Handbook of Electrical Installation Practice - BeKnowledge

EQUIPMENT DESIGN AND MANUFACTURE
British Standard 4363, Specification for distribution units and electricity supplies for
construction and building sites was published in 1968 and re-written in 1998 and provides
an invaluable base against which to manufacture construction site distribution
equipment. It is quite common for supply authorities in the UK to be asked to
provide 500kVA at l.v. which entails the installation of 800A switchgear at the
supply intake point.
There are a number of important aspects involved in the general design of
distribution units which are discussed below. BS 7375: 1996: Code of Practice
for Distribution of electricity on construction and building sites provides a wealth of
guidance for engineers, contractors, builders and others involved in provision of
equipment suitable for use is such arduous site conditions.
Mechanical
Robust construction is necessary to enable the equipment to fulfil its on-site requirements,
as exposure to rough handling, accidental vehicular nudging and unit repositioning
are common occurrences. In addition to this, the environmental conditions
experienced on construction sites require careful consideration. Equipment must be
capable of continuous operation in coastal locations without any additional protection;
similarly, tropical climates must be catered for with the humidity and sandstorms
that accompany them. Additional measures are necessary for very hostile
environments, such as the use of filters, anti-condensation heaters, etc., but the basic
design of the unit remains unaltered.
Electrical
Prevention of direct contact with live parts is achieved by insulation and barriers or
enclosures. Protection against indirect contact is effected by efficient earthing and
careful selection of protective devices to provide automatic disconnection.
Ruggedness, reliability, versatility and safety of operation are all combined to
provide an assembly which will operate satisfactorily for long periods in onerous
environments.
RANGE OF EQUIPMENT
Electricity on Construction Sites 99
The range of equipment likely to be found on a typical construction complex is
detailed below.
Incoming supply assembly (ISA)
The purpose of the ISA on a construction site is primarily to accept the Electricity
Distributor’s main cable, afford metering equipment space and consumer’s main
protection. The ISA comprises two compartments each with its own means of