--- title: "Electrical installation in a factory" subject: "Industrial Power Distribution and Illumination" chapter: 5 key: "semester_6/industrial_power_distribution_and_illumination:explain-electrical-installation-factory" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/explain-electrical-installation-factory site: BCT Engineering --- # Electrical installation in a factory Industrial Power Distribution and Illumination · Chapter 5: Electrification of Industrial Building - Asked in: 2070 Magh - 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/explain-electrical-installation-factory - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-5 ## Question Explain electrical installation in a factory. ## Short answer Factory installation: 11 kV substation with transformer, MDB with ACB/MCCB/APFC/DG changeover, SDBs per shop, armoured XLPE feeders in trenches/trays, motor starters with protection, high-bay lighting, equipment/neutral earthing with RCCBs, lightning protection, DG/UPS standby; designed per load list, demand factors, cable sizing, SLD, testing per IEC/IS/NEA. ## Answer Electrical installation in a factory is the complete system that takes power from the supply authority and delivers it safely to every machine, lamp and socket, with proper protection, earthing and control. #### Main parts ```text 11 kV → substation (TR) → MDB → SDBs → machines/lights | DG set + ATS, APFC panel ``` 1. **Substation**: 11/0.4 kV transformer with LA, isolator, HT fuse/VCB, placed near the load centre. 2. **Main distribution board (MDB)**: ACB/MCCB incomer, busbars, MCCB feeders, metering, APFC panel and DG changeover. 3. **Sub-distribution boards (SDBs)**: one per shop or bay; MCB/MCCB outgoing to machines, lighting and sockets. 4. **Cabling**: armoured XLPE cables in trenches or on trays for feeders; conduit or trunking for final circuits; bus trunking for machine rows. 5. **Motor circuits**: MCB/MPCB, contactor and overload relay (DOL, star-delta or VFD), isolator near machine. 6. **Lighting**: high-bay LED/HID luminaires designed for 200–500 lux, on separate circuits; emergency lighting. 7. **Earthing and safety**: equipment and neutral earthing, RCCBs, lightning protection, flameproof fittings in hazardous zones. 8. **Standby supply**: DG set and UPS for critical loads and fire pumps. #### Design steps 1. Prepare the plant layout and load list. 2. Estimate maximum demand (Ku, Ks) and size the transformer. 3. Locate substation, MDB and SDBs near load centres. 4. Size cables (current, voltage drop, short circuit) and protective devices. 5. Design lighting, earthing and power factor correction. 6. Prepare SLD, layout drawings, BOQ and cost estimate; test (insulation, earth resistance, polarity) before commissioning. The installation must follow IEC/IS standards and NEA regulations, and keep 20–25 % spare capacity for expansion. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the correct order of power flow in a factory installation? A. Substation -> SDBs -> MDB -> machines B. MDB -> substation -> SDBs -> machines C. 11 kV -> substation (transformer) -> MDB -> SDBs -> machines/lights D. DG set -> SDB -> MDB -> substation Answer: C. The 11/0.4 kV substation feeds the MDB, which feeds the SDBs in each shop, which supply machines and lights. (Key point: Power flow chain) 2. Which of these belongs at the main distribution board (MDB)? A. ACB/MCCB incomer, busbars, metering, APFC panel and DG changeover B. Only final-circuit lamp holders C. Lightning arresters and HT fuses D. Machine-side isolators only Answer: A. The MDB has the incomer, busbars, feeders, metering, power-factor correction and DG changeover. LA and HT fuse are at the substation. (Key point: Role of MDB) 3. What does a typical motor circuit include? A. Only a plug and socket B. MCB/MPCB, contactor and overload relay (DOL, star-delta or VFD), and a local isolator C. A capacitor bank in series with the motor D. Only a fuse with no starter Answer: B. Motor circuits need short-circuit protection, a starter (contactor + overload relay or VFD) and an isolator near the machine for safe maintenance. (Key point: Motor circuit parts) 4. Which design practice is stated for a factory installation? A. Size exactly for present load with no margin B. Keep 20-25 % spare capacity for expansion and estimate maximum demand using Ku and Ks C. Use the largest possible transformer regardless of load D. Put the substation far from the load to reduce noise Answer: B. Maximum demand is estimated with utilisation and simultaneity factors, and 20-25 % spare capacity is left; the substation is placed near the load centre. 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