What is a switch?

A switch is a type of electrical device that can connect or disconnect the path of an electric conductor. A switch interrupts the electric current or diverts it from one conductor to another. It is a type of electromechanical device that consists of one or more sets of electric contacts that are movable, and it is connected to an external circuit. An electric switch regulates the current between the load and the source of power.
Many different configurations of electrical switches are available. Controlled by the same knob or actuator they may have multiple sets of contacts. These contacts may operate sequentially, simultaneously, or alternately. A switch can be operated manually or can act as a sensing element.

Working of a switch in a circuit

Electrical switches help to regulate the current between the load and the source of power. The power source consists of the electrons pushing through the circuits. The quantity of force or pressure applied by the power source is its voltage. There must be a negative and positive endpoint in the power source. The electrons drive through the circuit when the negative terminal connects to the charge. On receiving the current, the load returns it via the positive terminal to the power source. Within this loop, an electrical switch is inserted.

Components of a switch 

An electric switch is connected to the fuse box and the load using a specific cable type that drives the load. The three insulated wires are; a hot wire, a neutral wire, and a ground wire.

1. One of the terminals on the switch and the load-powering outlet is connected via the hot wire.
2. The other terminal is connected to the load via the neutral wire.
3. The outlet is connected through the ground wire.

When you turn on the switch, the electrical contacts inside the switch join the two terminals together and a link is established. When the switch is turned off, these contacts break, and the connection is terminated. The position of the switch controls the flow of current in the circuit.

Types of switches

Mechanical switches

Mechanical switches are those type of switches which must be activated physically by pressing or moving or touching or releasing its contacts. A mechanical switch has two metal plates. The flow of current takes places when these plates touch each other and the current gets interrupted when these plates get separated from each other.

Some of the mechanical type switches are described below.

Single pole, single throw (SPST)

These types of SPST switches are one-way switches in British mains wiring, and while in American electrical wiring they are two-way switches. SPST switches are simple on and off switches. The two terminals are either connected or are disconnected from each other. An example of an SPST switch is a light switch.

Single pole, single-throw, normally open (SPST-NO)

It is also a normal on-off switch. The two terminals of the switch are normally disconnected or open and when it is activated then it is closed. For instance a push-button switch.

Single pole, double-throw (SPDT)

In British wiring, they are two-way switches and in American wiring, they are three-way switches. A simple break-before-make technique is used in these types of switches. The common C terminal is connected to the L1 or L2 terminal of the switch.

Single pole changeover or single pole, centre off or single pole, triple throw (SPCO SPTT, c.o.)

This type of switch is similar to SPDT. With a stable position in the center, some suppliers use SPCO/SPTT for switches and SPDT for those without.

Double Pole, single throw (DPST)

In British name and American wiring name they are called double pole switches only. The double-pole, single-throw (DPST) switches are equivalent to two of SPST switches and are controlled by a single mechanism of SPST switches.

Double Pole, double throw (DPDT)

These types of DPDT switches are equivalent to two SPDT switches. DPDT switches are also controlled by a single mechanism.

Double pole changeover or double pole, centre off (DPCO)

These types of switches are schematically the same as DPDT switches. With a stable center position, some suppliers use DPCO for switches. They use DPDT for those without a stable center position. With a center position, a DPDT/DPCO switch can be ON when connected to both L1 and L2 at the same time and can be OFF when not connected to either L1 or L2 at the same time. The position of these switches is usually referred to as "ON-OFF-ON" and "ON-ON-ON" respectively.

Two pole, six throw (2P6T)

These types of switches consist of a changeover switch with a common (COM) that can connect to terminals which are L1, L2, L3, L4, L5, or L6 with the help of a second switch that is a two-pole switch is controlled by a single type of mechanism.

Push button switch

As long as pressure is applied, it makes or breaks a connection or when the button is pushed. This pressure is only applied by someone's finger. Once the pressure is removed the button returns to its original position.

Toggle switch

With the help of a mechanical handle, a locking mechanism, or a lever, a toggle switch is activated. These are used for switching high currents and switching low currents. They are used in different types of switching applications and are available in different sizes, ratings, and styles.

Limit switch

There are many varieties of limit switches available. Some of the switches are operated with the help of the presence or absence of an object or instead of human hand operation they are operated by the motion of the machine.

Electronic switches

Electronic switches are generally solid-state switches and their switching does not depend on any physical movement or action. Some examples of electronic switches are Reed switch, Lever switch, SCR's, MOSFET's, TRIAC's, and IGBT's.
In the case of a switch such as a push-button switch, the contacts remain in one state unless actuated. These contacts can be normally opened or closed with the help of switch action.

A changeover switch or a double-throw switch is a type of switch which has both types of contact. These may be "break-before-make" which helps in interrupting one circuit before the other is closed or, maybe "make-before-break" which connects both circuits momentarily.

Some other types of switches

Do not disturb switch

It is a soft touch operating switch generally used in hospitals and hotels. It is used to ensure privacy and silence.

Light dimmer/stepless regulator

It is used to change or control the the intensity of a light fixture between bright and dim or speed of a fan. This switch allows one to rotate it freely and slowly without any steps unlike rotary switch that rotate in steps, each step representing a definite level of fan speed.

Bell push switch

This switch is connected to a doorbell. The connected bell rings when the switch is pushed. Such switches always maintain a broken circuit, the current flows only when the button is pressed.

Context and Applications

This topic is significant in the professional exams for Under-Graduate, Graduate, and Post-Graduate courses.

• Bachelors of Science in Electrical Engineering
• Masters of Science in Electrical Engineering

Practice Problems

Question 1: Which among the following is an electronic switch?

1. Reed switch
2. Momentary switch
3. Multi-pole switch
4. DPDT

Answer: Correct option a

Explanation: A reed switch is a type of electrical switch and is operated by a magnetic field.

Question 2: How are mechanical switches activated?

1. Physically
2. By semiconductor action
3. By push-to-break technique
4. By push-to-make technique

Answer: Correct option a

Explanation: Mechanical switches are operated or activated physically by pressing or moving or touching the switch.

Question 3: Which among the following is a mechanical switch?

1. DPST
2. Lever switch
3. Reed switch
4. SCR'S

Answer: Correct option a

Explanation: DPST is a type of mechanical switch.

Question 4: Which kind of switch operates only with pressure?

1. MOSFET switch
2. Toggle switch
3. Thyristor switch
4. Push-button switch

Answer: Correct option d

Explanation: In case of push-button switch, as long as pressure is applies, it makes or breaks a connection or when the button is pushed.

Question 5: What is the potential drop across an ideal switch?

1. Zero
2. Infinite
3. Minimum
4. Maximum

Answer: Correct option a

Explanation: There is a zero potential drop across an ideal switch.

Related Concepts

• Circuit breaker
• Commutator
• Electric switchboard
• Switchgear
• Switch access