Blue Sea 300A Red Mini m-Series 4 Position (OFF/1/2/1+2) Battery Selector Switch

Compact Dual Battery Management for Marine and RV Systems

The Blue Sea m-Series Battery Selector Switch is the industry standard for managing dual battery banks in boats, caravans, and 4WDs. Designed to provide safe and reliable switching between a starting battery and a house bank, this compact unit solves the common problem of accidental starting battery depletion. By isolating your electrical loads, you ensure that your engine always has the power it needs to crank, while your accessories run independently.

Engineered for the harsh marine environment, this switch features a robust construction suitable for systems up to 32V DC. Whether you are upgrading a tinny, fitting out a camper trailer, or replacing an old isolator in an engine room, the m-Series delivers professional-grade performance in a footprint that fits almost anywhere.

Versatile 4-Position Switching

This selector switch offers four distinct positions to give you complete control over your power management:

• OFF: Completely disconnects all batteries from the loads for storage or maintenance.
• 1: Connects Battery Bank 1 (typically the starting battery) to the loads.
• 2: Connects Battery Bank 2 (typically the house battery) to the loads.
• 1+2 (Combine): Parallels both battery banks for emergency starting if one battery is low.

Crucially, the unit utilises a make-before-break contact design. This allows you to switch between battery banks (e.g., from 1 to 2) while the engine is running or electronics are active without interrupting power. This prevents sensitive navigation equipment, radios, or engine management systems from resetting during operation.

Built for Safety and Durability

Safety is paramount in electrical installations, particularly where fuel fumes may be present. The Blue Sea m-Series is ignition protected, making it safe for installation in the engine rooms of gasoline-powered boats. The case design allows for versatile mounting options—surface, front panel, or rear panel—ensuring a clean finish in any setup.

The switch is built with tinned copper studs for maximum conductivity and corrosion resistance. The 3/8"-16 (Approx. M10) terminal studs are designed to accept heavy-duty ring terminals and handle the torque required for a secure vibration-resistant connection. With a 300A continuous rating, it easily handles the demands of most alternators and onboard appliances found in recreational vehicles and vessels.

Key Features

• 300A Continuous Rating: Handles high-current demands with a 500A intermittent rating (5 min) and 900A cranking (30 sec).
• Ignition Protected: Safe for installation aboard gasoline-powered boats.
• Make-Before-Break: Switch battery banks without power loss to electronics.
• Heavy-Duty Terminals: 3/8"-16 (Approx. M10) studs accept substantial cabling, accommodating up to 4/0 AWG (approx. 120mm²) lugs.
• Versatile Mounting: Fits standard industry cutouts for easy retrofitting.

Why Choose the m-Series?

Generic switches often fail under the stress of saltwater environments or high-vibration off-road use. The Blue Sea m-Series is tested to ensure longevity and reliability. Its tactile knob provides positive feedback, so you know exactly which position is engaged, even in low-light conditions. For anyone building a dual-battery system, this switch offers the peace of mind that your power distribution is secure, efficient, and ready for adventure.

Secure Your Power System Today

Upgrade your battery management with the reliability of Blue Sea Systems. Whether for a weekend fishing trip or a lap around Australia, ensure your batteries are isolated and ready when you need them.