I would not use a smaller cable on a circuit that was wired with 1.5 from the consumer unit I know in practice it may seem safe but it is bad practice in my book also what would you right on the cert 1.5 or 1mm
Oh dear Adrian..... looks like its going to have to be hand-bags at dawn,
if I cant get you round to thinking to what IMHO is a bit more of a common sense approach.
I shall put my case for the defence your honour!Blushing:x
Mixed CSA's
In an ideal it may be nice to have a "college test bench" wiring arrangement..
but there are many situations where varying cable sizes do appear around a circuit.
Extend an existing installation with old imperil stranded core conductors.. and now use solid core conductors... thus CSA change.
Old 2.5mm with 1.0mm earth mixed with 2.5mm/1.5mm earth!
Situations where you quite simply do not know all of the CSA's around the circuit
Do a PIR and find multiple sizes into the same MCB/fuse, e.g. 1x1.0mm 1x1.5mm in same lighting circuit.
Any cases where I do find mixed CSA's on the installation I would note the "smallest" on the cert and ensure the fuse/MCB rating is appropriate for the cable capacities found.
Lighting circuit
A lighting radial circuit, could be considered as a central main "backbone" supply with individual switch drops taken off it at appropriate intervals...
e.g. looped at Ceiling roses or Switches or mixture of both.
Any individual switch drop off the main supply "backbone" will only be carrying the load for the light fittings that it switches, NOT the whole circuit!! :|
Thus a 1.0mm switch drop.. even if supplying say a 500w floodlight, typically is still carrying LESS than 2.5amps...
So no load issues for the smaller CSA switch cable!!
Many pendant type light fittings have a flex with 1.0mm or even 0.75mm flexible cord... This smaller cable CSA IS connected directly onto the lighting circuit.
So EVEN if the circuit is wired in 1.5mm the actual light fittings are very rarely wired with 1.5mm!
There are other reasons for using a larger CSA rather than just the current capacity...e.g. reducing voltdrop on a long run.
Some light fittings have very small terminal connections, which can be a bit tight for 1.5mm conductors.
So on a long lighting circuit it could be beneficial to have a 1.5mm "backbone"... but still leave switch drops and supply into light fittings as 1.0mm.
I rest my case your honour!:|B-)
please let me off leniently PrayPray