Buzzing MCB

[tipu]

I've nearly completed the rewiring of my house. All the ceiling lights are LV downlighters. I have put in cheapo dimmer swithes from TLC. The business end seems to be made by Home Automation.

However I noticed that if i turn on lights in a room with a dimmer as a controller then I get buzzing in the CU coming from the MCB for that lighting circuit.

Is this normal? Whats causing this?

btw it is definitely the dimmers because same problem with the downstairs circuit.

 

[Big_Spark]

That is NOT normal and certainly cause for concern.

The buzzing from an MCB is usually connected to an overload of the MCB, however as the MCB has not tripped it is somewhat puzzling. The only part of an MCB that could cause such buzzing would be vibration in the flash reducers or the magnetic trip inside the MCB, neither should do this and I have never come across this situation.

Look at the MCB's, what is their rating and what type are they?

Depending on manufacturer it is likely it will say B6/C6/D6

They should be B6, as in 6A type B MCB's.

What make are the MCB's?

I very much doubt the MCB's are faulty, so the culprit is almost certainly your Dimmer switches, try changing these for standard switches and see if the buzzing goes away, if it doea, return the dimmers to TLC.

Remember, buying cheap does not always save you money in the long term.

 

[supersparks]

ive come across it before, it seems to be normal
did check it with other mcbs
did check it was well within limit(4 amps through 6 amp breaker MAX)
only buzzed when the main set of 8 lv downlights were dimmed
no heat from mcb
the mcbs and cu were MK, so no shoddy stuff either. swapped dimmer, still buzzed, it dident buzz overly loud but noticable when you were near it

 

[tipu]

Well I am very concerned! Its def not the MCB. There's two circuits. Both exhibiting the same behaviour.

As you rightly say they are not overloaded because a.) I've done the calculations before rewiring and b.) they havent tripped.

I've put in a brand new MK CU in there. Lighting is on 6Amps, Type B. Although intending to change one of the circuits to 10Amp. I've rewired a few places before and never seen this.

I didnt put them into save money .. I just needed to get all the lighting working so i can move in. In fact it's gonna cost me more. I intend to put some MK ones but they're gonna take 6 weeks to be delivered.

It def is the dimmers because I turned all the lights off and turned on lights in a room without dimmers and it didnt buzz.

Weird but why??

 

[Big_Spark]

It def is the dimmers because I turned all the lights off and turned on lights in a room without dimmers and it didnt buzz.

Weird but why??

Well then you need to ditch the dimmers, this behaviour will damage the MCB's over time, and when you do need them they may not work, or they may nuisance trip and cause you to have an accident.

Why, simple. magnetic inductance on the phase cable which is causing a backfeed on the core at a different frequency to the supply frequency. Due to this it is not cancelled out, and this will cause the magnetic trip section of the MCB to vibrate as it is being fed from by two different supplies. The voltage concerned is probably only about 20 to 30Vac, but it will be enough to cause eddy currents in the MCB via magnetic inductance effects.

 

[supersparks]

so how can it be resolved other than ditching the dimmers?]

 

[il78]

Just to add, my MCB for the downstairs lights (not overloaded) will ocasionally buzz...MEM board....

What fuse board have you got ?

 

[tipu]

Why, simple. magnetic inductance on the phase cable which is causing a backfeed on the core at a different frequency to the supply frequency. Due to this it is not cancelled out, and this will cause the magnetic trip section of the MCB to vibrate as it is being fed from by two different supplies. The voltage concerned is probably only about 20 to 30Vac, but it will be enough to cause eddy currents in the MCB via magnetic inductance effects.

Ahh I get you. All that scarily reminds me of uni!! Is this bad luck otherwise people would be returning dimmers all the time?

 

[Big_Spark]

Tipu, there are many factors that can cause this, the most common are cheap and thus poorely made dimmers and other similar inductive devices, however even the odd good quality dimmer can cause this.

Really good quality dimmers have electrolytic capacitors installed in them on the input and output to prevent feedback that will cause this, but I do know from personal experience that Home Automation are cr*p and thus can cause this problem.

The best dimmers are made by Hamilton Litestat, MK, Crabtree and Hagar.

One way around the problem is to fit line filters to your circuits, but it is cheaper to buy a decent dimmer.