Use of Different Types of Switches | Accessories | Electrical Engineering

In this article we will discuss about the use of various types of switches for domestic and commercial purposes.

Use of Single-Pole and Double-Pole Switches:

A single-pole switch may be used in a circuit in which normally the current does not exceed 5 amperes. Where the current exceeds 5 amperes, the practice is to use a double-pole switch there. When two single-pole switches are placed side by side and their knobs are tied together by a piece of wood or ebonite, the combination becomes a double-pole switch.

For switching ‘on’ or ‘off, a switch may be connected in any part of a circuit. Suppose a single-pole switch is to be connected in a circuit for controlling a light point or fan a point. Such a connection has been shown in two diagrams of fig. 93. A single-pole switch has been connected in the live line in fig. 93(a), while it has been connected in the neutral line in fig. 93(b).

It is clear from both the figures that the switch is in series with the lamp. Unless the switch is connected in this manner, it will not perform its function. The purpose of the use of a switch is to send current and to stop the flow of current through a load circuit as and when required.

If the switch would have been connected in parallel with the lamp instead of in series, not only the purpose of switching would not be served, but this would damage the line by causing a short circuit between the live line and the neutral at the point of connection. (To place a switch in parallel with the lamp, its terminals are to be connected across the live line and the neutral in fig. 93).

In this connection a special point is to be borne is mind. For this reason two diagrams have been drawn in fig. 93. It must be ascertained that the switch has been connected in the live line under all circumstances and never in the neutral.

Fig. 94 shows how a double-pole switch remains connected in the circuit.

Indian Electricity Rule states that a single-pole switch shall never be inserted in the neutral wire; it shall always be placed in the live line or phase wire. The reason behind Lamp this rule is that when the switch is put off, there shall be no voltage across the lamp terminals. As a result a person cannot suffer an electric shock even if there be any leakage in the line or in the lamp holder. The neutral will, however, remain at zero potential as there is no switch in it.

The Limits of Live and Neutral Wires:

While the wiring is in progress, an outer colour is normally used for identification of live or phase wires. Red colour is usually used for the live wire and black colour for the neutral wire. Having observed this colour code at the time of wiring, just a look at any portion of the circuit beginning from the terminals of the distribution board up to the farthest point of the load reveals whether it is a live wire or a neutral.

The wire from the live terminal of the distribution board up to one terminal of lamp, fan, motor or wall-plug with the switch in the ON-position is taken as live wire of phase wire. The wire from the other terminal of any of the above loads up to neutral terminal of the distribution board is taken as neutral wire.

Sometimes the wiring may become so complicated that a part of it may be considered neither live nor neutral, and specially so when the switch is in OFF-position. In that case it becomes advantageous if a third colour is used in such parts.

Fig. 93(a) shows only the scheme of connection. The actual wiring must include many details. The switch for the lamp in a room is usually installed on the wall at a height of about 120 cm from the floor level (i.e. up to the shoulder of a man of average height). Suppose the lamp will remain suspended from the ceiling at the centre of the room and two wires will be led from below along a wall. With the same schematic diagram, the actual wiring will assume a different sight. Fig. 95 shows the wiring diagram of such a connection.

Use of Switch for only One Point:

The connection diagram for only one lamp point or a fan point will be as shown in fig. 95. In case a fan has a regulator, a rectangular wooden board is to be fixed on the wall. The switch and the regulator of the fan are mounted on this board, and the regulator remains in series with the switch. The live wire connection will reach one terminal of the fan through the switch and the regulator.

But if there be a long corridor which is illuminated by three lamps placed at three different points, and if each lamp be controlled by its own separate switch, the connection diagram of this arrangement will be as shown in fig. 96.

Use of a Separate Switch for Each of the Many Points:

Here (fig. 96) it is seen that the live wire has reached the left terminal of the switch controlling the farthest lamp. For connection with the left side terminal of each of the other two switches, a wire has come down from the live wire at proper place. From the right side terminal of each switch a piece of wire has been drawn up to one terminal of the ceiling rose of its nearest lamp. So far, and with the switches ‘ON’, the wires are live, and proper colour representing live wire should be used.

