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Guide to the Wiring Regulations 17th Edition IEE Wiring Regulations (BS . The book's coverage is comprehensive, and all Parts of the Regulations have . The IEE Wiring Regulations Explained and Illustrated, Second Edition discusses the recommendations of the IEE Regulations for. This book clarifies the requirements and outlines the correct procedures to follow. Fully up-to-date with the 17th Edition IEE Wiring Regulations and the C&G.
Author: VENUS CERBANTES
ISBN: 326-5-47654-750-9
The IEE Wiring Regulations (BS ) are the national standard to which all reflects significant changes to both the technical content and structure of the book . download 17th Edition IEE Wiring Regulations: Explained and Illustrated (Iee Wiring 9 by Brian Scaddan (ISBN: ) from site's Book Store. download online IEE Official 18th Edition Wiring Regulations book with free 24 hr delivery.
Drops of condensed water falling on the enclosure shall have no harmful effect. Liquid splashed from any direction shall have no harmful effect. Water projected by a nozzle from any direction under stated conditions shall have no harmful effect. Water from heavy seas shall not enter the enclosures under prescribed conditions. It must not be possible for water to enter the enclosure under stated conditions of pressure and time.
It must not be possible for water to enter the enclosure. X Indicates no specified protection. Figure 3 14 Introduction Once again, great care must be taken to maintain the integrity of this type of system, as an inadvertent connection to earth, or interconnection with other circuits, would render the protection useless.
The use of enclosures is not limited to protection against direct contact they clearly provide protection against the ingress of foreign bodies and moisture. In order to establish to what degree an enclosure can resist such ingress, reference to the IP code BSEN should be made. Figure 3 illustrates part of the IP code. The X denotes that protection is not specified, not that there is no protection. For example, an enclosure that was to be immersed in water would be classified IPX8, there would be no point using the code IP What if other tests should have been carried out which may have revealed serious problems?
What if things go wrong after you have signed to say all is in accordance with the Regulations?
What if you were not actually competent to carry out the inspection and test in the first place? What if. Inspection, testing and certification is a serious and, in many instances, a complex matter, so let us wind the clock back to the point at which you were about to enter the premises to carry out your tests, and consider the implications of carrying out an inspection and test of an installation.
What are the legal requirements in all of this? Where do you stand if things go wrong? What do you need to do to ensure compliance with the law?
However, it is the Electricity at Work Regulations that are most closely associated with BS, and as such it is worth giving some areas a closer look. There are thirty-three Regulations in all, twelve of which deal with the special requirements of mines and quarries, and another four with exemptions and extensions outside the UK etc.
We are only concerned with the first sixteen Regulations, and Regulation 29, the defence regulation, which we shall come back to later. Let us start then, with a comment on the meaning of electrical systems and equipment.
Electrical systems and equipment According to the EAWR, electrical systems and equipment can encompass anything from power stations to torch or wrist-watch batteries. A battery may not create a shock risk, but may cause burns or injury as a result of attempting to destroy it by fire, whereby explosions may occur. A system can actually include the source of energy, so, a test instrument with its own supply e. From the preceding comments it will be obvious then, that in broad terms, if something is electrical, it is or is part of, an electrical system.
So, where does responsibility lie for any involvement with such a system? The EAWR requires that every employer, employee and selfemployed person be responsible for compliance with the Regulations with regards to matters within their control, and as such are known duty holders. Where then do you stand as the person about to conduct an inspection and test of an installation? Most certainly, you 18 An overview are a duty holder in that you have control of the installation in so far as you will ultimately pass the installation as safe or make recommendations to ensure its safety.
You also have control of the test instruments which, as already stated are systems in themselves, and control of the installation whilst testing is being carried out.
Any breach of the Regulations may result in prosecution, and unlike the other laws, under this Act you are presumed guilty and have to establish your innocence by invoking the Defence Regulation Perhaps some explanation is needed here.
Each of the sixteen Regulations has a status, in that it is either absolute or reasonably practicable. Regulations that are absolute must be conformed to at all cost, whereas those that are reasonably practicable are conformed to, provided that all reasonable steps have been taken to ensure safety. For the contravention of an absolute requirement, Regulation 29 is available as a defence in the event of criminal prosecution, provided the accused can demonstrate that they took all reasonable and diligent steps to prevent danger or injury.
No one wants to end up in court accused of negligence, and so we need to be sure that we know what we are doing when we are inspecting and testing. Apart from the knowledge required competently to carry out the verification process, the person conducting the inspection and test, must be in possession of test instruments appropriate to the duty required of them.
Instruments In order to fulfil the basic requirements for testing to BS , the following instruments are needed: 1 2 3 4 5 6 7 A low-resistance ohm-meter continuity tester. An insulation resistance tester. A loop impedance tester. An RCD tester. A prospective short circuit current PSCC tester. An approved test lamp or voltage indicator.
A proving unit. However, regardless of the various combinations, let us take a closer look at the individual test instrument requirements.
Introduction and Overview Table A 1. Let us look at a single Regulation Taking the first three digits, these relate as follows: Part 4 Section Chapter 41 The remaining numbers make up the group, sub-set and regulation, but really only the group is of any significance: Group Regulation Introduction and Overview A 3 Overview of major changes There is not much of the document which remains unchanged compared with the 16th Edition; many changes were due to formal incorporation of CENELEC drafts required to achieve harmonization.
