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# E003B basic circuits

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### E003B basic circuits

1. 1. UEENEEE003B<br />Solve Problems in Single Path DC Circuits<br />Basic Electrical Circuits<br />
2. 2. A circuit consists of:<br />SUPPLY<br />A topic by itself<br />LOAD<br />CONTROL<br />PROTECTION<br />CONNECTING CABLES<br />8/9/2011<br />Revision02<br />2<br />
3. 3. Load<br />We want many forms of energy to make our lives easier. <br />The load in a circuit converts electrical energy to:<br />heat<br />magnetic<br />chemical<br />This is then used to serve us.<br />Sometimes converted again:<br />a motor converts magnetic to mechanical <br />8/9/2011<br />Revision02<br />3<br />
4. 4. We need to control this conversion.<br />Discuss why using these examples:<br />lights<br />fridge<br />stove<br />the trigger on the MIG<br />starter motor in a car<br />indicators<br />the volume of a radio<br />a coal conveyor<br />lift<br />8/9/2011<br />Revision02<br />4<br />Control<br />
5. 5. The cables need to be big enough to carry the current.<br />A cable will heat when current flows through it. <br />H = I2Rt<br />A thin cable has a higher resistance, and a smaller surface area reducing the effective cooling. <br />A larger cable has less resistance (less heat) and improved cooling.<br />The insulation is affected at relatively low temperatures. <br />8/9/2011<br />Revision02<br />5<br />Cables<br />
6. 6. We need to consider protection as:<br />protection of equipment<br />protection of people<br />The protection of equipment is achieved using either:<br />fuses<br />circuit breakers<br />A common protection of people is an RCD. (discussed in safety)<br />8/9/2011<br />Revision02<br />6<br />Protection<br />
7. 7. Overload causes heating.<br />Short duration overloads are not a problem. <br />Longer duration overloads cause heat build up, and insulation failure.<br />Short Circuits are always a problem, even short duration. <br />The strong magnetic fields around the conductors produce high forces and stress.<br />8/9/2011<br />Revision02<br />7<br />Over current<br />