Choosing Cable Size


Choosing the right cable size for your DC electrical project is important, since a wire that is too small can overheat and possibly start a fire. The American Boat and Yacht Council (ABYC) publishes charts with valuable detail to help experienced electrical installers determine what wire size they need. Although these charts are an excellent resource, they are a bit intimidating. This technical brief distills the information on these charts to a more manageable size for installers and caravan/boatowners alike.

Quality marine wire, as specified by ABYC standards, will always be stranded rather than solid, and always tin-plated copper. In addition, the DC Cable Selection Chart shown below assumes a cable insulation rating of 105°C. A lower rating will decrease the current-carrying capacity of the wire.

To use the chart included with this technical brief, follow the instructions below.

Choosing the correct wire

A  Locate the CURRENT IN AMPS of your appliance across the top of the chart. Most electrical products include a rating label, or you can find the amperage rating in the documentation that came with the product.

B  Find circuit LENGTH IN FEET along the left side of the chart. Note that the total length of the circuit is the round-trip distance from power source (usually the battery) to the product and back.

C  Select the CIRCUIT TYPE. Allowable voltage drop is based on whether a circuit is critical or non-critical.

Critical DC circuits, with 3% allowable voltage drop, include

  • Battery Chargers
  • Inverters
  • Inverter/Chargers (Combi’s)
  • Fridges/Freezers
  • Electronics
  • Navigation lights

Non-critical DC circuits, with 10% allowable voltage drop, include

  • General lighting
  • Windlasses/Winches
  • Bait/Water pumps
  • General DC appliances

Follow down the column until you find your circuit’s LENGTH IN METERS

D  Intersect CURRENT IN AMPS with LENGTH IN METERS to identify the cable size.

Example: A winch rated at 80A is 25’ from the battery. Circuit length is 50’, circuit type is ‘non-critical’, and correct cable size is 4 AWG.

The Circuit Wizard, at, is a resource for a more detailed treatment of cable size selection for DC circuits. It allows you to input detailed information including cable insulation temperature rating and other de-rating factors. The Circuit Wizard is easy to use, and is accessible from any computer with an Internet connection or available for download via the iOS App Store or Android apps for mobile devices.

We’d like to thank Blue Sea Systems with their help in compiling this informative information.