Here's a specific question. If I'm cutting foam on my hot wire cutter using 5 volts AC (and 3 amps) that's coming out of my 12 volt transformer which is controlled by a 120 volt variac set at 50 volts AC output, what exactly makes that different or safer than controlling my voltage with a variac alone set at 5 volts?
I guess the physical separation of the primary and the secondary doesn't mean there won't be some big amp load if somebody inadvertently contacts the cutting wire.
They say to use a transformer after the variac because it's safer than going off the variac's single wire toroid style transformer for some reason. I believe I can change the size of the fuse in the variac to a smaller amperage rating, so I wonder what it is that makes it safer to run the 2nd transformer after the variac.
The transformer makes this infinitely safer, not because of current or voltage limiting, but because it provides electrical isolation.
A Variac (a variable autotransformer) has only a single winding, and provides no DC isolation between input and output. Shock hazard.
