6A Division of Installation into Circuits 6B Basic Requirements of Circuits
(1) Protection (2) Control (3) Identification
(4) Electrical separation for essential circuits (5) Load distribution
(6) Arrangement of neutral conductor 6C Ring Final Circuit Arrangement
6D Final Circuits Using 5A or 15A Socket Outlets to Requirements Prescribed in Appendix 1
6EFinal Circuits Using 13A Socket Outlets to Requirements Prescribed in Appendix 2
(1) General (2) Spurs
(3) Separate circuits
(4) Permanently connected equipment
6F Final Circuits Using 5A, 15A or 30A Industrial Socket Outlets to Requirements Prescribed in Appendix 3
(1) Socket outlets (2) Accepted practice
6G Final Circuits Using 16A Industrial Socket Outlets to Requirements Prescribed in Appendix 4
(1) Socket outlets (2) Accepted practice
6H Final Circuits Using 32A, 63A or 125A Industrial Socket Outlets to Requirements Prescribed in Appendix 4
(1) Socket outlets (2) Accepted practice
Code 6 CIRCUIT ARRANGEMENT
6A Division of Installation into Circuits
(a) An electrical installation should be divided into circuits where necessary or practicable and each circuit should be separately protected and controlled.
(b) A schematic wiring diagram showing the main distribution system should be displayed near the main switch with rating 100A or above.
6B Basic Requirements of Circuits (1) Protection
(a) Each circuit should be protected by an overcurrent protective device with its operating current value closely related to the current demand of the current using equipment connected or intended to be connected to it and to the current carrying capacity of the conductor connected. This arrangement will avoid danger in the event of a fault by ensuring prompt operation of the protective device at the appropriate current value which will otherwise cause damage to the cable or the current using equipment.
(b) A fault on one circuit should not result in the shutting down of any unrelated parts of the installation as far as reasonably practicable.
For this, it is recommended that—
(i) fixed lighting fittings of an installation should be arranged to be fed by two or more final circuits.
(ii) lighting final circuits should be electrically separated from power circuits except that it may be connected to bell transformers or electric clocks.
(iii) power circuits for kitchens should be electrically separated from other power circuits.
(c) Where the supply is designed to be taken from more than one transformer, interconnection facilities between the main incoming circuit breakers should be provided if requested by the electricity supplier. All incoming and interconnection circuit breakers should be of 4-pole type interrupting all live conductors (i.e. phase and neutral conductors) and electrically and mechanically interlocked to prevent the electricity supplier’s transformers from operating in parallel.
(2) Control
Each circuit should be provided with means of interrupting the supply on load and isolation for electrical servicing and testing purposes without affecting other circuits.
(3) Identification
(a) Protective devices of each circuit should be clearly labelled or identified so that the rating of the devices and the circuits they protect can be easily recognised.
(b) Every socket in a three phase installation should be marked with the appropriate phase colour in a permanent manner.
(4) Electrical separation for essential circuits
Final circuits for emergency lighting, fire fighting equipment and fireman’s lift should be electrically separated from one another and from other circuits.
(5) Load distribution
Single phase loads in an installation with a three phase supply should be evenly and reasonably distributed among the phases.
(6) Arrangement of neutral conductor
(a) Neutral conductor of a single phase circuit should not be shared with any other circuit.
(b) Neutral conductor of a three phase circuit should only be shared with its related phases in a three phase four wire system.
(c) For a polyphase circuit, the neutral conductor should have a suitable current carrying capacity to cater for any imbalance or harmonic currents which may occur in normal services.
6C Ring Final Circuit Arrangement
(a) The circuit conductor of a ring circuit should be run in the form of a ring, commencing from the origin of the circuit in the distribution board, looping into the terminal of socket outlets connected in the ring, and returning to the same point of the circuit as illustrated in Figure 6(1).
(b) The circuit protective conductor of a ring circuit (other than formed by the metal coverage or enclosure containing all conductors of the ring circuit) should also be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit.
(c) When two or more ring final circuits are installed, socket outlets and equipment to be served by these circuits should be evenly and reasonably distributed among these separate ring final circuits.
6D Final Circuits Using 5A or 15A Socket Outlets to Requirements Prescribed in Appendix 1
(a) Radial final circuits should be used.
(b) Each 5A and 15A socket outlet should be individually connected and protected by a high breaking capacity (HBC) fuse or miniature circuit breaker (MCB) of rating 5A and 15A respectively.
6E Final Circuits Using 13A Socket Outlets to Requirements Prescribed in Appendix 2
(1) General
(a) Ring or radial final circuits should be used.
