--- title: "Factory hall 15 × 12 m metal halide lighting" subject: "Industrial Power Distribution and Illumination" chapter: 7 key: "semester_6/industrial_power_distribution_and_illumination:factory-hall-metal-halide" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/factory-hall-metal-halide site: BCT Engineering --- # Factory hall 15 × 12 m metal halide lighting Industrial Power Distribution and Illumination · Chapter 7: Illumination Design Principles - Asked in: 2071 Bhadra, 8 marks - Video: [ILLUMINATION ENGINEERING - PART - 11 - LUMEN OR FLUX METHOD OF CALCULATION AND THREE PROBLEMS](https://www.youtube.com/watch?v=mB573i9S39A) — zenmurali Sachithanandam - 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/factory-hall-metal-halide - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-7 ## Question A factory hall size of 15 m × 12 m is to be illuminated by metal halide lamp of 70 W. Inside the hall, an average illumination of 200 lumen/m² is to be provided on the working plane. The walls and ceiling are brightly painted. Calculate the no. of luminaries required to be fitted in the hall. Draw lay-out diagram showing arrangement of luminaries, switches and distribution board. Decide the light sub-circuits and the supply is 400 V, 3-phase 4 wire system. Assume value for utilization and maintenance factor are 0.7 and 0.6 respectively, the lamp efficiency is 90 lum/watt. ## Short answer Required 70 W metal halide luminaires: 15, arranged 5×3. Lumen method: φ=6300 lm; lumens needed = 200×180/(0.7×0.6) = 85714 lm; N=13.61 → 15. Three light circuits (6 A MCB, one per phase) on a 6 A TPN MCB incomer with 25 A RCCB. ## Answer **Given:** hall 15 m × 12 m, 70 W metal halide lamp at 90 lm/W, E = 200 lm/m², UF = 0.7, MF = 0.6, supply 400 V, 3-phase, 4-wire. **Assumptions:** high-bay mounting with Hm = 4 m, SHR ≤ 1.5; pf 0.85 with compensated ballast; ballast loss neglected. #### Number of luminaires Lumen method: N = (E × A) / (φ × UF × MF), where φ is the output of one luminaire. ```text Area A = 15 × 12 = 180 m² φ per luminaire = 70 W × 90 lm/W = 6300 lm Total lumens = E × A / (UF × MF) = 200 × 180 / (0.7 × 0.6) = 85714 lm N = 85714 / 6300 = 13.61 ``` Rounding up and fitting a regular grid: **5 × 3 = 15 luminaires** (5 along the 15 m side, 3 along the 12 m side). #### Arrangement and spacing ```text Spacing along length = 15/5 = 3 m Spacing along width = 12/3 = 4 m End spacing (to wall) = half of these Max spacing = SHR × Hm = 1.5 × 4 = 6 m 3 m and 4 m ≤ 6 m → OK Actual E = 15 × 6300 × 0.7 × 0.6 / 180 = 220.5 lux (≥ 200 lux required) ``` #### Layout diagram ```text Plan 15 m × 12 m (letter = phase of lamp circuit) +-----------+ | R R R R R | | Y Y Y Y Y | | B B B B B | +-----------+ [DB] [SB] <- entrance: DB and switch board S S S S ... one switch per sub-circuit ``` Each light sub-circuit is controlled by one 6 A one-way switch; all switches are grouped on a switch board (SB) next to the entrance, and the DB is mounted beside it. #### Sub-circuits Rule (IS 732 / NEA practice): a light sub-circuit carries at most 10 points and 800 W. Here one luminaire is 70 W, so up to 10 luminaires per sub-circuit. Number of circuits is made a multiple of 3 for phase balance. | Circuit | Luminaires | Load (W) | Current (A) | Phase | MCB | |---|---|---|---|---|---| | L1 | 5 | 350 | 1.79 | R | 6 A | | L2 | 5 | 350 | 1.79 | Y | 6 A | | L3 | 5 | 350 | 1.79 | B | 6 A | #### Distribution board design | Phase | Circuits | Load (W) | Current (A) | |---|---|---|---| | R | L1 | 350 | 1.79 | | Y | L2 | 350 | 1.79 | | B | L3 | 350 | 1.79 | ```text Total connected load = 1050 W (lighting) Most loaded phase = 350 W Iph = 350 / (230 × 0.85) = 1.79 A Main MCB ≥ 1.25 × 1.79 = 2.24 A → 6 A TPN MCB ``` **DB specification:** 4-way-per-phase TPN DB (12 ways in all, spares included) with 6 A TPN MCB as incomer, 25 A 4-pole RCCB (100 mA) for earth-leakage protection, 6 A SP MCBs (B-curve) for light circuits. Incoming cable: 4-core 1.5 mm² Cu PVC (rating 21 A ≥ 6 A), plus earth continuity conductor. ```text 3-phase, 400/230 V, 4-wire supply | [Energy meter] | [6 A TPN MCB] | [25 A 4P RCCB] | ==R====Y====B====N== busbars | | | | | L1 L2 L3 ... ``` Metal halide lamps take 3–5 minutes to reach full output and 10–15 minutes to restrike, so a few LED lamps on a separate circuit are advisable for emergency/escape lighting. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. With Hm = 4 m and SHR 1.5, spacings are 3 m and 4 m. Is this acceptable? A. No, spacing must be below 3 m B. Yes, both are within 1.5 x 4 = 6 m C. No, spacing must equal Hm D. Yes, but only because walls are painted Answer: B. Spacing must not exceed SHR x Hm = 6 m, which both satisfy. (Key point: Spacing check) 2. What operational limitation of metal halide lamps does the answer mention? A. They take 3-5 min to reach full output and 10-15 min to restrike, so a few LED lamps are advised for emergency lighting B. They work only on DC C. They cannot be used above 3 m D. They turn on instantly but fade Answer: A. A long warm-up and restrike time means a quick-starting emergency lighting circuit is advisable after a power interruption. (Key point: Metal halide restrike) 3. Lighting totals 1050 W in 3 circuits of 5 luminaires, one per phase. How is the incomer found? A. Iph = 350/(230 x 0.85) = 1.79 A; 1.25 x 1.79 = 2.24 A, so a 6 A TPN MCB B. 1050/230 = 4.6 A, so 63 A C. Iph = 350 x 0.85 = 297 A D. Incomer equals 25 A RCCB rating Answer: A. Phase current is found at pf 0.85, multiplied by 1.25, and the next standard MCB (6 A) is picked. (Key point: Sub-circuits and incomer) ## Close variants set in other exams - [Hall 16 × 12 m LED lighting](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Ahall-16x12-led) — Industrial Power Distribution and Illumination, chapter 7, asked 4× - [Factory hall 55.75 m × 40.25 m LED lighting](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Afactory-hall-led-55x40) — Industrial Power Distribution and Illumination, chapter 7, asked 4× - [Production room 27 × 45 m twin 36 W tubes](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aproduction-room-27x45) — Industrial Power Distribution and Illumination, chapter 7, asked 4× ## Related in Industrial Power Distribution and Illumination - [Industrial shop 30 × 25 m LED lighting](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aindustrial-shop-30x25-led) — Industrial Power Distribution and Illumination, chapter 7 - [Conference hall 2×36 W CFL lighting](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aconference-hall-cfl) — Industrial Power Distribution and Illumination, chapter 7 - [Drawing hall 40 × 20 × 6 m lighting design](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Adrawing-hall-40x20-led) — Industrial Power Distribution and Illumination, chapter 7, asked 2× - [Lamp suspension height and illumination at offset](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Alamp-height-250cp) — Industrial Power Distribution and Illumination, chapter 7 - [Process room 30 × 15 × 5 m fluorescent lighting](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aprocess-room-30x15-fluorescent) — Industrial Power Distribution and Illumination, chapter 7 - [Workshop hall lighting and power distribution](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aworkshop-hall-lighting-power) — Industrial Power Distribution and Illumination, chapter 7