What Size Cable Do I Need? LV Cable Sizing Guide

When setting up your inverter system, correctly sizing your battery cable is crucial. It ensures safe operation, prevents voltage drop, and helps avoid costly damage to your components. In this guide, we'll walk you through the process step-by-step so you can confidently choose the right cable size for your inverter.

Prerequisites before you start

Before diving into the calculations, you'll need to identify a few key details:

• Cable length: Measure the total distance (in metres) between your inverter and your battery. This will directly affect your cable size. You will input this figure into a cable size calculator linked below. 
• System voltage: Know the voltage of your inverter and make sure it's consistent across all your components - your inverter, battery, and other system parts must operate at the same voltage for efficiency and safety.

Read more: How long will it take to charge a 12V/24V battery with solar?

Step 1: Calculate your maximum current draw

To determine your battery cable size, you first need to know how much power your system will use at its peak. Use this simple formula:

Maximum Current (Amps) = Power Draw (Watts) / System Voltage (Volts)

This gives you the maximum current your cable will need to handle.

We recommend that you multiply this value by 1.5x to oversize your system slightly. This helps to future-proof your system so that any additional loads run safely. 

Maximum Current (Amps) x 1.5

Step 2: Use a cable size calculator 

Once you know your maximum current, it's time to use a cable size calculator. These tools factor in your system voltage, current, and the total length to suggest the correct mm2 cable size. They also account for voltage drop, which is critical in DC systems.

Try using the linked cable size calculator and input your system voltage, current, and cable length. The calculator will recommend a minimum cable size in mm2 (see 'Active' in the cable size table). 

Why voltage drop matters:

• Long cable runs increase resistance, which can lead to a drop in voltage and system inefficiency.
• A larger cable diameter reduces resistance, helping to minimise voltage drop.

Tip: When in doubt, go bigger. Oversizing your cable slightly is a safe and smart investment - it improves efficiency and adds a layer of safety. 

Read more: 5 tips to tidy your DC & wiring setup

Step 3: Select the right fuse size

After sizing your cable, the final step is choosing a suitable fuse. Fuses protect your cable and system from overcurrent damage. 

Here's how to choose:

• The fuse rating should be less than the cable's maximum amp rating, but greater than your system's max current draw. 
• Ideally, pick a fuse that is as close as possible to your cable's amp rating without going over. 

Read more: DC circuit protection guide

Wrapping up

Sizing your cable properly isn't just about getting your system running - it's about keeping it running safely and efficiently. With a few measurements and the right calculations, you can ensure your inverter setup is ready to handle whatever load you throw at it. 

If you're unsure or want to double-check your cable size, feel free to reach out - we're here to help make sure you get it right the first time. 

Shop Alvolta for a complete 12/24V DC solution for your off-grid adventures or remote systems. 

Contact our DC component experts for assistance in setting up a 12/24V system. We are Australian-founded and operated and have been providing expert advice for over 23 years.