Copper is not a perfect conductor. So the choice of wire is related to the current flowing and the length.
Cable has to survive undamaged until the circuit protective device operates, undamaged from mechanical issues, and with sufficient volts left at the far end to do something useful.
However, private modellers aren’t constrained by the content of BS7671 when building railways.
As thermal dissipation in the cable is hardly a relevant issue at the track voltages modellers use, then one faces the other two constraints.
So let’s pass 1 amp through a hypothetical cable and see what happens:
- If I were wiring the track on a garden railway then I would use minimum 2.5mm2 omnibus cable to get to the other end with 12VDC on the basis of its internal resistance and the consequent low voltage drop in that size cable at that sort of length. 4mm2 might be a better choice if a feedback controller were not in use. Individual droppers onto the track power omnibus cable might be smaller.
- If I were wiring a 4ft-long alcove layout then I would not go below 0.5mm2 on 12VDC on the basis of its mechanical strength – it might have to survive a cat pawing at it, for example (though not in my case).
- This reply was modified 1 year, 9 months ago by Nick Ridgway.