*has actually considered making power armor
The peoblem with powered armors is not getting shorted out, or with rusting. the problem is power generation and heat removal.
Rusting is easily solved with a ceramic coating. Something like TiN (Titanium nitride) would work well, and would give you that "ironman gold" color.
This would also make the armor's outer surfaces nonconductive. coupled with hardened electronics with good floating ground, you have a pretty solid base to start with.
the problem is power generation. packing enough energy into a small enough package without resorting to an internal combustion engine of some kind makes power armor a nonstarter, unless you know how to produce useful fusion, and have very good nuke sheilding for the reactor you would have to carry around. Additionally, there's the heat problem. The suit is going to be gobbling down a lot of juice to power the actuators, and to dynamically stiffen parts of the suit on kinetic impacts-- this means the suit is going to have a very high TDP, which means it will need active cooling.
The obvious way to take out power armor is a fine mist spray of something that coats heatsinks and reduces thermal conductivity of the heatsink with the open air. Several synthetic oils come to mind as possible candidates, especially if followed up with some kind of dust contaminant.
Mineral oil mist followed by clay dust in a dispersal pack would clog up the active cooling of the power armor, making it overheat and either cook the occupant, or shut down to protect the occupant.