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The notes for this course have been drawn up to aid electricians in their understanding of
the requirements for testing as detailed in Part 6 of IEE Wiring Regulations, 17th Edition
(BS7671 : 2008).
References for the tests described have been taken from Guidance Notes No 3 entitled
'Inspection and Testing' published by the Institute of Electrical engineers.
Whilst every effort has been made to ensure that the information given in these notes is
correct and complete all parties making use of these notes should rely on their own skill
and judgment when using them.
These notes are not intended to replace the need for the 17th edition of the IEE Wiring
Regulations which should be referred to as the definitive source for questions arising in
relation to electrical installations.

Chapter 1 Standards & Regulations
1.1 Standards page 4
1.2 Plan of the IEE Wiring Regulations page 5
1.3 Safety page 6
1.4 Competent Persons page 7
Chapter 2 Earthing Systems
2.1 Reasons for Earthing
2.2 Earth Fault Path
2.3 Earthing Arrangements
Chapter 3 Inspection
3.1 General Requirements
3.2 Initial Inspection
3.3 Periodic Inspection
3.4 Frequency of Inspection & testing
Chapter 4 Testing
4.1 Sequence for Testing
4.2 Continuity of Protective Conductors
4.3 Continuity of Ring Final Circuit Conductors
4.4 Insulation Resistance
4.5 Site Applied Insulation
Protection by Separation of Circuits
Protection by Barriers or Enclosures
Insulation of Non-conducting Locations
4.6 Polarity
4.7 Earth Electrode Resistance
4.8 Earth Fault Loop Impedance
External Earth Fault Loop Impedance
Prospective Short Circuit Current
4.9 Residual Current Devices
4.10 Functional Tests
4.11 Periodic Tests

Chapter 5 Documentation
5.1 Electrical Installation Certificate
5.2 Alterations and Additions
5.3 Periodic Inspection Report
5.4 Minor Works
Chapter 6 Instrumentation requirements

1.1– Standards
It is necessary to understand the reasons for producing regulations which specify
standardized methods associated with the installation, inspection and testing of electrical
The Electricity Supply Regulations, 1988 and Electricity at Work Regulations, 1989, are
statutory regulations which have to be complied with in terms of safety and workmanship.
An electrical installation which complies with the 17 th Edition of the IEE Wiring
Regulations is viewed by the HSE as likely to achieve conformity with the relevant parts of
the Electricity at Work Regulations, 1989.
Certain types of premises, such as petrol stations, cinemas, night clubs etc.,are subject to
licensing. With this type of premises, statutory regulations which may add to, or differ from
the requirements of the IEE Wiring Regulations, apply. In this case the licensing
requirements would take precedence over the IEE Wiring Regulations.
ln certain areas of electrical work, where the requirements of the IEE Wiring Regulations
are not specific enough, reference will need to be made to the relevant British Standard
covering that subject.
ln addition to the above, due to the UK's membership of the EEC, it is seen as essential
that electrical installation practice be standardized throughout the Community.
CENELEC, the specifying and standards authority for all electrical technical matters for
Europe, have produced Harmonization Documents. In the preface to the IEE Wiring
Regulations these documents and their direct comparison with the relevant parts of the IEE
Wiring Regulations are listed.
Whilst differences of opinion do exist between the IEE Wiring Regulations Committee and
CENELEC on certain subjects, in theory a knowledge of the IEE Wiring Regulations will
enable an electrician to work in any Country within the EEC and to produce work which is
acceptable to the inspection authorities within that county.
By the acceptance of the IEE Wiring Regulations as a British Standard in October of 1992,
the regulations took on the required international standing. This now means that
electricians from other parts of the EEC wishing to carry out electrical work within the UK
are also bound by the IEE Wiring Regulations.

1.2 Plan of the IEE Wiring regulations
Whilst standardization is desirable, it does pose problems. The 17th Edition of the IEE
Wiring Regulations have been laid out according to the pattern agreed for CENELEC
documents which does not always make it easy for one to locate all the regulations
pertaining to a specific topic as these may not be located within the same section.
The major advantage of the current edition of the IEE Wiring Regulations over previous
versions is that it does contain a much improved index.
The Regulation numbers are set out in the arrangement as defined by the internationally
agreed standard for electrical installations, for example.
4 th part (Protection for safety)
Chapter 1 (Protection against electric shock)
Section 3 of chapter (Protective measure: Electrical separation)
Regulation 3 (Requirements for fault protection)
Finally part 3 of the regulation. (Live parts of a separated circuit shall not be connected to
any other circuit or to Earth or to a protective conductor)
The 17th Edition I.E.E. Wiring Regulations or BS7671 can be divided into 7 different
Part 1 Scope,object & fundamental Requirements for Safety
Part 2 Definitions
Part 3 Assessment of General Characteristics
Part 4 Protection for Safety
Part 5 Selection & Erection Of Equipment
Part 6 Inspection &Testing (Part 7 in the 16th edition)
Part 7 Special Installations or Locations (Part 6 in the 16th edition)
Appendices tables and information required to design a system
Part 1. Scope,Object & Fundamental Requirements For Safety
Chapter 11 - Scope.
Chapter 12 - Objects & Effects.
Chapter 13- Fundamental Principles.

Part 2
Part 3. Assessment of General Characteristics
Chapter 31 - Purpose, supplies & Structure
Chapter 32 - Classification of External Influences
Chapter 33 - Compatibility
Chapter 34 - Maintainability
Chapter 35 - Safety Services
Chapter 36 - Continuity of service.
Part 4. Protection For Safety
Chapter 41 - Protection Against Electric Shock
Chapter 42 - Protection Against Thermal Effects
Chapter 43 - Protection Against Over current
Chapter 44 - Protection Against Voltage disturbances and electromagnetic disturbances.
Part 5. Selection & Erection of Equipment
Chapter 51 - Common Rules
Chapter 52 - Selection & Erection of Wiring Systems
Chapter 53 - Protection, isolation, switching, control and monitoring.
Chapter 54 - Earthing Arrangements & Protective Conductors
Chapter 55 - Other Equipment
Chapter 56 - Supplies for Safety Services
Part 6. Inspection & Testing (was part 7 in 16th edition)
Chapter 61 - Initial Verification
Chapter 62 - Periodic Inspection & Testing
Chapter 63 - Certification & Reporting
Part 7. Special Installations Or Locations (was part 6 in 16th edition)
Section 700 - General
Section 701 - Locations Containing a Bath or a Shower
Section 702 - Swimming Pools and other basins
Section 703 - Rooms and cabins containing Sauna heaters
Section 704 - Construction and demolition Site Installations
Section 705 - Agricultural & Horticultural Premises
Section 706 - Conductive locations with Restrictive movements
Section 708 -Electrical Installations in Caravan, camping parks and similar locations.

