Introduction to Electrical Engineering - Basic vocational knowledge (Institut für Berufliche Entwicklung, 213 p.)
 (introduction...)
 Preface
 1. Importance of Electrical Engineering
 2. Fundamental Quantities of Electrical Engineering
 2.1. Current
 2.2. Voltage
 2.3. Resistance and Conductance
 3. Electric Circuits
 3.1. Basic Circuit
 3.2. Ohm’s Law
 3.3. Branched and Unbranched Circuits
 3.3.1. Branched Circuits
 3.3.2. Unbranched Circuits
 3.3.3. Meshed Circuits
 4. Electrical Energy
 4.1. Energy and Power
 4.2. Efficiency
 4.3. Conversion of Electrical Energy into Heat
 4.4. Conversion of Electrical Energy into Mechanical Energy
 4.5. Conversion of Electrical Energy into Light
 4.5.1. Fundamentals of Illumination Engineering
 4.5.2. Light Sources
 4.5.3. Illuminating Engineering
 4.6. Conversion of Electrical Energy into Chemical Energy and Chemical Energy into Electrical Energy
 5. Magnetic Field
 5.1. Magnetic Phenomena
 5.2. Force Actions in a Magnetic Field
 5.3. Electromagnetic Induction
 5.3.1. The General Law of Induction
 5.3.2. Utilisation of the Phenomena of Induction
 5.3.3. Inductance
 6. Electrical Field
 6.1. Electrical Phenomena in Non-conductors
 6.2. Capacity
 6.2.1. Capacity and Capacitor
 6.2.2. Behaviour of a Capacitor in a Direct Current Circuit
 6.2.3. Types of Capacitors
 7. Alternating Current
 7.1. Importance and Advantages of Alternating Current
 7.2. Characteristics of Alternating Current
 7.3. Resistances in an Alternating Current Circuit
 7.4. Power of Alternating Current
 8. Three-phase Current
 8.1. Generation of Three-phase Current
 8.2. The Rotating Field
 8.3. Interlinking of the Three-phase Current
 8.4. Power of Three-phase Current
 9. Protective Measures in Electrical Installations
 9.1. Danger to Man by Electric Shock
 9.2. Measures for the Protection of Man from Electric Shock
 9.2.1. Protective Insulation
 9.2.2. Extra-low Protective Voltage
 9.2.3. Protective Isolation
 9.2.4. Protective Wire System
 9.2.5. Protective Earthing
 9.2.6. Connection to the Neutral
 9.2.7. Fault-current Protection
 9.3. Checking the Protective Measures

### 3.1. Basic Circuit

If an incandescent lamp for illuminating a working place is to be caused to light, the following pre-conditions are required.

· A voltage source whose voltage is available at the point of connection (socket outlet). The voltage source may be far away from the point of connection (e.g. in a power station). A fuse is interposed in each line as overcurrent protection.

· A 2-core line leading to the incandescent lamp which conducts the voltage via a plug to the lamp. For conveniently switching on and off, a switch is interposed. Fig. 5.1. shows the described arrangement. Fig. 5.2 the schematic representation with symbols which is called wiring diagram.

Fig. 3.1. Simplified representation of the arrangement voltage source/table lighting fitting

1 - Voltage source
2 - Table lighting fitting
3 - Plug socket
4 - Plug
5 - Fuses
6 - Switch

This shows that a closed connection from the voltage source to the incandescent lamp is essential for operation. The charge carriers driven from the source pass through the conductor, transfer their energy to the lamp and return to the source where they receive again drive energy. This is a circulatory process and, therefore, such an arrangement is called circuit.

Fig. 3.2. Wiring diagram for Fig. 3.1

Graphical symbols:

1 - Voltage source
2 - Lighting fitting
3/4 Plugged connections
5 - Fuses
6 - Switch

Since no charge carriers are lost during the passage, the current is a phenomenon closed in itself, a band without start and without end which has the same intensity at any point.

The above described example is the simplest circuit. Therefore it is called basic circuit. For the principle illustrated here it is of no consequence if in the place of the generator a different voltage source (e.g. an accumulator) is used and a heater, washing machine, motor or another consumer operates in the place of the electric bulb. In the circuit diagram, frequently the fuses, the point of connection and the switch are not represented; the consumer is frequently represented simply by the resistance symbol, see Fig. 3.3.

Fig. 3.3. Fundamental circuit

1 - Voltage source