This unit provides 600VAC at 200mA +/-1% for precisely 1 second.
That's the story. We needed this equipment overnight, and for one thing it does not exist commercially, it has to be built custom. There was no time to order the parts including a custom power transformer and spend a week on it, not to mention the extra time it would have taken to custom-make a printed circuit board with a fancy controller. There was just enough time to rough-hew this thing out of a pile of parts..
What is this kind of thing used for? Good question. Say your DSL modem or other telcom equipment is sitting there happily and something outside happens, and for some reason a power line gets crossed with the telecom line.. Guess what happens to the modem? There are semiconductor devices designed to prevent the modem's destruction, and they are placed across the incoming telecom line, inside the modem case. So, one connects this to the modem's input, and punches the switch.. If the semiconductor devices have done their job, the modem will remain functional after the test. How about that! This very simple unit only does this one test. There are many other tests, all different, and some are quite destructive, like the 1000VAC/4A test. Some are done just to make sure nothing catches on fire or explodes. It's for your own good..
It took 7 hours to strip some used gear, find enough compatible parts to make a workable circuit, and screw/cut/solder it all together. It is not intended to be pretty. It is intended solely to perform a function in compliance with a standard test requirement. It may not look very safe, and that is because it is not very safe. It does have two fuses, mainly to prevent a fire. It is not for use by people who do not know what electricity is.