21/03/2026
Choosing the wrong contactor is one of the fastest ways to damage equipment and waste money, yet many people still focus only on current rating instead of the duty class.
The current rating may be the same,but contactor class matters too.
Not all 100Amps contactors are same.
AC-1 contactors are designed for resistive or slightly inductive loads where there is no significant starting current. In this case, the current rises smoothly and remains stable, so the contactor does not experience much electrical stress. This makes AC-1 suitable for applications like heaters, ovens, and simple lighting systems where there is no heavy switching demand.
AC-2 contactors are built for slip ring motors, also known as wound rotor motors, where there is some level of starting current but not as intense as in squirrel cage motors. These contactors are designed to handle the current during starting and disconnection, making them useful in applications such as crushers, mills, and certain heavy-duty industrial machines.
AC-3 contactors are the most commonly used in everyday electrical work because they are designed for squirrel cage induction motors. These motors draw high inrush current at startup, and AC-3 contactors are built to handle that stress and safely disconnect the motor while it is running. This makes them ideal for pumps, fans, compressors, and conveyors.
The key takeaway is simple: always select your contactor based on the type of load and starting conditions, not just the current rating.
What’s one contactor mistake you’ve seen or made on site that others can learn from?
