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Getting It Right

Story and photography by Capt. Vincent Daniello

Want to crimp the terminals on heavy battery cables? This $30 crimper is available at most automotive stores.

Doubling the length of wire doubles the voltage drop between a battery and an inverter. If you crunch the numbers you’ll likely find that a 1,000-watt inverter mounted very close to a battery needs only 4-gauge wire to stay within the acceptable voltage drop. But that same inverter also calls for a 175-amp fuse and 4-gauge wire rated to carry no more than 135 amps. So for safety’s sake, 2-gauge wire instead of 4-gauge is actually needed. “The fuse is there to keep the wire from getting too hot and potentially causing a fire,” says David Wiesemann, Marinco’s Shore Power Product Manager ( “It won’t do any good if the thing doesn’t open before the wire reaches maximum rating.”

Wiesemann also suggests Type 3 marine wire, which is thicker, more flexible, and more vibration-resistant than Type 2 wire of the same gauge, and also made from 100 individual strands, not just 40 strands, making it more flexible and vibration-resistant. Tinned wire—where each copper strand is encapsulated in tin—also protects strands from resistance-causing corrosion.

“Smaller wire runs hotter for a given amperage.” Wiesemann adds. “Run it through an engine room and that wire needs to be two wire sizes heavier to account for the added heat.”

Remember this, too. Wire sizes are based on amps, not volts. Doubling voltage from 12 to 24 volts halves the ampere draw for an inverter powering a given AC load. If long DC cable runs are called for, consider choosing a 24-volt inverter/charger with a dedicated 24-volt battery bank.

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