One of the most common issues that we observe in boats is improper wiring sizes being used for various appliances and electrical components.  All too frequently, wires that are much to small are expected to provide adequate power for demanding devices like refrigerators and air conditioners.  This isn't only a problem of providing enough power, either.  Using wire that is too small is a fire hazard and can be a serious safety issue.  The ABYC (American Boat & Yacht Council) has established industry-accepted standards for wire sizing, and in this article we will help you to understand those standards.

Marine-Grade Wire

One important factor to consider is that marine wire is NOT the same type of wire you might use in your home or purchase at your local hardware store.  Marine-grade wire comes with some important features that ensure it is safe to use in the marine environment.  For one, marine wire will be stranded, whereas typical household wire is solid.  Second, marine-grade wire is tin-plated copper, which ensures that it will be ignition-protected.  This is different than wire that might be used in other types of vehicles like RVs and buses.  For the purposes of this article, we are also assuming all the wire discussed has an insulation rating 105 degrees Celsius.  A lower insulation rating can reduce the current-carrying capacity of the wire.

Amperage

You need to establish the current required for the device that you are intending to connect, measured in amperage.  Most electrical appliances and devices will have documentation that includes this type of rating.  If you are unsure of the current rating of the device, contact the manufacturer to get this information.

Distance

The length of the circuit will be needed in order to properly choose the wire size for the circuit.  Make sure that you are measuring the entire round-trip circuit to calculate the distance.  You will need to measure the distance from the power supply to the device and back.

Circuit Type

The type of circuit is important in determining the wire size as well.  Critical circuits require a smaller allowable voltage drop than non-critical circuits.  Critical circuits, which can allow up to 3% voltage drop include circuits for panel main feeders, bilge blowers, electronics and navigation lights.  Non-critical circuits can allow up to 10% voltage drop, and include things like courtesy lighting, windlasses, bait pumps and general appliances.

Choosing the Correct Wire

Once you have the information listed above, you can consult the following chart to identify the correct wire size for your application.  

DC Wiring Sizing ChartDC Wiring Sizing Chart

For example, perhaps you have a windlass rated at 80 Amps, and it is located 25 feet from the battery. The entire circuit length would be 50 feet. Since it is a windlass, the circuit type is non-critical. Using the above chart, you would find the correct wire size to use is 4 AWG.

Please note that while this chart communicates the standards set by ABYC, it may not address certain unique characteristics of your application.  If you are in doubt or have any questions, please consult with an ABYC-certified marine mechanic for assistance.

We also highly recommend using the Circuit Wizard by Blue Sea Systems, which is a handy, interactive tool for assiting you with properly wiring the devices on your boat.

If you have any questions about proper wire sizing, feel free to contact the ABYC-certified experts at Marine Parts Source at (866)388-0390.