Caravan 12V Wiring Guide

CaravanParts.com.au Main Tips

  • Avoid voltage drop
  • Use the correct size wire for the application. This is primarily based on two factors:
    • load being drawn (in amps)
    • length of cable run (in metres)
  • Even if a 12v cable says "Rated for 50A" (e.g. this on 6mm auto cable), it does not mean that it can run a 50A load properly. It means that the cable will not physically deterioriate/burn under this load. But it WILL have a massive voltage drop which is what you want to avoid.
  • The cable designations are extremely confusing to newcomers. At the end of the day, what actually counts is how much COPPER is actually in the cable. The problem is that different sizes use different measurements.
  • Auto Cable (Small)
    • Commonly available in 3mm, 4mm, 6mm and used for most small loads like lighting
    • The number refers to the outside diameter of the cable INCLUDING insulation.
    • The actual amount of copper is NOT specified, and that is why the quality of "auto cable" varies so much and pricing varies accordingly.
    • Good manufacturers will specify the amount of copper in these size cables in mm2.
  • B&S Cable (Large)
    • Rated in "AWG" (American Wire Gauge) - common sizes are 8B&S, 6B&S etc.
    • Used for Anderson plug lines, battery interconnection, inverters.
    • The smaller the number the MORE the copper. 0B&S cable is HUGE! 10B&S cable is smaller than 6mm auto cable.

 

Auto Cable Sizes to Copper mm2

This is for reference only, based on Narva cable. Each auto cable manufacturer may be different - and that's part of the problem!

Nominal Diameter Rated Amps* Copper mm2 Strands/Diameter
2.5 5 0.64 8/0.32
3.0 10 1.13 14/0.32
4.0 15 1.85 23/0.32
5.0 25 2.9 36/0.32
6.0 50 4.58 57/0.32

 

B&S Cable Sizes to Copper mm2

AWG / B&S Copper Diameter Copper mm2
10 2.59 5.26
9 2.91 6.63
8 3.26 8.36
7 3.67 10.55
6 4.11 13.29
5 4.62 16.76
4 5.19 21.14
3 5.83 26.65
2 6.54 33.61
1 7.35 42.39

 

Cable Lugs and Terminals

Cable Type Lug Reference
2.5mm Auto Red Terminals
3mm Auto Red Terminals
4mm Auto Blue Terminals
6mm Auto Yellow Terminals
8 B&S 10-xx Lugs
50A Anderson Plug
6 B&S 16-xx Lugs

 

Voltage Drop Calculator

The tables below refer to ROUTE lengths – ie source to destination. (The conductor length is normally twice that – ie there and back). Calculated at an acceptable maximum 5% voltage drop. DC only.

Formula is     Voltage Drop = 2 x L x I x R ÷ A

A = cross section of cable in mm2
L = route length in metres (source to destination)
I = current measured in amps
R = resistance of cable    [copper = 0.017; aluminium = 0.028; Steel = 0.18]

RedArc have a great online calculator here : RedArc Voltage Drop / Cable Size Calculator

 

Acceptable Cable Size in Copper mm2 for 12V

Cable Length (metres)
Amps 1 2 5 10 15 20 25 30
0.5 0.4 0.4 0.4 0.4 1.84 1.84 1.84 1.84
1 0.4 0.4 0.4 1.84 1.84 1.84 1.84 1.84
1.5 1.84 1.84 1.84 1.84 1.84 1.84 2.9 2.9
2 1.84 1.84 1.84 1.84 1.84 2.9 4.6 4.6
3 1.84 1.84 1.84 1.84 2.9 4.6 4.6 7.9
4 1.84 1.84 1.84 2.9 4.6 7.9 7.9 7.9
5 1.84 1.84 1.84 4.6 4.6 7.9 7.9 13.6
7.5 1.84 1.84 2.9 4.6 7.9 13.6 13.6 25.7
10 1.84 1.84 4.6 7.9 13.6 13.6 13.6 25.7
15 1.84 1.84 4.6 13.6 25.7 25.7 25.7 32.2
20 2.9 2.9 7.9 13.6 25.7 25.7 32.2 49.2
25 4.6 4.6 7.9 25.7 25.7 32.2 49.2 49.2
30 4.6 4.6 13.6 25.7 32.2 49.2 49.2
40 7.9 7.9 13.6 25.7 49.2 49.2
60 13.6 13.6 25.7 49.2
80 25.7 25.7 25.7 49.2
100 32.2 32.2 32.2
125 49.2 49.2 49.2