Now we see that the neutral wire has reached the second terminal of the ceiling rose of the farthest lamp, and a piece of wire from the second terminal of each of the other two ceiling roses has been drawn for connection with the neutral wire. All these pieces of wire belong to the neutral and should follow the colour representing neutral wire.

A mere look at the colour of the wiring will reveal which fitting belongs to which circuit, all connections have been correctly done or not, which wire is live and which one is neutral at the farthest end of the circuit etc. This is also helpful for testing circuits and sub-circuits any time after completion of wiring. Colour code and its usefulness in complicated three-phase circuits cannot be over-emphasized.

Fig. 97 shows the simple schematic diagram of wiring connections shown in fig. 96. It is evident from fig. 97 that each lamp is connected in parallel with the other between live line and the neutral wire. Also there is one switch in series with each lamp. Each lamp can be separately switched on or switched off only when connected in this manner.

One thing is important here. To connect a lamp as per scheme shown in fig. 97, the voltage rating of the lamp must be the same as that of the circuit in which it is used. Usually lamps suitable for 110V, 220V and 230V circuits are available in the market. Of these again, by far the largest number is rated for 220-volt to 230-volt. The reason behind such practice is that, almost all the supply authorities of electricity maintain the supply voltage of lighting circuits at 225-230 volts.

If the circuit voltage is 225-volt, the voltage rating of the lamps should also be 225-volt. A 220-volt lamp will also do, but it is not recommended. In such a case although the lamp will glow rather brighter, its burning life will be shortened. If, however, a 110-volt lamp is used in a 225-volt circuit, it will burn out instantly.

Control of a Number of Points Together by a Single Switch:

If a number of lamps are to be switched on or switched off at a time, the entire wiring circuit of all the lamps should come under one switch.

This can be done in two ways:

(i) Connection of lamps in parallel:

The connection diagram is shown in fig. 98. To specify the size of the switch, it is to be kept in mind that the current flowing through the switch is equal to sum of currents drawn by individual lamps. The voltage rating of each lamp must be the same as the circuit voltage, i.e., if the circuit voltage is 225 volts, each lamp should also be rated at 225 volts. (If, however, voltage drop in the wires is appreciable, 220-volt lamps may also be safely used). In practice parallel connection of lamps is normally adopted.

(ii) Connection of lamps in series:

The connection diagram is shown in fig. 99. In this case also all the lamps will be switched on and switched off at a time. Voltage rating of individual lamps may be different, but the sum of their rated voltages must be equal to the supply voltage. Another essential feature of this connection is that, current rating of all the lamps in series must be the same; otherwise one lamp may glow too brightly and the other too dimly.

The current rating of the switch should be the same as that of a lamp. The size of the switch in this case is obviously less than that of a switch used for parallel connection. When arc lamps were commonly used, it was the practice to adopt series connection. Even to-day the series connection is adopted for low voltage coloured lamps which are used for the purpose of decoration during ceremonial functions or festivals. Usually the lamps rated for same voltage and same current are connected in series.

The differences between series and parallel connections of lamps are as follows:

It is evident from the advantages and the disadvantages shown in the above list that, on the whole, the parallel connection of lamps is more convenient for use than the series connection. This is the reason why we find the lamps in almost all places connected in parallel.

Control of a Light Point from Two Different Places:

It is not necessary that a stair-case light or a light in a passage like corridor should remain switched on for all the time, but arrangement should be provided for controlling it from either of the two positions. A special form of connection is to be adopted for this purpose. Such a connection essentially requires 2 nos. two-way switches and 3 nos. single-core wires (or one 3- core cable).

At first the neutral line of the circuit is connected directly with one terminal of the lamp. The other terminal of the lamp is joined with the blade of the distant two-way switch. The live line is connected with the blade of the nearby two-way switch, and the other two similar terminals of both the switches are joined together as shown in fig. 100.

