what ?? the buzzing has now stopped !!
Can anyone explain why this is ?? as mentioned by someone else 18 x 50w = 3.91A, so its not really as if a 6amp breaker was being overloaded ??

 

[zupos40]

what is the VA rating of each transformer rather then the lamp output, transformers are inductive and take more power, it could be this inductive. voltage and current not in phase, power factor harmonic noise etc.

 

[sparkycpu]

Just out of interest i wondered if you got this problem sorted ??
The reason your mcb is buzzing is that on rare occasions you can get a mismatch beween dimmers and transformers, I have had this problem before and you need to find out if your dimmers and transformers are ' leading or trailing edge ' as a mismatch will cause harmonic noise to travel back to the mcb which affects the coil inside the mcb, thus the humming...

 

[Mark.W]

Just out of interest i wondered if you got this problem sorted ??
The reason your mcb is buzzing is that on rare occasions you can get a mismatch beween dimmers and transformers, I have had this problem before and you need to find out if your dimmers and transformers are ' leading or trailing edge ' as a mismatch will cause harmonic noise to travel back to the mcb which affects the coil inside the mcb, thus the humming...

Good first post and welcome to the forums

 

[markyyy]

i only joined this forum to search out this very same problem. i have 18 lv fittings on one circiit, 4 are dimmed separately. the dimmers are 400 rated and are Click grid type. the transformers are aurora and are dimmable. i have swapped the dimmers for ones from my own house and the buzzing is still there. i have changed the mcb, still there. i have checked all the connections( bloody pain) and i have changed the lamps. i originally had 4 50ws in the separate 4 fittings and 20w lamps in the other 14 fittings so i was well within the ranges. i changed the lamps to 50w and even mixed them all about to see if i could get a change, no joy.

after going back to the suppliers and contacting Click they sent me out 4 of their own transformers and told me to randomly swap the transformers and they assured me that it would work, guess what, still buzzing. the only thing i haven't tried is to change the mcb to a 10A as suggested earlier, i will give it a go and post the results later, still haven't got paid for the job yet either.

 

[Andyfm]

What make of ccu/mcb is it

 

[chris gray]

Just out of interest i wondered if you got this problem sorted ??
The reason your mcb is buzzing is that on rare occasions you can get a mismatch beween dimmers and transformers, I have had this problem before and you need to find out if your dimmers and transformers are ' leading or trailing edge ' as a mismatch will cause harmonic noise to travel back to the mcb which affects the coil inside the mcb, thus the humming...

hi
what do you mean by 'leading or trailing edge'?

 

[pushrod]

Can anyone explain why this is ?? as mentioned by someone else 18 x 50w = 3.91A, so its not really as if a 6amp breaker was being overloaded ??

It is overloaded because of the fact that you are dealing with an inductive load. If you only have wattage ratings to work with - which is the true power - you actually have to multiply it by 1.8 to get the apparent power which is what you have to size your cable for.

Quite a common problem - this is why the c&g 2330 301 exam constantly bangs on about kW, kVA and kVAr. Hope that is a bit clearer.

 

[markyyy]

the consumer unit and mcbs are crabtree. i will probably need to look further into this as it is an annoying buzz. i could use one transformer for two fittings with 20w lamps, but that again is more time on the job.

 

[pushrod]

the consumer unit and mcbs are crabtree. i will probably need to look further into this as it is an annoying buzz. i could use one transformer for two fittings with 20w lamps, but that again is more time on the job.

did you try decreasing the load or increasing the breaker size?

 

[Crosswire]

It is overloaded because of the fact that you are dealing with an inductive load. If you only have wattage ratings to work with - which is the true power - you actually have to multiply it by 1.8 to get the apparent power which is what you have to size your cable for.

Quite a common problem - this is why the c&g 2330 301 exam constantly bangs on about kW, kVA and kVAr. Hope that is a bit clearer.

Hmmm , well spotted but OP said "when i tried replacing the dimmers with standard one way switches the buzzing stopped ??"

If the problem was a (slightly) overloaded breaker, why should removing the dimmer from the circuit, also stop the buzzing?

Not trying to contradict you, just curious.

 

[Crosswire]

Unless dimmer switch also acted as an inductive load in itself.....Is this possible? Anyone?


Just thinking out load, please don't gun me down if I'm being a fool