Part 7. Special Installations Or Locations(cont)
Section 709 - Marinas and similar locations
Section 710 – Medical locations Reserved for Future Use
Section 711 - Exhibition installation's, shows, stands, displays.
Section 712 - Solar Photovoltaic (PV) power supply systems (solar power)
Section 717 - Mobile or transportable unit.
Section 721 - Electrical installations in Caravans and Motor Caravans.
Section 740 - Temporary Installation's for structures, amusements and devices used at
fairgrounds, amusements and circuses
Section 753 - Floor and Ceiling heating systems
1 British Standards to which reference is made in the Regulations.
2 Statutory Regulations & associated memorandums.
3 Time/current characteristics of overcurrent protective devices & RCDs
4 Current carrying capacity and volt drop for cables & flexible cords.
5 Classification of external influences.
6 Model forms for certification and reporting.
7. Harmonized cable colours
8 Current carrying capacity and volt drop for busbar trunking and powertrack systems.
9 Definitions multiple source, DC and other systems.
10 Protection of conductors in parallel against overcurrent.
11 Effect of harmonic currents on balances in 3 phase systems
12 Voltage drop in customers installations
13 Methods of measuring the installation resistance or impedance of floors and walls to
earth or to the protective conductor system.
14 Measurement of fault loop impedance with consideration on the increase in resistance
to the conductors with the increase in temperature.
15 Ring and radial final circuit arrangements, Regulation 433.1
The IEE also publish a set of and guidance notes to be used in conjunction with the
1 Selection and erection of equipment
2 Isolation and switching
3 Inspection and Testing
4 Protection against fire
5 Protection against electric shock
6 Protection against overcurrent
7 Special locations
The On Site guide published by the IEE provides a short form guide for installations up to
100 amps per phase. It also includes many useful tables and checklists.

1.3 Safety
Electrical testing involves some degree of hazard both to oneself and to other people. As
the regulations primary concern is with the safety of persons, livestock and property, safe
working practices are a must. Safety procedures as detailed in the HSE Guidance Note
GS38 Electrical test equipment for use by electricians' should be observed at all times.
As regards fundamental safety, special note should be taken of Chapter 13 of the IEE
Wiring Regulations BS7671 (page 14) and this should then be compared with the
requirements of the EAWR,1989. It will be seen that these two documents exist in total
harmony as to their aims in regard to the safe use of electricity.
1.4 Competent, Person's Responsible for Inspection and Testing
As we progress through the course it will be appreciated that the person carrying out the
inspection and test of the installation will be responsible for deciding whether or not an
installation complies with the regulations in their entirety.
These course notes will be concentrating on Part 6 of the Regulations. These notes can
not be viewed as a replacement for the Regulations nor can they replace the need for a
sound working knowledge of the Regulations. It will seen that reference must be made to
the other Parts and Appendices within the Regulations other than Part 6.
Therefore the person carrying out the installation (IEE reg 134.1.1 page 19) and the
inspection and testing of any electrical installation work must competent (IEE reg 610.5
page 156). Competency encompasses skills, experience and technical knowledge. The
inspector needs to have experience and knowledge of the type of installation he will be
working on so as to ensure that danger to persons, livestock or property does not occur.

2.1 Reason for Earthing?
The ground under our feet, in fact the whole world can be considered as a conductor which
is at zero potential.
A shock hazard occurs when a person makes contact with two points which are at different
potentials. As people are in contact with the ground which is at zero potential there is a
danger that touching any other surface that may be at a different potential to this will result
in a shock being encountered.
By connecting all those parts, which may become charged to a different potential, to the
general mass of earth, we will do away with the possibilities of shock hazard. By the use of
earthing we also aim to provide a low resistance path for fault currents to flow through,
enabling a high current to flow and the protective device to open.
Electricity always takes the easiest path whether it is through the human body or through
the intended earth conductor. From this we can see the importance of keeping the
impedance of earth paths as low as possible.
The standard method of tying the electrical supply system to earth is by making a direct
connection between the two. This usually entails connecting the neutral or start point of the
three phage supply transformer to earth.
From this we can be fairly certain that the neutral of the system is at, or near zero volts and
that the line conductor will differ from this by 230 volts. We can also see that neutral and
earth will be at the same potential.
By connecting all metal work not intended to carry current to earth by means of protective
conductor, a path is provided for fault currents to flow. This is illustrated and discussed in
the next section.

2.2 Earth loop path
The earth fault loop of a circuit (Zs) includes the following,
Starting from the fault point:
The fault point
The circuit protective conductor
The main earthing terminal
The main earthing conductor
The earth return path
The path through the earth and neutral point of the transformer
The transformer winding
The line conductor from the transformer to the point of fault.
See diagram on page 11

Of what use to us is the measuring of the earth fault loop or Zs of a circuit?

If we know the value of it we can use Ohms Law to calculate the fault current that will flow
if a fault occurs.
The formula we can apply is: voltage = current
From this we can see that Fault Current and Earth Fault Loop Impedance are directly
linked, the lower the earth fault loop the higher the fault current and vice versa.
Therefore, the lower the earth fault loop, the higher the fault current, the quicker the
protective device will operate to cut off the current. If we limit the maximum value of the
earth fault loop we can be confident that the fault current will be of a higher magnitude to
operate the protective device before dangerous shock can occur.(IEE reg 411.3.2 page 46)
The values of Earth loop impedance are compared to tables in the regulations to determine
the required disconnection times are achieved. (IEE reg Table 41.2 page 48)
For example if a BS 1361 fuse is to be used as our protective device, for a disconnection
time of less than 0.4 seconds in a circuit with a Uo of 230 volts and rated at 20 amps the
maximum Zs value is 1.70 Ω.
More values for disconnection times can be found in Appendix 3 which have graphs and
tables for most of the common types of protective devices.
Using a BS 1361, 20 amp fuse, for a disconnection time of 0.1 sec what current would be
required to flow in order to satisfy the 0.1 second disconnection time?
IEE reg fig 3.1 (page 244) shows a graph and a table. The graph plot start at 0.1 sec and
for a 20 amp fuse it intersects the current lines at just under the 200 amp mark.
This can be confirmed by examining the table in the far right hand corner which confirms
that a current of 180 amps must flow to enable the fuse to disconnect within 0.1 seconds.

