14 gauge red and black twisted wire.
Aircraft quality wire is manufactured to MIL-W-22759/16 specs. It features standard tin-plated copper conductor with Tefzel insulation. Wire is rated for 600 volts rms & 150 degrees C.
FAA AC43.13-1B recommends 20 amp CB protection for 14awg wire.
See FAA AC 43.13-1B Tables 11-3 & 11-9 for protection & rating details.
See Military Specification Sheet MIL-W-22759-16a for wire construction details.
This wire is perfect for heated pitot power.
If one were to ground the heated pitot locally then the power wire would create a magnetic field. However, if the power and ground are run together, back to the power source and main ground bus, then the two wires cancel out the magnetic interference.