Guides

A utilization category is the IEC 60947-4-1 code stating what kind of load a contactor is proven to switch. The same contactor carries a different amp rating in each category — typically Ith ≥ AC-1 ≥ AC-3 ≥ AC-4 — because switching resistive load is far easier than switching a motor. An amp figure...

The small module wired across a contactor coil is a surge suppressor. Every time the coil de-energises, its collapsing magnetic field generates a spike of hundreds to thousands of volts. An RC snubber, varistor or diode absorbs that spike — protecting the controlling contact, the coil insulation, and nearby electronics.

Contactor coils burn out when they carry more current, for longer, or at a higher temperature than they were designed for. The dominant cause is a coil that never seals shut — through chattering or undervoltage — because an unsealed coil draws 6 to 10 times its holding current continuously.

A contactor chatters when its armature repeatedly pulls in and drops out instead of sealing shut. The most common cause is low coil voltage — below 85 % of rated, the magnet cannot close the air gap. Other causes are a broken shading ring, dirty pole faces, control signal bounce, control logic hunting, and...