Process room 40 × 20 m twin 40 W fluorescent

Given: room 40 m × 20 m, twin 40 W fluorescent (80 W) at 60 lm/W, Hm = 3 m, CU = 0.75, depreciation factor 1.2, supply 400 V, 3-phase, 50 Hz. Assumption: the required illumination is not given, so E = 200 lux (general process/industrial work) is taken; 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        = 40 × 20 = 800 m²
φ per luminaire = 80 W × 60 lm/W = 4800 lm
MF            = 1/DF = 1/1.2 = 0.833
Total lumens  = E × A × DF / UF
              = 200 × 800 × 1.2 / 0.75
              = 256000 lm
N             = 256000 / 4800 = 53.33

Rounding up and fitting a regular grid: 9 × 6 = 54 luminaires (9 along the 40 m side, 6 along the 20 m side).

Arrangement and spacing

Spacing along length = 40/9 = 4.44 m
Spacing along width  = 20/6 = 3.33 m
End spacing (to wall) = half of these
Max spacing = SHR × Hm = 1.5 × 3 = 4.5 m
4.44 m and 3.33 m ≤ 4.5 m  → OK
Actual E = 54 × 4800 × 0.75 × 0.833 / 800
         = 202.5 lux (≥ 200 lux required)

Layout diagram

Plan 40 m × 20 m (letter = phase of lamp circuit)
+-------------------+
| R R R R R R R R R |  <- L1
| Y Y Y Y Y Y Y Y Y |  <- L2
| B B B B B B B B B |  <- L3
| R R R R R R R R R |  <- L4
| Y Y Y Y Y Y Y Y Y |  <- L5
| B B B B B B B B B |  <- L6
+-------------------+
[DB]  [SB]  <- entrance: DB and switch board
       S1 S2 S3 S4 S5 S6  (one switch per sub-circuit)

Each row of 9 luminaires forms one sub-circuit, 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 lighting sub-circuit carries at most 10 points and 800 W. One luminaire here is 80 W, so up to 10 luminaires can go on one sub-circuit. The number of circuits is made a multiple of 3 for phase balance.

Distribution board design

Total connected load = 4320 W (lighting)
Most loaded phase    = 1440 W
Iph = 1440 / (230 × 0.9) = 6.96 A
Main MCB ≥ 1.25 × 6.96 = 8.7 A → 10 A TPN MCB

DB specification: 4-way-per-phase TPN DB (12 ways in all, spares included) with a 10 A TPN MCB as incomer, a 25 A 4-pole RCCB (100 mA) for earth-leakage protection, and 6 A SP MCBs (B-curve) for the light circuits. Incoming cable: 4-core 1.5 mm² Cu PVC (rating 21 A ≥ 10 A), plus an 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  L4   L2  L5   L3  L6   (6 A SP MCBs)