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This should clear it all up, il even bow down and correct myself, any of your alterations require an earth although the existing can remain without you need to be sure you satify the guidelines below.
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Lighting circuits in older installations may not include circuit protective conductors.
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Lighting circuits installed before 1966 often did not include a circuit protective conductor (cpc).
If Class I equipment, such as a metal luminair (lighting fitting) switchplate or the like is subsequently installed, the addition of a circuit protective conductor is essential
Without a cpc, there will be a risk of electric shock under fault conditions
Solution
There is no legal requirement, and no regulation in BS 7671, requiring and existing lighting circuit to be rewired or otherwise upgraded to current standards.
Furthermore, it is permissible to extend or alter and existing lighting circuit having no cpc. However, the new work must be carried out in accordance with the current edition of BS 7671, and the safety of the existing installation must not be impaired.
The following are some of the main requirements of BS 7671 that must be taken into account where an existing lighting circuit without cpc is to be extended or altered.
- 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 cable. The requirement does not apply where a residual current device is used for protection against electric shock
In practice, rather than making changes to an existing lighting circuit having no cpc, the designer or contractor may persuade the customer that it would be safer and more practicable to rewire the circuit
Regulation 131.8
No addition or alteration, temporary or permanent, shall be made to an existing installation, unless it has been ascertained that the rating and the condition of any existing equipment, including that of the distributor, will be adequate for the altered circumstances. Furthermore, the earthing and bonding arrangements, if necessary for the protective measure applied for the safety of the addition or alteration, shall be adequate.
Regulation 411.3.1.1 (part of)
A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lamp holder having no exposed-conductive-parts and suspended from such a point
Regulation 543.1.1 (part of)
... The cross-sectional area shall be not less than 2.5 mm² copper equivalent if protection against mechanical damage is provided, and 4 mm² copper equivalent if mechanical protection is not provided
Regulation 543.3.1
A protective conductor shall be suitably protected against mechanical and chemical deterioration and electrodynamic effects
Regulation 543.6.1
Where over-current protective devices are used for fault protection against electric shock, the protective conductor shall be incorporated in the same wiring system as the live conductors or in their immediate proximity
This article is extracted from Snags and Solutions Part 1 or Part 2 published by NICEIC
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