Handbook of Electrical Installation Practice - BeKnowledge

SUPPLY ARRANGEMENTS
Power Supplies in the UK 21
Electricity supply tariffs are normally specified according to the type of consumer,
i.e. domestic, commercial or industrial, and it is convenient to use the same categories
to discuss the supply arrangements.
Domestic supplies
Houses are now provided with a 100A single-phase supply. Flats without off-peak
heating are provided with a 60A supply. Service installation is an expensive labourintensive
activity and it is therefore important that the capacity and location are
such as to ensure that very few installations need early alteration. On the other
hand, the number that need installing every year means that even the most modest
economy is worthwhile.
Domestic meter reading is a heavy recurring expense and ease of access is therefore
an important factor in the siting of the meter. External meter cabinets are thus
preferred wherever practical but their use is not without problems. It has taken quite
a long time to get their general acceptance architecturally as they do little to enhance
the appearance of premises.
From the structural point of view there have also been problems, because the hole
they occupy in the wall causes a reduction in its fire resistance.The entry of the supply
cable also presents problems. It is important to arrange for the builder to install a
pipe which has a suitable diameter and radius, and if any cavity insulation is to be
used it should be omitted adjacent to the pipe as otherwise it will derate the cable.
The pipe has to be sealed at the bottom end in order to prevent the possible entry
of gas into the premises should a leakage occur outside the house (Fig. 1.7).
An external meter cabinet is outside the Faraday cage and therefore it is preferable
to use one of insulated construction.
The gas companies are also keen on external meter reading and there are pressures
for a common cabinet to be used, although clearly there are problems of
bonding and ensuring that there is no danger of ignition if a gas leak occurs.
Not all domestic development is in the form of individual housing; quite a large
proportion is made up of maisonettes and flats, either low- or high-rise, although
the latter have declined considerably in popularity. Where more than one dwelling
is to be fed from one service it is necessary to extend the mains from the termination
of the incoming cable to the remote dwelling units. For this purpose individual
rising or lateral connections will need to be installed. High-rise buildings may also
require a common main (Fig. 1.8).
The ownership and installation of these mains are dependent on agreement
between the developer and the local DNO. In many cases the DNO will pull their
cables into pipes, ducts or chases provided by the developer. Such installations must
resist interference and the spread of fire. Early agreement and architectural provision
is essential as some modern methods of construction can present acute problems
of routeing. If the local DNO is to be the owner then a PME system may be
employed using CNE cables.
The question which arises is the siting of the meters; the possibilities are for them
to be in a common intake room, in meter cabinets outside each flat or inside each