Workshop hall lighting and power distribution

Given: hall 120 m × 30 m, E = 300 lux, UF = 0.8, MF = 0.8, twin-tube LED fitting 2 × 20 W = 40 W at 100 lm/W. Assumptions: mounting height 3 m above work plane, SHR ≤ 1.5, pf 0.9 for LED, 3-phase 400/230 V supply, all motors and machines 3-phase.

Number of luminaires

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

Area A        = 120 × 30 = 3600 m²
φ per luminaire = 40 W × 100 lm/W = 4000 lm
Total lumens  = E × A / (UF × MF)
              = 300 × 3600 / (0.8 × 0.8)
              = 1687500 lm
N             = 1687500 / 4000 = 421.88

Rounding up and fitting a regular grid: 47 × 9 = 423 luminaires (47 along the 120 m side, 9 along the 30 m side).

Arrangement and spacing

Spacing along length = 120/47 = 2.55 m
Spacing along width  = 30/9 = 3.33 m
End spacing (to wall) = half of these
Max spacing = SHR × Hm = 1.5 × 3 = 4.5 m
2.55 m and 3.33 m ≤ 4.5 m  → OK
Actual E = 423 × 4000 × 0.8 × 0.8 / 3600
         = 300.8 lux (≥ 300 lux required)

Layout diagram

Plan 120 m × 30 m (o = luminaire)
+---------------------------------------------+
| o o o o o o o o o o ... o o o o o o o o o o |
| o o o o o o o o o o ... o o o o o o o o o o |
| o o o o o o o o o o ... o o o o o o o o o o |
| o o o o o o o o o o ... o o o o o o o o o o |
| o o o o o o o o o o ... o o o o o o o o o o |
| o o o o o o o o o o ... o o o o o o o o o o |
| o o o o o o o o o o ... o o o o o o o o o o |
| o o o o o o o o o o ... o o o o o o o o o o |
| o o o o o o o o o o ... o o o o o o o o o o |
+---------------------------------------------+
[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 40 W, so up to 10 luminaires per sub-circuit. Number of circuits is made a multiple of 3 for phase balance.

Largest light circuit: 400 W → I = 400/(230 × 0.9) = 1.93 A → 6 A MCB, 1.5 mm² Cu.

Power load calculation

Pump rating: 7.5 hp × 746 = 5595 W output; input = 5595/0.8 = 6993.75 W; kVA = 6993.75/0.8 = 8.742 kVA.

Assumed utilisation factor ku: 0.75 for machine tools, 0.8 for compressor and pumps, 1.0 for oven and ventilation. CB rating ≥ 1.25 × full-load current, D-curve for motors (high starting current), C-curve for the oven.

PDB demand = ks × Σ(ku × kVA) = 0.8 × 60.24 = 48.19 kVA
Lighting load    = 16920 W / 0.9 pf      = 18.8 kVA
Total max demand = 48.19 + 18.8 = 66.99 kVA
With 25 % future growth: 1.25 × 66.99 = 83.74 kVA

Transformer: standard 100 kVA, 11/0.4 kV, Dyn11 (full-load LV current = 100000/(√3 × 400) = 144.3 A).

Breakers and DBs

PDB current = 48.19 kVA/(√3×400 V) = 69.56 A
            → 1.25I = 86.95 A
            → 100 A TP MCCB for PDB feeder
LDB current = 27.25 A per phase  → 1.25I = 34.06 A
            → 40 A TPN MCB + 40 A 4P RCCB (100 mA)
Main LT breaker (transformer secondary 144.3 A)
            → 160 A TPN MCCB

• Power DB (PDB): 12-way TP DB with 100 A TP MCCB incomer and outgoing TP MCBs as in the table (3 × lathe, 2 × drill, 2 × ventilation, compressor, oven, 2 × pump = 11 ways + 1 spare).
• Lighting DB (LDB): TPN DB, 16 ways per phase, 45 light circuits of 9–10 luminaires (6 A SP MCB each), 15 per phase, with 40 A TPN MCB + RCCB incomer.

Single line diagram

 11 kV supply
     |
  [HT fuse/VCB]
     |
  (( 100 kVA, 11/0.4 kV ))
     |
  [160 A TPN MCCB]  Main LT panel
     |
 ====+==========+====  LT busbar
     |          |
 [100 A MCCB] [40 A TPN MCB+RCCB]
     |          |
    PDB        LDB
  |  |  |      | | | ...
 L1 L2 L3 ...  L1..L45 light
 (lathes,      circuits
 drills, fans, (6 A each)
 comp, oven,
 pumps)

Layout of power and light sub-circuits

+-------------------- 120 m --------------------+
| o o o o o o o o ... 47 luminaires per row     |
| (9 rows; 45 circuits of 9–10 lamps, R-Y-B)    |
|                                               |
| [Lathe][Lathe][Lathe]  [Drill][Drill]  [Oven] |  30 m
|                                               |
| [Fan]        [Compressor]   [Pump][Pump] [Fan]|
+--[LDB]-[PDB]--- entrance ---------------------+
 Power circuits: radial TP cables PDB → each machine