Electric motors

Frame size to IEC (for example "IEC 100" or "IEC 132") denotes, for electric motors, a standardised shaft height - the distance from the centre of the shaft to the mounting surface, given in millimetres as the number in the designation. This standardisation means motors from different manufacturers with the same frame size are mechanically interchangeable (mounting dimensions, shaft height), even if their power or efficiency differ. When replacing a failed motor, frame size is therefore often the most important first figure to check, ahead of the exact power rating, because it determines whether the new motor will even fit mechanically into the existing installation. Beyond the shaft height alone, standards often also distinguish the motor's length (with suffixes such as "S", "M", "L"), which likewise matters for fit. When replacing a motor it is therefore always worth comparing frame size and length with the old one, not just the electrical power rating.

The efficiency class (IE code, e.g. "IE2", "IE3" or "IE4") ranks electric motors by how efficiently they convert electrical energy into mechanical output - the higher the number, the lower the losses (mainly as heat) for the same output power. These classes are legally regulated and have been tightened over time, so many countries now require a minimum class for motors newly placed on the market. A motor with a higher efficiency class is usually more expensive to buy but saves on electricity costs over its lifetime - for motors running many hours in continuous duty this can pay off quickly, less so for rarely used motors. The stated efficiency usually applies to a specific load point (most often full load) and can differ at partial load. When comparing two motors with different IE classes, it is worth calculating based on the actually expected running hours rather than relying on the class label alone.

The protection class (IP code, e.g. "IP54" or "IP65") states how well an enclosure - typically on an electric motor, controller or switch cabinet - is protected against the ingress of foreign objects and water. The first digit after "IP" describes protection against solid objects and touch (0 to 6, higher is better), the second digit protection against water (0 to 9, also higher is better). An "IP65" enclosure, for example, is fully dust-tight and protected against water jets from any direction, while a lower code may only be suitable for dry indoor spaces. For outdoor use, dusty environments, or washdown with water (as in agriculture or the food industry), a sufficiently high protection class is essential to avoid failures caused by moisture or dust getting in. When buying an electric motor, the protection class should therefore always match the actual installation site, not just the price.