Adding a new ceiling rose

[ziggy1979]

Hi All

We want to add a new (4th) ceiling rose to our hallway by running a 1mm T & E from the last ceiling rose in the "chain" to the new one (the three current lights seem to be joined in parallel from one to the other so it would be a case of adding the 4th one). Only thing is that the current lights have been there a while and the new cable will run along the back of plasterboard with a whole load of rockwool over it.

Two questions:

1. Does it matter that the "old" lights run on a wider cable than 1mm (possible 1.5mm or 2.5 mm)?

2. Can you see any problems with regards to the insulation/plasterboard?

In case its relevant, there are three switches (3-way lighting). Please point out any "tricky" issues. Our builder also said that he could do not as its not Part P?

Thanks!!!

 

[electronicsuk]

It is unlikely the old lights will be wired in 2.5. If they are currently wired in 1.5mm^2 it would be nice to see the same size cable used on anything added to the installation, but on a (presumably) 6A circuit 1.0mm^2 will do the job.

Insulation above the plasterboard will hinder the cooling of the cable, but on a small circuit with such a light load (no pun ) and taking into consideration that the cable will be in contact with plasterboard on one side I wouldn't worry about it too much.