Enameled wire is commonly used in motors and transformers, playing a crucial role. Temperature rating is a crucial factor affecting enameled wire's performance.
For enameled wire, the temperature rating refers to the maximum temperature the insulating film can withstand over its expected lifespan (typically 20,000 hours). At this temperature, key enameled wire properties (such as breakdown voltage and flexibility) should remain within acceptable limits.
Internationally, letter codes are used to identify temperature ratings, with the most commonly used being the NEMA (National Electrical Manufacturers Association) and IEC (International Electrotechnical Commission) standards:
| Heat resistance grade |
Maximum allowable operating temperature (℃) |
Equivalent to the old standard |
Common insulating varnish types |
| 105 (A/105) |
105℃ |
Class A |
Oil-based varnish, polyvinyl acetal |
| 120 (E/120) |
120℃ |
Class E |
Polyesterimide (modified) |
| 130 (B/130) |
130℃ |
Class B |
Polyester resin |
| 155 (F/155) |
155℃ |
Class F |
Polyesterimide, polyurethane |
| 180 (H/180) |
180℃ |
Class H |
Polyimide, polyamideimide |
| 200 (N/200) |
200℃ |
Class C |
Polyimide (thickened), polyesterimide/polyamideimide composite |
| 220 (S/220) |
220℃ |
Class C |
Special polyimide, ceramic varnish |
| 240 (R/240) |
240℃ |
Class C |
High-performance composite varnish, ceramic varnish |
Why is temperature resistance so important for enameled wire?
Determines equipment lifespan and reliability: Insulation material aging follows the "10-degree rule" (i.e., for every 10°C increase in temperature, the chemical reaction rate approximately doubles, and the lifespan is halved). If a motor designed for 155°C (Class F) is operated at 180°C for a long period, its insulation system lifespan could be drastically reduced from 20 years to 1 year or even less, leading to premature inter-turn short circuits and burnout.
Impacts equipment compactness and power density: Higher temperature resistance allows engineers to design smaller motors for the same power (by using thinner wire, less material, and more efficient cooling methods) or achieve higher power output within the same volume. This is precisely why new energy vehicle drive motors pursue Class 180 (Class H) or higher—to unleash greater power within limited chassis space.
Impacts safety bottom line: Under abnormal conditions such as overload and stall, coil temperatures can soar. Enameled wire with a higher temperature rating provides a greater safety margin, buying valuable time for system protection devices (such as circuit breakers and thermal relays) to respond, thus preventing serious accidents such as fires caused by sudden high temperatures.
For enamel wire, the temperature resistance rating is more than just a simple technical parameter; it is a core indicator that determines the lifespan, reliability, safety, power density, and ultimately the cost of electrical equipment.
