General electrical rules for installation and wiring

Electrical installations must follow the rules of the regulator and the standards of good practice. In Nepal these come from the Electricity Regulations, 2050, NEA's connection requirements and NBC 207 (Nepal National Building Code, electrical design), which are largely based on the Indian Electricity Rules 1956 and IS 732. The main general rules are:

1. Approved materials: all wires, cables, switches and fittings must meet the relevant standard (NS/IS/IEC) and be rated for the circuit voltage and current.
2. Switches and fuses in the phase conductor: single-pole switches, fuses and MCBs go in the phase (live) wire only, never in the neutral, so that opening the switch makes the equipment dead.
3. Main switch and cut-out: every consumer installation must have a main switch (or MCB/MCCB) and a cut-out near the point of supply, easy to reach and clearly marked.
4. Earthing: the metal body of every appliance, the conduit, metal enclosures and the neutral of the supply transformer must be properly earthed. Earth resistance is kept low (about 1 Ω for large substations, a few ohms for installations). Three-pin sockets must have the earth pin connected.
5. Protection of every circuit: each sub-circuit is protected by a fuse/MCB rated for the cable. Earth-leakage protection (RCCB/ELCB) is used where shock risk is high (wet areas, sockets).
6. Separate circuits: lighting and power circuits are kept separate. A lighting sub-circuit normally has no more than about 10 points or 800 W; a power sub-circuit has no more than 2 power sockets (about 3 kW).
7. Polarity and colour code: phases R-Y-B (red, yellow, blue), neutral black and earth green (or green/yellow) must be used consistently.
8. Clearances: overhead lines and service mains must keep minimum clearances from ground, buildings and other lines as given in the regulations.
9. Mechanical protection: cables are run in conduit, trunking or trays, or are armoured, where they may be damaged.
10. Danger notices: HV equipment and substations must carry danger boards in Nepali and English.
11. Testing before energising: insulation resistance, earth continuity, polarity and earth resistance tests must be done and the results recorded before the supply is connected. Insulation resistance must not be less than the value required by IS 732/regulations (about 1 MΩ for new LV wiring).
12. Licensed persons: design, installation and testing must be done or supervised by a licensed electrician/engineer.
13. Accessibility: distribution boards and switchgear must be accessible, with enough working space in front, and not placed in wet or hazardous locations.