Darwin Award hopefuls, inspired by instructions and videos on the Internet, have been removing the transformers from scrapped microwave ovens to build infernal machines to burn Lichtenberg figures into wood with the high voltage, high current produced by the magnetron B+ winding of the transformer. Many of these “makers” have no safety interlocks on their devices, use car jumper cables with insulation utterly inadequate for the high voltages being used, and neglect insulation, shielding, and arc protection in the “design”.
A typical microwave oven transformer outputs around 2000 volts at 500 milliamperes, which packs a kilowatt of power and is more than sufficient to kill anybody who comes into contact with it, arc through many insulating materials, and trigger muscle contraction that prevents breaking contact with the conductor. So far, there are more than thirty reports of deaths from people using these devices, with the fatality rate from shocks of 70%, leaving many survivors with permanent injuries.
The high voltage secondary winding in these transformers is electrically isolated from the primary, so even a short-circuit across it appears to the mains-connected primary as a normal load and will not trip a ground fault circuit interrupter / residual current device protecting the circuit feeding it.
I am not going to link to or embed any of the videos showing geniuses building and operating these devices. If you want to see them, just search for “lichtenberg microwave transformer” on your favourite boob tube video site.
If you must burn your own Lichtenberg figures, here is a much safer way to do it using a low-current neon sign transformer, which also produces a result with more fine detail than the brutal and lethal current of the microwave oven transformer.