Contactor: when you need AC-3, when AC-1 is enough
Contactors in our shop go mostly into motor and pump panels. Our typical customer this year: a panel builder assembling a control cabinet for a 5.5-15 kW borehole pump, or a service tech on a boiler-room ventilation job. We always ask three things first: utilization category, motor current, coil voltage. Without those three numbers we do not size a contactor.
The mechanics are simple. Energize the coil with 220 V (sometimes 24 or 380, depends on the scheme), main contacts close, the motor starts. Drop the coil, the spring opens in 30-50 ms. AC-3 utilization for motors accounts for the 6-8x inrush, so we ship ABB AF or Schneider TeSys D with a 25-30% current margin. A purely resistive load (heater, lighting) runs under AC-1, where you can size at the rated current with no margin and pay less.
What we ask before you order
First question: motor or other load. If motor, give us either rated current or kW + voltage. A 7.5 kW 380 V motor pulls ~15 A, so we ship a contactor rated 18-25 A under AC-3 (for example ABB AF26, Schneider LC1D25, LS MC-25b). If it is a heating coil or a borehole pump starter sitting next to a VFD, the scheme is different.
Second: coil voltage. In most PLC-driven panels we use 24 V DC. It is safer for the operator. Wires straight from the controller output. Old-school panels and construction sites still run 220 V AC. 380 V is rare, mostly when there is no separate control loop. Tell us your scheme and we will recommend.
Third: where it sits. Contactor next to a VFD? One caveat: do not switch the VFD output under load, the IGBTs burn instantly. Auxiliary contacts (NO/NC) we count separately: 1+1 on the body, then either side blocks or front-mount modules. Manufacturer warranty runs 1 to 3 years. ABB AF and Schneider TeSys both carry 3 years. Shipping from our Kyiv warehouse in 1-3 days, popular ratings from 9 to 95 A are kept in stock.
How to Choose a Contactor
Proper contactor selection determines the reliability and longevity of your electrical system. Key selection parameters:
Rated current and utilization category. Contactors are classified by categories: AC-1 (resistive or slightly inductive load), AC-3 (motor starting and stopping), and AC-4 (reversing and braking). For motors, always select a contactor rated for AC-3 with a 20–30% current margin.
Coil voltage. The coil supply voltage must match the control circuit: 24V AC/DC for PLC-based systems, 110V for industrial panels, 220V (most common) for general industrial applications, 380V for direct connection to the power network.
Number of poles. 3-pole contactors are the standard for three-phase motors. 4-pole contactors are used for switching three-phase circuits with neutral or in single-phase systems requiring double-break disconnection.
Auxiliary contacts. Most contactors feature front-mounted and side-mounted auxiliary contacts (NO — normally open, NC — normally closed). These are essential for signaling circuits, interlocking, and self-holding schemes.
Mounting. Modern contactors mount on 35 mm DIN rail, enabling fast installation in distribution boards and control cabinets.
Popular Contactor Brands
The Chastotnik.ua catalog features contactors from manufacturers with decades of experience in industrial switching:
ABB — the A-line series (A9…A300) for general industrial use and the AF series with electronic coil for wide voltage range operation. ABB contactors stand out for their compact dimensions and high reliability under intensive operation.
Schneider Electric — TeSys D and TeSys K ranges for different power levels. TeSys D is the industrial standard for motors up to 75 kW; TeSys K is a compact solution for light-duty applications up to 5.5 kW.
LS Electric — the MC series (MC-9a…MC-800a) covering a broad lineup of rated currents. LS contactors offer a strong price-to-reliability ratio for industrial facilities.
Contactors for Use with Variable Frequency Drives
Contactors are frequently used alongside variable frequency drives (VFDs) in two primary configurations:
Input contactor (before the VFD). Installed between the circuit breaker and the VFD input. Provides safe power disconnection during emergencies or on command from the safety system. Mandatory in schemes requiring functional safety compliance (STO, SIL).
Bypass scheme (bypass contactor). Allows switching the motor to direct mains power if the VFD fails. Very important for continuous processes — pumping stations, ventilation systems, and conveyor lines.
Important: installing a contactor on the VFD output for switching under load is not recommended — it may damage the inverter's output IGBT transistors. If output-side switching is required, the contactor must operate only at zero frequency with the motor stopped.
Why Buy from Chastotnik.ua
- Genuine equipment — we work directly with authorized distributors of ABB, Schneider Electric, and LS Electric
- Technical consultation — we help select the right contactor for your specific application, considering load category and control scheme
- One-stop supply — contactors, soft starters, variable frequency drives, sensors, and auxiliary equipment from a single supplier
- Fast delivery — popular ratings from stock; custom orders from 5 business days
- Manufacturer warranty — official warranty on all contactors with full documentation package
