Contactor Accessories Selection Guide
How to select mechanical interlocks, coil surge suppressors (RC/varistor/diode), star-delta power links, and replacement coils for contactors.
Reversing motor starters, star-delta assemblies, and PLC-driven control panels require Contactor Accessories to guarantee mechanical safety, electromagnetic compatibility (EMC), and clean power wiring. Accessories must match the exact contactor frame size and coil voltage.
Essential contactor accessories and their functions
- Mechanical interlock unit: Mounts between two adjacent contactors to physically prevent both armatures from closing simultaneously—mandatory in reversing (forward/reverse) and star-delta circuits to prevent phase-to-phase short circuits.
- Coil surge suppressor (RC circuit / Varistor / Flyback diode): Clamps high-voltage inductive kickback spikes generated when the contactor coil de-energizes, protecting PLC relay/transistor outputs and nearby electronics.
- Reversing and star-delta power wiring kits: Pre-insulated busbar links that speed up assembly and eliminate wiring errors across contactor terminals.
Contactor accessories comparison table
| Accessory Type | Target Circuit | Primary Function | Key Selection Parameter | Category Link |
|---|---|---|---|---|
| Mechanical interlock kit | Reversing & star-delta starters | Physically prevents simultaneous closing of two contactors | Contactor frame series and side-by-side / vertical layout | Contactor Accessories |
| Coil surge suppressor (RC / Varistor) | PLC-controlled automation panels | Suppresses inductive switching overvoltage spikes | Coil voltage range (24 VDC, 24–48 VAC, 110–240 VAC) | Contactors |
| Pre-wired power link & spare coil | Star-delta & voltage conversion | Error-free terminal bridging or coil voltage replacement | Contactor current frame (9 A–38 A, 40 A–65 A, etc.) | Capacitor Contactors |
Frequently asked questions
Is a mechanical interlock necessary if electrical interlocking (NC contacts) is already wired?
Yes. Electrical interlocking only interrupts coil power; a mechanical interlock physically blocks the second contactor if the first contactor's main contacts weld or if someone presses the actuator manually.
Which coil surge suppressor should be used: diode, RC, or varistor?
Flyback diodes work only on DC coils and eliminate voltage spikes completely but slightly increase drop-out time; varistors and RC snubbers work on AC (and DC) coils without significantly delaying contactor opening.