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 Circuit Segregation
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 & 5.17 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

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 Conductor An 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