Lighting radial

[afswift]

Is there any reason why my lighting circuit would have been run in a combination of 2.5mm and 1.5mm? The lights are wired using junction boxes with the 2.5 running from the CU and between each box?

The circuit feeds 6 rooms, (about 9 light fittings)

 

[FingRinal]

A practical reason would be that the electrician had run out of one cable or the other.

A technical reason for running part of a circuit, typically lighting in a commerical/industrial situation (so why not a domestic one too) is to overcome excessive voltage drop or another one is to improve what would otherwise be a too high earth fault loop impedance.

 

[Click-Sure]

Probably just run out of 1.5mm, yes, guilty as charged, I've done it...