Production room 27 × 45 m twin 36 W tubes

Given: room 45 m × 27 m, twin 36 W fluorescent (72 W per luminaire) at 70 lm/W, E = 150 lm/m², 3-phase 4-wire supply. Assumptions: brightly painted walls and ceiling → UF = 0.7; MF = 0.8; Hm = 3 m, SHR ≤ 1.5; electronic ballasts, pf 0.9.

Number of luminaires

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

Area A        = 45 × 27 = 1215 m²
φ per luminaire = 72 W × 70 lm/W = 5040 lm
Total lumens  = E × A / (UF × MF)
              = 150 × 1215 / (0.7 × 0.8)
              = 325446 lm
N             = 325446 / 5040 = 64.57

Rounding up and fitting a regular grid: 11 × 6 = 66 luminaires (11 along the 45 m side, 6 along the 27 m side).

Arrangement and spacing

Spacing along length = 45/11 = 4.09 m
Spacing along width  = 27/6 = 4.5 m
End spacing (to wall) = half of these
Max spacing = SHR × Hm = 1.5 × 3 = 4.5 m
4.09 m and 4.5 m ≤ 4.5 m  → OK
Actual E = 66 × 5040 × 0.7 × 0.8 / 1215
         = 153.3 lux (≥ 150 lux required)

Layout diagram

Plan 45 m × 27 m (letter = phase of lamp circuit)
+-----------------------+
| R R R R R R R R Y Y Y |
| B B B B B B Y Y Y Y Y |
| B B R R R R R R R Y Y |
| B B B B B B Y Y Y Y Y |
| B R R R R R R R Y Y Y |
| B B B B B B B Y Y Y Y |
+-----------------------+
[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 72 W, so up to 10 luminaires per sub-circuit. Number of circuits is made a multiple of 3 for phase balance.

Distribution board design

Total connected load = 4752 W (lighting)
Most loaded phase    = 1584 W
Iph = 1584 / (230 × 0.9) = 7.65 A
Main MCB ≥ 1.25 × 7.65 = 9.57 A → 10 A TPN MCB

DB specification: 4-way-per-phase TPN DB (12 ways in all, spares included) with 10 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 ≥ 10 A), plus earth continuity conductor.

3-phase, 400/230 V, 4-wire supply
        |
   [Energy meter]
        |
   [10 A TPN MCB]
        |
   [25 A 4P RCCB]
        |
==R====Y====B====N== busbars
  |    |    |    |    |
  L1   L2   L3   L4   L5  ...