Industry room 30 × 20 m LED lighting and DB

Given: room 30 m × 20 m, 42 W LED at 110 lm/W, Hm = 3 m, CU = 0.75, depreciation factor 1.2, supply 400 V, 3-phase, 50 Hz. Assumptions: the required illumination is not given, so E = 300 lux is taken (medium industrial work, IS 3646); 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.

Area A        = 30 × 20 = 600 m²
φ per luminaire = 42 W × 110 lm/W = 4620 lm
MF            = 1/DF = 1/1.2 = 0.833
Total lumens  = E × A × DF / UF
              = 300 × 600 × 1.2 / 0.75
              = 288000 lm
N             = 288000 / 4620 = 62.34

Rounding up and fitting a regular grid: 9 × 7 = 63 luminaires (9 along the 30 m side, 7 along the 20 m side).

Arrangement and spacing

Spacing along length = 30/9 = 3.33 m
Spacing along width  = 20/7 = 2.86 m
End spacing (to wall) = half of these
Max spacing = SHR × Hm = 1.5 × 3 = 4.5 m
3.33 m and 2.86 m ≤ 4.5 m  → OK
Actual E = 63 × 4620 × 0.75 × 0.833 / 600
         = 303.2 lux (≥ 300 lux required)

Layout diagram

Plan 30 m × 20 m (letter = phase of lamp circuit)
+-------------------+
| R R R R R R R Y Y |
| B B B B Y Y Y Y Y |
| B B B R R R R R R |
| B Y Y Y Y Y Y Y R |
| B B B B B B R R R |
| Y Y Y Y Y R R R R |
| Y Y 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 42 W, so up to 10 luminaires per sub-circuit. Number of circuits is made a multiple of 3 for phase balance.

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.

Distribution board design

Connected load = 2646 W light + 12000 W power = 14646 W
Most loaded phase    = 4882 W
Iph = 4882 / (230 × 0.9) = 23.58 A
Main MCB ≥ 1.25 × 23.58 = 29.48 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.

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  ...