Electrical Drawing, Symbols and Circuit Diagrams
This domain tests reading and drawing electrical diagrams: symbols, wiring diagrams, single-line diagrams and circuit layouts. The exam checks whether you can translate a physical circuit into standard symbols and back again.
Core rules
- A lamp is shown as a circle with a cross. A one-way switch is shown as a break in a line with an operating arm. A fuse is a rectangle or a line with a break; an MCB has a specific rectangular symbol with a switching function.
- A wiring diagram shows physical connections. A schematic or circuit diagram shows electrical relationships, not physical positions.
- In a single-line diagram, one line represents a multi-conductor circuit; labels give conductor count and size.
- The live conductor goes to the switch, then to the lamp, and the lamp returns to neutral. The earth conductor is shown separately and connected to metalwork.
- Diagrams must be labelled with ratings, polarity and terminal identification.
Worked example
To draw a one-way lighting circuit, start at the live supply. Draw a line to the one-way switch symbol, then from the switch to the lamp symbol, then from the lamp to neutral. Add the protective earth line to the metal enclosure. The switch is in the live conductor, so the lamp holder is not live when the switch is off.
Traps
Do not place the switch in the neutral line. Do not omit the earth from a metal enclosure. Do not confuse a wiring diagram with a single-line diagram. Do not draw unlabelled symbols that cannot be identified by a technician.