Newnes Electrical Pocket Book

531 Pages·1992·12.696 MB·English

by  E.A. Reeves (Eds.)

Newnes
Electrical Pocket Book
Edited by E. A. Reeves
DFH (Hons), CEng, MIEE
Twenty-first edition
INEWNES
Newnes
An imprint of Butterworth-Heinemann Ltd
Linacre House, Jordan Hill, Oxford OX2 8DP
Ά PART OF REED INTERNATIONAL BOOKS
OXFORD LONDON BOSTON
MUNICH NEW DELHI SINGAPORE SYDNEY
TOKYO TORONTO WELLINGTON
First published by George Newnes Ltd 1937
Twenty-first edition published by Butterworth-Heinemann Ltd 1992
Reprinted 1993
© Butterworth-Heinemann Ltd 1987, 1992
All rights reserved. No part of this publication
may be reproduced in any material form (including
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means and whether or not transiently or incidentally
to some other use of this publication) without the
written permission of the copyright holder except in
accordance with the provisions of the Copyright,
Designs and Patents Act 1988 or under the terms of a
licence issued by the Copyright Licensing Agency Ltd,
90 Tottenham Court Road, London, England W1P 9HE.
Applications for the copyright holder's written permission
to reproduce any part of this publication should be addressed
to the publishers
British Library Cataloguing in Publication Data
Newnes electrical pocket book.
New ed.
I. Reeves, E. A. (Eric Alwyn), 1923-
621.3
ISBN 0 7506 0513 8
Typeset by Vision Typesetting, Manchester
Printed in England by Clays Ltd, St Ives pic
Preface
Although the twentieth edition of the Pocket Book was only
published in 1989 two important changes have occurred since then,
(i) the issuing in the 16th edition of the IEE Wiring Regulations and
(ii) the splitting up of the supply industry for privatisation. This has
necessitated extensive revision of Chapters 7 and 12 and other slight
modifications throughout the book, so it was felt only right to issue it
as the twenty-first edition.
The 16th edition of the IEE Wiring Regulations, published in May
1991, is quite different from its predecessor. One of the major
changes is that many of the Appendices of the 15th edition do not
appear in the new edition but will be published separately as
Guidance Notes. At the time of writing this preface, none of the
Guidance Notes are available, and so, after consultation with an IEE
technical committee member, it has been decided to leave the
relevant Appendices in Chapter 12 but draw the reader's attention to
the fact that the material is expected to appear in the form of
Guidance Notes. No doubt there will be some variations between the
original Appendices of the 15th edition of the Regulations (upon
which the extracts are based) and the Guidance Notes themselves but
such changes will not materially alter the meaning of the contents.
The heading (and subheading) of Chapter 12 Wiring Regulations,
is therefore not strictly true because it includes material, i.e.
Guidance Notes, which are not Regulations. However, the Appendi­
ces of the 15th edition, upon which the Guidance Notes are based,
were also not part of the Regulations, although no doubt many users
thought they were. Now that anomaly is made clear by their
exclusion from the 16th edition.
Another important difference is the inclusion of a new Part 6,
'Special installations or locations', the original Part 6 of the 15th
edition 'Inspection and testing' now being Part 7. For this reason we
have included lengthy extracts from Part 6 covering locations
containing a bath tub or shower basin, swimming pools, hot air
saunas, construction site installations, agricultural and horticultural
premises, restrictive conductive locations, earthing requirements for
the installation of equipment having high earth leakage currents,
electrical installations in caravans, motor caravans and caravan
parks, and highway power supplies and street furniture. Space is
reserved for future use and also for marinas.
The system of numbering the Regulations is rather more compli­
cated than for the 15th edition; the first digit signifies a Part, the
second a Chapter, the third a Section and the subsequent digits the
Regulation number. For example Section 413 is made up as follows:
Part 4 - Protection for safety, Chapter 41 - Protection against
electric shock, Section 413 - Protection against indirect contact.
The second important change since 1989 is that the full details of
the privatisation of the UK supply industry are now known. At the
time of going to press with the previous edition we only knew the two
bodies in England as Big G and Little G with Big G including all the
nuclear plants. This is now different, with nuclear power remaining
as two separate entities known as Nuclear Electric and Scottish
Nuclear, both owned by the Government, Big G becoming National
Power, and Little G, PowerGen. The transmission system is also a
separate company known as the National Grid. Area electricity
Boards have been formed into separate distribution companies.
Details of these organisations are given in the updated Chapter 7.