This section gives an overview of technical changes that will manifest a change in practice or will be something that you should be aware of. As stated in the preface the subject of BS can be heavy going and this part of the book has been kept as short as possible. Readers may wish to skip this part of the book and start with the two key chapters, C and D. Chapter 41 Protection against electric shock Revision of Chapter 41 is probably the most significant revision made for the 17th Edition.
The whole structure of the chapter has been modified. This terminology change by itself had ramifications in many other parts of the Regulations and these brought about logistical modifications.
The structure of Chapter 41 was accordingly modified. Thus, the main reading in the front end of Chapter 41 is about automatic disconnection. There have been changes to disconnection times.
As protection in TT installations will virtually always require an RCD, the reduced disconnection times in the 17th Edition are easily achieved 0. A very significant new Regulation Commercial installations will generally remain exempt, as in most such situations individuals will have received instruction. Guidance on the structure, disconnection times and the use of RCDs is given in Chapter C of this book.
Section now aligns with the European ethos; there is no Zone 3. Tables and methods of cable current-carrying capacity Appendix 4 of BS The whole of the front end of this appendix has been modified for the 17th Edition. The modifications include the following: Extensive additional rating factors for cables in free air called correction factors in the 16th Edition. Swimming pools For the 17th Edition, the scope of section now includes the basins of fountains and areas in natural waters including the sea and lakes, where they are specifically designated as swimming areas.
The new section deals with interior and exterior lighting installations and also applies to highway power supplies and street furniture. The section specifies such regulations as: New appendix with current-carrying capacity of busbars A new appendix has been added giving information on current-carrying capacity and voltage drop of busbars and powertrack.
It sets regulations for such subjects as circuitry under fault conditions, parallel operation, and specifies the life of certain critical back-up batteries. The former section has been incorporated into Chapter 54 with some limited removal of ambiguous regulations. High voltage to low voltage faults A new section for the 17th Edition, but this not particularly significant for installers or designers. Read Chapter D for a fuller explanation. Voltage drop Whilst in essence the basic requirements of the regulations on voltage drop have not changed, a new appendix suggests maximum voltage drops for both utility and private supplies.
These voltage drops are separated into suggested limits for lighting and other circuits. Atmospheric and switching overvoltages There are a few pages of regulations on this subject, but there is not much of significance unless you have overhead distribution cables within your installation.
Surge protective devices Although not required, there are regulations for installing surge protective devices SPDs. Insulation monitoring devices IMDs and residual current monitors RCMs Similarly, although optional, there are regulations for installing these devices. Introduction and Overview RCMs in particular are becoming more widely specified, and there is guidance on this subject provided in Chapter D of this book. New special installations or locations The following Special Installations sections are new to the 17th Edition: This chapter provides information and guidance on key UK legislation relevant to electrical installations.
It also provides guidance on some contractual obligations relating to designs and installations. The chapter is neither a full legal guide nor a full contractual guide to requirements but provides a short overview.
The chapter finishes with notes on the assessment of general characteristics i. Part 3 of BS B 1 Legal requirements and relationship B 1. Act or a Statutory Instrument e. The Electricity at Work Regulations Failing to comply with requirements of an Act of Parliament or a Statutory Instrument is a breach of criminal law and may result in a prosecution.
You should know the content of this document as well as know of its existence. The EWR covers the safety of people, including employees, involved in all aspects of electrical and electronic systems in the UK. It also includes any person undertaking any work activity on or near electrical equipment.
The legislation covers design, operation, isolation, maintenance, workspace and lighting equipment. There are Regulations on precautions for working on equipment made dead and on work on, or near, live conductors. There are also requirements for persons undertaking work to be competent to prevent danger and injury. Compliance with EWR is therefore a fundamental requirement for any organization, and it is recommended that organizations have in place a system of training to ensure compliance with the Regulations.
The document details and availability are as follows: To supplement this, a dead working policy should ideally be formalized together with a live working policy for those contractors that carry out live work.
It includes guidance on the following: The Regulations state that PME supplies cannot be used to supply installations supplying caravans or boats. This will possibly be the case on some farms, building sites and petrol filling stations. For all installations, DNOs will have to take a view on the safety of an installation and will use BS If the DNO feels that an installation is unsafe, they can refuse to provide a supply or, if connected, disconnect the supply.
However, there is a relevant point for installation designers and contractors to note: This book does not cover all the technical requirements relating to the Building Regulations. However, Part P of the Building Regulations, on the subject of electrical safety within dwellings, is summarized in this section.
The Building Act is the primary legislation and itself refers to the Building Regulations with its various Parts on structure, means of escape, spread of fire, ventilation, heat loss and, of course, electrical safety. The Building Regulations are statutory and a breach of the Regulations in itself is an offence under criminal law.
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As mentioned earlier, statutory instruments such as the Building Regulations must be complied with, otherwise a breach may result in a prosecution. It is important to recognize that the Approved Documents themselves are not statutory. This is demonstrated in Figure B 1. Table B 1. These moral codes were identified and legislated for, initially by the overlords, then monarchs, and ultimately by Parliament. Act is Parliament- enacted law and, as such, creates a criminal obligation upon any transgressor.
The civil law is concerned with providing restitution of rights, obligations or finances in the event of some form of dispute, termed a breach. Civil law governs both the circumstances where there is an intention to form a relationship, by creation of a legally binding agreement — we call this the law of contract — and where a relationship may exist but where no contract is present, which we call the law of torts. Tort may thus be considered liability where there is no contract.
