Electrical Drawing
Scope
The exam checks your ability to read and prepare schematic diagrams, wiring diagrams, single-line diagrams, layout drawings and cable schedules using IS 2032 symbols.
Core rules
- A schematic shows electrical function; a wiring diagram shows physical connections and terminal numbers. The two are not interchangeable.
- A single-line diagram uses one line for a three-phase circuit and shows protection, switching and ratings; it is used for panel and distribution schedules.
- Standard symbols to IS 2032: lamp, switch, socket, fuse, MCB, earth, motor, transformer, contactor coil, NO and NC contacts.
- A drawing needs a title block, scale, north point where relevant, legend and revision number. Layout drawings should show conduit routes, box positions and clearance from water lines.
- Ladder diagrams are read left to right with the supply rails vertical; each rung is one control function.
Worked example
Draw the stair-light circuit with two two-way switches. Feed the phase to the common terminal of switch A. Run two strapper wires from the L1 and L2 terminals of A to L1 and L2 of switch B. Take the common of B to the lamp, and the lamp to neutral. Either switch then toggles the lamp because the strappers are cross-connected. If the phase were taken to the lamp first and the neutral switched, the lamp would still work but the holder would remain live when off - a code violation.
Traps that cost marks
Confusing schematic and wiring diagrams, omitting the neutral or earth from a layout, and drawing a switch in the neutral. Terminal numbering must match the actual device; a drawing that cannot be followed on site loses practical marks.