For Rotor Machine Rewinding — Which Grade to Use?

Motor rewinding is a critical maintenance process that restores efficiency, extends equipment life, and ensures safe operation. One of the most important decisions during rewinding is selecting the correct enamelled copper wire. The wire’s grade and thermal class directly affect insulation durability, temperature tolerance, and overall motor performance.

What is Enamelled Copper Wire?

Enamelled copper wire, also known as magnet wire, is copper wire coated with a thin insulating enamel. Unlike conventional insulated wire, enamel allows coils to be wound tightly without short circuits. It is widely used in rotor machines, electric motors, transformers, generators, and pumps.

The enamel coating comes in different grades and thermal classes, which determine the wire’s thickness, mechanical strength, and heat resistance. Choosing the correct type is essential for safe and reliable motor operation.

Film Grades: Determining Insulation Thickness

The film grade indicates the number of enamel layers applied to the wire. Standard classifications include:

Grade 1: Single enamel coat. Thin and flexible but prone to damage during rewinding. Rarely used in industrial motors.
Grade 2: Double enamel coat. Standard insulation for most motors. Offers a balance of flexibility and protection.
Grade 3: Triple enamel coat. Thick insulation for high-voltage or high-stress applications. Provides maximum mechanical and electrical protection.

Recommendation: For most rotor machine rewinding, Grade 2 is ideal. Grade 3 is reserved for high-voltage or heavy-duty motors.

Thermal Classes: Heat Resistance Matters

Thermal class defines the maximum continuous operating temperature that the insulation can withstand. Common thermal classes include:

Class B (130°C): Suitable for small domestic motors and fans.
Class F (155°C): Standard for industrial motors; provides long-life insulation in typical operational environments.
Class H (180°C): Ideal for pumps, compressors, and high-temperature industrial motors.
Class C (200–220°C): Used in specialized heavy-duty or traction motors.

For rotor machines operating in hot or tropical environments, such as Malaysia, Class F or Class H wire is recommended for rewinding.

Recommended Wire Selection for Rotor Machine Rewinding

Motor Type	Voltage	Film Grade	Thermal Class	Suggested Enamel Type
Small fan or domestic motor	<240 V	Grade 2	Class B	Polyurethane
Industrial rotor motor	240–415 V	Grade 2	Class F	Polyesterimide
Water pump / chiller rotor motor	240–415 V	Grade 2	Class H	Polyesterimide + Polyamideimide
Compressor / heavy-duty rotor motor	>415 V	Grade 3	Class H/C	High-temp Polyimide
Submersible / explosion-proof rotor motor	415 V+	Grade 3	Class H/C	High-temp Polyimide

Key Takeaways

Film grade determines insulation thickness: Grade 2 is standard; Grade 3 for heavy-duty or high-voltage rotor motors.
Thermal class determines heat resistance: Class F (155°C) and Class H (180°C) are preferred for industrial rewinding.
Select enamel type according to application: Polyesterimide and Polyamideimide coatings provide durability in tropical and high-stress environments.

Choosing the right enamelled copper wire ensures long-lasting performance, minimal downtime, and safer rotor machine operation. For professional motor rewinding and repair services, always consult experienced technicians and refer to manufacturer specifications.