Wrap your wiring in this heat dissipative sleeve (This is good to 1000* F):
McMaster-Carr
Sorry I was in the hospital the past 37 hours back pain problems went beyond regular pain medication control.
Unless the above "dissipative sleeve" has a pressurized cooling system with the opposite end of the sleeves temperature still within the wires insulation maximum rating it is a useless sleeve. Time and heat will build up. On the good side this is a gas heated brewing system hence all control wires of #18 to #14 AWG zone not AWG in the #10 to #6 AWG. This alone allows for many more selections in wire insulation properties.
Fluorinated ethylene propylene (FEPB) 200*C /392*F avilable from 14 to 2 AWG. Outer covering of glass braid. This was required in a the foundries I have been stuck working on, yes you will itch from the glass fibers if working in 120*F plus temps with open sweat pores on your arms.
Mineral Insulation (metal sheathed) 250*C / 482*F, 9-4, 3-500MCM rather way out there for your control use plus a copper or alloy steel outer covering.
This would be not an option.
Perfluoroalkoxy (PFAH) 250*C / 482*F, 14 AAG to 4/0. Not cheap.
Modified ethylene tetrafluoroethylene ( Z) or (ZW) 150*C, 302*F, 14 AWG to 4/0 and #2 AWG.
Bottom line the insulation inside a conduit run or any other protected chamber, splice box or control panel you must be at or below the wires maximum insulation temperature. Besides that if your under a load you must derate the amperage of the wires rating as the temperature rises until you have peaked the AWG of that conductor.
Check for aviation surplus stores as they may have high temp insulated wire as a source for your needs.
The lowest cost would be fiber glass insulated wire that's operated within it's maximum insulation rating besides it is available in smaller AWG sizes for your control needs, this includes (TFFN) fixture wire. All the above will cost you, the best and lowest cost would be to go with glass fiber insulated wiring. It sounds like your operating at a temperature of not if but when the insulation of the wire your using will melt going to ground or cross feeding causing controller or other damage to your equipment. Hey i've been out of the trade since 10-2002 fighting for my SSD award, down to the legal paperwork now as "Award Approved". Again sorry for the delay reply.
inera