In this article, you will learn how a contactor works, what it is used for, and what role it plays in electrical systems.
Definition of a contactor
A contactor is a compact device that functions as a relay or electromagnetic component which, through its power contacts, controls the operation of motors, resistors, or other high-power loads. It acts as an electrical 'switch' within a circuit that establishes or interrupts the flow of current, thereby controlling the various devices connected to it.
It should be noted that while this component is not absolutely essential in every electrical installation, it offers significant advantages when properly implemented.
Different models are available with or without integrated auxiliary contacts (either normally open or normally closed). Additional auxiliary blocks can be fitted to these contactors specifically for remote control or signalling applications.
Components of a contactor
A contactor consists of the following elements:
- A coil
- A return spring
- Several power contacts or poles (single-pole, double-pole, triple-pole, or quadruple-pole)
- A magnetic circuit (comprising a fixed electromagnet and a movable armature)
- A phase shift ring (which stabilises vibrations in coils supplied with alternating current)
- Auxiliary contacts (normally open or normally closed)
How a contactor works
A contactor operates through its electromagnetic coil, which can be supplied with either alternating or direct current at various voltages (typically 24V, 48V, 110V, 230V, or 400V). When the coil is energised, it generates a magnetic field. This magnetic field attracts the movable metal armature towards the fixed electromagnet, causing all associated contacts to change state simultaneously.
There are specific terms used when describing contact types. You may encounter the designations NO, NC, NF, F, and O.
NO contacts are "normally open," meaning that when your contactor is de-energised, the contact remains open. When you energise the contactor, this contact closes, which is why it can also be designated as F (for "fermeture" or closing contact).
Conversely, NF (or NC) refers to "normally closed" contacts, which are closed when the contactor is de-energised and open when the contactor is energised. These can also be designated as O (for "ouverture" or opening contact).
This terminology applies to both main contacts (which control power to the connected load) and auxiliary contacts (which provide feedback signals about the contactor's operational status).
For further information, please consult our other articles on contactors to learn more about the two main types of contactors currently available on the market:
- Electrical contactors
- Day and night contactors
