---
title: "Industrial shop 30 × 25 m LED lighting"
subject: "Industrial Power Distribution and Illumination"
chapter: 7
key: "semester_6/industrial_power_distribution_and_illumination:industrial-shop-30x25-led"
source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/industrial-shop-30x25-led
site: BCT Engineering
---

# Industrial shop 30 × 25 m LED lighting

Industrial Power Distribution and Illumination · Chapter 7: Illumination Design Principles

- Asked in: 2076 Bhadra, 12 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/industrial-shop-30x25-led
- Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-7

## Question

An Industrial shop of size 30m x 25m is to be illuminated using 40W LED lamps. Inside the hall an average illumination of 150 lumen/m² is to be provided on the working plane. The walls and ceilings are brightly painted. Calculate the number of luminaries required to be fitted in the hall. Draw layout diagram showing arrangement of luminaries, switches, power sockets. Design the distribution board to supply lighting and power load if the supply is 3 phase, 400 V, 50 Hz. Assume suitable value for utilization and maintenance factor and take lamp efficiency as 100 lumen/watt.

## Short answer

Mounting height 3 m. Using UF=0.7, MF=0.8: N = (150 ×750) / (4000 ×0.56) =50.2 →54 luminaires arranged 9 ×6. Distribution board: 32 A TPN MCB incomer, 40 A RCCB, six 6 A SP lighting circuits, six 20 A power circuits.

## Answer

**Given:** shop 30 m × 25 m, E = 150 lm/m², 40 W LED lamp at 100 lm/W, supply 400 V, 3-phase, 50 Hz.
**Assumptions:** walls and ceiling brightly painted → **UF = 0.7**, clean industrial area → **MF = 0.8**; mounting height 3 m above working plane, SHR ≤ 1.5; pf 0.9; 12 power sockets of 16 A (1 kW each).

#### Number of luminaires

Lumen method: N = (E × A) / (φ × UF × MF), where φ is the output of one luminaire.

```text
Area A        = 30 × 25 = 750 m²
φ per luminaire = 40 W × 100 lm/W = 4000 lm
Total lumens  = E × A / (UF × MF)
              = 150 × 750 / (0.7 × 0.8)
              = 200893 lm
N             = 200893 / 4000 = 50.22
```

Rounding up and fitting a regular grid: **9 × 6 = 54 luminaires** (9 along the 30 m side, 6 along the 25 m side).

#### Arrangement and spacing

```text
Spacing along length = 30/9 = 3.33 m
Spacing along width  = 25/6 = 4.17 m
End spacing (to wall) = half of these
Max spacing = SHR × Hm = 1.5 × 3 = 4.5 m
3.33 m and 4.17 m ≤ 4.5 m  → OK
Actual E = 54 × 4000 × 0.7 × 0.8 / 750
         = 161.3 lux (≥ 150 lux required)
```

#### Layout diagram

```text
Plan 30 m × 25 m (letter = phase of lamp circuit)
+-------------------+
| R R R R R R R R R |
| Y Y Y Y Y Y Y Y Y |
| B B B B B B B B B |
| R R R R R R R R R |
| Y Y Y Y Y Y Y Y Y |
| B B B B 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. Power sockets (16 A, 3-pin, with earth) are placed along the walls at about 1 m height, spaced roughly evenly.

#### Sub-circuits

Rule (IS 732 / NEA practice): a light sub-circuit carries at most 10 points and 800 W. Here one luminaire is 40 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 | 9 | 360 | 1.74 | R | 6 A |
| L2 | 9 | 360 | 1.74 | Y | 6 A |
| L3 | 9 | 360 | 1.74 | B | 6 A |
| L4 | 9 | 360 | 1.74 | R | 6 A |
| L5 | 9 | 360 | 1.74 | Y | 6 A |
| L6 | 9 | 360 | 1.74 | B | 6 A |

Power sub-circuits (assumed): 12 sockets of 16 A, each taken as 1 kW, at most 2 sockets per power sub-circuit (IS 732), 2.5 mm² Cu wire, 20 A MCB.

| Circuit | Sockets | Load (W) | Phase | MCB |
|---|---|---|---|---|
| P1 | 2 | 2000 | R | 20 A |
| P2 | 2 | 2000 | Y | 20 A |
| P3 | 2 | 2000 | B | 20 A |
| P4 | 2 | 2000 | R | 20 A |
| P5 | 2 | 2000 | Y | 20 A |
| P6 | 2 | 2000 | B | 20 A |

#### Distribution board design

| Phase | Circuits | Load (W) | Current (A) |
|---|---|---|---|
| R | L1, L4, P1, P4 | 4720 | 22.8 |
| Y | L2, L5, P2, P5 | 4720 | 22.8 |
| B | L3, L6, P3, P6 | 4720 | 22.8 |

```text
Connected load = 2160 W light + 12000 W power = 14160 W
Most loaded phase    = 4720 W
Iph = 4720 / (230 × 0.9) = 22.8 A
Main MCB ≥ 1.25 × 22.8 = 28.5 A → 32 A TPN MCB
```

**DB specification:** 6-way-per-phase TPN DB (18 ways in all, spares included) with 32 A TPN MCB as incomer, 40 A 4-pole RCCB (100 mA) for earth-leakage protection, 6 A SP MCBs (B-curve) for light circuits and 20 A SP MCBs for power circuits. Incoming cable: 4-core 6 mm² Cu PVC (rating 45 A ≥ 32 A), plus earth continuity conductor.

```text
3-phase, 400/230 V, 4-wire supply
        |
   [Energy meter]
        |
   [32 A TPN MCB]
        |
   [40 A 4P RCCB]
        |
==R====Y====B====N== busbars
  |    |    |    |    |
  L1   L2   L3   P1   P2  ...
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why is UF = 0.7 assumed for this shop?
   A. Because walls and ceiling are brightly painted, so they reflect light well
   B. Because the lamps are 40 W
   C. Because the supply is 400 V
   D. Because the shop is 30 m long
   Answer: A. Bright walls and ceiling give good reflection, so a fairly high UF is assumed; MF = 0.8 is for a clean area. (Key point: Choice of factors)

2. Total lumens = 150 x 750 / (0.7 x 0.8). What does it equal?
   A. About 20089 lm
   B. About 200893 lm
   C. About 63000 lm
   D. About 4000 lm
   Answer: B. 112500 / 0.56 = 200893 lm, so N = 200893 / 4000 = 50.22. (Key point: Lumen method result)

3. N = 50.22. Why are 54 luminaires used?
   A. Because 54 is the next number that makes a regular 9 x 6 grid with acceptable spacing
   B. Because lamps are sold in 54s
   C. Because UF changes
   D. To reduce the lux
   Answer: A. The result is rounded up to a regular grid; 9 x 6 = 54 gives spacings 3.33 m and 4.17 m, both below 4.5 m, and actual E of 161.3 lux. (Key point: Rounding to grid)

4. How many luminaires does each of the 6 light circuits carry?
   A. 9 luminaires (360 W)
   B. 54 luminaires
   C. 20 luminaires
   D. 6 luminaires
   Answer: A. 54 luminaires over 6 circuits is 9 each, which is within the 10-point limit, with circuits spread R, Y, B, R, Y, B. (Key point: Sub-circuit loading)

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