Here is a quote from a previous thread about fuses for bilge pumps here Fuses Needed to Comply with ABYC Rules
. I assure you Charlie knows what he's talking about.
During seminars, I will deliberately overfuse a small Rule
centrifugal pump, jam the impeller with a screwdriver and then apply power and continue the lecture. Within about 10 to 15 minutes the pump starts to smoke. NOTE: THE FUSE NEVER OPENS DURING THIS DEMO! And this is why marine equipment
manufactures are required to provide the fuse rating for their rotating equipment
Here is the applicable section from the ABYC E-11 Standard:
18.104.22.168.1 Motors and motor operated equipment, except for engine
cranking motors, shall be protected internally at the equipment, or by branch circuit overcurrent protection devices suitable for motor current
. The protection provided shall preclude a fire hazard if the circuit, as installed, is energized for seven hours under any conditions of overload, including locked rotor.
1. It may be necessary to use thermally responsive protection devices on the equipment or system if the motor is not capable of operating continuously at maximum possible loading.
2. It may be necessary to test as installed in order to assure compliance with the locked rotor requirement. Voltage drop, due to wire size, and delay characteristics of the overcurrent protection device may have to be adjusted to protect the motor.
In the case of the Rule
500, if it was a 12VDC model, the technical specification is to protect it with a 2.5A fuse or circuit breaker. Rule 500 > ITT Flow Control - Engineered for life.
There is generally a lot more to this stuff then meets the eye.
Charlie will now relinquish his soapbox.
Hope this helps.