2.3 Earthing Arrangements
Electrical systems are classified according to their earthing arrangements. The following
letter designations are used:
The first letter indicates the Supply earthing arrangements.
T One or more points of the supply are directly connected to earth
I supply system not earthed, or one point earthed through a fault
limiting impedance. (Not used in this Country)
The second letter indicates the Installation earthing arrangements
T exposed conductive parts connected directly to earth
N exposed conductive parts connected directly to the earthed point of
the source of the electrical supply.
The third letter indicates the Earthed Supply Conductor arrangement
S separate neutral and protective conductors
C neutral and protective conductors combined in a single conductor.
The types of system detailed in the Wiring Regulations are: IEE part 2 definitions (page

TN-S System
With this system the neutral and CPC are separate throughout the system. This type of
system applies to underground cables where the metal sheath of the supply cable is
connected to the consumers earth terminal and therefore provides a continuous earth path
back to the star point of the supply transformer.
TT Systems
With this system the Supply Company do not provide an earth terminal. The supply is
usually via overhead lines. The consumer has to provide an electrode to connect the
protective conductors of the installation to earth. Effective earth connection is sometimes
difficult to obtain so therefore a residual current device will need to be installed.

TN-C-S Systems
With this system the Supply Company uses a combined protective and neutral (PEN)
conductor, at this stage the supply is a TN-C system. The consumer installation will consist
of separate neutral and protective conductors (TN-S). This combination is known as TN-CS.
The majority of new installations are of this type and are referred to as a PME supply.
With this system the neutral and protective conductors are combined in a single conductor
throughout the installation. This type of arrangement can only be used with permission
from the appropriate authority.
IT Systems
This type of system has either no earth connection or is connected via a high impedance.
This type of system is not allowable in the UK but is included in the Regulations for
European harmonization.

3.1- General Requirement
IEE reg 610.1 (page 156) Every installation shall, during erection and/or on completion
before being put into service be inspected and tested to verify, so far as reasonably
practicable, that the requirements of the Regulations have been met.
The reasons for an inspection and test of an electrical installation is to verify that the
installation complies with the Regulations with regard to its Design and Construction. To
help the person carrying out the inspection to for fill these requirements the Regulations
call for the following Information to be made available:
The results of the assessment of general characteristics required by sections 311,312 and
This would include:
1.The Maximum demand for the installation
2.The Number and type of live conductors ie, single phase two wire ac. Three phase four
wire ac.
3.Type of earthing arrangement ice. TN-C-S TN-S TN-S (See Chapter 2.3)
4.Nominal Voltage
5.Nature of current and frequency
6. Prospective Short Circuit Current at the origin of the installation
7. External Earth Fault Loop impedance Ze (see Chapter 4.8)
8. Type and rating of overcurrent device at the origin of the installation.
The Regulations also call for the information to a be made available as (IEE reg 514.9
page 93).This may be in the form of a chart. This would provide all the necessary
information as to circuit type, number of points and their positions, cable sizes, protective
device types and their ratings etc.
Without the above information the person responsible for the inspection will not be able to
carry out his job.

3.2 Initial Inspection
IEE reg 611.1 (page 156) Inspection shall precede testing and shall normally be done with
that part of the installation disconnected from the supply.
Guidance Note 3 suggests some 180 items to which special attention should be paid
during the Inspection process. From this it can be seen that a complete and concise list is
impossible to compile.
In the majority of cases deviations from the Regulations which one will come across while
carrying out the inspection will be down to the experience of the inspector rather than the
ticking of a checklist. From our discussions so far you will see that experience as well as a
sound working knowledge of the Regulations is a must.
It should always be in mind that the Regulations state (IEE reg 134.1.1 page 19)
Good workmanship by a competent person or persons under their supervision and proper
materials shall be used.
(IEE reg 612.2 page 156) calls for the inspector to confirm that equipment has been
selected in accordance with section 511 of the Wiring Regulations, and the equipment's
compliance with the relevant British or equivalent Standard.
It also calls for confirmation that, this equipment has been correctly selected and installed,
is suitable for the environment, and has no visible damage that may impair safety.
It can be seen from this that the Inspector has immense responsibility placed upon him as
to the safety of the installation.
Visual Inspection is essential to assess the safety of an installation before testing takes

(IEE reg 611.3 page 156) The inspection shall include at least the checking of the following
items, where relevant to the installation and, where necessary, during erection.
It should be noted from the above that the inspection of some of the items can only be
carried out during installation as they will be hidden from view upon completion.
The minimum inspection should include where relevant the following items:
1) Connection of conductors
2) Identification of conductors
3) Routing of cables in safe zones or protection against mechanical damage
4) Selection of conductors for current-carrying capacity and voltage drop, in accordance
with the design
5) Connection of single-pole devices for protection or switching in line conductors only
6) Correct connection of accessories and equipment
7) Presence of fire barriers and protection against thermal ejects
8) Methods of protection against electric shock
9) Prevention of mutual detrimental influences
10) Presence of appropriate devices for isolation and switching correctly located.
11) Presence of undervoltage protective devices.
12) Labelling of protective devices switches and terminals.
13) Selection of equipment and protective measures appropriate to external influences.
14) Adequacy of access to switchgear and equipment.
15) Presence of danger notices and other warning signs.
16) Presence of diagrams, instructions and similar information.
17) Erection methods.
(a) Method for Basic and Fault protection, i.e
Limitation of discharge energy
(b) Method for Basic protection (including measurement of distances where
appropriate), i.e:
Protection by insulation of live parts
Protection by a barrier or an enclosures
Protection by obstruction
Protection by placing our of reach
Protection by PELV

c) Method for Fault protection.
Earthed equipotential bonding and automatic disconnection of supply Presence of earthing
Presence of protective conductors
Presence of main equipotential bonding conductors
Presence of supplementary equipotential bonding conductors
Presence of earthing arrangements for combined protective and functional purposes
Use of class 2 equipment or equivalent insulation
Non-conducting location (including measurement of distances, where appropriate)
Absence of protective conductors
Earth-free local equipotential bonding
Presence of earth-free equipotential bonding conductors
Electrical separation

3.3- Periodic inspection (IEE chapter 62 page 162)
Periodic inspection is somewhat different to the initial inspection procedure.
The above Regulation refers to 'Careful Scrutiny' backed up by testing.
Visual Inspection is the VITAL initial operation and testing is in support of this Visual
In many cases diagrams and circuit charts will not be available so some exploratory work
will be required. The Visual Inspection shall be concerned with the Verification that the
safety of persons, livestock and property has not or will not be endangered.
A thorough Visual Inspection shall be made of all electrical equipment which is not
concealed. It will include many of the items listed under initial inspection.
It is a requirement of the Regulations that the person ordering the work be informed of the
need for Periodic Inspection and Testing. Installations which are subject to licensing have
mandatory intervals between tests which must be followed. Guidance Note 3 gives
guidance as to recommended intervals.

