State any four general rules for Electrical Installation.
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Following General rules for Electrical installation:- 1. Every installation is to be properly protected near the point of entry of supply cables by a two-pole linked main switch and a fuse unit. In a two wire installation if one pole is permanently earthed, no fuse, switch or circuit breaker is to be inserted in this pole. A 3-pole switch and fuse unit is to be used in 3-ph supply. 2. The conductors used are to be such that size of conductor should carry rated current and partial over load current safely. 3. The conductors installed are to be safe in all respects. 4. Every sub-circuit is to be connected to a distribution fuse board. 5. Every line (phase or positive) is to be protected by a fuse of suitable rating as per requirements. 6. A switch board is to be installed so that its bottom lies 1.25 to 1.5 meters above the ground floor. 7. A plugs and socket-outlets are to be of 3-pin type, the appropriate pin of socket being connected permanently to the earthing system. 8. All incandescent lamps, unless otherwise required, are to be hung at a height of 2.5 meters above the floor level. And ceiling fans are to be hung 2.75 meters above the floor. 9. Lights and fans may be wired on a common circuit. Each sub-circuit is not to have more than a total ten points of lights, fans and socket-outlets. The load on each subcircuit is to be restricted to 800 watts. 10. No fuse and switch is to be provided in earthed conductor. 11. Every circuit or apparatus is to be provided with a separate means of isolation such as a switch. 12. All circuit or apparatus requiring attention are to be provided with means of access to it. 13. In any building, light and fan wiring and power wiring are to be kept separate. 14. In 3-Phase, 4-wire installation the load is to be distributed equally on all phases. 15. No additional load is to be connected to an existing installation unless it has been ascertained that the installation can safely carry the additional load and that the earthing arrangements are adequate. 16. Lamp holders used in bath rooms are to be constructed or shrouded in insulating materials and fitted with protective shield and earth continuity conductor is not to be size less than 7/0.915 mm. 17. The metal sheaths or conduits for all wiring and metal coverings of all consuming apparatus or applications is to be properly earthed in order to avoid danger from electrical shock due to leakage or failure of insulation. 18. Each sub-circuit is to be protected against excessive current (that may occur either due to over load or due to failure of insulation) by fuse or automatic circuit breaker. 19. All light conductors are to be insulated or otherwise safe guarded to avoid danger. After completion of work the installations are to be tested (the test are to be carried out as described) before energisation. 20. Earth Resistance :should be very low for domestic installation it should be equal to or less than 5 ohm to 8 ohm

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