Torts include negligence, nuisance, defamation and trespass, to name but a few. It is possible to owe a duty in both tort and criminal law. The landmark case is Donoghue v Stevenson , wherein a friend of Donoghue downloadd for her a bottle of ginger beer, found to contain a partially decomposed snail. The question follows: Who is my neighbour?
Well, the answer is anyone who it is foreseeable to be likely to be affected by your actions. You can see that liability in tort is therefore very wide, and the rules governing its implementation are extremely complex. Seventy years on, the courts are still grappling with the principles and extent of this law. The level of damages may be similar or higher and it is easier to prove a breach under contract law. Negligence If you negligently design a system or provide a service, and as a result it causes death or personal injury, or causes damage to other property, then you can be held liable for these losses under the tort of negligence.
Making a mistake, or getting something wrong, is not being negligent. Thus, if you hold yourself out as being competent to design a lighting system, offer advice concerning that system, and others rely on that advice and install what is subsequently found to be deficient, then irrespective of payment, you may still be held financially liable.
It is for this reason that services designers and contractors are strongly advised to insure themselves with professional indemnity insurance. B 2 The role of Standards Definition of Standards Standards, including international, European and British Standards, are documents to bring about simplification, interchangeability, terminology, methodology, specification or codified practice.
Standards are voluntary codes of rules, and are not law nor are they legally enforceable. Indeed, individuals may take a view to ignore a particular standard.
However, some standards are boosted to an elevated status by being referred to either directly or indirectly in statutes. Depending upon the wording, this can make the standards themselves have a quasi- legal status. Again, though, there is a caveat. A good way to explain this further is to look at how BS is referred to in some legal documents. This will need updating to read correctly for BS Assuming the standard is relevant or if it is listed, then compliance with the Standard becomes binding under the UK law of contract.
B 3 Part 3 of BS It is intended that the requirements of Part 3 be considered prior to the design of an installation in compliance with other Parts of BS This works for some of the regulations in Part 3, but some are really repetitive of the general requirements given in Parts 4 or 5. The requirements are summarized in Table B 3. The regulation numbers have been omitted here for clarity and due to the fact that the requirements are so general. Table B 3.
Requirement of Regulations Notes and advice The installation shall be assessed for purpose, external influence, compatibility, maintainability, continuity of service and recognized safety services The characteristics of voltage, current, frequency, This can be done by inspection, by enquiry, measurement, prospective fault current, earth fault loop impedance calculation and applies to all sources of supply.
Like other chapters, the structure is topic led and can be read in page order. The chapter guides you through what you need to design and install circuits to BS It does not cater for very large or complex installations with, for example, interconnecting busbars, and such complexity is outside the scope of this book. There is a certain amount of overlap with Chapter D, and these two chapters should both be read prior to undertaking design or installation. Lastly, in this chapter, unlike other chapters, there are not numerous references to individual regulation numbers.
This is due to the fact that most of the circuitry aspects are covered by relatively few regulations in BS Extensive background knowledge and understanding is required to comply with these regulations and this chapter guides readers through all relevant aspects needed. The following flow diagram shows the logical order of steps in the design process. Discrimination between all upstream and downstream protective devices may be required for convenience or continuity of supply to essential equipment, but this may make the electrical system over-designed much too large for its designed use and thus carry a cost burden see C 6.
To provide for a cost-effective and efficient design it helps if the main incoming supply point is close to the load centre of the installation, and hence discussions with the electricity distributor should be started at an early stage. It is not essential that the main distribution board s are positioned close to the intake point, and their position has an effect on voltage drop on the whole installation including the submain cables.
The concept of how to achieve this will become clearer when this chapter has been read. C 3 Load assessment C 3. Many installations have major identifiable loads. Although beyond the scope of this book, data centres require vast amounts of power, but between a large purpose-built data centre and an installation with a few PCs there are installations with small and medium data storage or server rooms. These have notable electrical power and cooling loads, and these loads should be considered.
Firstly, it is important to clarify the terms used, as some of these are not defined in BS Connected load Connected load or total connected load is taken to be the sum of all loads in the installation. Care is needed in specifying this load; diversity See section C3.
Duty cycle For a device or piece of equipment used intermittently, this is the cycle of starting, operating and stopping.
Also included is the time interval that elapses during such a cycle. Alternatively expressed, for a device or piece of equipment used intermittently it is the ratio of its operating time to its rest time, or to total time.
Crest factor In a periodically varying function such as that of a. Both terms are further explained with the aid of an example. This example would be needed for cyclic loads Consider an installation with two motors of the same type installed in different applications.
One motor is used in a supply air fan, the other in a passenger lift application. The lift is in a busy, frequently visited building, particularly busy between 9. The duty cycle and crest factor for both motors is shown in Figure C 3. Figure C 3. Maximum demand Maximum demand or maximum power demand is the highest rate at which power is consumed. Alternatively expressed, it is the highest average rate at which electrical power is consumed.
In calculating the maximum demand in an installation, diversity can be applied To apply these definitions to an installation still requires appropriate experience and usually a lack of such experience leads to an overdesigned electrical distribution system. In practice, a combination of these two methods is often utilized.
For assessment by adding individual loads there are nearly always differences between the rated power expressed by the manufacturer, and the actual currents drawn. This can be true despite checking catalogues and data sheets as well as rating plates and this contributes to overdesign.
The watts per square metre method can be used to produce an overall maximum demand estimate, alongside information on known loads, or it can be used solely to produce an estimate.
