Domestic and Industrial Installation and Estimation
What is tested
Planning a domestic or small industrial installation: load assessment, sub-circuit division, protective device selection, material take-off and costing per IS 732 and the IE Rules.
Method
- List every point with its wattage. 2. Apply a diversity factor, since not everything runs at once; 0.5–0.7 is a common domestic figure for lighting. 3. Divide into sub-circuits, typically not more than 800 W or 10 points for lighting and 3000 W for power. 4. Size the cable, then the MCB, then the main switch and meter. 5. Prepare the schedule of materials and the estimate.
Worked example
Eight 60 W lamps, four 80 W fans, a 2 kW geyser and a 1 kW heater. Connected load = 480 + 320 + 2000 + 1000 = 3800 W. With a diversity factor of 0.7 the assumed demand is 2660 W; at 230 V and 0.9 pf, I = 2660/(230 × 0.9) = 12.8 A. A 16 A main MCB with 4 mm² incoming cable is reasonable, with a separate 6 A MCB for the lighting sub-circuit. If the lamps run 4 hours a day for 30 days: 0.48 × 4 × 30 = 57.6 kWh.
Industrial points
Balance three-phase loads across R, Y and B; give each motor a starter and a local isolator; earth cable trays and conduit; and label every circuit at the distribution board.
Traps
Skipping the diversity factor; putting lighting and 16 A power points on the same sub-circuit; and estimating cable length without allowance for bends, slack and the run to the board.