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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

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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

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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.

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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

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Control & Protection of Circuits

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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

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Socket Outlet Final Circuits

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Socket Outlet Final Circuits

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Final Circuit feeding Socket Outlets to BS546

Refer to Fig. 5.4, 5.5 & 5.6

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Final Circuits feeding Socket Outlets to BS1363

Refer to Fig. 5.7, 5.8, 5.9 & 5.10

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BS1363 Ring Circuit

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BS1363 Radial Circuit

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Final Circuits feeding Socket Outlets to BS196

Not popular in Hong Kong

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

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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

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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.

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Cooker Final Circuits in Household Premises

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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

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Lighting & Small Appliance Final Circuits

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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

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Large Power Final Circuits

Large power final circuit

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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

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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

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Transformers

L

N

L

N

Auto -T ransfo rmer

Pr i mary

Secondary

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Equipment in Bathrooms

This part will be covered in the topic ‘ Protection against Electric Shock’

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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

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Air-conditioners and Space-heaters

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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

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Fluorescent and gas discharge lamps

Without exact information, the demand in VA is taken as the rated lamp watts multiplied by 1.8

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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

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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

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Neutral ConductorAn Lighting Track Example

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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