Table 2.1.5 Recommended initial frequencies of inspection of electrical installations
Type of installation Routine check
sub-clause 2.1.4
Maximum period between
inspections and testing as
(see notes below)
General installations
Educational establishments
Residential accommodation
1 year
4 months
1 year
1 year
1 year/ Change of
1 year
1 year
1 year
Change of tenancy 10 years
Change of tenancy 5 years
5 years
5 years
5 years
5 years
5 years
5 years
5 years
Building open to the public.
Church installations
Leisure complexes
Places of public
Restaurants and Hotels
Public Houses
Village halls/ Community
4 months
1 year
4 months
4 months
1 year
4 months
1 year
1 year
1 year
5 year (quinquennially)
1 year
1 year
5 years
1 year
5 years
5 years
External Installations
Agricultural and Horticultural
Caravan Parks
Highway power supplies
Fish farms
1 year
1 year
6 months
as convenient
4 months
4 months
3 years
3 years
1 year
6 years
1 year
1 year
Special Installations
Emergency Lighting
Fire Alarms
Petrol Filling stations
Construction site installations
Daily/ Monthly
Daily/ weekly/
1 year
1 year
3 months
3 years
1 year
1 year
1 year
3 months
Reference Key
1. Particular attention must be taken to comply with SI 1988 No 1057. The Electricity Supply Regulations 1998 (as amended).
2. SI 1989 No 635. The Electricity at Work Regulations 1989 ( Regulation 4 and Memorandum
3. See BS 5266:Part 1: 1988 Code of Practice for the emergency lighting of premises other than cinemas and certain other specified
premises used for entertainment.
4. Other intervals are recommended for testing operation of batteries and generators
5. See BS5839: Part 1:1988 Code of practice for system design and installation and servicing (Fire detection and alarm systems for
6. Local Authority Conditions of Licence
7. SI 19995 No 1129 (Clause 27) The Cinematograph (Safety) regulations.

4,1 - Sequence of Tests
Testing of electrical installations can be divided into two distinct parts:
Tests to be carried out before the supply is connected, or with the supply disconnected.
Within this section the sequence for testing is:
(a) 4.2 Continuity of protective conductors, main and supplementary
(b) 4.3 Continuity of ring final circuit conductors
(c) 4.4 Insulation resistance
(d) 4.5 Site Applied Insulation
Protection by separation of Circuits
Protection by Barriers or Enclosures Provided During Ere
Insulation of Non-conducting Floors and Walls
(e) polarity
(f) Earth electrode resistance
Once the electrical supply has been connected recheck polarity using a suitable mains
voltmeter then carry out the following tests:
(a) 4.8 Earth fault loop impedance
External Earth Fault Loop Impedance
Prospective Short Circuit Current
(b) 4.9 Residual current operated devices
(c) Functional test of switchgear etc

Before continuing with the tests consideration must be taken with the subject of isolation of
the circuit.
When isolating it should be confirmed that after isolation the expected circuits are not live
by the use of a suitable test meter set to the suitable voltage setting.
The isolation method should be locked of by either removal of fuses, which are then
secured. Or the application of a locking device.
A notice should be placed at the isolation point to confirm the circuit is isolated and warning
not to re energize the circuit.
These are important steps in the test procedures, they should be included in any procedure
both in working practice and practical or written examination.
4.2 Continuity of Protective Conductors
(IEE reg 612.2.1 page 158)
The above regulation requires that every protective conductor including bonding
conductors shall be tested to verify that they are electrically sound and correctly
Note: Guidance Note 3 states that
For cables having conductors of a cross- sectional areas not exceeding 35mm their
inductance can be ignored. Above that figure the inductance becomes significant and an
A/C. Instrument should be used for the measurement.
We are unaware of any Company who at the present time manufactures or sells such an
For the purpose of the following tests a continuity tester able to read to a resolution of
0.01ohms is required. The full specification is detailed in the chapter dealing with
Instrumentation Requirements.

Test method 1 - Linking line and CP conductors at the distribution board.
Connect a temporary link between the line and the CPC conductors. Using a low
resistance ohmmeter test between the line and earth terminals at each outlet in the circuit.
The measurement obtained at the furthest point of the circuit should be recorded on the
results schedule. This reading is the value R1+R2.
Points to note
Multi Meter set to the low Ω range
a = Temporary link between line and CPC at the consumer unit.
All fuses should be removed or MCB'S switched off Main switch switched off.
* Ensure Removal of temporary link when testing is complete.

Test Method 2 Long lead Method
Connect one terminal of the ohmmeter to the earth terminal at the distribution board via a
lead long enough to reach the farthest extremity of the circuit under test. The other terminal
is then used to make contact with each outlet on the circuit.
Once the resistance of the test leads is subtracted from the readings the figures can be
Points to note
Multi Meter set to the low Ω range
Note All fuses out or MCB'S switched off Main switch turned off

From the foregoing descriptions it can be seen that in the majority of cases Method 1 will
be the preferred method. For the testing of bonding conductors Method 2 is the only
applicable method.
Where the protective conductor has been sized according to the alternative method to
IEE reg 411.3.2 62 page 46 of the Regulations a separate measurement of the protective
conductor is required using Method 2.
lt should be noted that the aforesaid methods of test can only be applied to an 'all insulated'
Installation's incorporating steel conduit or trucking, m.i.c.c. and swa cables will
introduce parallel earth paths which will effect the test readings.
Precautions will need to be taken to identify and eliminate these effects while testing. It can
be seen from this that this stage of testing may have to take place during the installation
process rather than being left till the end.
Guidance Note 3 contains details of the procedures to be followed when steel conduit, etc.
is relied upon as the protective conductor further test can be summarized as follows:
A standard continuity test as detailed in Tests 1 & 2 above. This should be followed by a
visual inspection along the length of the protective conductor path to identify any obvious
points where problems may arise.
The majority of electricians these days will not choose to use steel conduit, etc as the
protective conductor for a circuit, so the above problems should not arise.

