10 Simple Electrical Circuits Discussed

Daily life on the earth is nearly impossible without electricity. From homes to big industries, we all depend on electricity. We know that electric current flows in a closed circuit. An electrical circuit is a closed loop in which continuous electrical current goes from the supply to the load. If you are trying to describe an electrical circuit to your friend or neighbor, it is likely that you have to draw the connection. For example, if you want to explain a lighting circuit, it can take more time to draw the bulb, battery, and wires because different people draw various components of the circuit in different ways and this may take a long time to explain. Therefore, a better way is to learn how to show simple electrical circuits. In this article we give the drawings for some simple electric circuits: AC lighting circuit, battery charging circuit, energy meter, switch circuit, air conditioning circuit, thermocouple circuit, DC lighting circuit, multimeter circuit, current transformer circuit, and single phase motor circuit.

For a lamp we need two wires; one is the neutral wire and the other is the live wire. These two wires are connected from the lamp to the main supply panel. It is advisable to use different colours for live wires and neutral wires. The universal practice is to use the colour red for live wires and a black colour for the neutral wire. For switching ON and OFF the lamp we need a control called a switch - provided in the live wire between the main supply and lamp. If the switch is ON, the electric circuit is closed and the lamp glows, and if the switch is OFF, it will disconnect the power supply to the lamp. For safe operation this wiring is placed in a box called a switch box. The switch wire and live wire are a single wire; it is just cut in between to connect the switch. In case you want to change the lamp, don’t forget to switch OFF the lamp and if possible disconnect the power supply to the circuit.

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Battery charging is done by means of a rectifier. The main function of the rectifier is to convert AC (alternating current) into DC (direct current). The rectifier shown in the diagram is the bridge rectifier, which has four diodes connected in the form of a bridge. Resistance is added in the circuit to limit the flow of current. When the supply is given to the rectifier through a step down transformer, it converts the AC supply into DC supply and this flows to the battery, thereby charging it. Usually this circuit is enclosed in a battery charger unit or inverter and only the terminals emerge out of the charger unit to be connected to the battery for charging.

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Air conditioning is a process that heats, cools, cleans, and circulates air together with the control of its moisture content. The electric aspect of AC comprises the power equipment for motors and starters for the compressor and condenser fans. Associated electric equipment includes solenoid valves, high and low pressure switch, and high and low temperature switch, together with the safety cut-outs for over current, under voltage etc.

The compressor and condenser fans are driven by a simple fixed speed 3 phase AC induction motor, each with its own starter and supplied from a distribution board. Routine electric maintenance and fault finding on the motor and starters involves cleaning, checking of connections, insulation tests, etc.

We operate switches for lights, fans etc. many times a day but we usually don't try to see the connection made inside the switch. The function of the switch is to connect or complete the circuit going to the load from the supply. It has moving contacts which are normally open.

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As shown in the diagram, the power supply to the load is through the switching circuit, and therefore the power supply can be cut by keeping the switch open.

For a small LED lamp, normally we use a DC supply (battery). This circuit is very simple. The battery has two points, anode and cathode. The anode is positive and cathode is negative. A lamp has two terminals - one is positive and the other is negative. The positive terminal of the lamp is connected to the anode and the negative terminal of the lamp is connected to the cathode of the battery. Once the connection is made the lamp will glow. To enable switching ON or OFF, connect a switch (diagram above) in between any one wire that will cut off or supply DC voltage to the LED bulb.

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More simple electrical circuits and simple electrical devices are discussed on the next page.