Elecsa offer their technical support regarding CPC and what to do if a lighting circuit does not have this.
Lighting circuits installed before 1966 did not require a circuit protective conductor (cpc) to be run to and terminated at every point and accessory of a lighting circuit, as is currently required by Regulation 4220.127.116.11 of BS 7671.
It should be remembered that the Wiring Regulations are not retrospective, as is clearly mentioned in a note in the introduction to BS 7671 which states: Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every respect. This does not necessarily mean they are unsafe for continued use or require upgrading.
Therefore, there is no legal requirement, and no regulation in BS 7671, requiring an existing lighting circuit to be rewired or upgraded to current standards. However, it is essential that the safety of the installation is not compromised when any alteration and/or addition is carried out.
For example, any new work such as installing an item of Class I equipment which could typically be a metal luminaire (lighting fitting) or a metal switchplate as shown in Fig 1, where there is no cpc available, may present an increased risk of electric shock under fault conditions.
Where an existing lighting circuit without a cpc is to be extended or altered, a number of regulatory requirements should be taken into account
Requirements of BS 7671
1. Regulation 132.16 requires that no alteration or addition shall be made to an existing installation unless it is established that:
• the rating and the condition of any existing equipment, including that of the distributor, is adequate for the altered circumstances, and
• any earthing and bonding arrangements necessary for the safety of the alteration and/or addition are adequate.
2. Where protection against electric shock is provided by automatic disconnection of supply (as is usually the case), the cpc must be run to and terminated at:
• each new point in wiring and each new accessory, except a lampholder having no exposed-conductive-parts and suspended from such a point, and
• any existing point or accessory that is changed from the all-insulated type to a Class I type (Regulation 418.104.22.168 refers).
3. Where a cpc is not an integral part of a cable (such as a twin and earth cable) and is not contained in an enclosure formed by a wiring system (such as trunking), it must have a cross-sectional area not less than: • 2.5 mm2 if protection against mechanical damage is provided, or
• 4 mm2 if protection against mechanical damage is not provided (Regulations 543.1.1 and 543.3.1 refer).
4. Where a cpc consists of a separate green/yellow covered copper conductor, it must still be incorporated in the same wiring system as the live conductors or in their immediate proximity (Regulation 543.6.1 refers). This would require the cpc to be run along the same cable route(s) as the existing cables.
Typically for a domestic setting, the electrical contractor may recommend to the customer that rather than make changes to an existing lighting point or accessory that has no cpc and where one is required, it would be preferable if the complete lighting circuit was rewired using twin and cpc.
Where a new lighting circuit is to be installed, the following considerations should be taken into account.
Where ceiling roses are to be fitted as part of the lighting circuit, Regulation 522.214.171.124 requires that only one outgoing flexible cable be connected to each ceiling rose, except where the ceiling rose is specifically designed for more than one such pendant connection (see Fig 2).
a) Single point pendent arrangement
b) multi-point pendent arrangement
With reference to Table 52.3 of BS 7671, the minimum conductor size for a radial final circuit for lighting, protected by an overcurrent protective device with a rated current or current setting (In) of 6 A, is 1.0 mm2 for thermoplastic (PVC) or thermosetting insulated cables having copper conductors.
The flexible cable between the ceiling rose or similar and the lampholder is permitted to have a minimum cross-sectional area of 0.75 mm2 (see Regulations 433.3.1(ii), 524.1 and Table 52.3).
Details on the maximum mass supportable by a flexible cable are provided in Table 4F3A of BS 7671.
Sealing of wiring system penetrations
Section 527 of BS 7671 provides regulatory requirements that should be considered where cables pass through the fabric of a building. This includes where cables pass through a ceiling to a lighting point (Regulation 527.2.1 refers). The hole should be sealed with a fire retardant material which is compatible with the insulation properties of the cable sheath (Regulation 527.2.4 (iii) refers).
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