I use an isolation transformer and a variac combined with a light-bulb when I repair mains powered instruments. But that is not close enough if things go wrong. You know, the kinda problems that communicate with smoke….
This cabinet houses also a reset-able 15A fuse. Not really needed because the variac/isolation transformer unit is fused, the powermeter in between is double fused. I have three other mains outputs equipped on my desk controlled by a switch unit that contains two channels with 2 A resetable fuses and one that has beside the fuse a 60W lightbulb in series.
And besides that I can use a Tek A6901 Ground Isolation Monitor.
That is why the unit I made today is “stand-alone”. This way I can use it on all the units mentioned above. These things are not made for my own safety but for the safety of my patients.
I made this small box as a sort of remote for use behind powersupply’s. This way I can turn the output on or off without reaching over to one of the PSU’s and more important, the analog meter shows the current and because I can place it close to the thing I’m feeding , I can see it immediately if the current goes banana’s and shut it down. There is not much to see inside. Just a shunt resistor and some resistance to scale the meter. The meter can show the voltage and the current.