FAQ: How do I choose a cable of the right diameter?

By Bart van den Bosch – Product Manager Libra Energy

In response to the numerous questions on this subject, here is a link to a calculation tool for working out AC (230 V) cable diameters:


Bear in mind that the cable loss should stay below 1%. If this is not the case, the inverter could shut down regularly when there is high voltage. This mostly occurs when there is a lot of sunshine with the occasional cloud. The MPP tracker causes a rapid build-up of power which the cable is unable to cope with. Consequently the output voltage through the AC connector on the inverter increases, causing the inverter to shut down (and display a grid fault). This will cause you a loss of output. In the Netherlands the inverter will shut down at 253 VAC.

Here is another list of guide figures. Please note that it is the installer’s responsibility to take readings on location and check whether our recommendations apply there.

Without knowing all of the system’s environmental parameters, they are only advisory.


Power   \   cable length 5 10 15 20 25
1 kW 3 x 2,5mm2   3 x 2,5mm2  3 x 4mm2  3 x 4mm2 3 x 4mm2
2 kW 3 x 2,5mm2 3 x 4mm2 3 x 4mm2 3 x 4mm2 3 x 6mm2
3 kW 3 x 4mm2 3 x 4mm2 3 x 4mm2 3 x 6mm2 3 x 6mm2
4 kW 3 x 4mm2 3 x 4mm2 3 x 6mm2 3 x 6mm2 3 x 6mm2
5 kW 3 x 4mm2 3 x 6mm2 3 x 6mm2 3 x 6mm2 3 x 10mm2