Which cable dimension should you use for which consumer?

A practical guide to help you choose the right cable dimension based on current consumption, length, and safety requirements – with tips to avoid voltage drop and overheating in your onboard electrical system.

Choosing the right cable dimension for your boat installation is crucial for safety and function. Incorrect cable choice can lead to:

• Unnecessary voltage losses
• Overheated cables
• In the worst case, fire risk

Therefore, it is important to follow both rules of thumb 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 during boat installation:

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

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

How to choose the right cable dimension – easy with Victron Toolkit

Calculating the correct cable cross-section can be complicated, but with the Victron Energy cable calculator in the Victron Toolkit app, it becomes easy. The calculator takes into account:

• Cable length
• Current strength
• Permissible 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 rule of thumb is:

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

These values comply with ISO 13297:2021.

Check your boat installation

Do you suspect that the cable dimensions are incorrect? Perform spot checks on some consumers. This can reveal if adjustments are needed to avoid problems.

Example from Victron cable calculator

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

Below the values:

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