Final answer:
The protective device that prevents operation when there is inadequate fluid flow is known as a flow switch. It is vital for ensuring that machinery is not damaged due to lack of proper fluid flow, which can lead to overheating or inadequate lubrication.
Step-by-step explanation:
A protective device that prevents the operation of a unit when there is inadequate fluid flow is called a flow switch. This device is essential in systems where the sustained flow of fluid is crucial to the operation, such as cooling systems or lubrication systems. When the flow of fluid drops below a certain threshold, the flow switch activates and can trigger an alarm or shut down the equipment to prevent damage from overheating or insufficient lubrication.