In the harsh marine environment only top shelf boat wire or marine cable will suffice.
Start any repair or installation project by picking the right wire for the job by choosing good quality wire or cable properly sized and color-coded for the job at hand.
Get the Right Type and Color
When selecting wire for your boat stick with American Wire Gauge (AWG) standard sizes made from stranded tinned copper with oil resistant insulation rated at 105ºC dry and 75ºC wet or higher. This type of boat wire stands up well to hydrocarbons in or around engines and bilge areas while also providing good corrosion resistance.
Whenever possible use boat wire with insulation color-coded to the type of circuit you are wiring. For example, to color-code the wire for a livewell pump installation, the negative wire to the pump would normally be black and the positive wire from the controlling switch to the pump would be brown. This follows standard marine industry color-coding listed in the table below.
The table below lists a sampling of wire colors and uses.
| Wire Color | Uses |
| Black or Yellow | Ground, Returns, Negative Mains |
| Red | Main Power Feeds, Unfused Positive Mains |
| Brown | Switch to Pump |
| Green | Bonding Wires |
| Grey | Navigation Lights, Tach Sender to Gauge |
| Orange | Accessory Feed, Distribution Panel Feed |
| Pink | Fuel Sender to Gauge |
| Purple | Ignition Switch, Instrument Feed |
| Brown w/Yellow | Bilge Blower |
| Yellow w/Red | Starting Circuit |
| Light Blue | Oil Pressure Sender to Gauge |
| Dark Blue | Cabin and Instrument Lights |
Right Size the Wire
To select the proper size wire to do a particular job requires you know two things.
First, you’ll need to know the the total distance between the power source (battery, bus bar, or circuit breaker) and the equipment being powered.
Next, you’ll need to know the current draw of the unit you are installing or rewiring. This is usually clearly stated in the accompanying documentation.
The table below shows wire sizes (purple) for low-voltage DC circuits (under 40 volts) based on the distance (red) from the power source to the appliance and the current draw (blue) of the unit. Wire sizes specified in the table should limit voltage drop in a 12-volt DC circuit to under 3%.
| Amps | 5 | 10 | 15 | 20 | 25 | 30 | 40 | 50 |
| 10 ft. | 18 | 14 | 12 | 12 | 10 | 10 | 8 | 8 |
| 15 ft. | 16 | 12 | 10 | 10 | 8 | 8 | 6 | 6 |
| 20 ft. | 14 | 12 | 10 | 8 | 8 | 6 | 6 | 4 |
| 25 ft. | 14 | 10 | 8 | 8 | 6 | 6 | 4 | 4 |
| 30 ft. | 12 | 10 | 8 | 6 | 6 | 4 | 4 | 2 |
| 40 ft. | 12 | 8 | 6 | 6 | 4 | 4 | 2 | 2 |
| 50 ft. | 10 | 8 | 6 | 4 | 4 | 2 | 2 | 1 |
| 60 ft. | 10 | 6 | 6 | 4 | 2 | 2 | 1 | 1/0 |
Sticking with our previous livewell pump example, if it were located 10 feet from the power source and had a current draw of 5 amps it would need #14 wire.
To get the correct wire size for this livewell pump from the table you would need enter the table at 5 amps. Then move down to a distance of 20 feet, the total length of wire needed to provide power to the pump located 10 feet from the power source. This yields the proper #14 wire size for this circuit.
Boat Cable
Sometimes boat cable is a more appropriate choice than single conductor boat wire.
Boat cable is nothing more than several marine grade wires contained inside a protective jacket.
Whenever you are going run wire for a circuit where the conductors need extra protection from chafing or weather boat cable would be the correct wire choice. Boat cable would also be the right pick on long wire runs where several conductors are needed to complete a circuit or series of circuits.
Normally boat cable is available in a variety of wire sizes and color-codes. A single boat cable usually contains from 2 to 4 conductors.