Correct cable dimension for boat installation

Choosing the right cable size for your boat installation is crucial for safety and functionality. The wrong cable choice can lead to:

• Unnecessary voltage drops
• Overheated cables
• In the worst case, a fire hazard

That’s why it’s important to follow both general guidelines and the ISO standard for electrical systems in recreational boats.

ISO Standard Requirements for Voltage Drop

According to ISO 13297:2021, the following guidelines apply for voltage drop in boat installations:

• 3% for circuits critical to safety (e.g., navigation systems, lights, pumps)
• 10% for other consumers (e.g., bow thrusters, windlasses, winches)

These are not just recommendations – they are international standards to avoid risks and ensure optimal operation.

How to Choose the Right Cable Size – Easily with Victron Toolkit

Calculating the correct cable cross-section can be tricky, but with the Victron Energy cable calculator in the Victron Toolkit app, it’s simple. The calculator considers:

• Cable length
• Current (amperage)
• Allowed voltage drop

The app works for both AC and DC installations and helps you comply with ISO standards.

How Much Voltage Drop Is Acceptable?

A good rule of thumb is:

• < 3% for small consumers and safety-critical circuits
• < 10% for larger consumers such as bow thrusters, stern thrusters, windlasses, and winches

These values follow ISO 13297:2021.

Check Your Boat Installation

Do you suspect your cable sizes might be incorrect? Test a few circuits. This can reveal if adjustments are needed to avoid problems.

Example from Victron Cable Calculator

A consumer drawing 10 A with a total cable length (both positive and negative) of 2.4 m requires a cable of 2.5 mm² to keep the voltage drop below 2.8% (equivalent to 0.3 V).

Values:

• Current: 10 A
• Length: 2.4 m 
• Cable size: 2.5 mm²
• Voltage drop: 0.3 V
• Loss: 2.8%