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7
Significant changes affect installations where cables are buried in the
wall. This is the normal practice in dwellings.
Cables buried in the wall
Here we need to consider Section 522, Selection and erection of
wiring systems in relation to external influences. The particular
requirements of this section apply to cables which are concealed in a
wall or partition at a depth of less than 50mm, or where metal
partitions are used.
The definitions for persons are once again important for this section.
There are 5 options of installing cables in walls. The cables shall:
i. incorporate an earthed metal covering which is suitable as a
protective conductor. Eg SWA cable.
ii. Be enclosed in earthed metal conduit, such that is suitable as a
protective conductor.
iii. Be enclosed in earthed metal trunking, such that is suitable as a
protective conductor.
iv. Be protected against damage from penetration by nails or screws.
v. Be installed in a safe zone.
This is much the same as the 16
th
Edition requirements and the usual
option is to install cables in a dedicated safe zone. However, where
an installation is not under the supervision of someone skilled or
instructed, regulation 522.6.7 applies.
In this regulation where (v) only from above is used then the cable
must have additional protection by the use of a RCD not exceeding
30mA. This would apply where thermoplastic (PVC) wiring systems
are used, this is typical in most domestic installations and some com-
mercial installations.
Where buried cables are
not mechanically
protected additional
protection by an RCD
not exceeding 30mA
must be provided
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