4.3 Continuity of Ring Final Circuit Conductors
(IEE reg 612.2.2 page 158) A test shall be made to verify the continuity of each conductor
including the protective conductor, of every ring dual circuit.
As a rink circuit relies on both sets of three conductors to be connected for the circuit to
meet the design criteria as regards current carry capacity and short circuit protection, and
due to the fact that faults occurring may not be immediately apparent, ie. the circuit will still
function with one 'Live' conductor disconnected, it can be seen that testing is of utmost
Tests need to be carried out to Confirm that line, neutral as well as CPC form uninterrupted
Correctly connected ring circuit showing equal current sharing on each leg of the ring.

Possible Dangerous Ring Circuit Faults
Here a brake has occurred in on leg of the ring circuit, this results in the cable on the other
leg of the ring becoming overloaded, especially towards the consumer unit side of the leg,
the load could be 27A .

A bridge in the circuit hides the fact the ring is not complete, this fault would not be picked
up in the test for the continuity of CPC, as tested earlier pages 24 and 25.

Test 1 To Confirm the ring is complete
Each individual leg of the ring needs to be identified. The line conductor of one leg of the
ring is conceded to the neutral conductor of the other at the distribution board. The
resistance is measured between the remaining line and neutral conductors. This test
confirms that both the line and neutral conductors form rings.
Points to note
Multi Meter set to the low Ω range

This above test is repeated using the line conductor and the circuit protective
Test 2 to confirm the absence of bridges

lt is possible that Test 1 will indicate that the ring is complete, because of a bridge in the
ring as per page 29. This shortening of the ring could cover up the fact that the ring may be
broken at another point, resulting in an overloading of the cables at that point.
Test 2 confirms that the above situation does not exist.
With the conductors connected as in Test 1, connect the remaining line and neutral
conductor together. The resistance been line and neutral at each outlet is then measured.
This reading will remain substantially the same at each outlet that is incorporated into the
ring provided that no multiple loops exist. This test will also indicate any outlets which may
be connected as a spur to the ring.
The values should be within 0.05 Ω of each other.
Points to note
Multi Meter set to the low Ω range

The above test is repeated using the line conductor and the circuit protective conductor.
The highest reading taken is considered as the measured value of R1+R2.
The values should be within 0.05 Ω of each other.

Where the protective conductor is in the form of a ring, the above two tests will need to be
repeated, substituting the protective conductor for the neutral conductor in each test.
The reading obtained in Test 2 at each outlet between the line conductor and protective
conductor will be equal to the value of R1 + R2 for that circuit and should be recorded. This
result will also be equal to one quarter of the value obtained in Test 1.
When testing between line conductor and protective conductor.
R1+R2 = result of Test 2 = result of test 1
While it should be easy to identify each leg where multi core cables are used, this may not
be the case where single core cables are used. An error in identification and connection of
the legs of the ring will be immediately apparent while conducting Test 2.
An error in this respect will show up as progressively increasing readings towards the
midpoint of the ring and then a decrease away from the midpoint. If this encountered then
the error in connection will need to be rectified and both Tests 1 & 2 repeated.

Insulation tests
(IEE reg 612.3 page 158)
These tests are to confirm that the insulation of conductors and equipment is satisfactory
and that short circuits do not exist.
Testing is carried call with an insulations tester that generates the required voltage as
specified in Table 61 of the regulations at a current of 1mA.
In the case of electrical installation up to and including 500V the test voltage required will
also be 500V.
Whereas in the past the Regulations called for various pieces of electrical equipment to be
disconnected from the mains and for lamps etc to be removed this is now recognized as
not always practical.
The Regulations now state that 'where appropriate line and neutral conductors may be
connected together and a test to earth carried out. Simple installations which do not
contain distribution circuits may be tested as a whole rather than as individual circuits.
Although Table 61 calls for an insulation value of not less than 1 megohms for an
installation of up to 500V if the result is below 2 megohms each circuit will need to be
tested separately The-result for individual circuits must exceed 1 megohms.
Example of IEE reg table 61 page 158
Minimum values of insulation resistance and meter test voltage settings
Circuit nominal voltage
Test voltage D.C
Minimum insulation
SELV and PELV 250 ≥ 0.5
Up to and including 500v
with the exception of the
above systems
500 ≥ 1.0
Above 500v 1000 ≥ 1.0

Insulation test for a complete installation
Points to note
Meter set to a test voltage of 500 volts DC (IEE reg table 61 page 158), for testing a 230
volt circuit
Range set to MΩ
The main switch is isolated
All fuses are in and MCB's switched on.
A temporary link is placed between the line a neutral conductors
All fuses should be left in place or MCB'S switched on Main switch switched off.
• Ensure Removal of temporary link when testing is complete.

Three Phase
Testing of three phase circuits involves making a series of tests. The conductors will be
grouped into two groups and an insulation test carried out between the two groups.
Group A Group B
Test 1 Phase 1 Phase 2
Phase 3
Test 2 Phase 2 Phase 3 Neutral
Test 3 Phase 3 Neutral
Test 4 Phase 1 Earth
Phase 2
Phase 3
Where it is not possible to group conductors as above, they may be tested singularly.

4.5 Other Tests
Guidance Note 3 includes several tests which we do not intend to cover in any great detail
within these course notes. For further details reference should be made to the Guidance
The relevant tests are as follows:
Site Applied Insulation
This test is only applicable where insulation is applied during installation. It involves the use
of a high voltage tester capable of apply a voltage of 3750 V
Protection be Separation of Circuits
This relates to the testing of SELV and FELV transformers to confirm separation of primary
and secondary parts of the circuit.
Protection by Barriers or Enclosures Provided During Erection
This test does not apply to factory built equipment, but only to those provided on site during
the course of assembly or erection. It is concerned with checking that the enclosure meets
the relevant ip rating.
Protection by a non conducting Location
This deals with insulation of non-conducting floors and walls. It includes details of the
required high voltage testing.

4.6 Polarity Testing
(IEE reg 612.6 page 159) A test of polarity shall be made and it shall be verified that :-
Every fuse and single-pole control and protective device is connected in the line conductor
Center-contact bayonet and Edison screw landholders to BS EN 60238 in circuits having
an earthed neutral conductor have the outer or screwed contacts connected to the neutral
Wiring has been correctly connected to socket-outlets and similar accessories.
If a switch or fuse is connected in the Neutral conductor of a circuit rather than in the line
conductor, mains potential voltages will continue to be present throughout the circuit when
the switch is opened or the fuse pulled.
This would give rise to the scenario of a circuit appearing to be 'dead' but in actual fact
posing very real danger.
Use an Ohmmeter or the continuity range of an Insulation and Continuity tester for this
sequence of tests.