Good in theory, but where does the table come from? CIBSE the Chartered Institution of Building Services Engineers does publish a certain amount of such data in its journal, but this information is connected load and not actual running load. BSRIA www. Table C 3. Medium-sized data centres are excluded from this table. Diversity is the engineering principle that in any given installation, some of the connected loads will not be running at the same time instant as other loads.
This principle can be further broken down into two types of load as follows: A Loads that, due to the law of averages, will not be on at the same time. B Loads that, due to fact, will not be on at the same time. Examples of type A include instantaneous electric showers in a multiple block of flats, lift supplies in general and motors for building services. Examples of type B include electrical heating loads and electrical cooling loads; obviously, while it is possible to run both together, the fact is that they do not.
There are many examples of both types of load. In attempting to make an assessment of diversity, there is no substitute for knowledge and experience. The extent of knowledge and experience needed must match the type of installation being assessed. It should be recognized that diversity can be applied in a number of ways as follows: It should also be noted that many engineers, technicians and electricians are inclined to significantly overestimate loadings — perhaps to play safe — and this leads to an overdesigned electrical system.
It is more skilful to produce an ample design with capacity built-in, but which is not grossly overdesigned. This figure says much about diversity when applied correctly. It should be noted that Table C 3. Item Diversity factor Notes Lighting in small office and similar, 0. Modern cable sizing software programs can be quite sophisticated and, for most projects, save considerable time. However, as engineers you must know if the inputs you are making, as well as the outputs that you are receiving, are correct.
In this section, the design procedure common to all circuits is considered. With reference to BS , there are four separate subject areas that will determine the cable size as follows: Readers should note that ultimately only one of these factors will, at any point and for a particular circumstance, determine the cable size. Experience and some rules of thumb given in this chapter may, for example, lead you to carry out a voltage drop check in preference to one of the other sizing factors.
In order to visualize the cable sizing process, Figure C 4. Overcurrent 43 Overload Faults Overcurrent Current in an abnormal or in a sound circuit unintended path It should be noted that an earth fault current in terms of BS The earth fault current requirements specified in Chapter 54 of BS are in essence the same as the short circuit requirements specified in Chapter 43, and aspects of protective conductor sizing are therefore included in this part of the book.
These are discussed later. For most circuits overload protection is required, and this protection should become second nature to installation engineers. A basic requirement given in What is meant by small overloads are those that will not be detected by the protective device. For MCBs this would be somewhere between 1 and 1. Another fundamental requirement of Pictorially represented this requirement is as follows: Fusing, non-fusing and conventional times are given for common devices in Table C 4.
Table C 4. At longer circuit lengths, voltage drop requirements can lead to cable sizes significantly larger than the base size. In order to minimize this in calculations, an accurate design current Ib can be key in ensuring a good design.
The basic formulae to apply to obtain a design current are as follows: V is the nominal phase voltage to earth, also denoted by U0 Vl is the line voltage, also denoted by U pf is the power factor Il is the line current in a three-phase system. For a given insulation, the rating depends upon both load current and the rate of heat dissipated by the cable to its immediate environment. The basic sizing principle is as follows: Next the initial, tabulated cable size It is obtained by using the protective device rating and correcting for ambient temperature, grouping factor and, where applicable, correction factors for thermal insulation and rewirable fuses step 2.
It is the tabulated current-carrying capacity from Appendix 4 of BS C denotes a correction factor as follows: Although not given in Appendix 4 this factor is 0. It should be noted that some 17th Edition tables include a certain amount of thermal insulation and where these are used no further correction should be made. For example, new Table 4D5, included due to ECA suggestion, includes thermal insulation for cables in loft-roof spaces, and the Ci correction should not be used as it is already in the It value.
Cc is for semi-enclosed fuses to BS A cable with tabulated current-carrying capacity Iz is then selected such to exceed the It step 3. The procedure can be depicted as in Figure C 4. Current rating tables for some common cables are found in Appendix 2 of this guide. Correction factors are discussed in sections C 4. On completion of obtaining an installed current rating for the relevant cable size, it is then further checked for voltage drop, thermal withstand under fault conditions and size for earth fault loop impedance.
These are discussed later in the chapter. As the factors for thermal insulation and fusing semi-enclosed are not used all that often, Equation 1 becomes: A new table of grouping factors for buried cables has been added Table 4C2 reproduced below.
Also new is a method for calculating the grouping factor for circuits where cables are of different sizes, as follows: This formula will give a lower group factor than BS Tables 4C1 to 4C5 as these tables assume that cables in the group are of the same size. An overriding point to note before the grouping factor tables are given is the note This is invaluable and should be utilized for BS The procedure for applying grouping factors is either to use the factor from BS Tables 4C1 to 4C2 or to use the following method: Compare the formula: This method can only be used where the circuits within a group are not expected to be simultaneously overloaded.
For circuits that are not fully loaded, the use of this Equation 3 method produces a lower It than the grouping factor method using tables 4C1 to 4C5 from BS The procedures are summarized as: The following tables of grouping factors are reproduced from BS NOTE 1: NOTE 2: NOTE 3: NOTE 4: NOTE 5: NOTE 6: NOTE 7: NOTE 8: NOTE 9: For example, a group of N loaded cables would normally require a group reduction factor of Cg applied to the tabulated It.
