A contactor is a magnetic device based on a two-position mode of operation, designed for permanent intermediate (remote) switching on of power galvanic circuits, in the presence of a standard operating mode.

Basically, one- or two-pole direct current devices or three-pole ones - alternating current are used. The frequent switching on and off of the contactors places high demands on this type of device (electrical and mechanical resistance of the material).

Contactors contain:

• contact system.
• electromagnetic system.
• Arc quenching chamber.
• A system of auxiliary contacts that switch alarm levels.

Principle of operation

Unlike switching contact assemblies, contactors can only nominally conduct currents, since they are not intended to disconnect a circuit (for example: a short circuit).

With the help of an additional current circuit, the device is controlled, passing through an inductive coil with voltage from 24 to 220-380 volts. In order to increase safety during operation of the product, the total current value should be slightly lower than the operating current level in the passing circuits. The contactor does not have a mechanical resource to hold the contacts in the active position, therefore, in the absence of a guiding voltage flow on the inductive coil, it opens the circuit. To hold the circuit in the active position, an "auto-pickup" system using two open contacts is used (example: using a programmable logic controller).

The magnetic starter is an electromechanical control and distribution device, the purpose of which is to start the electric motor and ensure its continuous operation. This device works as a transformed (modified) contactor, it can be supplemented with accessories. Starters are endowed with an emergency shutdown system in case of an open circuit, or one of the power phases of the electric motor.

The starter performs the function of changing (switching) the direction of the reversing circuit by changing the phases, for which, for this purpose, another contactor is placed in the device.

In order to reduce the motor current output, a three-phase power supply system switch is used.
The operation of the magnetic starter can be both open and protected (with built-in motor protection).
Magnetic starters are reversible and modular. Reversible ones produce the circulation of three-phase electric motors by means of voltage alternation and represent two contactors (contactors) connected in one device by electrical or mechanical blocking. They exclude the possibility of a short circuit (interphase).

Modular starters are electromagnetic devices designed for installation in electrical distribution boards of modular standard products with fasteners. These models of starters are distinguished by electrical safety and uninterrupted operation.

Common features of a contactor and a magnetic starter

The above products are complementary devices with a single principle of operation in an electrical circuit, that is, they are used for switching. Equally used to start AC motors, I/O resistance levels. The magnetic starter and contactor have several contacts for control - a closed and an open circuit.

Differences between a contactor and a magnetic starter

Starters are used for switching low voltage circuits. Products also differ in their dimensions: the contactor is larger than the starter.

The following difference lies in the design: the contactors have powerful power contacts, and are endowed with arc extinguishers. The starters do not have arc chutes, and the power contacts are much weaker. The devices also differ in their purpose: magnetic starters are generally used to supply electrical power to devices (lamps, electrical receivers), and contactors are intended for switching absolutely any power circuit.