Contactor
This is a switching element reinforced with arc-quenching features so that high-current loads can be switched safely. What sets it apart from a relay is the contact mass, the arc chamber and a continuous current capacity that can reach hundreds of amperes. It is used at main supply isolation and motor switching points.
A contactor also works with a coil, but the contacts are larger, the contact pressure is higher, and the arc formed at the moment of opening is quenched by magnetic blowout or an arc chamber. Thanks to this it withstands repeated switching of inductive loads far longer than a relay.
- Where it is needed: the main isolator between battery and driver, the crane main contactor, the high-current DC motor supply line.
- DC versus AC: a DC arc does not extinguish by itself because there is no natural zero crossing. Using a contactor made for AC in a DC circuit can cause the contacts to weld; a type with a DC rating must be selected.
- Coil consumption: DC contactor coils typically draw 0.5–2 A. Do not try to drive this directly from a control output; put a small relay in between.
The main contactor that isolates the control box from power is also the physical end of the emergency stop chain. In the energy isolation discipline before maintenance, you are expected to verify with a multimeter that this element really has opened and that no voltage remains on the contact terminals.
Context in which this term is used: Complete guide to IP protection ratings