Why cable and fuse sizing matters
Correctly sized cables keep voltage drop in check, prevent overheating, and protect your gear from premature failure. The right fuse steps in as the last line of defence, blowing before a fault can cook your wiring or put your vehicle, boat, or off-grid cabin at risk. This guide merges the essentials of cabling and fuse protection into one clear workflow so you can size everything right the first time.
Read more: What's needed for a dual battery system?
1. Gather key facts about your system
What you need | Why it matters | Typical sources |
System voltage (12V/24V/48V) | Dictates current flow and compatible fuse ratings | Battery bank spec sheet |
Load rating (W or VA) | Sets the maximum current the circuit must carry | Inverter, MPPT, fridge, DC-DC charger label |
Cable run length (metres, round-trip) | Longer runs mean higher resistance and more voltage drop | Tape measure or wiring diagram |
2. Calculate peak current
Use the below formula to determine your load's peak current, then add a safety buffer for future expansion and start-up surges:
Peak current (A) = Power (W) / Voltage (V)
Buffered Current (A) = Peak Current x 1.5
Example
A 3000W inverter on a 24V system:
3000W / 24V = 125A
125A x 1.5 = 188A
3. Choose the correct cable size
3.a. Enter the buffered current, system voltage, and cable length into a DC cable-size calculator (there are heaps of free ones online).
3.b. Check the recommended cross-section (mm2)
3.c. Round up if you're on the fence... oversize slightly. This will help reduce voltage drop, lower cable temperature, and leave room for extra loads later.
Rule of thumb: bigger is better and rarely regretted.
4. Match the fuse to the cable, not the load
Fuses exist to protect the cable, so they must blow before the wire gets hot, yet hold long enough to pass normal current.
1. Minimum fuse rating: above your buffered current draw
2. Maximum fuse rating: below the cable's continuous amp rating
3. Ideal fuse: as close to (but not over) the cable limit
Example
Cable ampacity: 200A
Buffered current: 188A
Recommended fuse: 190 - 195A (next standard size is fine)
Fuse size chart courtesy of Alvolta
5. Pick the right fuse type
Fuse type | Typical use-case | Pros |
MEGA | Battery-to-inverter links, winches | High current, compact |
ANL | Large lithium banks, marine installs | Low voltage drop, bolt-on |
MIDI | MPPTs, DC DC chargers | Mid-current, easy to source |
Blade / ATC | Low-draw loads (lights, fridges) | Cheap, quick to replace |
Manual reset circuit breaker | Where fast re-use beats fuse swaps | Button reset, visual flag trip |
6. Final checklist before you energise
- System voltage printed on every component and fuse
- Cable lugs crimped and insulated properly
- Fuse located as close to the battery positive as practical
- Spare fuses or a reset breaker on hand
- Voltage-drop test under load (multimeter) shows <3%
Springers Solar | Your Trusted 12V/24V Components & Accessories Supplier
We only stock the best brands in the extra-low voltage industry for the best prices - you can trust that when you buy gear from Springers, you are setting up your system to perform long-term. We don't waste our time or your time with low-quality products.
With an in-house team of 12V/24V experts, we can offer advice and support as you set up your off-grid, off-road, or DIY battery system. We are Queensland-based and house our stock, so check out our online store here or visit us at Lawnton or Capalaba for in-store help.
Cable and Fuse Guide