Since such a short time has elapsed between the publication of the
20th and 21st edition we reproduce below part of the Preface of the
20th edition as being relevant in 1992.
Other changes that have occurred during the last few years include
the growing importance of building automation systems and work
on superconductivity. At the same time many minor changes have
occurred and so these have also been incorporated as necessary. For
example, publication of a new British Standard in 1986 (too late for
inclusion in that edition) had radically altered the classification of
insulating materials in the upper temperature regions. The concept
of Groups Y, A, and E etc. no longer exists, but a table in another
British Standard, BS 5691 Part 2, lists materials and their tests which
to some extent tie up with the old Group concept.
In the last two to three years so much has changed in the computer
industry that this chapter has again been lengthened and completely
rewritten.
Many of the tabulated figures in the lighting chapter have been
modified to take into account latest practice, and advantage has been
taken to include details of the recently introduced high frequency
electronic ballast which provides silent, instant, flicker-free starting
for single and twin fluorescent lamps up to 1,800 mm long and both
26 mm and 38 mm diameter.
Updating of the chapter on switchgear and protection has
involved replacement of some circuits and mention of the latest
microprocessor-controlled overcurrent and earth-fault relays. The
restriction placed on current balance protection schemes when
applied to transformers is now included, in which a harmonic biased
relay has to be employed rather than an unbiased design which is
suitable for use on generator protective schemes.
Since 1986 the 4,000 MW Drax power station has been commis­
sioned, Berkeley and Hunterston A nuclear station have ceased
generating while Bradwell nuclear station will be subject to an
annual review. Britain's first pressurised water reactor (PWR)
station, at Sizewell, is now under construction, the 1,200 MW plant
being estimated to cost £2.03 billion (1991 cost). It should become
fully operational by 1994. Wind generation is becoming more
fashionable and three demonstration wind parks are to be built, each
with twenty-five wind turbines having a combined capacity of
24 MW.
Another area of fast growth is in Building Automation Systems
(BASs), which rely heavily on computers, microprocessors and other
electronic artifices. The majority of BASs are based on the relatively
inexpensive personal computer, with only the largest systems
employing a mini-computer. Intelligence and stand alone capability
are today included in individual controllers rather than being
concentrated in a central processing unit or in field processing units.
E. A. Reeves
Introduction
The chief function of any engineer's pocket book is the presenta­
tion in convenient form of facts, tables and formulae relating to
the particular branch of engineering dealt with.
In the case of electrical engineering, it is essential that the
engineer should have a clear understanding of the methods by
which the various formulae are derived in order that he can be
quite certain that any particular formulae is applicable to the
conditions which he is considering. This applies with particular
force in the case of alternating current work.
The first section of the Pocket Book is, therefore, devoted to
the theoretical groundwork upon which all the practical applica­
tions are based. This covers symbols, fundamentals, electrostatics
and magnetism.
When an engineer is called upon to deal with any particular
type of electrical apparatus, for example, a protective relay
system, a thermostatically controlled heating system, or industrial
switchgear and control gear, the first requirement is that he shall
understand the principles upon which these systems operate. In
order to provide this information, much space has been devoted
in the various sections to clear descriptions of the circuits and
principles which are used in the different types of electrical
apparatus.
The inclusion of technical descriptions, together with the
essential data embodied in the tables, will be found to provide the
ideal combination for those engineers engaged on the utilisation
side of the industry, where many different types of equipment and
electrical appliances, ranging from semiconductor rectifiers to
electrode steam boilers, may have to be specified, installed and
maintained in efficient operation.
An extensive summary of the sixteenth edition of the 'Regulations
for Electrical Installations' published by the Institution of Electrical
Engineers is contained in Chapter 12. The layout and content are
markedly different to the previous editions and for those personnel
1
working in electrical contracting it is important that they obtain their
own copy of the Regulations. One of the most important changes is
the exclusion of many of the Appendices which are being published
(over a period of time) as separate Guidance Notes. Another change
in the inclusion of a new Part 6, 'Special installations or locations'.
More is said about these in the Preface and Chapter 12.
2
1
Fundamentals and theory
FUNDAMENTALS
Current. The term 'current' is used to denote the rate at
which electricity flows. In the case of a steady flow the current is
given by the quantity of electricity which passes a given point in
one second. The magnitude of the current depends not only upon
the electromotive force but also upon the nature and dimensions
of the path through which it circulates.
