Electrical Drawing and Estimation
Electrical Drawing and Estimation tests reading symbols, preparing layouts and schedules, and taking off quantities for a priced estimate.
Core rules
- A single-line diagram shows the electrical relationship; a layout shows physical positions; a wiring diagram shows actual terminal connections.
- Standard symbols should follow IS conventions: lamp, switch, socket, ceiling fan, distribution board, MCB and earth.
- Estimate from the drawing: count points, measure conduit runs, calculate wire length = run × number of cores, then add wastage and fixing allowance.
- Use the schedule of rates for labour and material; separate controllable from non-controllable items.
- Circuit loading and diversity must be checked before finalising the distribution board schedule.
Worked example
A room has 8 light points, each with an average run of 10 m from the switch/DB. Each point uses 1.5 mm² phase, neutral and earth, so 3 cores. Total conductor = 8 × 10 × 3 = 240 m. Add 10% for wastage and looping = 264 m. If the SOR price is ₹18/m for 1.5 mm² copper, material cost = 264 × 18 = ₹4,752. Add conduit, boxes, switches and labour separately; do not bury them in the cable rate.
Traps
Do not count only the phase wire; do not forget the earth core; do not use the plan area as the conduit length; and do not omit wastage, switch drops or the service connection.