In the illustration, it shows a short occurring far away from the CWT. The idea is that high voltage ran down the sensor wires to the tank, and the sensors created a spark.
Since the sensors are electrically isolated, how did they produce a spark ?
The independent test (I can find the link to the video again, if you wish) just used a spark gap and kept increasing the output until the tank exploded. Of course a spark gap creates a spark when you apply enough current.
I don’t know how the level sensors work on airplanes. I do know quite a bit about instrumentation in power plants however.
We use many different methods to measure level from magnetostrictive floats to differential pressure transmitters to conductivity probes to radar at my plant.
All of our instrumentation is in class 1 div 1 explosion proof enclosures near the fuel systems.
I can’t think of how any of my instruments would create a spark if the signal wiring (usually 4 to 20 miliamps powered from 24vdc supplies) had say 120vac leaked onto them.
But these instruments are in pretty heavy enclosures. Not sure how the aircraft equivalents are constructed or how they operate.