Cable Sizing Guide – 48V Systems

48V cable sizing guide for emerging DC architectures — read the caveats before you start

Before you start — read this first

This 48V cable sizing guide covers emerging 48V DC systems in leisure vehicles, light commercial vehicles and some off-highway applications. It is not yet a mainstream installation voltage and this guide should be treated with appropriate caution — component availability, installer familiarity and the standards landscape are all less mature than for 12V or 24V systems.

If you are designing a 48V system, you should already have a clear reason for doing so. The physics are compelling: the same power at four times the voltage means one quarter of the current, which means significantly smaller cable, less volt drop, lower losses and lighter wiring. But the infrastructure, tooling and knowledge base around 48V DC in these applications is still developing.

For 12V leisure vehicle and campervan installations see our 12V Cable Sizing Guide. For 24V plant and commercial applications see our 24V Cable Sizing Guide.

The 48V case — why it makes engineering sense

At 48V, the current for a given power load is one quarter of the 12V equivalent. One quarter of the current means dramatically smaller cable, far less volt drop over long runs, significantly lower wiring losses and a lighter, more manageable loom. For larger leisure vehicle builds, serious overlanders, extended off-grid systems and any installation where cable runs are long or power demands are high, the engineering argument for 48V is strong.

The passenger car industry has already made this call. 48V mild hybrid systems are now mainstream across European vehicle platforms — Audi, Mercedes, Renault, Volkswagen Group, Land Rover and others. The components, thinking and infrastructure are coming whether the leisure vehicle industry is ready for them or not.

48V is not a gimmick. It is where intelligent system design is heading. This guide positions Voltforge ahead of that curve — not as speculation, but as a technically grounded engineering argument.

A word on stranding and insulation

The same cable construction principles apply at 48V as at 12V or 24V. Use fine-stranded Class 5 automotive flex as a minimum. For the voltage range involved, ensure all cable, terminations and components are rated for the actual system voltage ceiling — remember, design to 60V, not 48V nominal.

📖 For a full explanation of cable construction and conductor classes, see our Cable Construction Know How guide. For full ampacity data across insulation types and ambient temperatures, see our Ampacity Ready Reckoner.

Common applications — what size do I need?

Use this table as a starting point. Always check the current draw of your specific device on its datasheet or label. At 48V the current figures are approximately one quarter of the 12V equivalent for the same load.

All cable sizes are minimum recommendations for free air runs at normal ambient temperature using quality 105°C cable rated for the actual system voltage ceiling (60V). Go up a size for runs in conduit, behind panels, or in bundles.

Quick current rating reference

The figures below are for a 48V system. At 48V the current for a given power load is one quarter of the 12V equivalent — which is why cable sizes can be significantly smaller. Current carrying capacity is determined by the conductor and insulation, not the voltage. For 12V or 24V systems see our dedicated guides at voltforge.co.uk.

Figures for quality 105°C PVC insulated stranded copper flex, single conductor, free air, 25°C ambient. Ensure all cable and components are rated for the actual system voltage ceiling of 60V, not 48V nominal.

Volt drop — the strongest argument for 48V

Every cable has resistance. Current flowing through resistance causes a voltage drop along the run. On a 48V system volt drop has far less impact than on 12V for the same power delivery — this is one of the key engineering advantages of the higher voltage architecture.

A rough rule of thumb: keep volt drop to 5% or less of your supply voltage on any circuit. On a 48V system that’s 2.4V maximum. The volt drop advantage of 48V over 12V is substantial — the same cable carries four times the power for the same volt drop percentage. This is one of the strongest practical arguments for 48V in larger builds.

Volt drop = (cable resistance in mΩ/m) × current (A) × run length (m) ÷ 1000. Your cable datasheet will give you the resistance figure.

📖 For full resistance data (mV/A/m) for all cable sizes, see our Ampacity Ready Reckoner at voltforge.co.uk

Standards and regulatory note

48V DC systems in vehicles are subject to evolving standards. BS EN 1648 (leisure vehicles) has a 15V bus voltage limit that excludes many 48V architectures from its scope. The SELV boundary at 60V is directly relevant to 48V system design and has significant regulatory implications that are outside the scope of this document — a dedicated guide covering this will follow. Always verify the applicable standards and regulatory framework for your specific application before proceeding with a 48V installation.

Disclaimer

This document is provided for general reference and educational purposes only. 48V DC systems represent an emerging architecture and the guidance in this document reflects current engineering understanding of a rapidly developing field. The figures and guidance contained in it are derived from published industry standards and are intended to support informed decision-making — they are not a substitute for a full engineering assessment of a specific installation. It is the responsibility of the installer to verify the suitability of all components, cable, protection and installation methods for the actual system voltage (including the fully charged voltage ceiling), and to ensure compliance with applicable standards, regulations, and any vehicle or equipment manufacturer requirements. Voltforge and Zeromachine Ltd accept no liability for loss, damage, injury or consequential loss arising from the use of or reliance on the information in this document. If you are in any doubt, stop and get proper advice before proceeding.