Sailing Advantage!
Sailboat Marine Battery Wiring
Looking for marine quality wire and hardware for your marine batteries and electric outboard motor? After the HOME page introduction and the first page on MOTORS, and second page on BATTERIES, this is the WIRING page, the third of three pages in our step-by-step discussion of how to choose and install the best electric outboard motor for your sailboat.
We cover the basics of marine battery wire and hardware requirements. We present the facts, comparisons, and essential information to help you choose the best marine battery cable and hardware to connect your battery with your electric outboard.
We strive to provide accurate information about the equipment and only recommend products that meet our exacting standards and have a reputation for quality, reliability, and applicability, but please take time to read customer reviews and seller-published specifications. Throughout this site, product links are provided for suggested equipment and clicking on the product image or name-link gives you an opportunity to read customer reviews, ratings, and pricing so you can decide what is best for you*. This site is focused on electric outboard motors for sailboats up to 27ft, and up to 5,000 lb. displacement.
Boat, Motor, Battery
Putting it all together
Wiring: For safety, install an in-line circuit breaker or fuse on the positive wire (red) coming from the battery(s) to the motor. Also install an on/off switch so you can easily turn off power to the motor in an emergency and when not in use. The fuse and switch should both be rated for the same amps as the motor. Although here we use the terms "circuit breaker" and "fuse" interchangeably, we highly recommend using circuit breakers because they are easily reset. It is important for you to be keenly observant in case of a "blown" or "tripped" circuit breaker. Before resetting it, you should check for a broken or faulty motor connector, or wires getting too hot and for any obvious causes such as burnt, broken, or "shorted" wires causing the circuit breaker to "pop".Circuit Breaker
Fuse and Switch
| Volts | Amps | find on Amazon* Make/Model |
|---|---|---|
| 12-48 | 40-150 | Blue Sea Systems 285-Series Circuit Breaker |
| 12-36 | Minn Kota MKR-18 12V Plug & Receptacle | |
| 48 | 275 | BEP Battery Switches |
| 12 | 200 | Cllena Battery Isolator Disconnect Switch |
Wire Gage
We discussed battery volts and amps earlier, so now let's discuss wire size and how that affects motor power. Wire has resistance and as such, it reduces the power (volts and amps) to your motor. Wire resistance increases with wire length and inversely with diameter. Thinner wire and longer wire will have more resistance than thicker wire and shorter wire. We use the American Wire Gauge (AWG), not the smaller SAE gage. The lower the number, the bigger the wire (larger diameter conductor). The wire cables should be stranded, tinned, AWG sized and marine UL-listed for quality.Think of wire this way: wire resistance increases when the wire is thinner or longer. More resistance means less current (amps). So, our goal for wire is to reduce length and increase diameter (similar to a water hose: thicker shorter hose delivers more water).
Wire Gage Recommendation
| Feet | 10 amps | 15 amps | 20 amps | 25 amps | 30 amps | 40 amps |
|---|---|---|---|---|---|---|
| 10ft | 14ga | 12ga | 12ga | 10ga | 10ga | 8ga |
| 15ft | 12ga | 10ga | 10ga | 8ga | 8ga | 6ga |
| 20ft | 12ga | 10ga | 8ga | 8ga | 6ga | 6ga |
| 25ft | 10ga | 8ga | 8ga | 6ga | 6ga | 4ga |
| 30ft | 10ga | 8ga | 6ga | 6ga | 4ga | 4ga |
| 40ft | 8ga | 6ga | 6ga | 4ga | 4ga | 2ga |
| 50ft | 8ga | 6ga | 4ga | 4ga | 2ga | 2ga |
| Feet | 50 amps | 60 amps | 70 amps | 80 amps | 90 amps | 100 amp |
|---|---|---|---|---|---|---|
| 10ft | 8ga | 6ga | 6ga | 6ga | 4ga | 4ga |
| 15ft | 6ga | 4ga | 4ga | 4ga | 2ga | 2ga |
| 20ft | 4ga | 4ga | 4ga | 2ga | 2ga | 2ga |
| 25ft | 4ga | 2ga | 2ga | 2ga | 1ga | 1ga |
| 30ft | 2ga | 2ga | 2ga | 1ga | ||
| 40ft | 2ga | 1ga |
EXAMPLE: If your motor requires a maximum of 50 amps and the wire run is 15 feet, you should choose 6ga wire (minimum). If the wire run is 20 feet, you should use 4ga wire for that same 50-amp motor.
EXAMPLE: If your motor requires a maximum of 40 amps and the wire run is 10 feet, you should choose 8ga wire (minimum). If the wire run is 20 feet, you should use 6ga wire for that same 40-amp motor.
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Wiring Summary
Ok, you've chosen an electric outboard motor that delivers your desired "pounds of thrust" and calculated how many batteries you need for the required volts and battery ampere-hours (Ah). Now connect them with the proper hardware, wire, switches, motor connector, and fuses.For your consideration:
1.) Hardware and connectors should be marine-rated and sized properly for the required volts and current.
2.) Wires should marine-rated and be the largest gage and shortest lengths as reasonably possible.
3.) Improperly installed batteries and wiring can be dangerous. Hire an experienced and licensed marine electrician if you have any doubts as to your own ability.