Fuse and Circuit Breaker Overview
Circuit breakers are not only great insurance for protecting your new motor, but they are also required by the Coast Guard for ungrounded current-carrying condutors. If a prop is caught on an underwater object (rock, log, thick weeds, etc) and prevented from rotating, the motor will respond by using more and more power from the battery in an attempt to turn the shaft. If this goes on for too long, the high level of current will permanently damage the motor, usually resulting in a completely totaled motor.
A trolling motor circuit breaker is designed to “trip” at a certain amperage, which breaks the circuit and prevents the motor from overloading and damaging itself. At between $20 and $40, they are significantly cheaper than purchasing a brand new motor! Circuit breakers come in varying amperages, and you want one that has an amperage rating (or amperage trip point) that is just above the amperage draw of your motor at max speed.
Both Minn Kota and MotorGuide make their own breakers that are rated to break at an amperage level above what their motors draw. As just about all Minn Kota motors pull less than 60 amps at full speed, the Minn Kota circuit breaker is rated at 60 amps. The reasoning is that if 60 amps is being drawn from the Minn Kota motor, it's operating above the level it was designed for, and should be tripped. Similarly, MotorGuide's circuit breaker is rated at 50 amps as most MotorGuide models are desgined to draw less than that at full speed.
Do you have to get a brand-specific circuit breaker? Definitely not. As long as the breaker is rated for a level slightly above the maximum amperage rating for your motor your should be just fine.