I really don't know what the concern is.....
Voltage may be 300V referenced to ground, but two points where meter or whatever will be inserted, voltage differential is minimal. Since it has to be automated, cutting a wire or a trace probably isn't an option. Then find a point where there is a constant resistance, and measure a voltage across that. Make sure your measuring apparatus is FLOATING. Then it should be fine.
300V is not that high of a voltage, especially if the current is in micro amp range. It can sting you but that's about it. Unless OP can go into detail of what kind of automation it is, I don't think anyone can give a concrete advice. But this should be pretty basic.