Cabeldimensioning

Dimensioning of cables with uservoltage of 12VDC is depending of how high current that flows in the wire, but also it's length. Calculating of voltagedrop start from OHM´s law.

OHM´s law: U = R x I, R = U / I or I = U / R

U= Voltage

R = Resistance

I = Current in Ampere

A sample:

A wire of 1,0 sqmm is 10 meters. The voltage is 12 Volt and the current is 10 Ampere.

The Voltagedrop is then(20 Ohm/1000) x 10 = 0,02 Volt x 10 = 0,2 Volt

The resistance in the wire can variate between different producers and therefore it must be carefully controlled before the calculations begin. The tables below should therefore only be used as a generell help.

Caution ! Think of the returnwire when you dimensioning.

A voltagedrop should be under 0,5 Voltand are in the tables green. A voltagedrop between 0,5 - 1,0Volt is a temperary solution and are in the tables pink and a voltagedrop over 1,0Volt should be avoided and are in the tables red.

 

Voltagedrop in a wire at 5A load

Dimension Resistance/km 1m 5m 10m 15m 20m
0,75sqmm 26 ohm 0,13 V 0,65 V 1,3 V 1,95 V 2,6 V
1,0sqmm 20 ohm 0,1 V 0,5 V 1 V 1,5 V 2 V
1,5sqmm 13,7 ohm 0,0685 V 0,3425 V 0,685 V 1,0275 V 1,37 V
2,5sqmm 8,21 ohm 0,041V 0,205 V 0,4105 V 0,6157 V 0,821V
4sqmm 5,09 ohm 0,02545 V 0,1272 V 0,2545 V 0,3817 V 0,51 V
6sqmm 3,39 ohm 0,01695 V 0,0847 V 0,1695 V 0,2542 V 0,339 V
10sqmm 1,95 ohm 0,0097 V 0,0487 V 0,0975 V 0,1462 V 0,195 V

Voltagedrop in a wire at 10A load

Dimension Resistance/km 1m 5m 10m 15m 20m
0,75sqmm 26 ohm 0,26 V 1,3 V 2,6 V 3,9 V 5,2 V
1,0sqmm 20 ohm 0,2 V 1 V 2 V 3 V 4 V
1,5sqmm 13,7 ohm 0,13 V 0,68 V 1,37 V 2,05 V 2,74 V
2,5sqmm 8,21 ohm 0,082 V 0,41 V 0,82 V 1,23 V 1,64 V
4sqmm 5,09 ohm 0,0509 V 0,2545 V 0,509 V 0,7635 V 1,018 V
6sqmm 3,39 ohm 0,0339 V 0,1695 V 0,339 V 0,5085 V 0,678 V
10sqmm 1,95 ohm 0,0195 V 0,0975 V 0,195 V 0,2925 V 0,39 V

Voltagedrop in a cable at 15A load 

Dimension Resistance/km 1m 5m 10m 15m 20m
0,75kvmm 26 ohm 0,39 V 1,95 V 3,9 V 5,85 V 7,8 V
1,0sqmm 20 ohm 0,3 V 1,5 V 3 V 4,5 V 6 V
1,5sqmm 13,7 ohm 0,2055 V 1,0275 V 2,055 V 3,0825 V 4,11 V
2,5sqmm 8,21 ohm 0,123 V 0,6157 V 1,2315 V 1,8472 V 2,463 V
4sqmm 5,09 ohm 0,0763 V 0,3817 V 0,7635 V 1,1452 V 1,527 V
6sqmm 3,39 ohm 0,0508 V 0,2542 V 0,508 V 0,7626 V 1,0168 V
10sqmm 1,95 ohm 0,0292 V 0,1462 V 0,2925 V 0,438 V 0,584 V

Voltagedrop in a cable at 20A load

Dimension Resistance/km 1m 5m 10m 15m 20m
0,75sqmm 26 ohm 0,52 V 2,6 V 5,2 V 7,8 V 10,4 V
1,0sqmm 20 ohm 0,4 V 2 V 4 V 6 V 8 V
1,5sqmm 13,7 ohm 0,274 V 1,37 V 2,74 V 4,11 V 5,48 V
2,5sqmm 8,21 ohm 0,1642 V 0,821 V 1,642 V 2,463 V 3,284 V
4sqmm 5,09 ohm 0,101 V 0,509 V 1,018 V 1,527 V 2,036 V
6sqmm 3,39 ohm 0,0678 V 0,339 V 0,678 V 1,017 V 1,356 V
10sqmm 1,95 ohm 0,039 V 0,195 V 0,39 V 0,585 V 0,78 V

The effect you can get out in the caravan is a result of the voiltage multiplicated with the current, so it is important to not have to high voltagedrop to get full effect at the load.