Huming Mcb

[davetherave69]

Hi

installed some lv down lights recantly 1 x 6am type b feeding circuit but when the lounge lights are switched on which are controlled by lowv oltage dimmer you get a hum at the fuse board from the breaker ints not that loud but if you put your ear near the board u heare it i have noticed this before when dimmers are fitted to lv lights there are ok when a switch is used any one else had this happen.

[Guest RJBsec]

if you put your ear near the board u heare it

Got any burnt edges to your ears?

[SUBS]

Hi

installed some lv down lights recantly 1 x 6am type b feeding circuit but when the lounge lights are switched on which are controlled by lowv oltage dimmer you get a hum at the fuse board from the breaker ints not that loud but if you put your ear near the board u heare it i have noticed this before when dimmers are fitted to lv lights there are ok when a switch is used any one else had this happen.

Used to get it if you used a soft start with old type infra reds.

Dimmers ( and most soft starts ) use a Triac, which works by clipping the shape of the mains waveform, so I reckon the sudden change in current makes the MCB rattle. If your really interested see.

www.allaboutcircuits.com/vol_3/chpt_7/6.html

Never actually had an MCB apart to find out though. LV lights probably act as an inductive load, and the transformer rattles as well.

Anybody got a better theory ? ?

[Mavrick_001]

Have exatally the same problem at my parents house, the old dear went out and bought some stupidly expensive ligt fitting for the front room which has in-built electronic transformer, the fitting may be used with only an electronic dimmer, fitted both for her (As I can be nice like that at times....not often.... but at times) 2way switching works great and so does the dimmer..... but the fitting makes a low level buzz when used on dimmer which also travels back to the consumer unit. I've taken no notice other than the fact the electronic dimmer must be emmitting a hum along the cable, no hum when used off the light switch and the other side of the 2way, just one of things my parents have to live with lol.... next time she'll think twice about buying daft lights, but hasn't caused us any problems, ear plugs or turning up the tv usally works.... all the best

[Paul P]

Mine in the bedroom have done the same for years, I would not worry about it.

[arfur mo]

dead simple really, like bee's they hum -------

because they don't know the words ha! - ha ha! get it? eh? ha!

oh please yourselves

not sure about mcb's construction, bout often alarm panel trannies hum, usually caused by a loose mounting screw/bolt or the trannie plates being loose and vibrating, you can usually quieten them by tightening the bolts and/or stopping the box lid etc. from vibrating in harmony, this my be direct vibration or some times magnetic vibration from the field of the transformer.

with lv and dimmers on lighting like said above, the mains wave is clipped, this cause a more sudden pulse swuare wave rather than the more rounded normal sign wave causes through the coils.

regs

alan

[mojo]

dead simple really, like bee's they hum -------

because they don't know the words ha! - ha ha! get it? eh? ha!

oh please yourselves

not sure about mcb's construction, bout often alarm panel trannies hum, usually caused by a loose mounting screw/bolt or the trannie plates being loose and vibrating, you can usually quieten them by tightening the bolts and/or stopping the box lid etc. from vibrating in harmony, this my be direct vibration or some times magnetic vibration from the field of the transformer.

with lv and dimmers on lighting like said above, the mains wave is clipped, this cause a more sudden pulse swuare wave rather than the more rounded normal sign wave causes through the coils.

regs

alan

If u get 10 amp breaker in the board try to move the wires there as temprory measure

if the huming stays the same it may be trasformer in the downlight sending back to the board abit of frequency I wouild recomend to change it

[DirectFS]

Used to get it if you used a soft start with old type infra reds.

Dimmers ( and most soft starts ) use a Triac, which works by clipping the shape of the mains waveform, so I reckon the sudden change in current makes the MCB rattle. If your really interested see.

www.allaboutcircuits.com/vol_3/chpt_7/6.html

Never actually had an MCB apart to find out though. LV lights probably act as an inductive load, and the transformer rattles as well.

Anybody got a better theory ? ?

Well, an MCB is essentially spring loaded contacts, so it would make sense that it chattered from time to time - just like your typical cheap AC rim release.

That said, over current is generally the most likely reason - which again is a common problem with ELV lighting.

Would recommend a load test first, and check of any dimmers in the circuit too.

Bill.

[electric-ian]

Hi Dave,

This can be a problem. MCB hum isn't a good thing!

I am guessing that you have several small electronic transformers on the same circuit?

The reason is that LV transformers can be either capacative, inductive or resistive.

If you have several LV transformers on one circuit the effects add up and cause the hum.

The best way round it is to use resistive transformers if you can, -I think Varilight do one- also make sure the dimmer is correct for the type of transformer...... leading edge or trailing edge dimmers ..... cant remember which is for which but you'll find it on the web.

Another trick, if you have a lot of fittings is to use a larger transformer (105W) and use it for two fittings as it seems to be the number of transformers that makes the effect.

Hope this is useful..

Ian

[Cathexsis]

Try closing the consumer unit door? Lol

Try closing the consumer unit door? Lol