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[pscocoa]

The mcb in the consumer unit covering upstairs lights tripped out at my daughters house. There was no apparent load at the time so suspect it is the mcb itself. Is it possible to test an mcb and how difficult is it to change one of these?

[hercules]

very easy to change just trip the rcd and that cuts power to the mcb,remove cover and if you have the new one in your hand you will see what holds it on as to how to remove the old one with a blade driver,i changed an rcd today in 5 mins start to finish

[Kevin Wood]

The normal issue is that a bulb has blown and taken the MCB out. I would reset it and see if it trips again.

I assume it's not an RCD or RCBO? In that case, you could have an earth leakage fault that has caused it to trip.

Kevin

[Vamps]

The normal issue is that a bulb has blown and taken the MCB out. I would reset it and see if it trips again.
I assume it's not an RCD or RCBO? In that case, you could have an earth leakage fault that has caused it to trip.

Kevin

We have that problem, every time a bulb blows..

[I_want_an_Omega]

They also tire with age. Our landlord conducted an extensive wiring test a few weeks ago (took 6 hours) and replaced all the RCDs.

[pscocoa]

Thanks - will get onto this now. Even with no load on circuit it still trips out so change of MCB is favourite.

[Ken T]

The normal issue is that a bulb has blown and taken the MCB out. I would reset it and see if it trips again.
I assume it's not an RCD or RCBO? In that case, you could have an earth leakage fault that has caused it to trip.

Kevin

We have that problem, every time a bulb blows..

halogen bulb ?.

They tend to fail by the element breaking off and falling across the terminals, a shorter bit of element, so tries to draw a lot more current and causing an overload. This used to take out normal bulb dimmers quite quickly, as they can't cope with the momentary surge.

Ken

[Andy B]

...
halogen bulb ?.  .....

In our  house, 'normal' tungsten bulbs/lamps will pop the RCD when they fail  .

[Kevin Wood]

Thanks - will get onto this now. Even with no load on circuit it still trips out so change of MCB is favourite.

That doesn't mean there isn't a fault on the circuit. I would disconnect it at the consumer unit and make some measurements before fitting a new MCB.

Does the MCB stay on with the circuit live disconnected from it?

Kevin

[derry lad]

very easy to change just trip the rcd and that cuts power to the mcb,remove cover and if you have the new one in your hand you will see what holds it on as to how to remove the old one with a blade driver,i changed an rcd today in 5 mins start to finish

an rcd shouldnt be controlling lighting circuits,at least not over here

[Kevin Wood]

an rcd shouldnt be controlling lighting circuits,at least not over here

17th edition made it a requirement here for

"wiring concealed in walls or partitions at a depth of less than 50mm"

and

"where cables are concealed in walls constructed with metal stud partitions, irrespective of the depth from the surface, unless provided with protection in the form of earthed metallic covering, trunking, conduit or other mechanical protection so as to avoid damage to the cable during installation or construction of the wall."

So, if it's a new install, pretty much everything needs RCD protection.

Of course, it may not be, in this case.

Kevin

[pscocoa]

House was rewired in 2005. Box is a Wylex NHRS4504 - I can get the mcbs fom Screwfix in Farnborough whch is very local. Cannot get to it today though.

It may well not be the mcb of course but will start with that.

[Kevin Wood]

House was rewired in 2005. Box is a Wylex NHRS4504 - I can get the mcbs fom Screwfix in Farnborough whch is very local. Cannot get to it today though.

It may well not be the mcb of course but will start with that.

Will the MCB hold in with the mains turned off at the main switch? If so, then there is a load on it which is causing it to trip. It might still be a small load and a faulty MCB,of course, but worth a check before you replace it.

Kevin

[pscocoa]

If you turn main switch of CU to off and reset MCB it will hold until you switch on at main switch again.

[CaptainZok]

Sounds like the breaker is tripping out due to a fault on the circuit to me.