AC Contactor Selection: AC-1 and AC-3 Ratings and Coil Voltage Codes

AC-1 and AC-3 in plain terms

IEC 60947-4-1, the standard for electromechanical contactors and motor starters, defines utilization categories that describe what the contacts must survive. AC-1 duty is easy on contacts: resistive or slightly inductive loads at near-unity power factor, so the contactor is rated for its full frame current. AC-3 duty is the standard motor case: the contactor closes on a stalled motor (starting current around six times running current) and breaks the running current, which is an easier break but a much harder make.

Because of that difference, one frame carries two ratings. The digits in the model give the frame current: NXC-09 is a 9 A frame, NXC-12 a 12 A frame, up through NXC-32 and beyond. The AC-1 ampacity is higher than the AC-3 figure for the same frame, and the motor power each frame handles at AC-3 comes from the manufacturer's table, listed per frame size in the Chint documentation for the NXC series.

Coil voltage: the marking that decides whether it pulls in

The coil voltage printed on the contactor (or in its ordering code) is the control-circuit voltage, not the load voltage. A contactor switching 380 V three-phase power can have a 24 V, 110 V, 220 V or 380 V coil depending on what the control circuit supplies. AC and DC coils are wound differently, so match the voltage and the current type from the original unit's marking.

• 24 V and 36 V coils: control circuits fed from a control transformer, common in machines where operators touch the controls.
• 110 V and 220 V coils: standard control supplies in industrial panels, the most common replacements.
• 380 V coils: coil fed directly from phase-to-phase on a 380 V supply, common in simpler starters without a control transformer.

Reading a CJX1 code

CJX1 contactors use a two-part code such as 12/22. The first figure is the frame rating in amps (9, 12, 22 and up); the second encodes the auxiliary contacts, where /22 means two normally open and two normally closed auxiliary contacts on top of the main poles. The series is dimensionally compatible with the Siemens 3TB frames it descends from, which is why listings pair the two names.

Contactors in stock now

Listings verified October 2026. Frames or coil voltages not listed above are sourced on request; send the full marking from the side of your old contactor.

A selection example

Say a 3 kW, 400 V three-phase motor needs a new contactor, and the control circuit supplies 220 V. The motor's running current is roughly 6 A, so a 9 A frame (NXC-09 class) covers it at AC-3 duty with headroom, and the coil goes to the 220 V listing. The frame's AC-3 power rating and the auxiliary contact count the control circuit needs are the two figures to check against the manufacturer table.

Failure signs worth acting on

• Chattering or buzzing: usually a coil voltage mismatch or a weak control supply, not a worn contactor. Check the coil marking before replacing.
• Welded main contacts: the contactor broke a current beyond its category, often a start against a stalled load. Find the overload cause before fitting the same frame again.