9.1 - What is data cabling and why do we need it?
First of all, why should a book concerned
with the Wiring Regulations seek to cover the subject of
data cabling, to which the Regulations (BS 7671) do not
apply? The simple answer must be that most of todays
electricians are almost certain to be concerned with the
technology sooner or later, and an introduction to the subject
will be useful.
Data cabling (often referred to as a network)
has become extremely common in business and in academic
installations, and will shortly almost certainly be a necessity
for many domestic applications. Data terminals and computers
these days are seldom separate stand alone items,
but are networked together, so that all can communicate
with the others and so that the data input to them may be
collected and analysed centrally. For example, all the tills
in a supermarket must be linked so that any price changes
can be relayed to all of them simultaneously, and so that
the sales information they obtain from the bar code readers
can be gathered centrally to provide exact data concerning
the merchandise checked out. Again, all the individual computers
in a college will be linked by a network so that all can
use a single set of programs, such as for word processing.
The system to interconnect these systems
is the data cabling which forms the network. In its most
basic form it will consist of copper cables which exist
in pairs, which are twisted throughout their length as an
aid in combating the problem of interference due to electrical
noise from other electrical wiring and equipment.
One method of ensuring that there will be no interference
is to send the signals in the form of light. A glass fibre
cable is used as path for light pulses injected at one end
by a laser and read at the other end by a photocell. Both
of these methods will be considered here. However, it must
be appreciated that one chapter like this one can only provide
the briefest coverage, and that a specialist work, or a
training course, is necessary to obtain a fuller understanding
of the subject.