Indian practice: 230 V single-phase and 400 V three-phase, cable in sq mm (1.5, 2.5, 4, 6…), with IS 732:2019 harmonized to IEC 60364. Where the spec is silent, the IEC 4% default applies; CPWD and most project specifications adopt 3% for lighting and 5% for power circuits — all three selectable below.
Domestic circuits follow familiar patterns: 1.5 sq mm for lighting, 2.5 sq mm for 6/16 A socket circuits, 4–6 sq mm for AC and geyser points, with FR/FRLS PVC copper the standard. The drop math is pure IEC — Vd = 2ILρ/A — and the long runs that bite are the usual suspects: borewell pumps, gate and compound lighting, and rooftop solar DC strings, where this site's DC calculator applies directly.
Supply-side context: distribution licensees must hold the declared 230/400 V within statutory tolerance (typically ±6% LV under the Electricity Rules), which is exactly why keeping the installation's own drop inside 3–5% matters — the two stack. For three-phase services, check unbalance too; it is endemic on rural feeders and kills pump motors faster than drop does.
IS 732:2019 follows IEC 60364, whose default is 4% where no other value is specified; most Indian project specs and CPWD general specifications adopt 3% for lighting and 5% for power. Design to the spec governing your project.
Yes — all standard sq mm sizes from 1.5 to 120, at 230 V single-phase, 400 V three-phase, and 12/24/48 V DC for solar work.