AC-3 vs AC-4 Usage Category Comparison
Why Utilization Categories Matter for Contactor Selection Specifying a contactor by rated current alone is one of the fastest ways to end up with welded contacts, short electrical life, and unplanned downtime. The contactor utilization category—defined in IEC 60947-4-1—tells you what kind of load the contactor can switch and how severe that switching duty is. Two contactors with the same ampere rating can have completely different real-world performance depending on whether they are rated for AC-3 or AC-4 duty. If you are selecting an AC contactor for a motor application, understanding the difference between AC-3 and AC-4 categories is not optional—it is the single most important factor that determines whether your installation will […]
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