GFI protection at 80 vac

[rlaft]

I am planning on installing a power distribution system to provide 80 vac for heating inside vacuum chambers. 80 vac is the accepted limit to prevent the occurence of corona which occurs violently with higher voltages as the absolute pressure is being decreased. These chambers may be "inhabited" by a human being (astronaut) for testing purposes. So, I need to provide GFI protection for all the circuits.
The various available units that are sold commercially seem to only be rated for use down to 102 v (120 v -15%).
I am sure I could design a GFI which uses a separate control circuit to sense the output of the current transformer etc. but this would surely be expensive. Obviously it would also lack industry approvals.
So where can I find an approved GFI for my needs?

 

[nbucska]

You would need special 80V heaters, too !

Wouldn't be simpler to insulate the wires with
e.g. silicon rubber and heatsink the ends of the
tubuler heaters -- where the wires enter -- to
keep them at the temperature safe for the silicon
rubber -- i.e. keep the "vacuum" away from the wiring ?

 

[rlaft]

Resistance heaters will provide heat directly proportional to the line voltage squared assuming their resistance remains constant.
The heaters that I plan to use are called mineral insulated (MI) and the heating conductors are completely encapsulated by a metal sheath.
Nevertheless, we must provide limits on the voltage so that a broken sheath does not bring on a "lightning storm" which is how some describe the corona. And we need GFI protection to eliminate the shock hazard for the astronaut if the heater was broken open.