Let us now see how the lamp is switched on or off. Fig. 100 shows the blade of the switch on the left-hand side touching the upper contact and that of the switch on the right-hand side touching the lower contact. Proceeding from the live wire of the supply line and tracing the path of current if we come to right-hand side, it will be found that the path of the current is broken at the point where the blade of the right-hand switch touches the lower contact.

The lamp cannot be switched on at this stage. It can be made on if the blade of the left-hand switch is pulled down or that of the right-hand switch is pushed up. Thus, when the lamp remains switched off, it can be switched on either from the left-side or from the right side.

Now suppose, somebody pulls down the blade of the left-hand switch. This will put the lamp on. When he comes down (or goes up) the stair case and pushes up the blade of the right-hand switch, the lamp is switched off again. Thus, it is clear that whichever direction one may come from, he can put the lamp on or off as required by simply pulling down or pushing up the blade of the nearby switch. In the same manner one can switch on the lamp from one side and switch off the same from the other side.

The two-way switch method is applicable in a bed room also. One two-way switch at the door of the room and another at the bedside enable a person to switch on or off the lamp when he is either near the door or in bed. It is no longer necessary for him to get up from bed in order to put the lamp on or off.

The advantage of colour code for the outer cover of wires, can be understood clearly in case of staircase wiring. If the particular colour of the neutral wire is maintained from the neutral of the supply mains up to the lamp terminal, and the colour of live wire is maintained from the live line of the mains up to the blade of the left-hand switch and the remaining wiring is done with wires having a third outer colour, there remains no anxiety for any confusion.

Control of a Light Point from Three or more Different Places:

Very often it becomes necessary to put the switch on or off from a place (or places) in between the two ends of a long corridor. In such cases connections are to be made as shown in fig. 101. Here 2 nos. two-way switches are placed at the two ends of the circuit, and in between these two switches one or more intermediate switch is used.

An intermediate switch has four terminals. It can be put on or off in two ways. In fig. 102 the four terminals A, B, C & D of an intermediate switch have been shown. The connections of these four terminals may be seen in fig. 101. The blade of an intermediate switch sometimes connect terminal A with B and C with D (right-hand diagram of fig. 102), and sometimes connect terminal A with C and terminal B with D (left-hand diagram of fig. 102).

Let the intermediate switch be in a position so that the blade makes connection between terminals as shown in the right-hand diagram of fig. 102. Now a reference to fig. 101 will make it clear that current will move from the live line of the circuit to the upper terminal of the two-way switch on the left- hand side, then through the contacts A-B of the intermediate switch to the upper terminal of the two-way switch on the right-hand side and finally back to the neutral wire through the lamp. But if the blade of one of the two-way switches is pulled down, the lamp will be switched off.

The lamp will be switched on again when the blades of both the two-way switches are pulled down, but this time the current will flow through the contacts D-C of the intermediate switch and not through the contacts A-B.

Similarly, if the blade of the intermediate switch makes connection between terminals A-C and terminals D-B (left-hand diagram of fig. 102), then also the lamp may be switched on or switched off by operating the blade of one of the two-way switches. Thus it is seen that the lamp may be switched on or switched off with help of any one of the two-way switches on two sides without touching the intermediate switch.

Now, let us see how the intermediate switch can perform the on and off control of the lamp. It is clear from fig. 101 that when current flows through the contacts A-B of the intermediate switch, the lamp is switched on. If now the knob of the switch is turned to the other side, the blade will connect terminal A with C and terminal- D with B. This will put the lamp off.

If now the lamp is to be switched on again with the help of same intermediate switch, its knob is again turned to the other side so that the blade connects terminal A with B and terminal D with C. But if the lamp is to be switched on with the help of two-way switch on the left-hand side instead of intermediate switch, the blade of this two-way switch is to be pulled down.

