Insulation classes

Electric motors are an important component of many industrial and commercial applications, ranging from HVAC systems to manufacturing processes. To ensure the durability and reliability of these motors, it is essential to protect them from electrical faults, in particular by choosing the appropriate insulation class. In this article, we will look at the different insulation classes of electric motors, their characteristics and applications. The international standard for motor insulation classes is essential to ensure the safety, efficiency, and reliability of motors. The maximum operating temperature depends on the design, size and application of the motor. The maximum operating hot spot temperature is achieved by adding the nominal ambient temperature of the machine (often 40 °C), the temperature rise, and a 10°C hotspot allowance (Fig. 1). Electric machines are usually designed with an average temperature below the rated hot spot temperature to ensure the required service life.

Fig. 1 (Maximum operating temperature of the hot spot)

Insulation ratings are a standardized system that indicate the ability of insulating materials to withstand electrical loads and temperature increases. The American National Standards Institute (ANSI) and the International Electrotechnical Commission (IEC) have established the following insulation ratings:

Control over insulation classes is established by various international standards that define the maximum permissible temperature rise for electrical equipment depending on the insulation class. The most common standards are the following:

- International Electrotechnical Commission (IEC) 60085: This standard defines the insulation classes of electrical equipment and establishes the maximum permissible temperature rise for each class. In IEC standards, an insulation system is a classification based on the level of protection against electric shock provided to the user.

1) Functional insulation is the insulation required to prevent a short circuit within the equipment. Practical examples of this insulation are plastic switch housings, insulator bushings, cambrics, plastic tubes, and other types of dielectrics. For this type of insulation, materials are used that differ in their physical properties from the standard forms of dielectrics that are the main insulation of electrical appliances.

2) Basic insulation is any material added to protect the user from accidental contact with live parts. Additional insulation can withstand 1500 V AC. This is, in fact, the main protection of electrical installations, which ensures their normal and stable operation, without the occurrence of short circuits, and protects against direct contact with current. According to the standards, the entire surface of wires, cables, and other elements through which electric current passes must be covered with working insulation. For example, the cords of electrical appliances are always covered with insulation (Fig. 2).

Fig. 2

3) Double insulation is a design concept in which the failure of one insulation system does not expose the user to the risk of electric shock due to the presence of a second independent layer of insulation. Potential hazards to people, such as electric shocks from indirect contact with equipment elements, can be significantly reduced by installing double insulation.

These durable protective materials are used in electrical devices with voltages up to 1 kV. There are 2 degrees of protection - basic and additional. Manufacturers install double insulation in various electrical appliances: handheld lamps, hand-held power tools, and isolation transformers.

4) Reinforced insulation is an additional insulation system that is strong enough to work effectively as if double insulation were present. In production environments, there are times when double insulation is problematic to apply due to the design features of electrical devices. For example, in switches, brush holders, etc. In this case, you have to use another type of protection - reinforced insulation. Reinforced insulation is installed on electrical installations with a rated voltage of up to 1 kV. It is able to provide a degree of protection against electric shock that is equivalent to the properties of double insulation.

- MG 1 standard of the National Electrical Manufacturers Association (NEMA): This standard provides recommendations for the selection and use of electric motors, including insulation class requirements.

- Underwriters Laboratories (UL) 1446: This standard specifies requirements for the use of insulation systems in electrical equipment.

- Institute of Electrical and Electronics Engineers (IEEE) Standard 85: This standard provides guidance for the design of electrical installations, including insulation class requirements.

Several factors must be considered when selecting the appropriate insulation class for a motor, including the operating environment, thermal loads, and motor size and design. Factors such as humidity, dust, and vibration can affect the performance of a motor insulation system, so it is very important to choose an insulation class that can withstand these environmental factors. Here are some examples of how insulation classes are applied in different types of electric motors:

1) Household appliances: Class A insulation is typically used for small electric motors in household appliances such as vacuum cleaners, blenders, and food processors.

2) Industrial fans and pumps: Class B insulation is often used for motors that drive industrial fans and pumps, which typically have moderate duty cycles and operate at temperatures below 80°C.

3) Conveyor belts and mixers: Class F insulation is suitable for motors that run continuously, such as in conveyor belts and other industrial equipment that requires high torque and continuous operation.

4) Heating, ventilation and air conditioning systems: Heating, ventilation, and air conditioning systems typically use electric motors with Class B or Class F insulation, depending on the specific application and operating conditions.

5) Compressors: Motors used in compressors and other equipment that operate in harsh environments may require Class H insulation to withstand high temperatures and other loads.

6) Electric vehicles: Electric vehicles use different types of motors, but many of them require high-temperature insulation to withstand the heat generated during operation. Insulation class R is often used for such applications.

7) In large machines, different systems may be used according to the projected temperature rise of the machine. For example, in large hydroelectric generators, the stator windings may be class B and the rotor winding, which is more difficult to cool, may be class F.

One of the key benefits of the insulation class system is that it helps to ensure the safety and reliability of motors. Overheating of the motor can lead to insulation breakdown and potential electric shock or even fire. By choosing the right insulation class, motor manufacturers can minimize the risk of overheating and ensure the safety and reliability of their motors.