# Copper wire thickness

What diameter copper wire (single core, not isolated, open air) is needed to safely conduct 120A current from 22.2V battery to a load on 30cm distance?

Of course I searched on the Internet and there is way too much information. Different sources state different things, which is not obvious for me. If for someone it is obvious, please explain here. Some resources state 5x difference.

25C ambient temperature, drop is not critical, but less is better.

## 2 Answers

You may consider the following: current density 1000 Amps / sq. inch of cross section area of conductor ( valid for copper. Alternatively 1 amp per 1000 mils.

• If you double the diameter of the conductor and use the same current density, the power loss is quadrupled but the surface area to transfer the heat to the air is only doubled. The conductor will get hotter. – Uwe Oct 28 '16 at 11:32

It depends also on the temperature of the air, the air movement, the maximum alowable temperature of the copper wire. You have to calculate the resulting voltage drop too, it depends on the temperature of the copper of the wire. The diameter must be large enough to get an acceptable temperature rise AND voltage drop. It depends on your application if a voltage drop of 0.1 V or 2 V is acceptable.