The current will then flow from the live wire to the lower terminal of the two-way switch, then through the contacts D-B of the intermediate switch to the upper terminal of the two-way switch on the right-hand side and finally back to the neutral wire through the lamp. In the same way the lamp may be put on or off with the help of two-way switch on the right-hand side. Thus, it is clear that the lamp may be controlled from any of the three places.

If necessary, instead of using only one switch, as many intermediate switches as desired may be used. Fig. 103 shows the connections of four intermediate switches between two-way switches at two ends. In this case the same lamp (or the same group of lamps) may be switched on and switched off from six different positions.

An idea is given below as to the cases where intermediate switches may be used with advantage. If necessity arises, many more such cases may be found by reasonable thinking.

1. The lamp of the car-parking shed in the ground floor may be switched on and switched off from any floor of a multi-storeyed building.

2. If there are three, four or even more number of chambers with doors leading out into a common long narrow corridor, an intermediate switch near the door of each chamber and two two-way switches at the two ends of the corridor will remove the disadvantage of darkness while moving into or out of any of the chambers.

3. In a dormitory there may be three, four or more number of beds. One suitable switch near each bedside (i.e. two two-way switches and the rest intermediate switches) will make it easy to put the dormitory lamp on or off from each bedside.

4. If there is a large hall with many doors, each leading to a different adjoining room, the arrangement of two two-way switches at the two end doors and intermediate switches at other doors will facilitate movement into or outside any room.

Switching any One of Two Lamps ‘ON’ by means of a Single Switch:

There may be two light points in a room. If, however, it is not necessary to use more than one point at a time, connections may be made as shown in fig. 104. In this type of connection only one two-way switch is sufficient, but such a switch must have one extra off position which will not connect either of the two points. Fig. 104 shows this third configuration of the switch. The switch is usually specified as Two-way and Off switch.

Twinob Switch:

When two single-way (also single-pole double break) switches are set side by side on the same porcelain base, the combination is called a Twinob Switch. With a chandelier or with some other multi-lamp fittings or in a hall where there are many lamps and only some of the lamps are switched on at a time, a twinob switch may be conveniently used.

A look at fig. 105 will clearly show the use of this switch as well as the mode of connection of the lamps. Pulling the left-hand knob of this switch will put the two right-hand lamps on and right-hand knob will put the two left-hand lamps on. When both the knobs are pulled, it will light all the four lamps. Each switch may, however, light more than two lamps at a time.

Lighting as many Lamps as Required at a Time:

Suppose there are six lamps in a room. If it is necessary to have an arrangement so that any number of lamps from one to six may be switched on at a time, the easiest method is to use six switches. But there is no need to use so many switches. Only an ordinary single-pole tumbler switch and a twinob switch can serve the purpose. Fig. 106 shows the connections. Here the tumbler switch is connected in one lamp circuit and five lamps are controlled by the twinob switch—left-hand knob controlling two lamps and the right-hand knob controlling the remaining three lamps.

Now, if only one lamp is to be lighted, only the tumbler switch is put on. When two lamps are to be lighted, the left-hand knob of the twinob switch is pulled on; when three lamps are to be lighted, the right-hand knob of the twinob switch is pulled on.

Similarly, when four lamps are to be lighted, the right-hand knob of the twinob switch and the tumbler switch are put on. When five lamps are to be lighted, both the knobs of the twinob switch are pulled on, and when all the six lamps are to be lighted, both the knobs of twinob switch and the tumbler switch are put on.

In similar manner there may be various other arrangements according to requirements.

All, Part and Off Switch:

(i) Both the blades of the switch are on; all lamps are lighted.

(ii) The upper blade of the switch is on; only two left-hand lamps are lighted.

(iii) The upper blade of the switch is off; no lamp is lighted.

With this switch either all the lamps or only a few of them will be lighted together. The connections of the switch and the lamps are shown in fig. 107.

This switch is also of the tumbler type, but there are three contact terminals in it. One position of the knob connects all the lamps, the second position connects only a few, and the third position does not connect any lamp at all. These are clearly shown in three separate diagrams (i), (ii) & (iii) of fig. 107.

