I was going to fit a relay at the source, a 230/48 V power supply to supply a relay in the outbuilding.

Instead I am going to run the 12 VDC to the outbuilding and fit as small 5 amp relay (power = 0.02), use the N/O contact to switch a 32 amp relay (power 0.35)

I will test the volt drop tomorrow.

Quote Originally Posted by Justloadit View Post
If you are simply powering the coil of a relay, then there should not be an issue.
Most 12V relays are less than 0.5W, which means a current of approximately 35mA.
Coil impedance is around 350 ohms, so 10 ohms from the cable resistance is negligible.