IEC contactors are typically going to say they are rated for 1 million electrical operations, but only under the specific conditions of use they are selected for. So in the IEC world, those conditions of use are divided into AC or DC, then in AC, there are 22 separate "Utilization Categories" with numbers assigned to them and bizarrely specific conditions. The most common one you see in the catalog will be AC-1, which is what we would call the "Thermal current" rating, meaning the amps you can use it at for non-inductive loads, like resistance heaters. Then there is AC-3 which is inductive loads like AC Squirrel Cage induction motors. Then within AC-3 there is a graph that you apply by determining how often you will turn it on and off, how long in between starts, what the power factor of the motor will be during starting, the ambient temperature in the enclosure, the phase of the moon and the angle of the dangle. That graph will then tell you how long you can expect it to last. If you want it to last longer, you can de-rate a contactor accordingly based on your operating onditions. But although they sell replacement contacts on larger sizes, that's only because people in North America insisted on it when they started selling them here. Elsewhere in the world they know that the contactors will have beaten themselves to death by the time the contacts wear out, they rarely ever replace contacts.
NEMA contactors are designed for a minimum of 10 million mechanical operations and 1 million electrical operations, meaning it is inherently designed to have the contacts replaced 10 times. Also, that rating is at full load Across-The-Line starting, and also must have a basic 50% derate for what we call "Inching and Plugging Duty" (the theoretical equivalent of AC-4 in IEC ratings). Inching means banging the contactor on for a second to creep a load forward, over and over and over, Plugging means to try to stop an AC motor and load by using a reversing contactor and putting the motor into reverse while it is going forward. When you do that, the PF of the motor rarely gets out of the .2 range, so the contactor will be switching on and off at 500-600% FLA. It just can't get worse than that. An AC-4 rated IEC contactor could do that too, but requires a minimum rest period between operations (differs by size). NEMA does not, you can do it as fast as your control system can make it happen.
