Detecting dry-running of water pump
Given this additional detail:


  Not familiar with the typical plumbing terminology, but it is
  certainly not submerged. Pump inlet is fed by an underground sump
  (about 10 feet deep), pump itself is at ground level, and it pumps up
  water into an overhead tank, which is about 40 feet above ground.
  Typically it is a 1.5HP 2000W 220VAC monoblock pump. I am just
  guessing that the configuration is "in-line", I could be wrong.


I've got a very simple, cheap, reliable solution for you: remote monitoring.

Nothing says your sensor has to be at the pump's inlet. You could place your sensor at the system's inlet. Submerge a cheap float sensor at the level of the inlet to the feeder pipe in your well (or whatever water source). Run wires back to the pump's power controller. 

When the float sensor says the water level is below the feeder pipe, turn off the pump. Ten bucks, totally reliable. Done. =)



This figure shows multiple float switches at increasing depths in a tank to illustrate operation. You just need one at the bottom of your feed pipe. You do not need to disturb any existing plumbing to do this.