--- title: "Locating substation and floor distribution board" subject: "Industrial Power Distribution and Illumination" chapter: 4 key: "semester_6/industrial_power_distribution_and_illumination:locate-substation-floor-db" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/locate-substation-floor-db site: BCT Engineering --- # Locating substation and floor distribution board Industrial Power Distribution and Illumination · Chapter 4: Distribution Substation of Industrial Plant - Asked in: 2075 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/locate-substation-floor-db - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-4 ## Question How can you locate the distribution substation within the premises of an industry? What factors should be considered when deciding the location of floor distribution board in a building? ## Short answer Locate the substation as close as possible to the calculated electrical load centre (x̄,ȳ) after adjusting for site constraints. For floor DBs, place them near the floor 's load centre and the rising main, in dry accessible areas with front clearance, away from water and heat, with separate DBs for lighting, power and emergency circuits. ## Answer #### Locating the distribution substation within the industry premises The substation should be as close as practical to the **electrical load centre**, subject to safety and site limits. 1. **Find the load centre**: draw the plant layout on x-y axes, mark each load (or SDB) with its demand Pᵢ at (xᵢ, yᵢ) and compute ```text x̄ = Σ Pᵢ·xᵢ / Σ Pᵢ ȳ = Σ Pᵢ·yᵢ / Σ Pᵢ ``` The point (x̄, ȳ) gives the least product of load × distance, so LT cable cost, voltage drop and I²R loss are minimum. 2. **Adjust for practical constraints**: if the load centre falls inside a production hall or on a road, shift the substation to the nearest suitable free place, preferably towards the heaviest loads. 3. **Check the HT supply route**: the 11 kV line or cable should reach the site easily. 4. **Access and space**: crane/truck access for transformer replacement, space for fencing, clearances and future transformers. 5. **Safety and environment**: away from fire-prone stores, explosive or corrosive areas, flooding and vibration; good ventilation (or indoor/package type in dusty plants). 6. **Large plants**: if loads are spread over a large area, use more than one substation (unit substations), each near its own load group, connected by an HT ring. #### Location of floor distribution board in a building 1. **Load centre of the floor**: so that final circuits are short and voltage drop is within limits. 2. **Near the rising main / shaft**: the DB should be close to the vertical rising main or electrical shaft so the tap-off is short. 3. **Accessibility**: easily reachable by authorised staff, in a corridor or electrical room, not inside private rooms or store rooms; at a convenient height (about 1.5–1.8 m to top). 4. **Safety**: away from water lines, toilets, kitchens, heat sources and fire escape routes; dry, ventilated place. 5. **Space**: enough wall space and front clearance (about 1 m) for operation and maintenance, and spare ways for future circuits. 6. **Separation**: separate DBs for lighting, power and emergency circuits where required; emergency DB in a fire-protected location. 7. **Aesthetics**: recessed or in a cupboard in offices and residences. 8. **Cable routing**: easy entry for cables and conduits from the riser and to the final circuits. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does the point (x, y) from the weighted-average calculation give? A. The point of maximum voltage B. Least product of load x distance, so minimum LT cost, voltage drop and loss C. The geometric middle of the plant D. The location of the largest single load always Answer: B. It is the centre of gravity of the loads. (Key point: Finding load centre) 2. If the load centre falls inside a production hall, what is done? A. Build the substation inside the hall B. Ignore load centre and place at the gate C. Remove the heaviest load D. Shift the substation to the nearest suitable free place, towards heavier loads Answer: D. Practical constraints may displace the site slightly. (Key point: Practical adjustment) 3. For loads spread over a large area, what is recommended? A. One large substation at the plant entrance B. Several unit substations each near a load group, linked by an HT ring C. One substation at the farthest load D. Use only LT distribution from one site Answer: B. Multiple substations reduce LT lengths. (Key point: Large plants) 4. Where should a floor distribution board be placed? A. Inside a toilet or kitchen B. Inside a private store room C. On the fire escape route D. Near the floor load centre and the rising main, in an accessible dry area Answer: D. It should keep final circuits short, with clearance of about 1 m, away from water and heat. 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