I want to annoy you with an old story:
Many years ago I worked for a Company who manufactured live sound systems. It was a small company, and sometimes, when no service technician was available, I had to service the equipment that our customers (bands and pop groups) carried in (or at least I had to listener to the customer's lamentations).
There was this gentleman, the "factotum" of a big folk group (they were very famous, and played about 300 gigs a year), who had to drive the bus, unload and install the sound system, reload it into the bus and drive again.
It was a little drunk most of the times (or at least that was my impression), and he told me that the bigger problem, apart multicore microphone cables punched by the ladies' stiletto heels, was to find the electrical power for the sound and light system when they had a show in a small town fair.
At those times the Italian power distribution system was a real mess, with many small towns still powered by 110 V dual phase, other (most) with 220 single phase, and the junction boxes where he had to screw-in his wires were unlabeled, and many carried 380 V three-phase without neutral. So he usually opened the box and touched an uninsulated wire end with his palm.
By the "strength" of the shock he could tell the voltage, and after one or two shocks he could realize how to get reliable 220 V. He had a big callus in his palm...