Reminds me of a 'funny' story from the other year.
My RCD (earth leakage trip) kept triggering, and I isolated it to the immersion heater element in the hot water tank leaking to earth.
So I purchased a suitable spanner and a replacement element, but was unable to undo it, as the tank deformed excessively, and I was worried it was going to split - I checked with a few electrian friends who have done this before, to be told success is probably under 50%, and mine hadn't been undone for many decades.
As my central heating was pretty crap anyway, I decided to have an entire new central heating system, with a combi boiler and no tanks - which is now done and works wonderfully.
In the meantime though we had no hotwater, but I had a crude plan
At work I've got three identical 1000W isolation transformers in metal boxes, and the heater was 3000W, so I borrowed then from work and connected them in parallel - switched on,
BIG bang, fuse disappeared and switch contacts welded together.
This is when I found out that the identical transformers were wired differently!, so I had to find out which phase each one was wired in. I did this by connecting all primaries in parallel, and two secondaries in series - feeding a load consisting of two 60W bulbs in series. If the windings were in phase the bulbs would light, if out of phase they wouldn't. By doing this twice I was able to identify the phase of the outputs and wired them accordingly.
This crude bodge worked perfectly for the few weeks required for the plumbers to come and install the new heating, and I took the transformers out the night before they came.
But I can certainly confirm that you get HUGE currents with two 1000W transformers out of phase