Choosing the correct service wire size is essential for safety, efficiency, and compliance with Indian and international standards. Below are reference charts for aluminium and copper wires as per Indian standards (IS 732) and BS 7671. Always consult a qualified electrician and follow local codes for final selection.
IS 732 is the Indian Standard for Code of Practice for Electrical Wiring Installations. It specifies the requirements for safe installation, selection of wire size, earthing, and protection against overcurrent and short circuits in residential, commercial, and industrial buildings. Following IS 732 ensures safety, reliability, and compliance with Indian regulations.
BS 7671 (IET Wiring Regulations) is the UK standard for electrical installations. It provides detailed recommendations for cable sizing, including correction factors for grouping, ambient temperature, and installation method. For three-phase systems, BS 7671 recommends using 415V for calculations. The basic formula for current is:
I = P / (√3 × U × pf), where P is power (W), U is voltage (V, 415V for three-phase), and pf is power factor (typically 0.8 for motors).
| Aluminium Size (sqmm) | Max Amps | Typical Use |
|---|---|---|
| 1.5 | 7 | Lighting |
| 2.5 | 12 | Sockets, Small Loads |
| 4 | 18 | Heavy Loads, AC |
| 6 | 24 | Main Supply, Submains |
| 10 | 32 | Main Service, High Loads |
| 16 | 42 | Main Service, High Loads |
| Copper Size (sqmm) | Max Amps | Typical Use |
|---|---|---|
| 1.5 | 14 | Lighting |
| 2.5 | 20 | Sockets, Small Loads |
| 4 | 26 | Heavy Loads, AC |
| 6 | 32 | Main Supply, Submains |
| 10 | 44 | Main Service, High Loads |
| 16 | 57 | Main Service, High Loads |
These values are for reference only. For long cable runs, high ambient temperatures, or installation in conduit/trunking, derating factors must be applied. Always follow IS 732, BS 7671, and local codes for safe and compliant installations.