Code of Practice for the Electricity (Wiring) Regulations - 2009 Edition

Code 9 OVERCURRENT PROTECTIVE DEVICES
9A General Requirements
(1) Overcurrent protection for circuit
Every circuit must be protected by one or more devices for automatic
interruption of the supply in the event of overcurrent resulting from:
(a) overload, or
(b) fault.
(2) Examples of overcurrent protective devices
The following devices are acceptable as protective devices against
overcurrent:
(a) Miniature Circuit Breakers (MCB)
(b) Moulded Case Circuit Breakers (MCCB)
(c) High Breaking Capacity (HBC) Fuses
(d ) Semi-enclosed Fuses
(e) Circuit Breakers incorporating overcurrent release, or in conjunction
with fuse.
(3) Requirements of overcurrent protective devices
(a) Overload protective devices and fault current protective devices
should satisfy the requirements of Codes 9B, 9C, 9D and 9E.
(b) For devices providing protection against both overload current and
fault current, they should satisfy both the requirements of overload
protective devices and fault current protective devices.
(c) The characteristics of devices for overload protection should be
coordinated so that the energy let-through by the fault current
protective device does not exceed that which can be withstood by
the overload protective device without damage. For a circuit
incorporating a motor starter, this CoP does not preclude the type of
co-ordination described in IEC 60947-4-1, in respect of which the
advice of the manufacturer of the starter should be sought.
9B Relation Between Circuit Conductors and Overcurrent
Protective Devices
(1) Overload protective devices
(a) Overload protective devices should be capable of breaking any
overload current flowing in the circuit conductors before such a
current could cause a temperature rise detrimental to insulation,
joints, terminations, or surroundings of the conductors.
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