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9
Q
What do the Wiring
Regulations specify for the
selection and erection of the
wiring system?
Chapter 52 specifies the
requirements for:
•
types of wiring system;
•
selection and erection in
relation to external influences;
•
current-carrying capacity of
the conductors;
•
cross-sectional area of
conductors.
Note: the latter two points
have been covered in previous
articles.
Q
Are there any other British
Standards to consider?
BS 7540 provides a guide
to the proposed safe use of
electric cables. This identifies
that cables should be selected
so that they are suitable for
any external influences that
may exist, for example:
•
ambient temperature;
•
presence of rain, steam or
accumulation of water;
•
presence of corrosive,
chemical or polluting
substances;
•
mechanical stresses such as
through holes or sharp edges
in metal work;
•
fauna - rodents;
•
flora - mould;
•
radiation - sunlight.
Q
Are there any key
requirements with respect
to the increased use of
suspended ceilings in
commercial premises?
You must take into account
the sharp edges forming the
grid of such ceilings. Flexible
cords with pvc or similar
sheathing should not rest on
the grid, but be supported
clear of the framework to
avoid deviating from BS
7671 regulation 522.8.1, ie
avoid damage to the sheath
and insulation of the flexible
cord during installation and
subsequent use (see figure 1).
Q
Is there a quick and
simple method of supporting
the flexible cord?
There are a number of
supporting systems available.
One of the simplest is to use
a self adhesive cable clip.
Alternatively, clips are easily
attached to a supporting
structure using adhesive.
Fig 1: Protecting the flexible cord from mechanical damage
Concrete floor slab
Sharp
edges
Suspended ceiling
Flexible cord
suitably supported
clear of suspended
ceiling framework