A 480volt 3 phase motor control box can arc over, it sounds like a concussion grenade and blows itself off the wall. All an explosion is normally is a rapid release of energy due to burning something. A High volt arc over does the same thing.
I saw a motor control room that blew at a log mill I worked in, heard it really and came running. Sounded like a couple of sticks of dynamite. Some idiot had replaced the mains with cut pieces of copper pipe and forgot to replace the fuses later. When it arced over, the flash burned through a 6x6 3/4 of the way in a half a second. The fire was out in less that 20 seconds due to a quick worker with an extinguisher.
The beam looked like it had been in a campfire for an hour. We ended up rebuilding and rewiring the whole room.
Lousey way to save a buck... But the explosion was awsome.
480 would be phase to phase. I can hardly believe someone other than myself would be brave and/or stupid enough to bypass the fuses. I hope nobody was injured.