Method 1 - Linking the Line and CP conductors at the Distribution Board
The method used here is the same as the test described as method 1 for checking the
continuity of protective inductors. This involves connecting a temporary link between the
line conductor and the protective conductor. And then checking at each outlet, including
switch positions, for a low resistance reading between line and Earth.
Ensure that the circuit is isolated before carrying out this test
Remove the link after the test.

Method 2 - Using a Long Lead
Method 2 involves using a long lead. One end of the long lead is connected to the line
conductor at the distribution board and the other end is connected to one terminal of the
ohmmeters The other lead of the Ohmmeter is then used to check each line connection
throughout the circuit for continuity.
If the tests for ring circuits have been carried out as described, correct connection will
already have been verified and no further testing is required
Ensure that the circuit is isolated before carrying out this test

4.7 Earth Electrode resistance
IEE reg 612.9 page 160 Where protective measures are used which require a knowledge
of the earth electrode resistance, this shall be measured.
Testing to check Compliance with IEE reg: 415.2.2 Page 59
Method 1 Using a Dedicated Earth resistance Tester (Figure 4.7)
The earth electrode under test needs to be disconnected from the earthing system of the
installation. As this electrode is likely to be the primary means of earthing for the
installation, this will necessitate the complete isolation of the installation for safety reasons.
Two temporary earth spikes are driven into the ground for testing purposes. The distance
between these earth spikes is important. If the earth spikes are placed too close together
their resistance areas will overlap and false readings will be obtained.
The first, or 'current' spike is driven into the ground at a distance away, from the electrode
under test , equivalent to 10 times the length of the electrode under test.
ie. for an earth electrode 2 meters long the current spike should be placed 20 meters away
from the electrode under test.
The second, or 'potential' spike, is driven into the ground midway between the electrode
under test and the 'current' spike. The earth electrode resistance tester is connected and a
reading is taken. The 'potential' spike is then moved 10% closer to the earth electrode
under test and another reading taken. The 'potential' spike is then moved 10% closer to the
'current' spike and a final reading taken.
The average of the three readings is taken. If there is a difference greater than 5%
between any of the above three readings and the calculated average, then the test
distance between the earth electrode under test and the 'current' will need to be increased
and the above testing procedure repeated.
Upon Completion, Ensure Bonding is reconnected before switching on the
Figure 4.7

Test method 2 Using a Loop Impedance meter
Testing For compliance with IEE reg: 411.4.5 (page 48)
This method is intended as an alternative to method 1 for TT installations where the earth
electrode is used in conjunction with a residual current device to provide fault protection.
As with method 1 the main bonding needs to be disconnected from the equipotential
bonding. This is to eliminate the possibility of erroneous readings due to parallel earth
paths and to ensure that the full test current passes through the earth electrode under test.
A loop impedance tester is connected between the line conductor at the source of the
installation and the earth electrode under test. The impedance reading taken is treated as
the electrode resistance.
Upon Completion, Ensure equipotential Bonding is reconnected before switching
on the installation.

What results should we be looking for?
What we are trying to accomplish with our use of earth electrodes is to make sure that
when a fault occurs the voltage between earthed metalwork and earth will not exceed 50
Where an RCD with a tripping current of 30mA is used, this means that if we apply Ohms
Law to the problem, we would come up with a theoretical value of 1.666ohms
50 V
0.03 A = 1,666 Ohms
BS 7430 Code of Practice for Earthing suggests that earth electrodes with values
exceeded 220 ohms are prone to be unstable.
Maximum values for earth electrodes will more likely be dictated by other regulations such
as HS(G)41 detailing petrol station installations, which calls for a value not exceeding 21
Obviously the lower the resistance of the earth electrode the better.

4.8 Earth Fault Loop Impedance
IEE reg: 612.9 (page 160) Where protective measures are used which require a
knowledge of earth fault loop impedance, the relevant
impedance's shall be measured, or determined by an
alternative method.
Testing for compliance with IEE reg: 411.4.5 (page 48)
Earlier on in the notes we discussed the meaning of Earth Fault Loop impedance and we
saw the reasons for limiting its upper value.
The earth fault loop impedance (Zs) should be determined at the furthest point of each
circuit. This includes socket outlets, lighting points, sub-main cables and other circuits
supplying fixed current using equipment.
Measuring of the earth fault loop impedance (Zs) for circuits incorporating socket outlets
involves no more than plugging in the loop tester and taking a reading. The result obtained
includes the earth fault loop external to the installation (Ze).
For other circuits such as lighting circuits or circuits feeding fixed equipment not connected
via a plug and socket, use will have to be made of a purpose designed set of leads and
A loop tester which does not trip RCD will need to be used or the value calculated.
With the loop tester, the neutral connection is there only to power the test instrument.
Where a neutral is not available, such as in a 3 phase motor circuit the neutral lead will
need to be conceded to earth along with the earth lead of the tester.

Once we have obtained an earth fault loop impedance reading to what does one compare
it? IEE reg: 411.3.2 (page 46) including table Table 41.1 give the required disconnection
times for TN and TT systems.
IEE Tables 41.2, 41.3, 41.4 and 41.5 (pages 48,49 and 50) of the Wiring regulations give
maximum earth fault loop impedance's for various types and ratings of MCB'S and fuses. It
should be noted that these values are intended as design values only. When a person
responsible for the design of a circuit calculates the maximum earth fault loop or Zs for a
circuit the formula is as follows:
Zs = Ze + (R1+R2)
Zs = Earth Fault Loop Impedance of the System
Ze = Earth Fault Loop Impedance External to the Installation
RI = Resistance of the line conductor from the origin of the circuit to the furthest point of
R2 = Resistance of the protective conductor from the origin of the circuit to the furthest
point of utilization
Under fault conditions the temperature of the conductors will rise until the fault current
reaches a point where the overcurrent protective device operates. To take a account of
this rise in temperature the designer applies a factor to the R1+R2 figure before comparing
his figures with the values shown in IEE Tables 41.2, 41.3, 41.4 and 41.5 (pages 48,49
and 50) . The values for this factor can be found in the 'On Site Guide' published by the
Obviously our testing takes place at a temperature far less than the temperature the cable
reaches under fault conditions. To take this into account we would have to apply the same
multiplier as well as to correct the values of R1 and R2 for differing temperature.
Alternatively we could compare our readings with the maximum values detailed in the 'On
Site Guide' , published by the IEE, as the figures contained within this publication have
been adjusted to take the above into account.
Another acceptable method is to divide the reading obtained by our loop tester by a factor
of 0.75. This applies to protective devices listed in the regulations. For protective devices
not listed the factor is 0.66.
i.e.: For a loop tester reading of 1 ohm the adjusted value will be 1 =1.33 ohms
This value can then be compared directly with tables IEE Tables 41.2, 41.3, 41.4 and 41.5
(pages 48,49 and 50)

