Auxiliary contacts

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Auxiliary contacts

Auxiliary contacts, if they are implemented in the form of separate devices, are interchangeably called auxiliary contactors. They belong to switching devices and are used in control circuits and other auxiliary circuits. They are used to implement signaling, control and electrical interlock systems. The role of auxiliary contacts is basically to transmit information about the operation of a given receiver or other apparatus.

Contactors - switching devices for normal operation and in overload conditions

There are several types of contactors on the market, but the most common and popular are electromagnetic contactors. Such an apparatus is a mechanical electric switch , the working contacts of which are closed by an electromagnet. They are kept short-circuited as long as the coil voltage is sufficiently high. Breaking the circuit of the electromagnet coil results in the armature dropping under the action of the spring and opening of the working contacts.

Contactors are designed and operated to resemble electromagnetic relays. However, contactors are usually larger structures and are used to connect high power circuits, i.e. main circuits supplying electrical receivers such as motors, heaters, pumps, fans etc.). The relays, in turn, connect auxiliary (control, signaling, etc.) circuits of lower powers. When designing an installation, the choice of a contactor or relay depends to the greatest extent on the type of connected load.

Auxiliary contactors - integrated and connectable

Many modular electromagnetic contactors are equipped with both main contacts, which are designed to switch the operating currents, and auxiliary contacts, which are used to connect control or signaling circuits. However, this is not the only available option.

Almost all well-known manufacturers of electrical apparatus also offer auxiliary contacts in the form of separate devices that can be integrated with contactors in the event that additional auxiliary contacts are needed. Due to their construction, auxiliary contactors are divided into:

  1. leading,
  2. side.

Front contactors are installed on the contactor from the top. As a result, the width of the contactor does not change, but its height changes. In turn, the side contacts are mounted on the right or left side of the contactor, thus not changing its height, but extending the set. Although the side auxiliary contactors visually look similar to the actual on and off circuits (they have a similar shape and screw or spring terminals), they are usually narrower than the width of one module, and therefore take up relatively little space in the electrical switchboard. It is worth knowing that regardless of the design, some manufacturers allow for the construction of auxiliary contacts, but a limited number of them can be connected to one device - usually a maximum of 3.

Both the side and front auxiliary contacts contain different combinations and numbers of contacts:

  1. NO (normally open contacts),
  2. NC (normally closed contacts),
  3. changeover contacts.

Role of auxiliary contactors in the electric circuit

Auxiliary contactors are used for control and regulation tasks. They are most often used for indirect control of engines, clutches, valves and heating devices. In addition to the simplicity in designing electrical installations with their participation, ease of control execution, as well as its commissioning and maintenance, the use of auxiliary contactors is also supported by the high level of safety provided by switching devices . The guarantee is provided by design solutions, e.g. with the use of galvanic separation between the control circuit and the switched on circuit and, similarly, in the switch-off state, between the contact input and output. Of course, each manufacturer of auxiliary contacts uses its own, to some extent, unique design, but all auxiliary contactors must, as a rule, safely control and regulate the selected electrical circuits.