Estimation and Energy Conservation
Estimation and Energy Conservation tests electrical installation estimating, load and cable sizing, cost calculation, energy audits, and conservation measures.
Core rules
- Estimate quantities from wiring layout: points, circuits, conduit, cable, switches, distribution board. Add wastage and labor as specified.
- Load estimate uses connected load, demand factor, and diversity factor. Maximum demand is less than connected load when diversity applies.
- Cable size is chosen for current-carrying capacity, voltage drop, and short-circuit withstand. Voltage drop for DC two-wire: Vd=2ILR/1000 if R is Ω/km.
- Energy = power × time; tariff may include energy charge, demand charge, and power-factor penalty. Power-factor correction reduces current and losses.
- Energy audit: measure, benchmark, identify waste, and compute payback = investment/annual saving.
Worked example
A 10 kW load runs 8 h/day for 30 days. Energy=10×8×30=2400 kWh. At ₹7/kWh, energy charge=₹16,800. If a 2 kW improvement cuts 400 kWh/month, saving=400×7=₹2,800/month; a ₹28,000 investment pays back in 10 months.
Traps
Do not confuse kW (demand) with kWh (energy). Diversity factor is not a safety margin. Do not size cable by load current alone; check voltage drop and fault level. Power-factor penalty is not an energy charge.