Measurement of the External Earth Fault Loop Ze
The Ze or, External Earth Fault Loop impedance, is measured using a phase earth loop
impedance tester at the source of the installation supply. The outgoing supply needs to be
isolated along with the means of earthing, which involves isolating the main bonding
conductor from all other earthing conductors. The reason for isolating the main earth is to
remove the possibility of erroneous readings due to parallel earth paths.
Do Not Forget To Reconnect Bonding

Measurement of Prospective Short Circuit Current
Prospective Short Circuit Current (PSCC) is the current likely to flow in a circuit under fault
conditions. It is the largest current that is likely to flow in a circuit. Protective devices such
as fuses,MCB must be able to break this fault current safely and should be selected in
accordance with the PSCC.
Zt + Z1 + Z 2
Zt = Impedance of transformer winding
Z1 = Impedance of line conductor
Z2 = Impedance of Neutral conductor
U0 = Voltage
By Using a loop tester to measure the line - Neutral loop we can calculate the PSCC.

4.9 Residual Current operates Devices
IEE reg 612.10 (pages 160) Where RCD's are required for additional protection, the
effectiveness of automatic disconnection of supply by RCD's shall be verified using
suitable test equipment according to BS EN 61557-6 (see regulation 612.1) to confirm that
the relevant requirements of Chapter 41 are met.
In order to test the effectiveness of an RCD it is necessary to carry out a series of tests to
confirm that the RCD operates within correct time and current parameters. This sequence
of tests is in addition to using the integral test button incorporated in the RCD. IEE reg
612.13.1 (page 161)
The test is made on the load side of the RCD, between the line conductor and the CPC of
the circuit. The test current is obtained from the live and neutral of the circuit under test.
Any loads connected should be disconnected.
The sequence of tests is:
1)To apply a current equal to 50% of the rated tripping current of the RCD for a period of 2
seconds. The RCD should not trip.
2)Application of a current equal to 100% of the rated tripping current of the RCD. The RCD
should operate within 200mS.
3)Where the RCD is used to provide supplementary protection for basic protection, a test
current of 150 mA is applied for a maximum period of 50 mS. The RCD should operate
within 40 mS.
4)The integral test button incorporated in the RCD is now operated. This checks the
operation of the mechanical parts of the RCD. It does not check the continuity of the
protective conductors or the rest of the earthing system.
The above sequence and results apply to non delayed RCD'S complying with BS 4293. For
time delayed RCD'S the results for test 2 should be within the following range:
50% of rated time delay plus 200mS, and
100% of rated time delay plus 200mS
i.e For an RCD with a delay of 200mS it should trip within a time range of:
( 100 + 200 ) mS = 300mS and
( 200 + 200 ) mS = 400mS

Testing of 3 Phase RCD'S
With certain 3 phase circuits protected by RCD'S a neutral may not be available. As the
RCD tester obtains its test current from the line and neutral of the circuit under test this
poses a problem. We can overcome this by connecting the neutral lead of the tester to
earth. However, it should be noted that the test current will be increased and may trip the
RCD on the 50% test. The RCD should not necessarily be failed in this instance.
Care must be exercised while carrying out the testing of RCD'S as potentially dangerous
voltages may appear on exposed and extraneous conductive parts when the earth fault
loop impedance approaches the maximum acceptable limit.

4.10 Functional Test Of Switchgear
IEE reg 612.13.2 (page 161)
Assemblies such as switchgear and control gear assemblies, drives controls and
interlocks, shall be subjected to a functional test to show that they are properly
mounted adjusted and installed in accordance with the relevant requirements of these
As a final test the above should be carried out. This would include the switching off and on
of MCB'S etc, to make sure that their mechanical operation is satisfactory.

4.11 Periodic Testing
Periodic testing of an installation should be carried out in the following order:
(a) Continuity of protective conductors and earthed equipotential bonding.
(b) Polarity.
(c) Earth fault loop impedance.
(d) Insulation resistance.
(e) Operation of devices for isolation and switching.
(f) Operation of residual current devices.
Where appropriate, the following tests should also be made:
(g) Continuity of ring circuit conductors.
(h) Earth electrode resistance.
(i) Manual operation of overcurrent protective devices other than fuses.
(j) Electrical separation of circuits.
(k) Protection by non-conducting floors and walls
How much testing needs to be done?
Guidance Note 3 suggests that a random selection of points is tested. This should be equal
to 10% of the installation. If faults were discovered within this batch the batch should be
expanded to 25% and then on to 100% if further faults are discovered.
All socket outlets should be checked for correct polarity.
When checking the continuity of bonding or equipotential bonding conductors the
installation should be isolated from the mains. On no account should bonding conductors
be disconnected with the mains on.

5.1 Certification and Reporting
Chapter 63
Once the initial verification ( this includes both inspection and testing) has been completed
the above regulations call for the issuing of an Electrical Installation Certificate, together
with a schedules of test results. This Certificate should be given to the person ordering the
work. The above mentioned Certificate would be incomplete and void if a schedule of test
results was not included.
Who is responsible for signing the certificate? The Certificate includes space for three
signatures, the person responsible for the Design, the person responsible for the
construction and the person carrying out the Inspection and Test of the installation.
It should be emphasized that the signature for the Inspection and Test section is the
person who actually carries out the Inspection and Test and not someone else who may be
in authority. In some cases all three sections will be signed by the same person. This is
perfectly acceptable.
The Electrical Installation Certificate should not be signed until any defects, which the
person responsible for inspection and test may have identified, have been corrected.
Alterations and Additions
An Electrical Installation Certificate as above or a Minor Electrical Installation Works
certificate , stating the extent of the works covered, shall be issued once the Inspector is
satisfied that the works comply with the Regulations. Any defects found in related parts of
the installation, not effecting the safety of the alteration or addition, should be reported in
writing to the person ordering the work.
If existing defects effect the new work then these defects would have to be corrected
before an Electrical Installation Certificate could be issued and before the new work could
be put into service. An example of this is where bonding or equipotential bonding is
inadequate or omitted as this would seriously effect the safety of the whole installation
including the new work.
The Electrical Installation Certificate should not be used for Periodic Inspections.

Periodic Inspection report
The Periodic Inspection Report form is only to be used for the inspection of an existing
installation. It shall include both inspection and test results.
Again the Extent and Limitations as to the report shall be stated. Recommendations as to
defects and their remedied shall be made.
The report includes a numbering system for this purpose, as follows:
1 Requires Urgent Attention
2 Requires Improvements
3 Requires Further Investigation
4 Does Not Comply With BS 7671:2008 (as amended)
(this does not necessarily imply that the electrical installation is unsafe)
Again, with the Periodic Inspection and Test the main consideration is safety.