Ohm's Law. Ohm's law states that the current in a d.c. circuit
varies in direct proportion to the voltage and is inversely prop­
ortional to the resistance of the circuit. By choosing suitable units
this law may be written
Current = Electrom°tive f°rce
resistance
The commercial units for these quantities are
Current - the ampere (A)
Electromotive force - the volt (V)
Resistance - the ohm (Ω)
Using the symbols /, V and R to represent the above quantities
in the order given, Ohm's law can be written
or V = / x R
The law not only holds for a complete circuit, but can be applied
for any part of a circuit provided care is taken to use the correct
values for that part of the circuit.
3
POSITIVE + BATTERY 1» 1 fr
NEGATIVE - VOLTMETER ©
AC "O AMMETER ®
SINGLE-PHASE ^ WATTMETER (w)
THREE PHASE 3 -v
EARTH ± POWER FACTOR
RESISTOR / ~V/
NON-INDUCTIVE Γ -TJUUlr- FREQUENCY 0 OR ®
RESiSTOR ^ -nfSn- METER
VARIABLE
RESISTOR INSTRUMENT ______
IMPEDANCE
SHUNT Ϊ 1
WINDING (INDUCTOR,ί Γ^ΓΊ
COIL,CHOKE ETC) |^—^ p-n JUNCTION ___OR__L
CURRENT TRANSFORMER p-n-p TRANSISTOR ß)
SINGLE PHASE DIODE OR(±) OR ($)
TRANSFORMER RECTIFIER^ ^
THYRISTOR
AUTO-TRANSFORMER GENERAL SYMBOL
RECTIFIER £|—
3-PHASE STAR
DELTA
TRANSFORMER REVERSE-BLOCKING /Ώ\
DIODE THYRISTOR \C/
CROSSING CONDUCTORS —|—
3-PHASE VOLTAGE JUNCTION OF CONDUCTORS
TRANSFORMER:
STAR : STAR CAPACITOR II
MOTOR OR ®OR©
GENERATOR
FUSE^ OR
INDUCTION MOTOR
CAGE
SINGLE-PHASE
INDUCTION MOTOR
CAGE 3-PHASE SPARK GAP
DELTA CONNECTED
INDUCTION MOTOR
WOUND ROTOR
3-PHASE
Figure 1.1
Graphical Symbols - BS3939
4
Resistivity. The resistivity of any material is the resistance o fa
piece of material having unit length and unit sectional area. The
symbol is p and the unit is the ohm metre. The resistivity of a
material is not usually constant but depends on the temperature.
Table 1.1 shows the resistivity (with its reciprocal, conductivity)
of the more usual metals and alloys.
Table 1.1 Resistivities at 20°C
Resistivity Conductivity
Material
Ohm metres Siemens per metre
Silver 1.64 x 10-8 6.10 x 107
Copper (annealed) 1.72 x ΚΓ8 5.8 x 107
Gold 2.4 x 10-8 4.17 x 107
Aluminium (hard) 2.82 x ΚΓ8 3.55 x 107
Tungsten 5.0 X KT* 2.00 x 107
Zinc 5.95 x ΚΓ8 1.68 x 107
Brass 6.6 x ΚΓ8 1.52 x 107
Nickel 6.9 x IO"8 1.45 x 107
Platinum 11.0 x ΚΓ8 9.09 x 106
Tin 11.5 x 10-8 8.70 x 106
Iron 10.15 x ΚΓ8 9.85 x 106
Steel 19.9 x ΚΓ8 5.03 x 106
German Silver 16-40 x ΚΓ8 6.3 - 2.5 x 106
Platinoid 34.4 x 10-8 2.91 x 106
Manganin 44.0 x 10"8 2.27 x 106
Gas carbon 0.005 200
Silicon 0.06 16.7
Gutta-percha 2 x 107 5 x ΚΓ8
Glass (soda-lime) 5 x 109 2 x 10"10
Ebonite 2 x 1013 5 x IO"14
Porcelain 2 x 1013 5 x 1(T14
Sulphur 4 X 1013 2.5 x IO"14
Mica 9 x 1013 1.1 x 1(Γ14
Paraffin-wax 3 x 1016 3.3 x ir17
Resistance of a conductor. The resistance of a uniform conduc­
tor with sectional ala A and length / is given by
/
R =
P~A
The units used must be millimetres and square millimetres if p is
in ohm millimetre units.
Temperature coefficient. The resistance of a conductor at any
temperature can be found as follows:
R = R (1 +crt)
t 0
R - resistance at temperature i°C
t
R = resistance at temperature 0°C
0
5