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wiring systems and fault finding for installation electricians fourth edition pdf

The aim of this book is to help the reader to approach the drawing
and interpretation of electrical diagrams with confidence, to understand the principles of testing and to apply this knowledge to fault
finding in electrical circuits.
The abundant colour diagrams with associated comments and explanations lead from the basic symbols and simple circuit and wiring
diagrams, through more complex circuitry, to specific types of wiring
systems and, finally, to the methodical approach to fault finding.
The new edition has been brought fully in line with the 17th Edition
IEE Wiring Regulations.
Brian Scaddan, April 2008

The four most commonly used diagrams are the block diagram,
interconnection diagram, the circuit or schematic diagram and the
wiring or connection diagram.
Block diagrams
These diagrams indicate, by means of block symbols with suitable
notes, the general way in which a system functions.

They do not
show detailed connections ( Figure 1.2a and b ).

Interconnection diagrams
In this case, items of equipment may be shown in block form but
with details of how the items are connected together

Circuit or schematic diagrams
These diagrams show how a system works, and need to pay no
attention to the actual geographical layout of components or
parts of components in that system.

For example, a pair of contacts which form part of, say, a timer may appear in a different and
quite remote part of the diagram than the timer operating coil that
actuates them. In this case some form of cross-reference scheme is
needed (e.g. T for the timer coil and T1, T2, T3, etc. for the associated contacts).
It is usual for the sequence of events occurring in a system to be
shown on a circuit diagram from left to right or from top to bottom. For example, in Figure 1.4 , nothing can operate until the
main switch is closed, at which time the signal lamp comes on via
the closed contacts of the push-button.

When the push is operated
the lamp goes out and the bell is energized via the push-button’s
top pair of contacts.
Wiring or connection diagrams
Here the diagrams show how a circuit is to be actually wired.
Whenever possible, especially in the case of control panels, they
should show components in their correct geographical locations.

It is probably sensible at this point to introduce the reader to
circuit convention. This is simply a way of ensuring that circuit

In order to construct or interpret a circuit/schematic diagram of the
controls of a particular system, it is necessary to understand, in broad
principles, how the system functions.

A logical approach is needed,
and it may take the novice some while before all ‘clicks’ into place.
Here is an example to consider.