Minor Works certificate
Several associations and trade bodies allow the issuing of a 'Minor Works Certificate'. A
minor works is defined as 'work which does not include the provision of a new circuit'
Testing is still essential and the following tests should be carried out to confirm safety.
The Tests are as follows:
1) Circuit impedance R1+R2
2) Insulation Resistance line/Earth
3) Earth Fault loop Impedance
4) Polarity
5) RCD Operation
Included on the form is space to allow the Inspector to comment on the existing installation.

6.1- instrumentation requirements
Continuity Tester
Accuracy +/- 2%
Resolution 0.01 ohms
No Load Voltage 4 - 24v ac or dc
Test Current 200 mA
Insulation Resistance
Accuracy +/- 2%
Test Current 1 mA at the minimum allowable resistance value
i.e 250k for 250v range
500k for 500v range
1M for 1000v range
Other requirements i.e. Must have the capability to discharge capacitance which has
become charged during the test.
Earth Electrode Resistance Tester
Accuracy +/- 2%
Other requirements Facility to check potential and current spikes are within the
testers limits.
Loop Impedance Tester
Accuracy +/-2%
Test Current 20-25A for up to two or four cycles
RCD Testers
Accuracy of test currents + /- 10%
Accuracy of times +/-5%
Time resolution 1mS
Other requirements Able to perform tests for Reg. 713-12
Suitable for RCD ratings of 6,10,30,100 & 500mA
Must apply 150mA test current for no longer than 50mS

International Protection provided by
I.P Ratings
To BS EN 605299

Number Degree of
protection against
ingress of solid
foreign objects
Number Degree of
protection against
ingress of water
0 Not protected 0 Not protected
1 Protected against
access to hazard
parts by back of hand
Protection against
foreign objects of
50mm diameter and
1 Protection against
vertically falling water
2 Protected against
access to hazard
parts by a finger
Protection against
foreign objects of
12.5mm diameter
and greater.
2 Protection against
vertically falling water
drops when
enclosure tilted at 15º
3 Protection against
tools wires and
others 2.5mm and
3 Protection against
water spraying up to
an angle of 60º on
either vertical side.
4 Protection against
tools wires and
others 1mm and
Protection against
foreign objects of
1mm diameter and
4 Protection against
water splashing from
any direction.
5 Protection against
tools wires and
others 1mm and
Dust protection
5 Protection against
water jets from any

Degree of
protection against
ingress of solid
foreign objects
Degree of
protection against
ingress of water
Dust may enter but
not interfere with the
operation of the
6 As above 6 Protection against
powerful water jets
from any angle.
No code 7 Protection against
ingress of water
when enclosure is
immersed in water in
standard conditions

Degrees of Protection provided by Enclosures
This was better known as Ingress Protection
IP Code Of Protection. -
This C of P is given in BS EN 60390-2, this document is the standard document, which is
used to form the basic requirements of electrical equipment Standards.
The construction for IP ratings of a specific type of equipment are given in a British
Standard document.
Also in the document are the relevant construction requirements for various plugs and
socket outlets, including ( BS 4343 -- now BS EN 60309-2 ), that is why there is no nation
of this IP classification in BS 7671 .
The degree of protection provided by this enclosure is indicated by two numerals and
followed by an optional letter and /or optional two supplementary letters as follows
IP Coded letters International Protection
First characteristic numeral, (from 0 - 6, or could be letter X, not defined )
Second characteristic numeral, (from 0 - 8 or could be letter X.)
Additional letter (optional ) ; A, B, C, D
Supplementary letter (optional ); H, M, S, W.
the reference could be IP 23CH
Where there is a non specific reference, the numbers can be replaced by the letter X ie. IP
XX , if both the numbers are omitted.
The additional letter / (s) can be omitted without replacement.
Where more than one letter is used then the alphabetical sequence shall apply.

Degrees of Protection provided by enclosures
Supplementary Letter
In the relevant product standard classification, supplementary information may be indicated
by a supplementary letter following the second characteristic numeral or the additional
The following letters are currently in use, but extra letters will probably be used as the
standards of various products change.
Product Marking
The requirements for marking a product are specified in the relevant product standard.
For example, IP23CS
The IK code of impact PROTECTION

This IK code of classification was introduced to provide protection for electrical equipment
against mechanical impart.
The code classifies the degree of protection.
Continental countries have their own classification, the IK is now The UK classification,
where there was no previous classification for mechanical impact.
The obvious reason for the introduction of this classification in this country, is that we as a
nation are increasingly selling our products in Europe.
They need to understand our reference with respect to their own.
The standard only describe the general requirements and designations of the system the
application of the system to a specfic enclosure type will be covered by the BS which is
applicable to the enclosure
The IK coding used is marked separately on The equipment from the IP rating.
Coded letters IK Characteristic group 00 to 10
each group represents an impact energy value as shown in the table below

Drip Proof and Splash Proof
Certain electrical equipment has been graded against water ingress by a pictorial
representations which is now superseded by the IP rating, nevertheless these should be
able to be identified and recognized and understood.
The comparisons between the differing references are not exact, but the installer, designer
and the tester of such equipment must be able to recognize the seals used, so that the
equipment being used is suitable for the location of use.

Choice of Protective Devices
The selection of protective devices depends upon :
l . prospective fault current
2. circuit load characteristics
3. cable current – carrying characteristics
4. disconnection time limit.
Show circuit capacities of the protective devices Device type
Device Short-circuit Device Spec Short Circuit Capacity kA
Semi-enclosed fuse to BS 3036 S1A 1
S2A 2
S4A 4
Cartridge fuse to BS 1361 16.5
General purpose fuse to BS 88 50 @ 400v
16.5 @ 230v
80 @ 400v
Circuit breakers to BS 3871 M1 1
M1.5 1.5
M3 3.0
M4.5 4.5
M6 6.0
M9 9.0
Icn Ics
Circuit Breakers to BS EN 60898 1.5 (1.5)
3.0 (3.0)
6.0 (6.0)
10 (7.5)
15 (7.5)
25 (10)
Icn = rated ultimate S / C capacity.; Icn > Ipsc , except where it is used as back-up
protection ref To manufactures information
lcs = This is the max level of fault current operation after which further service is assumed
without loss of performance Protective devices must cater for both: -protection
against overload/ short circuit protection

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