Which statement best describes how IEC contactor life expectations are specified?

• A. They are described by a single metric
• B. They are described by a single metric relating to electrical operations
• C. They are described by a single metric relating to mechanical operations
• D. They are described by a pair of counts for electrical and mechanical operations

Answer: (D)

The key idea is that IEC contactors have two separate endurance ratings: mechanical life and electrical life. Mechanical life counts how many times the device can be operated without any load on the contacts, focusing on wear from the actuator, springs, and linkage. Electrical life counts how many times the contacts can make and break under the rated electrical load, capturing wear from arcing and contact erosion during switching. Because these wear mechanisms are different, a single metric wouldn’t capture how long the device will last in real use. In practice, the electrical life is what limits performance when you switch under load, while mechanical life matters when you cycle the device frequently with little or no load. That’s why the specification is a pair of counts for electrical and mechanical operations.