Changing lighting circuit MCB

[Durhamdan]

My upstairs lighting circuit is wired in 1mm^2 twin and earth cable, and protected by a 10A MCB (Wylex type B).

This past spring we had new (more) loft insulation fitted, and now the lighting circuit cable is under the insulation through much of its length, increasing the chance of overheating, I'd have thought.

So.....I'd like to increase the protection on the circuit by changing the 10A MCB for an 6A MCB, like this one:

http://www.screwfix.com/app/sfd/cat/pro.jsp?id=73464&ts=78471

Is this a job for a DIYer? Is it hard to fit new MCBs? Can I be sure that once I shut off the 100A main isolator switch on the consumer unit, the busbar and all cables in the CU will be 'dead'? I have a digital multimeter, but am a novice at using it.

My CU looks like this:

http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331831&ts=78792&id=60251

Cheers for any help.

 

[chaban48699]

just to let you know even switching off the main switch on your CU the tails supplying it (ie from the meter) will still be live!!!!

It's an easy enough job to switc the MCB but if you are not fully confident I would not even touch it, might be worth getting a spark in.

 

[JohnD]

...but the busbar will be dead, so will the load side terminals of the main switch.

The supply side terminals will be live, I don't know if that wylex switch has insulating shutters over the screw heads like MEM use but you have no reason to touch them, and they will be recessed into the plastic body of the switch so that you need a screwdriver to poke them.

There is a slight risk that it was fitted by a clumsy electrician who stripped the insulation too far and left exposed copper; but you will be able to see that and have no reason to touch it.

 

[Durhamdan]

Thanks very much for the replies. I'll give it a go this weekend. From what I can see it looks like I need to unclip the MCB at the bottom, then slide it off the finger of the busbar, while at the same time removing it from the DIN(?) rail, all in one action I suppose? Reverse procedure to install the new one, ensuring all contacts are tight.

Thanks again.

 

[CallEdsFirst]

You will need to remove the outgoing circuit live from the other end of the mcb too!

Whilst I am impressed that you see an mcb as cable protection, i assume there is not too much load on the circuit for 6a mcbs to hold? Not one of these people with 18 downlighters in a 2 foot square bathroom?

Incidentally, this has to be notifiable, but why. Technically just swapping out a component, but obviously modifying a circuit that supplies a bathroom no doubt and requires testing before and after. Can Part P expert clarify?

 

[RF Lighting]

It is because you are altering the circuit characteristics shuch as maximum permitted Zs, and you need to check the suitability of accesories and cable CCC.

I think TBH it is probably aimed more at people who increase the size of an OCPD without a thought about cable size etc. (Such as buying a 9.5kW shower and trying to fit it to an old 30A supply which starts tripping so they stick a 40A fuse in and carry on regardless) rather than in this case it is being decreased which probably will not makie the installation more dangerous.

 

[CallEdsFirst]

Wow comprehensive answer! and a new abbreviation for my list. Strangely similar to ODPM, John Prescott's padded room in Parliament!

 

[RF Lighting]

OCPD = Over Current Protective Device. (Encompasses rewireable fuses, cartridge fuses, HBC fuses (High breaking capacity ) MCBs etc)


I though JP resigned at the same time as Bliar