Electrical installation in a factory

Electrical installation in a factory is the complete system that takes power from the supply authority and delivers it safely to every machine, lamp and socket, with proper protection, earthing and control.

Main parts

11 kV → substation (TR) → MDB → SDBs → machines/lights
                           |
                 DG set + ATS, APFC panel

1. Substation: 11/0.4 kV transformer with LA, isolator, HT fuse/VCB, placed near the load centre.
2. Main distribution board (MDB): ACB/MCCB incomer, busbars, MCCB feeders, metering, APFC panel and DG changeover.
3. Sub-distribution boards (SDBs): one per shop or bay; MCB/MCCB outgoing to machines, lighting and sockets.
4. Cabling: armoured XLPE cables in trenches or on trays for feeders; conduit or trunking for final circuits; bus trunking for machine rows.
5. Motor circuits: MCB/MPCB, contactor and overload relay (DOL, star-delta or VFD), isolator near machine.
6. Lighting: high-bay LED/HID luminaires designed for 200–500 lux, on separate circuits; emergency lighting.
7. Earthing and safety: equipment and neutral earthing, RCCBs, lightning protection, flameproof fittings in hazardous zones.
8. Standby supply: DG set and UPS for critical loads and fire pumps.

Design steps

1. Prepare the plant layout and load list.
2. Estimate maximum demand (Ku, Ks) and size the transformer.
3. Locate substation, MDB and SDBs near load centres.
4. Size cables (current, voltage drop, short circuit) and protective devices.
5. Design lighting, earthing and power factor correction.
6. Prepare SLD, layout drawings, BOQ and cost estimate; test (insulation, earth resistance, polarity) before commissioning.

The installation must follow IEC/IS standards and NEA regulations, and keep 20–25 % spare capacity for expansion.