240 MLD Sewage Treatment Plant, Vasana

A 240 million-litre-a-day sewage treatment plant at Vasana in Ahmedabad, built for Ahmedabad Municipal Corporation. Power arrives at 11 kV to an HT room and a metering kiosk and is stepped down by three 3,150 kVA transformers, two working and one standby, to a power control centre feeding the motor control centres and variable-speed drives of the fine screens, pump houses, air blowers, the centrifuge building, the chlorination room and the dosing tanks, with DG sets, a PLC room and an administration building. The process and the panels are by others; our scope is the plant's cabling, earthing, lightning protection and lighting.

We issued the power and control cable schedules with their voltage drop calculations, the power, control and instrument cable and tray route layouts, the lighting layout with its lux level calculation and the lighting single-line diagram and distribution boards on 26 November 2025. Earthing: at a measured soil resistivity of 53.08 ohm-m and a 36 kA fault for one second, the earth strip works out at 450 sq mm, 495 sq mm with a 10% corrosion allowance over ten years, so a 50 x 10 mm GI strip is used, 2,080 m of it; each 3 m pipe electrode gives 7.6 ohm, 59 of them in parallel 0.129 ohm, and with the strip the whole grid comes to 0.035 ohm, well under the 1 ohm limit. The layout, revised to R3 in April 2026, gives every pit its job - the HT room, the metering kiosk, each transformer, the DG sets, the power control centre, each MCC and VFD panel, the air blowers, the fine screen panels, the pump houses, the centrifuge building, the chlorination room, the dosing tank, the PLC room and the administration building - with chemical copper and GI earthing pits, test links and two lightning arresters with copper spikes on 25 x 6 mm down conductors.