Old Wylex Db issues safety hot MCB

[Chrishands]

Hi I have an old Wylex Db serving my house. It is basic with MCB's and protected by an added RCD box on the incommer at a later stage.
Iv'e had a few concerns with it.
1.When i put the lighting circuit on the DB would buzz, i think i found it was the Dimmer switch, which i've Got rid of,in place of a normal 1g1w switch
However 2. When somebody uses the shower, the 40A breaker serving it gets HOT, just as hot as clothes that have just come out of a tumble drier, not scorching but Hot. Any Ideas what this could be? The MCB is Hot not the Female part it pushes into just the push in MCB.

When i fully qualify in another year i will be looking to change it as its way out of date and out of spec with 7671, but untill then i would like to know the possible causes, as it could potentially cause a fire.

I have checked it is not loose and not vibrating.

 

[alanl]

Loose connections, or overloaded circuit causing excess heat?
What do you think the working temperature of the CB is?

 

[Chrishands]

Loose connections, or overloaded circuit causing excess heat?
What do you think the working temperature of the CB is?

Hi alanl thankyou for your reply, the CB says on it ref.cal 30 Degrees C.
I will also check the shower to see what its supposed to be pulling

 

[telectrix]

it will get warm. need to know the rating of the shower and the cable size. don't forget that the max. rated working temperature of MCBs is 70deg.

 

[Lucien Nunes]

Both of these symptoms might not be faults.

MCBs are designed to get at least warm in use, they rely on heat to operate their overload tripping mechanism. Your idea of hot might be within spec for the breaker running at full load as Tel describes. If the breaker is in fact overheating, then the likely cause is poor internal contact.

The other tripping mechanism in an MCB is magnetic, using a coil to attract an armature in the event of a fault current passing. This construction can make them behave like miniature loudspeakers, reproducing as sound the waveform of any current passing through them. A lighting dimmer chops the waveform to reduce the mean voltage delivered to the lamp, creating a high harmonic content that the MCB emits as a buzz. I expect you will find that any traditional leading-edge tungsten dimmer will produce a similar buzz from the MCB, without indicating that the dimmer is faulty. Obviously a well-engineered MCB should ideally remain silent but an old Stotz Wylex might buzz without being faulty either.