Lesson 4· 5 min
Reading a wiring diagram
Symbols, lines, joints and labels: how to trace the path of power in a simple circuit, from the supply to the lamp and back. Switch it ON and OFF to see.
Tap a number, or press Next.
Supply sourceसप्लाई का स्रोत
Where the power comes from, such as the mains or a DG. A wave (~) inside a circle means an AC supply.
Phase (L)फेज़
The wire that carries power from the supply to the load. It is marked L on a diagram.
Fuse / MCBफ्यूज़ / एमसीबी
Breaks the circuit when too much current flows. A fuse wire melts; an MCB trips and can be switched ON again.
Switchस्विच
Makes or breaks the circuit. At ON the path is complete; at OFF it is broken.
Lampलैंप
The circle with an X inside on the diagram. It lights when current flows through it. It is this circuit’s load.
Neutral (N)न्यूट्रल
The wire that brings current back from the load to the supply. It is marked N on a diagram.
Earth (E)अर्थ
The safety wire that connects metal bodies to the ground. Normally no current flows in it; in a fault it carries current to the ground and makes the fuse or MCB trip.
A wiring diagram is a map: it doesn’t show how the real wires are laid, but the path the power takes. Once you understand its language, a diagram is easy to read, whether it’s for a DG panel or a house. Tap each number on the circuit above, and use the Switch button to turn the switch ON and OFF.
Symbols and lines
Every component in a diagram has a fixed symbol: a wave inside a circle is an AC supply, a small long rectangle is a fuse, and an X inside a circle is a lamp. A line means a wire. Where two lines meet at a solid dot, the wires are joined. If lines cross each other without a dot, they are not joined; one simply passes over the other.
Labels: L, N and E
Wires carry labels. L is the phase, which carries power from the supply to the load. N is the neutral, which brings the current back to the supply. E is earth, which connects metal bodies to the ground.
Wire colours vary with place and age: older wiring often uses red for phase, black for neutral and green for earth; newer wiring often uses brown for phase, blue for neutral and green-yellow for earth. So when you read a diagram, go by the L, N and E labels more than by colour.
Tracing a path
The most useful way to read a diagram is to trace a path. Start at the supply and follow the line with your finger:
- Leave the supply on the phase (L).
- First comes the fuse or MCB, which breaks the circuit if too much current flows.
- Then the switch, which makes or breaks the circuit.
- Then the load, here a lamp, where the power does its work.
- Back to the supply through the neutral (N).
If the path breaks anywhere, such as the switch being OFF or the fuse having blown, no current will flow. Press the Switch button on the diagram to see: the moving line stops and the lamp goes out.
Earth: the safety path
The earth wire is normally idle; no current flows in it. If the phase wire ever touches the lamp’s metal body by mistake, current flows through the earth into the ground, and that current is enough to trip the fuse or MCB. That is why earth is a separate path in the diagram, not part of the load.
To practise recognising symbols, play Schematic Sprint. It has these symbols, and many more.