Buzzing MCB

[SKY]

Been to a job today, customer heard a buzzing noise from fusebox when the kitchen ring was loaded.

Loaded = Kettle boiling, tumble drier on and microwave on. (approx 6kw in total).

I had a look and replicated the loading and there was a buzzing noise but I could not be sure it was from the kitchen ring MCB.

CU is a crabtree starbreaker, no signs of arcing and all connections are tight as a ducks backside.

Was gonna try another MCB but they are the starbreaker plug in type that I do not carry so may go back tomorrow.

Can anyone shed some light to assist?

Cheers Chaps

 

[vernam616]

must be another breaker in the board of the same size?

swap the circuit onto that temporaily to check before purchasing a new breaker

 

[SKY]

must be another breaker in the board of the same size?

swap the circuit onto that temporaily to check before purchasing a new breaker

Could not do that, the only other 32A breaker was for the ring (its a 2 bed flat). they have a baby that is on a feeding machine plugged into that other ring so I was not going to play with circuits.

 

[vernam616]

ok i see

 

[Octopus]

Connect all four cables temporarily into the other breaker??? Its only a flat so unless they are growing weeds I can't imagine an issue.

Dam nuisance those Crabtree breakers!

 

[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 if you're lucky.

 

[telectrix]

sky, how urgent is it. i've got spare 32A starbreaker. can post if you're stuck.

 

[Farmelectrics]

had a similar problem with a rcbo put a clamp meter on and the 32a was pulling 36a so switched some kit off and the buzzing stopped a breaker can take 1 half times its load does anyone no how long it will take 1 & half times its load before it will trip

 

[telectrix]

check the time/current tables.

 

[Farmelectrics]

will do tel not got reqs with me thought some bookworm like yourself would rattle it off to me lol

 

[telectrix]

roughly around 1 hour at 1.45 x rated current.

 

[Farmelectrics]

see i new youd no haha cheers tel

 

[Engineer54]

Whilst i agree with MarkieSparlies post (#6), more often than not, in a domestic setting a buzzing protective device indicates the device to be working close to, or over it's current rating, or has become defective....

 

[SKY]

sky, how urgent is it. i've got spare 32A starbreaker. can post if you're stuck.

Thank for the offer Tel - sorted it today with a new breaker from screwfix.

the circuit was pulling 26amp when buzzing so it was no-where near its max, must have been a dodgy breaker.