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CGLI 2330 Certificate in Electrotechnical Technology Level 2 Inst Tech: Unit 202 – Principles of Electrotechnology

Unit 12 – The Electric Circuit

The Electric Circuit Unit Aims By the end of the unit participants should be able to: 

State the component parts of an electrical circuit as a) source of supply a.c. or d.c. b) circuit conductor – cable c) circuit protection d) circuit control e) load Syllabus Reference: 2.3.01

The Electric Circuit

Electric Systems Electric systems, regardless of their purpose, comprise of a number of components which have specific purposes. These are as follows:     

source of supply circuit conductor circuit protection circuit control load

Source of Supply As the term suggests, this is where the electricity comes from. This can be either an a.c. or d.c. source. The source of d.c. supplies can include generators and batteries. The source of a.c. can be from local generators but more often than not comes from the main public supply system via the Regional Electricity Company (REC). Circuit Conductors The circuit conductors connect the various electrical system components together conveying the electric current from one point to another. These conductors take many forms but are usually in the form of cables, e.g. copper insulated single and multi-core, mineral insulated, etc. A good conductor is one that offers a very low resistance to electric current flow. Load The load is the equipment that actually uses electrical energy to perform useful work. This equipment can take many, many forms. In the simplest example, it can comprise a resistance that will convert electrical energy into heat that can be used in heaters and incandescent lamps. It can also use the magnetic effect of electric current to produce motion, e.g. electric motor, relay, contactor, solenoid, etc. To list every example of a ‘load’ would require a large amount of paper!!!!

The College at Clacton

Unit 12 Page 1

January 2012


CGLI 2330 Certificate in Electrotechnical Technology Level 2 Inst Tech: Unit 202 – Principles of Electrotechnology

Unit 12 – The Electric Circuit Circuit Control We could connect the source of supply to the load via the circuit conductors and the load would produce the required effects. However, we would have no control over it, that is, it would be permanently on. Therefore, all circuits must have some form of control to allow us to turn the load ‘on’ or ‘off’. In its simplest form, this circuit control is a simple switch that makes or breaks the circuit thus controlling. However, this control can be extremely complicated and take the form of numerous relays and contactors as well as electronic control using computers etc. Circuit Protection So far we have looked at the vital components of a circuit namely a source of supply, circuit conductors, circuit control and a load. As it stands, this is all we need to have a functional electrical system that we can control. This is satisfactory providing that nothing goes wrong with the system. However, many things can go wrong including:   

Overcurrent due to short-circuit Overcurrent due to overloading of the circuit Leakage of electric current to parts outside the circuit.

These can have a number of very detrimental effects including harm to persons and livestock, damage to property and even to the system itself. To prevent this harm from occurring all electrical systems must be provided with circuit protection that will disconnect the source of supply in the event of something going wrong. This protection includes:      

Fuses Circuit breakers Cut-outs Overloads Trips Residual current devices (RCDs)

A typical electrical system is shown below:

The College at Clacton

Unit 12 Page 2

January 2012


IT1 U12 - Electric Circuit - Complete