However, if M cables in the group carry loads which are not greater than 0. Installation method in Table 4A2 Number Number of cables per tray or ladder of trays or ladders 1 2 3 4 6 9 20 mm 20 mm mmmm Cable ladder 32 Touching 1 See item 4 of Table 4C1 systems, cleats, 33 2 1. Values for such installations may be significantly lower and must be determined by an appropriate method.
For closer spacing the factors should be reduced. Installation method in Table 4A2 Number Number of three- Use as a mm mm of trays or phase circuits per multiplier to mm mm ladders tray or ladder rating for 1 2 3 Cable ladder 32 Touching 1 1. Note 3 mm mm mm mm 20mm 20 mm mmmm Perforated 31 2De 2D 1 1. Ambient temperature Ca This is a factor for ambient temperature of the installation where the cables are run.
Tables 4B1 and 4B2 of Appendix 4 of BS give the relevant factors to be used, including the new correction factors for cables buried in the ground. Where there are mixed installation temperatures in a cable length it is best to use the higher temperature alternatively, larger cables can be installed for that portion.
Thermal insulation Ci A careful application of this factor is required, as many of the cable rating tables 4D to 4F already allow for some thermal insulation. Semi-enclosed fuse factor Cc This factor, equal to 0. The first of these is not utilized as much as it could be, and is for circuits with loads not likely to cause an overload An example would be a circuit supplying a fixed water heater, but this regulation applies to many fixed loads.
Fault current protection is still a requirement and must be provided. The other category of loads for which overload protection need not be provided is where disconnection could cause danger, such as sprinkler pump supplies, lifting electromagnets, safety supplies in general may not apply to all of them and others.
It is noted that supply cut-out fuses are allowed to be utilized for overload protection of the main supply cables Fault currents now include all faults, i. There are two aspects of protection against fault currents: The fault currents to be considered include faults between line conductors and earth, line conductor and neutral, and line-to-line conductors. The highest fault currents will arise with three-phase line conductors shorting together and to earth.
The BS requirements for fault protection are summarized in Table C 4. Requirement Regulation number Fault current shall be determined at every position For small and medium installations with LV utility supplies, this is satisfied by determination of the fault currents at the incomer. This is a theoretical maximum that is rarely found in practice.
A solution here is to measure the incoming fault currents or loop impedances, and use these values. For installations with private transformers, calculations are required, and this is outside the scope of this book. The short-circuit capacity of devices to BS EN —2 is specified by the individual manufacturer.
This confirms that the circuit energy let through by the protective device does not cause a damaging heat rise in the cable. Icn is the rated short-circuit capacity marked on the device , Ics is the service short-circuit capacity. Icn is the maximum fault current the breaker can interrupt safely, although the breaker may no longer be usable. Ics is the maximum fault current the breaker can interrupt safely without loss of performance. The Icn value is normally marked on the device in a rectangle, e.
I is the effective short-circuit current in amperes, due account being taken of the current limiting effect of the circuit impedances k is a factor taking account of the resistivity, temperature coefficient and heat capacity of the conductor material, and the appropriate initial and final temperatures. The adiabatic equation Equation 5 can be used to find a tripping time that will not overheat the cable being used.
This can be a little confusing and it can be easier to calculate the minimum size required using a transposed adiabatic equation as follows: It is worth noting that the factors in Table This is summarized in Table C 4.
It is recognized in the body of Section and Appendix 12 that high inrush currents may cause higher voltage drop levels, and reference to equipment product standards is made.
In essence this does not change the basic requirement that equipment must work! In commercial and industrial installations, voltage drop design will depend upon the nature of the supply. As such, the voltage drops in Table C 4. For private transformers the subject is more complicated, as the voltage regulation of the transformer is now under the control of you, the designer.
The secondary terminal voltage of the transformer will largely depend upon the magnitude of the total load at any instant. Generally it is good practice to simulate the values of statutory voltage limits found in the Electricity, Safety, Quality and Continuity Regulations. This may be set to say 2. For submains, diversity will need to be considered with a slightly different approach than when applying diversity for cable sizing. Whilst short time overload currents will not cause problems to a system, voltage dips below a certain value may cause equipment to stop or malfunction.
Therefore a more rigorous approach to individual submain diversity is required. The definition of voltage drop is the voltage difference between any two points of a circuit or conductor, due to the flow of current. Voltage drop information for installation cables is given in BS Appendix 4 tables expressed in millivolts for a current of one amp for one metre of the cable.
At lower loads, the temperature and the resistance of the cable are lower. Again, manual calculations can be tedious, and the graphs in Figures C 4. The voltage drop is calculated using the formula: As well as terminology changes, the whole of Chapter 41 has been revised. It is important to become familiar with the structure of the chapter, and this is depicted in Figure C 4. As these methods are rarely used they have been discussed in Appendix This measure makes up the bulk of Chapter 41 totalling some 40 regulations.
Although the whole of Chapter 41 has been revised, highlights of automatic disconnection include reduced disconnection times compared with the 16th Edition and an increased use of RCDs, both explained in this part of the book. Chapter 41 first sets down the main requirements for automatic disconnection, followed by specifics for TN, TT and IT systems. Automatic disconnection requires disconnection within the time given by Table System Final circuits disconnection time s Distribution circuits disconnection time s TN a.
