Wire Insulation Temperature Limits

The temperature rating of a wire or cable is generally the maximum safe temperature that the wire can carry full-load power without the cable insulation melting, oxidizing, or self-igniting. A full-load wire does heat up due to the metallic resistance of the wire. The table below illustrates the maximum absolute temperature that different insulation types can withstand.

Note: Electrical equipment should be serviced and inspected only by qualified personnel. No responsibility is assumed by the Infrared Training Center for any consequences arising out of the use of this material. This document is not intended as an instruction manual for untrained persons.

Wire Conductor Ampacity to Temperature Rating

Maximum Operating Temperature (ref. NEC table 310-16)
Insulation Types	Insulation Types	Insulation Types
60°C (140°F)	75°C (167°F)	90°C (194°F)
TW, UF	FEPW, RH, RHW,	TBS, SA, SIS, FEP,
	THHW, THW, THWN,	FEPB, MI, RHH,
	XHHW, USE, ZW	RHW-2, THHN,
		THHW, THW-2,
		THWN-2, USE-2,
		XHH, XHHW,
		XHHW-2, ZW-2