BINGO
Before retiring, I managed a service organization. We seviced all kinds of heavy duty equipment. One device had 3 phase 240 Vac 100 amp supply, and as long as the safety covers are installed it was safe electrically. Also we had some 480 volt 100 amp equipment installed which my reps serviced. Remove the covers on any of these devices and you expose yourself to some pretty hefty live contacts, just like a water heater with covers removed.
Electric water heaters have historically been exceptionally safe electrically as they are currently designed and manufactured. Of course this assumes that one understands how they are wired and follows proper servicing guidelines. I just did a quick search and found that in a 4 year period there were 12 electrocution deaths directly related to electric water heaters. I would not be surprised if these all were unqualified people trying to service one with the safety covers removed. Reguardless that is a pretty low number. My other hobby is as a private pilot. In that same time period there were almost 1,500 people killed in the US in private aircraft accidents.
Bingo! your 3 phase unit had a relay - 20 to 50 bucks that shut off ALL THREE LINES.
Bingo! your residential yugo water heater is dumbed down SO LOW that they cant add a .5 cent sticker saying : "we are cheap: danger, one line to an element is always hot, even thought its immersed in water" i.e. NO warning label.
Hey - dont drive, dont fly and you upped your odds of dying of a broken hip or alheizemers by 99%. Add a 6 cent double pole switch to cheap water heaters, and you saved at least 10 lives. pretty fair return on investment.
By the by - no one without a death wish opens a metal cover on a 480 volt box without shutting the breaker and wearing approved gloves and garb and a good mat.
