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Chapter 5

CIRCUIT ARRANGEMENT (Note: All the mentioned tables in this course refer to, unless otherwise specified, Low Voltage Electrical Installation Handbook, by Johnny C.F. Wong, Edition 2004). Chapter 5. Introduction. Every installation shall be divided into circuits to

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Chapter 5

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  1. CIRCUIT ARRANGEMENT(Note: All the mentioned tables in this course refer to, unless otherwise specified, Low Voltage Electrical Installation Handbook, by Johnny C.F. Wong, Edition 2004) Chapter 5

  2. Introduction • Every installation shall be divided into circuits to • avoid danger in case of fault • facilitate safe operation, inspection, testing and maintenance • Examples • at least 2 lighting circuits should be provided • separate final circuits shall be provided for lighting and power • exclusive final circuits for fixed appliances in kitchen • 1Ф loads should be evenly and reasonably distributed among the phases

  3. Circuit Segregation • Categories of Circuits • Category 1: A low voltage circuit (exclude cat. 3 cct) • Category 2: An extra-low voltage circuit (exclude cat. 3 cct) • Category 3: A circuit for emergency or fire services (exclude that for self-contained battery luminaires) • Category 4: A high voltage circuit • Circuit Segregation • Circuits having different insulation voltages and for different purposes shall be segregated from one another to prevent danger and electrical interference.

  4. Control & Protection of Circuits • Every circuit shall be provided with: • means of interrupting the supply on load • means of isolation for electrical servicing and testing without affecting other circuits • means of interrupting the supply in any fault conditions

  5. Control & Protection of Circuits

  6. Final Circuit • Final circuits are generally divided in the following • Conventional socket outlet final circuits • Conventional cooker final circuits in household premises • Lighting and small appliance final circuits • Large power final circuits

  7. Socket Outlet Final Circuits

  8. Socket Outlet Final Circuits

  9. Final Circuit feeding Socket Outlets to BS546 • Refer to Fig. 5.4, 5.5 & 5.6

  10. Final Circuits feeding Socket Outlets to BS1363 • Refer to Fig. 5.7, 5.8, 5.9 & 5.10

  11. BS1363 Ring Circuit

  12. BS1363 Radial Circuit

  13. Final Circuits feeding Socket Outlets to BS196 • Not popular in Hong Kong

  14. Final Circuit feeding Socket Outlets to BSEN 60309-2/ IEC 60309-2

  15. Final Circuit feeding Socket Outlets to BSEN 60309-2 / IEC 60309-2 • Refer to Fig. 5.16 & 5.17 for details. 16A Socket >= 32A Socket

  16. Cooker Final Circuits in Household Premises • Separate circuits should be used for supply to electrical equipment in kitchen other than luminaires. • Every cooking appliance with more than one boiling or cooking surfaces and with total current rating > 15A should be fed from exclusive radial final circuit and controlled by a double-pole switch within 2m from the appliance.

  17. Cooker Final Circuits in Household Premises

  18. Lighting & Small Appliance Final Circuits • Lighting and small appliance can share the same final circuit • General light switches controlling discharge lighting circuits should have a nominal rating ≥ 2 times the total steady current • Switches specifically intended for a.c. inductive circuits or fluorescent lamp circuits are marked with an ‘X’, e.g. 10AX

  19. Lighting & Small Appliance Final Circuits

  20. Large Power Final Circuits • For a single-phase circuit exceeding 15A, an separate radial final circuit should be used and should be controlled by a double-pole switch in a readily accessible position near the appliance • Each fixed equipment, except for fixed lightings, shall be connected permanently to an exclusive radial final circuit controlled by a switch placed in a readily accessible position

  21. Large Power Final Circuits Large power final circuit

  22. Other Final Circuit Requirements • Transformers • Equipment in bathrooms • Air-conditioners and space-heaters • Electric heaters/boilers for liquids or other substances • Fluorescent and gas discharge lamps

  23. Transformers • When an auto-transformer is connected to a circuit having a neutral conductor, the common terminal of the winding should be connected to the neutral conductor • Where a step-up transformer is used, a linked switch should be provided for disconnecting the transformer from all live conductors (i.e. phase and neutral conductors) of the supply

  24. Transformers

  25. Equipment in Bathrooms • This part will be covered in the topic ‘ Protection against Electric Shock’

  26. Air-conditioners and Space-heaters • Each air-conditioner or space heater of any rating shall be fed by a separate radial final circuit • If the circuit exceeds 15A, 1-phase, then double pole switch is required

  27. Air-conditioners and Space-heaters

  28. Electric heaters/boilers for liquids or other substances • All metal parts (other than current-carrying parts) which are in contact with water shall be solidly connected to a metal supply water-pipe which in turn is connected to the main earthing terminal by separate cpc • Double pole switch must be used

  29. Fluorescent and gas discharge lamps • Without exact information, the demand in VA is taken as the rated lamp watts multiplied by 1.8

  30. Minimum fire resisting cable requirements for fire services installation • Should follow and comply requirements laid down in FSD’s CoP and Circular Letters • For selection of appropriate types of cable, refer to Circular Letter No. 1/2003

  31. Neutral Conductor • The wiring of each final circuit shall be electrically separate from that of every other final circuit, to prevent indirect energisation of the final circuit to be isolated • The neutral conductor of a 1-phase circuit shall not be shared with any other circuit • For a 3-phase 4-wire circuit, the neutral conductor shall only be shared with its related phases

  32. Neutral ConductorAn Lighting Track Example

  33. Cables in Parallel • Need for connecting cables in parallel • Less cost • Smaller bending radius • Even the largest cable has limited CCC • Cables in parallel should be • of same construction • have the same material & cross-sectional area • of approximately the same length • have no branch circuits throughout their length

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