Ouch! How do you know it was 3 phase? And was it a phase to phase shock or phase to earth? I suspect if it was the former, he hould have been alot worse off.
Remember back in the 1950's. I was living in a MoD apprentice hostel, electrical and mechanical apprentices about 100 of us. The warden used to put the main lights off at 10pm and we had to survive with bedside lights of the ring main.
Being electrical/electronic apprentices we made up a lead with a bayonet connector on each end. You can guess what for! That evening when the lights went out we were to connect a bedside light to a main light with said lead to make the main lights come on again.
Must say it partially worked. For about 10 secs all bedside lights dimmed, all main lights came on altra bright, then complete darkness
They were different phases, and we were without lights for four days until the incoming transformer was replaced.
Amazing what you can learn by a little experimentation. What was never known was the persons responsible