You can now very easily get a Solid State Overload Relay for your motor starter that can be programmed to detect a load loss. What you do is to measure the no-load current, then set the trip threshold for the Load Loss trip at a value slightly higher than that. So let's say your 75HP motor has a FLA of 104A, which is where you program the Overload Trip. Then with the motor uncoupled, lets say that the motor current is 40A and coupled, but with the lowest permissible flow, it is 50A. You set the Load Loss trip to 45A, so if there is no flow or the coupling breaks and the current drops to 40A, the relay trips.
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