Hi, I have just installed some LV downlighters in the downstairs of my house and now when the lights are switched on the MCB makes a buzzing sound. Some of the lights are running off a dimmer, would this maybe cause trhe buzzing? or is it something more? thanks in advance
MCB Buzzing
- Thread starter nikwalker69
- Start date
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Are all connections satisfactorily terminated (including at the MCB and the MCB to the busbar) ?
What is the rating of the MCB ?
What is the current demand on the circuit ?
Safe isolation required if you need to access the consumer unit insides.
What is the rating of the MCB ?
What is the current demand on the circuit ?
Safe isolation required if you need to access the consumer unit insides.
current demand is apporx 4.6A on my calculations, it is a 6A MCB, and the terminations all seem fine
low voltage or extra low voltage?
ie are the lights being used via a transformer?
ie are the lights being used via a transformer?
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yeah theyre being run by a transformer
With a switched mode power controller ( such as a dimmer ) there are often high current pulses. 100 of them every second and they will be considerable higher than the expected average current.
a 20amp pulse for one twentieth of the time equates ( roughly ) to a constant current of 1 amp. A wire fuse is slow acting and will consider it be be a current of one amp. An MCD's magnetic over current trip mechanism is much faster acting and will see it as short duration 20amp current. The mechanism will start to act on the 20amp (which is an overload to a 6amp MCB ) but before it has moved enough to trip the MCD to OFF the 20amp pulse will have ended and the mechanism will "relax" until the next 20amp pulse occurs on the next mains half cycle.
The small movement of the mechanism could be the source of the buzzing noise.
thanks for that, that seems to make sense. what would you recommend doing about it?
Some dimmers switch ON at the point the mains is zero volt and then switch off during the mains half cycle when the required power has been taken from the supply. These have less troublesome current pulses as they start at near zero current and increase relatively slowly.
Some dimmers switch when the mains voltage is high and the peak pulse current in these dimmers can be instantainuously very high but very short in duration. These are the most troublesome pulses.
The first option would be to try and reduce the peak pulse currents, that would require a change of dimmer and transformer to one that has a higher duty cycle and lower impulse currents. ( instead of 20 to 1 try one at 5 to 1 ).
Second would be to move circuits with high peak currents onto their own MCB and look for a type of MCB less responsive to pulsed currents. One option would be to use wired fuses for those circuits. But the regulations may now prevent that option.
Some dimmers switch when the mains voltage is high and the peak pulse current in these dimmers can be instantainuously very high but very short in duration. These are the most troublesome pulses.
The first option would be to try and reduce the peak pulse currents, that would require a change of dimmer and transformer to one that has a higher duty cycle and lower impulse currents. ( instead of 20 to 1 try one at 5 to 1 ).
Second would be to move circuits with high peak currents onto their own MCB and look for a type of MCB less responsive to pulsed currents. One option would be to use wired fuses for those circuits. But the regulations may now prevent that option.
I've seen this before per the above. It usually seen on a circuit that is running close to its limits.
Its fixable by using a different curve CB but that needs proper testing before its changed.
Its fixable by using a different curve CB but that needs proper testing before its changed.
so if it is just because the circuit is running close to its limit, does this buzzing pose and danger?
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