Figures C 4. For TT systems Zs includes the resistance of the installation cables Z1 and Z2 , the installation earth electrode Za , the supply distribution cable and the supply earth electrode Zd. Maximum design earth fault loop impedance values for common devices are given in Tables Within this book, in order to distinguish the BS tabulated design earth fault loop impedance values from measured values, design earth fault loop impedance values have been given the symbol Z41 note: Circuitry and Related Parts of BS For conductor sizes 16 mm2 and less, reactance is not a factor and resistance can be used, and the equation becomes: An alternative way of expressing this is by calculating the maximum length of a circuit and using the following formula: This makes the use of an RCD or circuit breaker with a residual element virtually essential.
For most installations, the installation earth electrode value Za see Figure C 4. For simplicity, therefore, the following formula is used: When an RCD is used for shock protection it is necessary to provide short circuit protection between line conductors and neutral by an overcurrent device.
However, for single vertical rod electrodes, depth is an important factor and a 2. Thus the effects of freezing and drying out can be all but eliminated in the UK by installing 2. Measured values of ELI need to be adjusted to take account of the fact that when measured they are not at maximum operating temperature.
While this point is discussed in Chapter F of this book, the necessary compensation step often gets missed; the design engineer thinks the tester will do a compensation and vice versa. A new appendix, Appendix 14, has been included in the 17th Edition, and this suggests a compensation value of 0.
ELI measurement under these circumstances is a futile exercise. The circuit will have been checked for continuity, and this is all that is needed together with, of course, functional checks of the RCD. This criterion satisfies requirements for automatic disconnection. An exception is permitted for: Note 1: See also Regulations Note 2: The requirements of Regulation C 5 Submains C 5.
General notes on diversity and load profiles were given in Section C 3.
The most suitable can be selected with assistance from Table C 5. Of course, regional material and labour costs will have to be factored into this decision of wiring system. This is usually proposed to reduce the loop impedance such that disconnection will occur within the required five seconds. If possible, designers should manually check the calculation at this point.
The armouring of cables can and should be used as a protective conductor. All protective conductors are required either to: In , the ECA commissioned the Electrical Research Association ERA to carry out an investigation into the merits or not of running additional cpcs externally to armoured cables. The report included a comparison of the fault current withstand of the armour of cables to BS , using the k values given in Chapter 54 of BS Also, calculation of the current sharing between the armour and an external cpc showed that if a small external cpc was run in parallel with the armour of a large cable there is a risk that the fault current withstand of the external cpc will be exceeded.
Because of this it is recommended that the cross-sectional area of the external cpc should not be less than a quarter of that of the line conductors. More details of the findings from this report are discussed in Chapter E, Section E5, and a full copy of the report is included in Appendix The following guidance is recommended: Manually check ELI calculations where they specify a small external cable cpc.
C 6 Discrimination co-ordination C 6. For some installations, depending upon the number of protective devices between final circuit and incomer protection, it may be an expensive luxury to design for full discrimination.
Consider Figure C 6. As can be seen, by using a 2: This demonstrates that, for many installations, whole system discrimination is not justified unless there are life-critical constraints. Regulation Chapter 36 gives an example of life-support systems where discrimination should be considered. There is a fair bit of judgement to be made. Take Figure C 6. It would be reasonable for circuit breaker A to discriminate with circuit breaker B, but the discrimination between circuit breakers C and D may still be regarded as a luxury.
We all know that despite the turnover of the client, there would be a limit to what they would pay for the electrical installation. There are many options and combinations that can assist; for example, in Figure C 6. In order to carry out an accurate discrimination study, fault current magnitudes are required at every protective device position.
As a rule of thumb, an upstream circuit breaker will always discriminate with a downstream fuse of half its rating. This applies for all currents of both overload magnitude and for fault currents.
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Fuses have characteristics described as follows: This information is widely available from product standards, manufacturers and is included in Appendix 5 of this book. Fuses to BS 88 and BS have relatively very high fault ratings and will be able to interrupt all short circuit currents in the installation, with no need for cascading see Section C 6. The 2: The normal method of manual co-ordination is by plotting the relevant protective device characteristics onto the same time-current graph paper.
Due to scaling this is carried out on log-log paper; the graph in Figure C 6. Discrimination in this area is a subject vaguely addressed by some manufacturers and, for critical applications mentioned in C 6. This technique should not be a substitute for a system discrimination co-ordination. Where cascading is used, the upstream breaker must have sufficient short-circuit breaking capacity to interrupt the fault, and the downstream breaker must be able to handle the through fault currents sufficiently long enough for the upstream breaker to operate.
Although now always readily available, the use of fuses is often to assist with achieving a system discrimination scheme. Figure C 6. The principle outlined in Figure C 6. Take point X in the figure; larger fault currents will be interrupted by the fuse, smaller fault currents will be interrupted by the circuit breaker.
Thus point X should be at a current less than the fault rating of the circuit breaker. C 7 Parallel cables C 7. The other reason to use two or more cables in parallel is for ease of running and the logistics of termination.
Sometimes switchgear may simply not have the space in the termination area for a single cable over a certain size.
BS requirements for cables run in parallel are summarized in Table C 7. Table C 7. Requirement Regulation No branch circuits allowed The requirements of Table C 7. It should be noted that grouping factors are applicable to parallel cables. This is achieved if all the factors that affect the current-carrying capacity of the cables are the same, i.
Where this is not the case, it is possible to calculate and design the unequal current sharing based upon the different impedances, and methods for this are included in Appendix 10 of BS Discussion of this is outside the scope of this book. C 8 Harmonics C 8. Table C 8. Requirement Regulation Notes Balanced polyphase circuits require no action Most modern installations contain equipment that causes harmonic currents; for example, equipment with switched mode power supplies found in personal computers, photocopiers, printers, fluorescent lighting and motor drives.
