Blue Sea 5065 Waterproof In-Line Fuse Holder ATO/ATC

When you're wiring up gear on a boat, the last thing you want is a fuse sitting exposed to spray, dust, or a stray wave over the gunwale. The Blue Sea Systems 5065 is a waterproof in-line fuse holder built for exactly that. It takes a single standard ATO or ATC blade fuse, seals it inside a hinged cover, and gives you clean overcurrent protection right at the wire, no panel required. It's a small part, but it's the kind of thing that keeps a circuit alive after a wet season.

Here's how it's built. The holder comes with 12 AWG pigtails already attached, so you're splicing into your run rather than fussing with terminal screws in a tight space. It handles fuses up to 30 amps, which covers the vast majority of accessory circuits you'll run on a small to mid-size boat. Think nav lights, a bilge pump, a livewell pump, a stereo feed, or a single electronics load. The hinged cover snaps over the fuse and protects it from impact, water, and grit, and it flips open in a second when you need to check or swap a fuse dockside.

We reach for this one a lot on center consoles and trailer boats, where circuits get run to spots that see real weather. Say you're adding a set of courtesy lights or a raw-water washdown pump halfway back in the cockpit. Running a dedicated feed with a 5065 near the load means you're protected right there, and you're not fishing a blown fuse out of a soaked panel later. It's also handy when you're expanding a system and don't have a free slot on your main fuse block. Drop one of these in the line, size the fuse to the load, and you're done. Fuse is sold separately, so grab the amperage you need.

A few install notes from doing plenty of these. Give yourself a drip loop on both wire entries so water tracks down and away instead of following the wire into the ends. That one habit does more for longevity than anything else. Go easy tightening the cap, too. It seals fine with firm hand pressure, and cranking on it can crack the body. If your boat lives on a trailer or you run in chop, a short piece of adhesive-lined heat shrink over each wire entry adds strain relief and keeps things tidy. And a dab of dielectric grease on the fuse contacts every season keeps corrosion from creeping in on boats that see a lot of bilge splash.

It pairs naturally with a Blue Sea fuse block like the 5025 or 5045 when you want a central point for several circuits and a 5065 out at the loads that sit in the weather. Just know its limits. This is a 30-amp holder for a single circuit, so it's not the part for a windlass, a big inverter, or anything living in the heat of an engine compartment, where you'd want to derate or step up to a heavier holder. For everyday accessory feeds that need to shrug off water, though, it's hard to beat.

One more thing worth knowing. It takes both ATO and ATC blade fuses, which are the common automotive-style blades you'll find at any parts counter, so replacements are cheap and everywhere. If your install sees heavy vibration, like a transom rigged for an outboard, a locking-style ATC fuse holds a little more securely than a standard blade. And because the whole thing is sealed, it's just as at home tucked behind a console as it is out in the open. That flexibility is a big part of why it's such a go-to for accessory wiring.