Overview

The Blue Sea Systems 187-Series is a switchable thermal circuit breaker for DC marine circuits where circuit protection and a manual reset switch need to sit in the same accessible device. This 48V DC breaker family covers amperage ratings from 25A to 200A, with panel-mount and surface-mount versions for different electrical layouts on board.

Each breaker uses a thermally responsive bi-metal blade and Type III switchable manual-reset operation. The trip-free mechanism means the lever cannot be held closed against a fault, which matters on battery feeds, windlass circuits, inverter feeds, charging circuits, and other DC loads where fault current needs to be interrupted safely.

The range uses 5/16 inch-18 terminal studs, accepts #10 or M5 mounting screws, and has published interrupt ratings of 5000A at 14V DC, 3000A at 28V DC, and 1500A at 48V DC. The operating temperature range is -40 C to 85 C, giving it room for engine room heat, exposed lockers, and colder storage conditions.

Key features

• Combines DC circuit protection and manual switching in one breaker for circuits that need accessible shutoff and reset.
• 48V DC maximum voltage rating, with amperage options from 25A to 200A across the range.
• Type III switchable manual-reset operation with a trip-free mechanism that cannot be held closed during a fault.
• Panel-mount and surface-mount configurations support different helm panels, electrical lockers, battery compartments, and distribution layouts.
• 5/16 inch-18 terminal studs give high-current cable lugs a secure termination point.
• Large clearance around the terminal studs helps accommodate heavy gauge wire lugs used on higher-amperage DC circuits.
• Interrupt capacity is rated at 5000A at 14V DC, 3000A at 28V DC, and 1500A at 48V DC.
• Ignition protected to SAE J1171 for installation aboard gasoline-powered boats.
• Thermoset polyester case material supports use in demanding marine electrical spaces.

Variants

This range varies by mounting style and amperage. The available configurations include panel-mount and surface-mount versions, with ratings from 25A through 200A to match the protected circuit and the cable size selected for the installation.

The breaker family remains a 48V DC switchable thermal breaker with manual reset and trip-free operation across the range. Select the mounting format that matches the physical location of the breaker, then match the amperage to the circuit protection requirements of the equipment and wiring.

Installation and setup

Panel-mount versions suit installations where the breaker face is intended to be visible and reachable through a panel. Surface-mount versions are useful where the breaker needs to be installed directly onto a bulkhead, backing board, or electrical mounting surface without building it into a finished panel.

The breaker should be placed where the lever can be reached for reset and isolation, while keeping cable runs practical and protected. As with any high-current DC circuit, the breaker rating must be coordinated with the conductor size, expected load, voltage drop plan, and the equipment manufacturer’s requirements.

Electrical and system integration

The 187-Series is commonly used in DC distribution where a fuse alone is less convenient because the circuit also benefits from a visible lever and manual reset. The lever gives a clear indication of breaker status and allows the circuit to be opened for service without removing a fuse.

For circuits with heavy startup current, confirm the breaker rating and trip behavior against the load profile before installation. Motors, windlasses, pumps, chargers, and inverter circuits can draw inrush current that needs to be considered during circuit protection planning.

Use cases on board

This breaker family is a practical match for boat owners, technicians, and builders working on DC electrical systems that need serviceable protection in a compact mounting footprint. It fits well in battery compartments, DC distribution panels, equipment lockers, and other locations where a resettable breaker is easier to manage than replacing a fuse.