Factory hall 15 × 12 m metal halide lighting

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.

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

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

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.

Distribution board design

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.

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.