--- title: "Factors in power and lighting system design" subject: "Industrial Power Distribution and Illumination" chapter: 5 key: "semester_6/industrial_power_distribution_and_illumination:power-lighting-design-factors" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/power-lighting-design-factors site: BCT Engineering --- # Factors in power and lighting system design Industrial Power Distribution and Illumination · Chapter 5: Electrification of Industrial Building - Asked in: 2069 Bhadra, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/power-lighting-design-factors - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-5 ## Question While designing the power and lighting system for an industry, what factors should be considered? Explain briefly each of them. ## Short answer Key factors include load assessment (demand and diversity), supply voltage selection, safety (earthing, RCCB, short-circuit protection), voltage regulation (≤5% power, ≤3% lighting), environmental conditions (IP rating, wiring type), required illumination levels, energy efficiency (LEDs, capacitor banks), and provision for future expansion (20–25% spare capacity). ## Answer The power and lighting system of an industry must be **safe, reliable, economical and flexible**. The main factors to consider are: 1. **Load assessment:** list of machines, their kW/kVA, power factor, duty cycle and starting current; lighting load from the required lux levels. Demand factor and diversity factor are applied to get the maximum demand, which fixes transformer, cable and switchgear sizes. 2. **Supply system and voltage:** HT or LT supply, number of phases, 400/230 V or 11 kV distribution, and whether an in-plant substation is needed. Large motors may need 11 kV or 3.3 kV supply. 3. **Safety:** correct earthing (equipment and system), protection against shock (RCCB/ELCB), short circuit and overload protection, insulation suited to the environment, and compliance with the Electricity Regulations and IS/IEC codes. 4. **Reliability and continuity:** critical processes need ring or duplicate feeders, standby DG sets, UPS and emergency lighting so that a single fault does not stop production. 5. **Voltage regulation:** cable sizes chosen so that the voltage drop stays within limits (about 5 % for power, 3 % for lighting), because low voltage reduces motor torque and lamp output. 6. **Environment of the area:** dust, moisture, corrosive fumes, high temperature or explosive gases decide the type of wiring (conduit, armoured cable), luminaire (dust-proof, flameproof) and enclosure (IP rating). 7. **Illumination requirements:** required lux for each task (IS 3646), uniformity, glare control, colour rendering, and avoiding stroboscopic effect near rotating machines. 8. **Energy efficiency and power factor:** efficient motors and LED lamps, capacitor banks for pf correction, and good control (switching, sensors) to cut running cost. 9. **Flexibility and future expansion:** spare ways in DBs, spare capacity in cables and transformer (about 20–25 %), and bus-duct systems where machine layout may change. 10. **Economy:** balance of initial cost (cable, switchgear) against running cost (losses, maintenance) over the life of the plant. 11. **Ease of maintenance and operation:** accessible DBs, clear labelling, isolation of each machine, and standard equipment ratings to reduce spares. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does load assessment use to fix transformer, cable and switchgear sizes? A. Only the number of lamps B. Machine ratings with demand and diversity factors to get maximum demand C. The colour of the cable D. Only the length of the cable run Answer: B. Applying demand and diversity factors to the connected load gives the maximum demand, which sizes transformer, cables and switchgear. (Key point: Load assessment) 2. Why must voltage drop be kept within limits (about 5 % power, 3 % lighting)? A. Low voltage reduces motor torque and lamp output B. It makes cables cheaper C. High voltage drop improves power factor D. It only matters for DC supplies Answer: A. Excess voltage drop lowers motor torque and light output, so cable size is chosen to limit it. (Key point: Voltage regulation) 3. How is continuity of supply to critical processes ensured? A. Single radial feeder with no backup B. Ring or duplicate feeders, standby DG sets, UPS and emergency lighting C. By increasing lamp wattage D. By removing protection devices Answer: B. Redundant feeders and standby sources ensure a single fault does not stop production. (Key point: Reliability) 4. In a dusty or explosive area, what does the environment factor decide? A. Only the lamp colour B. Type of wiring, luminaire (dust-proof/flameproof) and IP rating of enclosures C. Only the transformer size D. Nothing; standard fittings are always fine Answer: B. Dust, moisture, corrosive fumes, heat and explosive gases determine wiring type, luminaire type and enclosure IP rating. 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