40A mcb buzing/humming

[sparky-s-w]

Hi, not as interesting as the heating engineer/plumbing thread, sorry but.

i've recently installed a new CCU for my dear old mother, however on a recent visit to raid the fridge
they said whenever they have a shower there's a buzing/humming coming from the CCU. i checked the connections etc, but cant find anything.
Any thoughts what this could be?:confused5:

 

[Guest123]

Sounds like a cheap MCB working quite hard.

What is the KW rating of the shower???

 

[telectrix]

as lenny said, and check to make sure you've not got the busbar behind the MCB terminal

 

[sparky-s-w]

sorry yea its only an 8.5kw, on a10mm cable, the breaker is cheap (niglon), done job for free as its the old dear.
did check connections both ends and buss bar side, but didnt think to check the bar hadnt gone behind the terminal, ill check that.

 

[Deleted member 9648]

sorry yea its only an 8.5kw, on a10mm cable, the breaker is cheap (niglon), done job for free as its the old dear.
did check connections both ends and buss bar side, but didnt think to check the bar hadnt gone behind the terminal, ill check that.

I'd check it rather quickly....with a heavy load it wont take long to cook if the connection isnt good.

 

[sparky-s-w]

i've just give em a call, told them not to use it till ive sorted it, going round for a bit of sunday lunch this aft.
beats the wife's cooking.

 

[needasparks]

The joys of cheap gear. Buy once fit twice, normally in re-visits.
Thats not to say regular makes don't fault but you do get what you pay for usually.

 

[Dave 85]

I'd never buy a cheap CU again. Only one I ever installed the main switch melted (no neautral continuity at all when on) and cooked 5 of the RCBO's. Never again. I'd maybe suggest getting a different brand 40a MCB to replace the faulty one if you can find one to fit. Nuts to what the manufacturer sais.....ie "It's dangerous to replace our cheap shoddy MCB's with good quality ones"

 

[MarkieSparkie]

MCBs and RCBOs contain mechanical parts. Normally the supply is a nice smooth 50 or 60Hz sine wave and the designer of the MCB/RCBO 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 and SMPS) are introduced the supply waveform can be distorted far from a sine wave and the harmonics that are generated on the fast rising and falling edges are not often related to the basic supply frequency, this can in some unfortunate cases resonate the MCB/RCBO mechanical mechanism causing an intense humming or buzzing noise. Often all you can do in such circumstance is change the protective device, usually the manufacturing tolerances of the mechanical linkages result in a different natural frequency of resonance and the buzzing or humming is reduced to acceptable or even non-audible levels.