Medium Duty. For use with two or more batteries and single or dual engine systems. Permits selection between batteries for starting and charging or operation of both batteries in parallel. They allow addition of an extra battery for use with accessories. The "OFF" position also acts as an emergency disconnect in the event of an electrical problem. Ignition protected. Surface mount. For use with systems under 50 volts. Capacity - 250 amps continuous, 360 amps intermittent. Alternator Field Disconnect (AFD) Models, when used with non-utilized alternators, these models will interrupt the field current (reducing the possibility of damage) if turned "OFF" with the engine running. Size": 5-1/4 dia. x 2-5/8 deep.