The summation of these harmonic currents can cause an overload in the neutral conductor. It can be seen that a de-rating factor of 0. This de-rating should be used in conjunction with the general cable sizing philosophy given in Sections C 3 and C 4.
Appendix 11 of BS C 9 Standard final circuit designs C 9. The designs provide circuit type, protective device and most importantly a maximum circuit length. Standard circuit designs are usually used for common circuits, particularly domestic circuits. The designs in this Section C 9.
The tables have been calculated using particular parameters as follows: External earth fault loop impedances Those used by the UK supply industry are as follows: Where RCDs are used, the tables in this section have been calculated so that the earth fault loop impedance values comply with the limiting values for overcurrent devices in Chapter This gives maximum lengths, which are generally recommended, but considerably longer lengths are possible.
Cable types and installation methods The standard circuit tables have assumed flat twin and earth cable to BS with reduced cpc size and installed as Table 4A2 of BS with current rating taken from Table 4D5 of BS see Table C 9.
Table C 9. Reference Examples Description Rating of method 2. Note 3: NP means not permitted. Circuits are suitable for the installation reference methods listed in the tables. The load assumed is the rating of the overcurrent device.
Some values of maximum length in the tables have the notation s , indicating that the length is limited by earth fault loop impedance. If you have an external loop impedance lower that that used in the table then longer lengths are possible. NP, not permitted. C 10 RCDs and circuitry C The increased use of RCDs includes the following: All circuits within a bathroom Other special locations, including swimming pools and caravan parks. They are now required for most domestic socket-outlet circuits as well as some commercial and industrial socket- outlet circuits, and this section of the book details how to arrange the circuitry aspects of RCDs in order to maintain compliance with the Regulations.
Short of this, the figures in this section show some useful arrangements. Figure C This information is included within Appendix 15 of BS The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2. Such circuits are deemed to meet the requirements of Regulation Recommendations on how to achieve this are as follows, noting that this advice may differ from that in Appendix 15 of BS Kitchen appliances should preferably be supplied via dedicated radials or rings.
Consideration conductors must be given to the forming the 2. An unfused spur may be connected to the origin of the circuit in the distribution board. Fused connection unit FCU supplying fixed equipment Fixed equipment 2. An unfused spur may be connected to the origin of the circuit in the consumer unit.
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Consistent with the general philosophy of this book, all areas are amply covered with particular practical guidance on more difficult or contentious areas. The selection of equipment generally is a very important aspect for the designer, but often understated is that the installer selects equipment. In this case the installer is carrying out part-design, and installers should obtain selection advice from their designer unless contracted to do otherwise.
The term equipment, as the BS definition makes clear, relates to all equipment to be utilized in an electrical installation. So as to be clear as to what is included, the BS definition of electrical equipment is repeated in the box below.
Electrical equipment abbr: Any item for such purposes as generation, conversion, transmission, distribution or utilization of electrical energy, such as machines, transformers, apparatus, measuring instruments, protective devices, wiring systems, accessories, appliances and luminaires. Fundamental requirements for selecting all equipment It is important to note that the selection and erection requirements of the 17th Edition do not in general repeat requirements within the product standards to which the equipment is made.
Instead, BS addresses equipment so far as selection and equipment within the installation is concerned Regulation When selecting equipment, the following must be considered: D 2 Compliance with Standards One of the most fundamental rules of the 17th Edition is that equipment shall comply with an acceptable and current equipment Standard. Most equipment will have a specific British Standard or BS EN written for it, and these standards would need to be used for specifying or selecting equipment.
However, for many reasons, it may not be possible or desirable to select equipment to an appropriate BS or BS EN Standard, and in these cases alternatives are permissible. In cases such as this there are two routes to compliance and the flow diagram below provides some further guidance.
Firstly, equipment to a foreign national Standard which is based on the corresponding IEC Standard may be used provided that, as the 17th Edition requires: In practice this exercise will usually approach the impossible and, in many cases, a sensible view has to be taken. Some will find this judgement to be unacceptable but it is your responsibility, if you are the designer; you may wish to use only BS EN equipment. Another route applies where you wish to use equipment not covered by a Standard, or where it is used outside of scope, and here the designer must confirm its safety to the 17th Edition.
This option is at least achievable. A diagram of how to select a product standard in relation to Section is given in Figure D 2. It should now be obvious that selection of equipment is very much dependent upon knowledge of the equipment Standards and, from this aspect, the BSI website is invaluable. Look again; there is maintained Examples: D 3 Identification of conductors Introduction Harmonized cable colours were introduced into BS in the Amendment, and transitional arrangements were made.
The 17th Edition makes no changes to the regulations on cable identification or to Appendix 7 of BS , which provides details of interfaces with existing installations.
Cable cores shall be identifiable at their terminations either by colour or by alphanumeric characters. While this has not changed from the 16th Edition it is worth discussing the principles. It is noted that cores should preferably be identifiable throughout their length. For many applications coloured cables, either single- or multicore, will be used and these cables are obviously identified throughout their length.
However, in many other applications installers will need to make use of this Regulation The principles and applications of identification are now discussed with the use of diagrams. Figure D 3. In Figure D 3. It should be noted that the colour of the cables originally used is not important and overmarking by tape or similar takes precedence. Building on this principle, Figure D 3. It is perhaps more obvious now that marking throughout the length is not necessary.
