70 MLD Sewage Treatment Plant, Vinzol

A 70 million-litre-a-day sewage treatment plant at Vinzol in Ahmedabad, built for Ahmedabad Municipal Corporation. Power comes in at 11 kV through a VCB, a metering unit and an HT panel to two transformers and a power control centre, which feeds three motor control centres, two variable-speed drive panels for six 315 kW air blowers, a power factor correction panel, the lighting boards and the PLC and air-conditioning board, with DG sets standing by. The process and the panels are by others; our scope is the plant's cabling, earthing, lightning protection, lighting and electrical rooms, through to the as-built drawings.

We issued the power and control cable schedules, the cable and tray routes, the earthing and lightning layout with its calculation, the lighting layout with lux levels, the lighting single-line diagram and the earthing and cable tray bills of quantities in November 2025. Power: every feeder from the 11 kV incomer to the last motor was sized for current, derating and voltage drop - the VFD panels on six runs of 3.5-core 300 sq mm aluminium cable, each 315 kW blower on three runs. Control: 6,128 m of shielded, armoured copper control cable from 1 to 20 pairs. Routes: cable trenches of 600 x 900 to 1,200 x 1,200 mm, ladder trays for power and perforated trays for control from 100 x 50 to two 600 x 75 mm, and NP3 hume pipes of 600 and 1,200 mm under the roads. Earthing: at 37.32 ohm-m soil and a 36 kA fault, a 50 x 10 mm GI strip (495 sq mm with ten years of corrosion), 950 m of it, and 44 pipe electrodes bring the grid to 0.045 ohm; in January 2026 the two VFD panels were given their own earthing for a 50 kA fault, with 70 x 10 mm GI strip and two 3 m electrodes each. The earthing layout went to R4 in June 2026 as the PLC panel and the architect's layout were added, and we drew the transformer room (December 2025), the PCC panel room (February 2026) and the HT metering panel room (April 2026), then the as-built set in June 2026: PLC room, earthing, panel room, cable trays, voltage drop, lighting, cable routing and lux levels.