What causes light to dip and come back up when for example kettle is turn on and if I'm working in my garage the same thing occurs to the garage light when using power saw or router on 13amp ring main to mcb garage C.U. The house C.U is the wired type fuse. £800.00 to replace for a 12 way MCB unit. £60 for the replacement plug in MCB's. In U.k. that is

bob, August 2009

I don't know who quoted you £800 to replace your distribution board (consumer unit) but I hope you don't count them amongst your friends.
Depending on where you live in the UK a more realistic price would be £300-£500. Get a few quotes from reliable & certificated tradesmen.

Harry, August 2009

We are encouraged by well-meaning people not to offer advice on matters electrical - danger lurks in bad advice.

There is only one thing that will cause the lights to dim and that's a drop in the voltage being presented to the lamp.

The AC mains supply to a property in the European Union is 230 V ± 10% at 50 Hz and your kettle, saw or router should not be able to cause a noticeable voltage drop when switched on.

The fault you have very probably lies in the area of the distribution board and the services of a certificated specialist will be safer as will a more modern consumer unit with protection devices.

If you're concerned about the suggested cost then perhaps you could seek a second opinion/quotation.

Take care...Good luck...

Peccavi, August 2009