ON-OFF Two-Position Rotary Marine Battery Isolator Switch with 250A Continuous and 1000A Cranking Battery Disconnect Switch

If you have ever climbed into a locker to find a corroded selector with four detents and no clear OFF, the MT067 is the answer to that. It has exactly two positions. Turn it one way and everything downstream is dead; turn it back and the bank is live again. There is no third detent to remember and no key to lose.
Under the housing, a copper bridge carries 250A continuously and absorbs the 1000A surge of an engine start. The shell is moulded ABS, chosen because it keeps its shape when a heavy lug is torqued onto the stud — a soft housing will bow, the stud will tilt, and the joint will heat up. That failure mode is what this design avoids.

Buyers sometimes ask why a switch that starts a 1000A engine is only labelled 250A. The two figures describe two different jobs. 250A is the current it can sit at all day long without the contacts turning blue. 1000A is the half-second inrush of a starter motor, gone before the metal has time to heat. Design the cable around the 250A number, and let the 1000A figure do the starting.
Reverse the logic — pick cable for 1000A and assume the switch can carry it continuously — and the contacts will pit, resistance will climb, and the switch becomes the hottest point in the circuit.

• Confirm nominal system voltage sits inside 12V–48V DC.
• Add up the continuous loads on the circuit — keep the total under 250A with margin.
• Check the stud diameter against your existing ring lug barrel.
• Measure the mounting footprint and allow clearance for the dial to turn.
• Decide whether the switch sits before or after the main fuse — typically switch first.
• Confirm the panel behind the base is rigid enough for heavy cable weight.

Almost every field failure in a high-current DC switch traces back to the termination, not the contact set. Work through this in order and the joint will outlast the rest of the installation.

1. Isolate the bank at the source, negative lead off first, then prove dead at both studs.
2. Crimp closed ring lugs with the die matched to the lug, never with a hammer or a bench vise.
3. Seat the lug flat against the stud face — no washer stack between lug and terminal.
4. Torque the nut fully, then mark it with a paint pen so a later check is a glance, not a guess.
5. Cycle the dial once with no load, reconnect, then run a load and feel the studs afterwards.
6. Any stud that runs warm under normal load has a bad joint — strip, inspect and rebuild it.

A disconnect switch is at its most useful when a boat or a camper is not being used. Leave the dial at OFF through the off-season, and the self-discharge and parasitic drain stop fighting the charger. Before lay-up, spray the studs with a corrosion inhibitor, and at recommissioning wipe the housing down and cycle the dial a few times so the contacts clean themselves before any real current flows.

• Minimum order quantity — 5 pieces
• Price — negotiable, quoted on quantity and packing requirement
• Supply ability — 50,000 pieces per month
• Delivery time — 30 days for standard production
• Payment terms — T/T or Western Union, 30% deposit and balance before shipment
• Packaging — carton