1. UEENEEE003B Solve Problems in Single Path DC Circuits Basic Electrical Circuits

2. A circuit consists of: SUPPLY A topic by itself LOAD CONTROL PROTECTION CONNECTING CABLES 8/9/2011 Revision02 2

3. Load We want many forms of energy to make our lives easier. The load in a circuit converts electrical energy to: heat magnetic chemical This is then used to serve us. Sometimes converted again: a motor converts magnetic to mechanical 8/9/2011 Revision02 3

4. We need to control this conversion. Discuss why using these examples: lights fridge stove the trigger on the MIG starter motor in a car indicators the volume of a radio a coal conveyor lift 8/9/2011 Revision02 4 Control

5. The cables need to be big enough to carry the current. A cable will heat when current flows through it. H = I2Rt A thin cable has a higher resistance, and a smaller surface area reducing the effective cooling. A larger cable has less resistance (less heat) and improved cooling. The insulation is affected at relatively low temperatures. 8/9/2011 Revision02 5 Cables

6. We need to consider protection as: protection of equipment protection of people The protection of equipment is achieved using either: fuses circuit breakers A common protection of people is an RCD. (discussed in safety) 8/9/2011 Revision02 6 Protection

7. Overload causes heating. Short duration overloads are not a problem. Longer duration overloads cause heat build up, and insulation failure. Short Circuits are always a problem, even short duration. The strong magnetic fields around the conductors produce high forces and stress. 8/9/2011 Revision02 7 Over current