To Light the Bed Room Lamp Dimly at Night:

If a lamp has to be kept dimly glowing all through-out the night, usually a small lamp of very low wattage is connected to a point in addition to the point for normal lighting. But such an arrangement requires at least two light points in the room. If there be only one point it can be arranged for full glow or dim glow according to requirements at any time. This may be achieved in two ways.

One method is to connect in series with the lamp a regulator (similar to a fan regulator) by means of which the glow of the lamp may be regulated as desired. But it costs more on account of the loss of power in the resistance of the regulator coil. The second method is to use a two-way and off switch. One way of the switch puts the lamp in series with a capacitor of suitable capacitance. This keeps the lamp dimly glowing.

Connected to the other way of the switch, the lamp glows with full brightness. When the switch is put off, the lamp does not glow at all. Capacitances suitable for different wattages of 230-volt lamps are given below. It is to be noted that second method of connection can be adopted only in a.c. circuits. The connections of the lamp and the switch along with a capacitor is shown in fig. 108.

Time Switch:

It is a switch which works in conjunction with a clockwork mechanism. Just as the alarm bell in a time piece goes on ringing at a pre-set time, so also an electric circuit can be automatically switched on or off at a pre-set time by means of a time switch.

Time switches are very extensively used for automatic on and off control at pre-determined times of street lights. Fig. 109(a) shows how a time switch of a particular make looks and fig. 109(b) shows the connection diagram.

A time switch is to be connected in series with the circuit which the switch must put on or off at pre-set times. Sometimes, in parallel with the switch terminals, a hand-operated short-circuiting switch is also provided. It may be used when there is no need for time control. However, time control may be restored by manually disconnecting the short-circuiting switch.

Bed Switch:

While discussing about how to control a lamp from two different places, it has been shown how to switch on or off a lamp from bed by means of 2-nos. two-way switches. As it can switch on or off a lamp from bed, one may think it to be a bed switch. But a real bed switch is of different type. Various kinds of push switch available in the market in the shape of a small egg or guava or of oblong form are popularly known as ‘bed switch’.

Two long narrow strips of brass are affixed to the two terminals of this switch. In between these two strips a brass disc like a toothed wheel, ground on both sides, is so fixed that on pushing a small lever of Bakelite or plastic, the disc turns quarter of a revolution. As a result the two narrow brass strips are in electric contact with each other through the disc and the lamp lights up.

Later on, the lever may be pushed up again for further quarter revolution of the disc. This time the two brass strips are out of contract with the disc and the lamp is switched off. A spring inside is compressed at the time of pushing the lever. When the lever is released, it restores its position due to this spring action. Thus, pushing the lever repeatedly leads to alternate on and off positions of the bed switch. The connection of this switch is shown in fig. 110.

The two wires at one end of a twin flexible cable are connected to the two terminals of the bed switch. At the other end the two wires are connected to the two terminals of the wall switch. This is parallel connection and the bed switch works all right with this connection. One precaution is that the wall switch must remain at off position when the bed switch works. Otherwise the lamp will continue to glow in-spite of operating the bed switch.

The disadvantage of this method of connection of a bed switch is that the long flexible cable going up to the wall switch cannot be disconnected when the operation of bed switch is not necessary during day time. The sight of the twin flexible from the wall looks odd during the day.

In case of objection this may be removed by the following method:

The wires of the twin flexible may be connected at the wall end to the shoe of a wall plug instead of to the terminals of the wall switch. The terminals of the wall switch in this case are connected to the two terminals of the socket of the wall plug which is fixed by the side of the wall switch. This type of connection is shown in fig. 111. Now for operating the bed switch, at night or whenever necessary, the shoe of the wall plug is to be pushed into the socket outlet.

There is a precaution here that the socket outlet of the wall plug must be carefully labelled so that it is never confused with any other wall plug. If the shoe of the plug connected with the bed switch is, by mistake, pushed into any other socket outlet, there will be instant short-circuit along with the main fuse being burnt out.