Electromechanical Relay Construction with Working

The electrical and electronics circuits are usually operated over a wide range of voltage, current, and power ratings. For every circuit or equipment or electrical network or power system protection system is desired to avoid the breakdown or temporary or permanent damage. Such that, equipments or circuits used for protecting are called as protecting equipment or circuit. In case of a small amount of voltage ratings, protection of the circuit depends on the cost of the original circuit to be protected and cost of the protection system essential to protect the circuit. But, in case of high cost circuits or equipments, it is desired to adopt a protection system or protection circuit and controlling device or controlling circuit to avoid economical loss and damage.

Electromechanical Relay


The relay is an electromechanical switch used as a protecting device and also as a controlling device for various circuits, equipments, and electrical networks in a power system. The electromechanical relay can be defined as an electrically operated switch that completes or interrupts a circuit by physical movement of electrical contacts into contact with each other.

Electromechanical Relay Construction

The flow of current through an electrical conductor causes a magnetic field at right angles to the current flow direction. If this conductor is wrapped to form a coil, then the magnetic field produced gets oriented along the length of the coil. If the current flowing through the conductor increases, then the magnetic field strength also increases (and vice-versa).

Eelctromechanical Relay Coil - Magnetic Field
Eelctromechanical Relay Coil – Magnetic Field

The magnetic field produced by passing current through coil can be used for various purposes such as inductors, construction of transformer using two inductor coils with an iron core. But, in electromechanical relay construction the magnetic field produced in coil is used to exert mechanical force on magnetic objects. This is similar to permanent magnets used to attract magnetic objects, but here the magnetic field can be turned on or off by regulating current flow through the coil. Thus, we can say that the electromechanical relay operation is dependent on the current flowing through the coil.

Electromechanical Relay Working

The electromechanical relay consists of various parts such as movable armature, movable contact & stationary contact or fixed contact, spring, electromagnet (coil), the wire wrapped as coil with its terminals represented as ‘C’ which are connected as shown in the below figure to form electromechanical relay.

Electromechanical Relay Construction
Electromechanical Relay Construction

If there is no supply given to the coil terminals, then the relay remains in the off condition as shown in the below figure and the load connected to relay also remains turned off as no power supply is given to load.

Electromechanical Relay Working (OFF condition)
Electromechanical Relay Working (OFF condition)

If the relay coil is energized by giving supply to the coil terminals at ‘C’, then the movable contact of the relay is attracted towards the fixed contact. Thus, the relay turns on and the supply is connected to the load as shown in the below figure.

Electromechanical Relay Working (ON condition)
Electromechanical Relay Working (ON condition)

There are various types of relays, the relays which are energized by electrical supply and performs a mechanical action (on or off) to make or break a circuit are called as electromechanical relays. There are various types of relays such as Buchholz relay, latching relay, polarized relay, mercury relay, solid state relay, polarized relay, vacuum relay, and so on.

Applications of Electromechanical Relay

There are numerous applications for electromechanical relays. Various types of relays are used in various applications based on different criteria such as rating of contacts, number & type of contacts, the voltage rating of contacts, operating lifetime, coil voltage & current, package, and so on. Relays are frequently being used in power system networks for controlling purpose, automation purpose, and protection purpose.

The typical applications of electromechanical relays include motor control, automotive applications such as an electrical fuel pump, industrial applications where control of high voltages and currents is intended, controlling large power loads, and so on.

Electromechanical Relay Logic

The method of using relays and contacts to control the industrial electronic circuits is called as relay logic. The inputs and outputs of relay logic circuits are represented by a series of lines in schematic diagrams and hence relay logic circuits are also called as line diagrams. An electromechanical relay logic circuit can be represented as an electrical network of lines or rungs where each line or rung have continuity for enabling the output device.

Application of Electromehanical Relay Logic

The railways routing and signaling are controlled using relay logic and is considered as a key application of relay logic. This safety critical application is used to reduce the accidents and to avoid the selection of conflicting routes by using interlocking. The human elevator operator was replaced by large relay logic circuits in elevators. The relay logic circuits are used in electro-hydraulics and electro-pneumatics for controlling and automation purpose.

Do you want to know the basic design of relay logic? Are you interested in designing electronics projects? Then, post your queries, comments, suggestions, ideas in the comments section below.

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