Bad 12V wiring doesn't usually cost you a flat battery. It costs you a hot cable. Two things stop that: cable thick enough for the run, and a fuse that's there for the cable. This one sizes a cable from Victron's own table (counted there and back), then covers the bit most people get backwards: you fuse the wire, not the device. Which fuse goes where, why lithium needs a fuse that can break a huge fault current, and what the 50 in an Anderson SB50 really means.
Read the guide: 12V cable sizing and voltage drop: how thick does the cable need to be?
Also: Fusing a 12V system: what size, where it goes, and which type
Also: Anderson plugs explained: sizes, ratings and what the colours mean
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Chapters
- 0:00 Intro
- 0:31 What a cable has to do
- 0:59 Count the cable there and back
- 1:20 Cable size: Victron's table and the worked example
- 2:00 Fuse the wire, not the device
- 2:45 Which fuse, where (and the lithium rule)
- 3:24 Anderson plugs: the 50 is a nickname
- 3:41 The guides and the parts
The parts
Grouped by type: Wire · Fuses · Fuse holders · Circuit breakers · Connectors and lugs (incl. Anderson).
Sources
- Victron Energy, Wiring Unlimited (book), PDF pp. 8, 11-14, 24-27, 35-40: victronenergy.com
- Victron Energy, Orion XS 12/12-50A DC-DC battery charger manual, PDF pp. 4, 10, 27: victronenergy.com
- Victron Energy, Lithium Battery Smart manual, section 4.5.1: victronenergy.com
- Exotronic, Alpha Smart Bluetooth Lithium Battery manual: exotronic.com.au
- Enerdrive | Dometic, DC-DC+ Battery Charger Owners Manual (Rev. 2.05), p. 14: enerdrive.com.au
- Blue Sea Systems, Fuse Blocks (category page): bluesea.com
- Tycab NZ, 1 x 20.26 mm² ABC128703 (4 B&S): tycab.co.nz
- Anderson Power Products, SB50 datasheet (DS-SB50 REV 9): p1.aprimocdn.net
Sources read 7 October 2026.
The worked example (a 50 A DC-DC charger 4 m from the starter battery) uses Victron's voltage-drop table; the maker's manual wins if it gives a size or a fuse for your gear. Interrupt ratings quoted are Victron's table figures for those makers' fuses. Check the manual for your own gear. Fixed 230V wiring in a van or caravan is a licensed electrician's job.
Voiceover is AI; script and facts checked by NB Camping Equipment.
Transcript
Intro
G'day. In this one: what a cable has to do, why you count the run there and back, how to pick the size, the one thing most people get backwards about fuses, which fuse goes where, and Anderson plugs. Bad 12V wiring doesn't usually cost you a flat battery. It costs you a hot cable, and in the worst case, a fire. Two things stop that: cable thick enough for the run, and a fuse that's there for the cable. You fuse the wire, not the device. Let's get into it.
What a cable has to do
A cable has two jobs: carry the amps without getting hot, and get them there without losing too much voltage. 12V makes both harder: low voltage means high current. Victron's example: a 2400 W inverter pulls 200 A, and through two short 16 mm² cables loses 5% of the energy as heat. Victron advise no more than 2.5% drop. On 12V, 0.3 V, over both cables together.
Count the cable there and back
Current goes out on the positive and back on the negative, so the length that matters is there and back. Victron's Orion XS manual works a 5 m run as 10 m of cable. Too much drop costs you heat, batteries that never quite get full, and hot cables. Victron: "In extreme cases, cable heating can cause a fire."
Cable size: Victron's table and the worked example
Victron's table gives the most current each cable size carries at 0.259 V of drop, by total length. 16 mm²: 48 A up to 5 m, 24 A up to 10 m. Worked example: a 50 A DC-DC charger 4 m from the starter battery. There and back is 8 m, so the 10 m column. 16 mm²: 24 A. 25 mm²: 38 A. 35 mm²: 53 A. That covers 50. If the charger's manual gives a size for that length, the manual wins. One trap: cable is sold by gauge and by mm², and makers convert differently. Work from the mm² printed on the cable.
Fuse the wire, not the device
Now the bit most people get backwards. A fuse isn't there to protect the fridge or the charger. It's there to protect the cable. Victron: a fuse "protects wires in a circuit from excessively high currents, which can cause overheating or fire." So it's sized to the cable. One device on the circuit: the lower of the device's rating and the cable's. Several devices on one cable: the cable's. Which is why a bigger fuse "so it stops blowing" is how cables burn. If a fuse keeps blowing, something is wrong with the load, the cable or the fuse size. Fix that. And check the manual. Victron's Orion XS 12/12-50: 60-70 A, both ends. Exotronic: no more than 2C on their Alpha batteries. 200 A on a 100 Ah one.
Which fuse, where (and the lithium rule)
In the positive cable, one per device, plus a main fuse at the battery. Every cable that leaves a battery gets one. As close to the battery as practical: Enerdrive say within 20 cm for their DC-DC charger. Solar gets a fuse between the panels and the controller. It must be DC-rated at your voltage. Lithium adds one more. A lithium battery can dump a huge current into a short, so Victron say at least one fuse must be able to break the bank's full short-circuit current. They call it mandatory. A Class T fuse breaks 200 kA; a MEGA, 1000 A. That's why Victron rate Class T for lithium.
Anderson plugs: the 50 is a nickname
Anderson plugs: the 50 in SB50 is a nickname. Their datasheet gives 50 A on one test and 120 A on another, in ideal conditions. Size the cable first, pick the plug that takes it, and crimp it properly. A plug is not a fuse.
The guides and the parts
Size the cable for the drop, there and back. Then fuse the wire, not the device, close to the battery. The guides and the parts are on the site: wire, fuses, Anderson plugs. nbcampingequipment.com.au, guides.