Over-size feed to high level lighting circuit ?

[Eagle497]

Is it acceptable to over-size the feed cable to a 20A 230V lighting circuit to overcome volt drop ?
The circuit would be :-
20A type B RCBO protecting 100m x 16mm 3 core SWA connected to 3 x 100m, 4mm lighting circuits.
I know that I could treat the 16mm SWA as a sub-main and fit a small distribution board for the 3 x 4mm circuits but it would be at high level and resetting tripped breakers would be problematic.
If the above is acceptable, how should I record the cable size on the installation certificate ?

 

[Andy™]

why wouldnt it? its common on longer runs to use a larger CSA cable, and often you won't meet volt drop or Zs without doing so. record smallest CSA and write larger CSA on the circuit notes

 

[Eagle497]

why wouldnt it? its common on longer runs to use a larger CSA cable, and often you won't meet volt drop or Zs without doing so. record smallest CSA and write larger CSA on the circuit notes

Thanks Andy.
I thought it was OK but just needed confirmation.

 

[Phoenix]

Nothing wrong with it, but you've probably not got the most efficient design.

Consider that your feed cable is not opperating at capacity, and therefore temperature, theres a calculation you can do for a corretcion factor to volt drop, may allow you to go down a size.

Consider also, if you wouldn't be better off making at least the feed to the joint with the 4mms 3ph. You might be able to end up with a a smaller CSA 4 core cable on a 10A breaker.

If Loop impedance is the thing thats biting, consider tagging your joint box where it converts onto the steelwork of the building (if so constructed)

Probably ought to be avoiding RCD on industrial lighting, it shouldn't be necessary if designed properly