It should be noted that the colour of the cables originally used is not important and overmarking takes precedence. This principle holds whatever the colour of cores of the original cable, and applies at terminations by coloured tapes or by characters. Termination Termination Figure D 3. In summary, an important principle is established in that, wherever marking at terminations by either tapes, lettering or numbering is used, the original cable colours must be ignored; this can be against your gut feeling but you must get used to it!
Common examples and applications where identification is only practised at terminations include the following: Control applications wired in single-core conductors.
Applications where coloured cable is not available, including connections to large generators or transformers, where often only black cable is available. It should now be established that installers may wish to use any single cable colour, or combination of colours, and overmark at terminations, and this is not considered a lesser option. For green-and-yellow conductors in multicore cables, overmarking in another colour at terminations is permitted. Overmarking at terminations is prohibited for single-core green-and-yellow conductors.
The general principles are now discussed further and some applications are included. Following the principles of the Regulations, it should be stressed that the alphanumeric column was added to Table 51 for reference and if the colour option is used, these are not required. This can be for any application where the general standard power colours are not preferred. An example of where this would be used would be a lock-stop button control cable, where it is desired to use, say, violet as a colour.
It should be noted that additional termination marking by colour or characters would not be necessary the information relating to violet as a colour for the lock- stop cable would normally be contained on schedules or schematic diagrams. In these cases, or where the designer or installer simply does not prefer colour, identification by marking at terminations is used. Section of BS This may either be the alphanumeric identification of Table 51 or can be by numbering Numbering may be the preferred method of identification; for example, multicore armoured termination kits.
Take a core armoured cable. The cores are numbered from 0 to 26; in the installation, a number of these may be used for neutrals and others used for earths They are all coloured black. Normally, to satisfy other parts of BS , a suitable wiring diagram or equivalent will be required, indicating the use of the numbers unless there is no possibility of confusion.
This installation has wiring colours to two versions of BS Great care should be taken before undertaking extension, alteration or repair that all conductors are correctly identified.
It should be noted that this label need not be applied at all other points on circuits, only at the point of the circuits most likely to be used for isolation in the future, most commonly the distribution boards or items of switchgear.
This appendix is reproduced in the 17th Edition. In practice, the installer will need to learn the principle and apply it accordingly, but no marking is required for most single-phase correctly coloured interfaces — see Figure D 3. For three-phase applications, Appendix 7 of BS suggests applying L1, L2, L3 and N at interfaces, again, where there is no possibility of confusion. The requirements are illustrated for some typical three-phase installation interfaces.
There are examples when interface marking will not be required, but the decision is for the installer, and if you are uncomfortable with interpretation it is recommended that you always apply the interface marking. However, there are of course applications where interface marking is not required, as per the Figure D 3. Many engineers feel that the d. Selection and Erection — Equipment Figure D 3.
These topics are all discussed in this section as many of the recommendations overlap. BS Part EMC. This applies to cables on cable tray as well as within conduit, trunking and ducting. Of course, this insulation requirement is not required where compartments physically separate the cables. The directive and official guidance indicates that best practice is followed, and cites HD , the European harmonization document upon which BS All main documents and guides on these sites were, at the time of writing, free of charge.
So, what is the impact and what advice can be provided to installation designers and installers? Three key points of action are required: Immunity and emission are written into standards and, irrespective of this, manufacturers have an obligation to manufacture to the EU EMC levels. If you need to use equipment to a different standard it is a good idea to obtain confirmation that equivalent immunity and emission has been achieved.
It is important to note that it is the EU retailer who has the duty to confirm this e. This means to BS and other recommended guides. At the time of writing, a new section was being drafted by the Wiring Regulations committee and is likely to include new regulations and some guidance on this subject.
By completing these three actions, designers and installers will have fulfilled their duties under the EMC directive as well as BS Indeed, it is interesting to note that many data IT installation EMC problems have been discovered to be infringements of BS , particularly poor earthing. Some of the recommendations will have to be balanced against cost and performance. Recommendations — cable separation for sensitive equipment The following optional solutions may be considered to mitigate the effects of EMC on sensitive equipment: There will be practical limits to most of the options, and compromises will often be necessary: Separation distances are found in Table D 4.
The separation distances given in Table D 4. However, for horizontal cabling where the final circuit length is less than 35 metres no separation is required in the case of screened cabling. Table D 4. For lengths greater than 35 metres, the separation shall apply to the full length, excluding the final 15 metres before it is attached to the outlet see Figure D 4. Plastic cable management systems can also offer some protection but are only recommended where the system has a low emission level, or where optical fibre cabling is used.
Figure D 4. Where metallic system components are used, the shape flat, U-shape, tube, etc.This does not restrict such maintenance to just a yearly calibration, but requires equipment to be kept in good condition in order that it is safe to use at all times.
Look again; there is maintained Examples: Further investigation revealed, that just under the floor at each end, the 10 mm2 conductor had been terminated in a connector block and the join between the two, about 8 m, had been wired with a 1 mm2 conductor. However, for horizontal cabling where the final circuit length is less than 35 metres no separation is required in the case of screened cabling.
Consider an installation with two motors of the same type installed in different applications. Atmospheric and switching overvoltages There are a few pages of regulations on this subject, but there is not much of significance unless you have overhead distribution cables within your installation. Interestingly, one of the items on the check list is the presence of diagrams, instructions and similar information.
It is quite important to get the principle of Regulation Figure C 6. This is also true of a single employee workplace whatever the nature of the business.
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