Sea-Dog 12/3 AWG Triplex Marine AC Cable, 100 Feet, Tinned Copper

This is Sea-Dog's 12/3 AWG triplex, a flat marine cable built for running alternating current around a boat. You get three 12-gauge stranded conductors, color-coded white, green, and black, wrapped in a flat encasement that lies against a bulkhead or slips through a chase without fighting you. It comes as a 100-foot spool, and every strand is tinned copper. That tinning is the whole point on the water.

Here's why tinned matters. Bare copper corrodes in salt air. It doesn't have to sit in bilge water, just breathe the same damp air, and over a couple of seasons you'll see green creep up under the insulation and resistance climb at the terminals. Tinned copper puts a thin coat of tin over every strand, so the wire shrugs off that corrosion and keeps carrying full current years down the road. It's the difference between a wiring job you do once and one you're back chasing with a meter every spring.

The flat triplex shape earns its keep in tight spaces. We've pulled a lot of this through narrow lazarettes and along stringers where a round cable would bunch up and bind. Flat lies down and stays put. One thing to respect: don't fold it into a sharp bend during the pull. Flat cable will kink if you crank it around a hard corner, so keep your radius easy and it'll feed clean.

Where does 12/3 fit? This is your cable for AC branch circuits, shore-power feeds to a sub-panel, genset runs, and inverter output on small to mid-size boats. The three-conductor setup follows the standard AC color code, white for neutral, black for hot, green for ground, so anyone who opens the panel later can read the run at a glance. That matters for the next tech, and it matters at survey time. The UL 1426 and ABYC stamp on this cable is exactly what a surveyor wants to see on a documented boat, and some owners tell us it smooths the conversation with their insurer too.

Why 12 gauge and not something heavier? Twelve AWG is the sweet spot for a lot of onboard AC circuits, receptacle runs, a battery-charger feed, a modest genset branch, where you want real current capacity without wrestling stiff, thick cable through the boat. For longer runs or higher-draw loads you'd step up to a heavier gauge to keep voltage drop in check, but for typical branch work 12/3 hits the mark. Match the gauge to the load and the distance, and this cable handles the everyday AC wiring most boats actually need.

And it's genuine marine-grade wire, not automotive cable pressed into service. Automotive wire uses fewer, coarser strands and bare copper, which is fine in a dry car and a poor choice in a damp bilge. Marine cable like this uses finer, more flexible stranding that stands up to constant vibration and flexing, plus the tinning that keeps corrosion out. On a boat, that distinction is the difference between a circuit you trust and one you don't.

Termination is straightforward if you do it right. Strip the flat jacket with a sharp utility knife rather than side-cutters, which can crush the three conductors underneath. Then use adhesive-lined heat shrink over every terminal to seal out moisture. The 12-gauge conductors drop cleanly into standard screw terminals and terminal blocks without needing ferrules, so wiring up a fuse block or a panel is quick work.

A note on planning your buy. A 100-foot spool is plenty for most jobs, but on a 30 to 35-foot boat you may finish with 20 or 30 feet left over. That's fine if you've got other AC runs to do, and honestly it's nice to have spare marine-grade wire on the shelf. Where the cable runs past a sharp chine edge or any hard corner in the structure, protect the jacket with split loom. Left unprotected, the outer jacket can chafe and split at a sharp edge after a few seasons, and a little loom up front saves you that headache.

Bottom line: if you're wiring AC on a boat and you want it done to code and done once, this is the right cable to reach for. Tinned copper, flat and easy to route, correctly color-coded, and stamped to the standards that actually matter out there.