On 14/02/2019 21:39, John Rumm wrote:

Going to 6mm^2, that would be 7.3mV/A/m or ~7V

So you could easily argue that 6mm^2 will get you close enough -
especially as it does not sound like the circuit will likely have
anything near that load on it normally. (you could also argue that the
effects of small voltage drops with modern low energy lighting are
overstated anyway).


This is where the tightening up of lighting circuits to a 3% voltage
drop in the regs may need to change.

The 3% voltage drop for lighting became a reg before the use of LED
lighting became mainstream.

The use of a deviation from the regs is a useful tool. If the OP fits
LED lighting that works from 80 to 250V (most of it does) then you can
ignore the 3% voltage drop and calculate for a 5% drop.

There are other reasons not to design the circuit to the absolute
minimum allowed.

The three most obvious ones are

1. Most of the cost is actually the labour to fit the supply cable. You
only have to do the job once.

2. If running at near max allowed current for long periods you get
wasted power in the cable.


3. Future expansion of the system (if 2 does not apply)

--


Adam