IEC (International Electrotechnical Commission) is an international organisation responsible for developing and publishing electrical, electronic, and other related technologies' standards. In the context of electric motors, IEC Design N and IEC Design H refer to different motor designs and performance characteristics, mainly concerning torque and slip.

1. IEC Design N: These are standard motors designed according to IEC 60034-1 standards. Design N motors have a normal starting torque and a relatively low starting current. They provide a good balance between performance and efficiency for general-purpose applications. These motors are widely used in various industries, such as pumps, fans, compressors, and conveyor systems, where the load torque requirements are moderate.

2. IEC Design H: IEC Design H motors are high-slip motors with high starting torque, which means they can handle higher loads during the startup phase. They have a higher rotor resistance, leading to a higher slip, which enables them to deliver more torque at a lower speed. Design H motors are used in applications where a high starting torque is required, such as crushers, mills, or other heavy-duty machinery. However, these motors typically have a lower efficiency than Design N motors.

In summary, the main difference between IEC Design N and IEC Design H motors is the starting torque and slip characteristics. Design N motors are suitable for general-purpose applications with moderate load torque requirements, while Design H motors are designed for heavy-duty applications that require high starting torque. When selecting a motor for your application, it is essential to consider the specific requirements of your system and choose a motor that meets those needs.