(b) The circuit, with spurs if any, may feed permanently connected equipment and an unlimited number of socket outlets in a limited floor area determined by Table 6(1). A typical circuit is illustrated in Figure 6(2).
(2) Spurs
(a) For a final circuit in compliance with Table 6(1), the number of fused spurs connected is unlimited but the number of non-fused spurs should not exceed the total number of socket outlets and fixed equipment permanently connected in the circuit.
(b) A non-fused spur should feed only one single or one twin socket outlet or one permanently connected equipment. Such a spur should be connected to a circuit at the terminals of socket outlets or at joint boxes or at the origin of the circuit in the distribution board.
(c) A fused spur should be connected to the circuit through a fused connection unit, with the rating of the fuse not exceeding that of the cable forming the spur, and not exceeding 13A in any event.
(3) Separate circuits
Separate circuits are to be used for:
(a) socket outlets and fixed appliances in kitchens;
(b) electric water heaters;
(c) permanently connected space heaters; and (d ) air-conditioning units.
(4) Permanently connected equipment
Equipment, except shaver supply unit complying with BSEN 60742 or equivalent, connected permanently (i.e. not through a plug-socket arrangement) to a final circuit arranged in accordance with Table 6(1) should be locally protected by a fuse of rating not exceeding 13A and should be controlled by a switch in a readily accessible position or protected by a miniature circuit breaker of rating not exceeding 16A. This is illustrated in Figure 6(3).
6F Final Circuits Using 5A, 15A or 30A Industrial Socket Outlets to Requirements Prescribed in Appendix 3
(1) Socket outlets
These are protected type non-reversible socket outlets. Socket outlet without a key and a keyway is for use with non-fused plug and an exclusive radial final circuit must be used for the socket outlet. Socket outlet with a key and a keyway is for use with fused plug.
(2) Accepted practice
(a) Either radial or ring final circuits may be used.
(b) The current demand of the equipment fed by the circuit will depend on the type of equipment and the operational requirements, and should not exceed the rating of the overcurrent protective device. In assessing the current demand, no diversity is allowed for permanently connected equipment.
(c) The overcurrent protective device should have a rating not exceeding 32A.
(d ) The number of socket outlets can be unlimited.
(e) The total current demand of socket outlets served by a fused spur should not exceed 16A.
( f ) A fused spur should be connected to a circuit through a fused connection unit with the rating of the fuse in the unit not exceeding that of the cable forming the spur and, in any event, not exceeding 16A.
(g) Non-fused spurs should not be used.
(h) Equipment permanently connected to a circuit should be locally protected and controlled by a fuse of rating not exceeding 16A together with a switch, or by a miniature circuit breaker of rating not exceeding 16A.
(i ) Figure 6(4) illustrates such a circuit arrangement.
6G Final Circuits Using 16A Industrial Socket Outlets to Requirements Prescribed in Appendix 4
(1) Socket outlets
These are industrial socket outlets with retaining devices for either indoor or outdoor applications and are for single-phase or three-phase supplies.
(2) Accepted practice
(a) Only radial final circuits should be used.
(b) Fused or non-fused spur is not allowed.
(c) The current demand of the equipment fed by the circuit will depend on the type of equipment and the operational requirements, and should not exceed the rating of the overcurrent protective device.
(d ) The overcurrent protective device should have a rating not exceeding 20A.
(e) The number of socket outlets can be unlimited.
( f ) Figure 6(5) illustrates such a circuit arrangement.
6H Final Circuits Using 32A, 63A or 125A Industrial Socket Outlets to Requirements Prescribed in Appendix 4
(1) Socket outlets
These are industrial socket outlets with retaining devices for either indoor or outdoor applications and are for single phase or three phase supplies.
(2) Accepted practice
(a) Only exclusive radial final circuits should be used.
(b) The number of socket outlets in a final circuit should not be more than one.
(c) The overcurrent protective device should have a rating not exceeding the rating of the socket outlet or that of the cable forming the circuit.
Table 6(1)
Final Circuits Using 13A Socket Outlets Complying to Requirements Prescribed in Appendix 2
Note: 1. If cables of two or more circuits are bunched together or the ambient air temperature exceeds 30°C the size of conductor should be increased and appropriate correction factors (see Appendix 5) should be applied such that the conductor size should correspond to a current carrying capacity not less than:
(i) 20A for A1 or A3 circuits (ii) 30A or 32A for A2 circuits
2. The conductor size of a fused spur should be determined from the total current demand served by that spur, which is limited to a maximum of 13A. When such spur serves socket outlets, the minimum conductor size is 1.5 mm2for rubber or PVC insulated cables, copper conductors.