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74
INSPECTION, TESTING AND
VERIFICATION
H.R. Lovegrove
Consultant
1. INTRODUCI'ION The Regulations recognise that, in many instances,
a great deal of the installation is concealed either
The IEE's publication "Regulatiohsfor Electrical within the fabric of the building or buried
Installations" is generally accepted as the standard u d r r u d It is. therefore, necessary to adopt
negon
governing the design and conshuction of electrical procedures that enable conduits. trunlringand cables
installations in the United Kingdom. n e s e to be inspected once installed and before being
Regulations are the basic rules that cover all concealed.
installations operating at voltages up to 1,OOOV.
For high risk installations the British Standards Similarly, testing of protective conductorsshould be
Institution (BSI) publish additional requirements, carried out as the work progresses before
either as a Standard or as a Code of Practice. components and accessories are bonded together
through connections to exposed parts and/or
Part 7 of the BSI 7671: 1992 - Requirements for extnrneous conductive parts. Other testing may
Elecoical Installations (The I E Wiring
E require parts of an installation to be enmgised but
Regulations) covers Inspection and Testing and those parts should not be available for general use
Chapter 71 contains the requirements for Initial until the testing is complete.
Verification.
Some tests will require instruments that either
Initial Verification requires that an installation be generate a high voltage o q u i r e the supply
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inspected and t s e as the work proceeds,ie during
etd ra
voltage t be available. G e t care should be talcen
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erection and before being put into service, in order by the inspector to ensure t a the site personnel are
ht
to verify that the design of the installation, the not exposed to danger.
selection of materials and the equipment as well as
the methods of installation, al conform to the
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relevant Regulations.
To enable the Inspection and Testing to be properly 2. INSPECTION
conducted and to ensure compliance with the
Regulations, the Inspector must be provided with Detailed inspection is required before testing.
certain information from the designer. The usually prior to energising the installation, in order
minimum information required is: the designer's to verify that all equipment used complies with
assessment of general characteristics of the supply; BSI's or other international harmonised stadards.
the purpose and anticipated loadings of the
installation; cable sizing and protective device Additionally, it is important to ensure that materials
selectioncalculations;prospectivefault currents and have been correctly selected for the purpose of use
earth loop impedances at distribution boards, earth and the environment in which they are working,
fault loop impedances of all f d circuits at the that they are properly installed and that neither
point of utilisation; main d i n g and bonding materials nor equipment have been damaged - either
arrangements; positions of isolating and switching during the progress of the works or by any other
devices; and details of any emergency switching trades after installation.
arrangements.
The minimum number of items that require
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checking as part of the inspection process are: From these it becomes obvious t a the inspection
ht
procedure is on-going throughout t e constnrction
h
Terminations, connections and period up to the time the installation is put into
identifcation of conductors. service.
H Selection of conductors for current
canying capacity and voltage drop.
3. TESTING
Selection of equipment and protective
measures appropriate to external It is important that the petson canying out the
influences. testing is both competent and suitably experienced
in the work to be done. Knowledge on the use of
Correct methods of erection including: appropriateinstruments and famikukation with the
adeqwy of fixings and support Health and Safety documents HS(G)U and
of cables HS(G)38 is important. The Regulations define a
-g competent person as someone having a sound
cables and their routing through knowledge and experience relevant to the nature of
safe zones (to avoid damage or the installation and to the technical standards set
deterioration due to heat, down in the Wiring Regulations, who is fully
moisture, dust, corrosive versed in the inspection an testing procedures
substances, etc.). contained in the Regulations and employs adequate
testing equipment.
Connection of single pole switching or
protective devices in phase conductors T s s need t be canied out in a specific order and
et o
only and polarity of socket outlets and if any test indicates failure to comply then the fault
centre contact lampholders. should be corrected before any further tests are
applied.
rm
Protection f o direct contact with live
parts by insulation,barriers and enclosures, The following tests are listed in the sequence of
placing out of reach or by whatever means application:
selected by the designer.
Continuity of protective conductom;
Protection from indirect contact with live Continuity of ring circuit conductors;
parts, normally by earthing and bonding - Insulation resistance;
this involves checking t a protective
ht Site Applied Insulation:
conductors are present and continuous, or Protection by Separation of Circuits:
by Class 2 insulation, o by any other
r Protection against Direct Contact by
acceptable methods that have been chosen B r i r or Enclosures applied during
ares
by the designer. erection;
Insulation of Non-Conducting Floors and
Prevention of mutual detrimental influence, Walls;
either from or to, the equipment. Polarity:
Earth Fault Loop Impedance;
Presence of appropriate isolation and at l c r d
E r h E e t o e Resistance;
switching devices and, if necessary, Operation of Residual Current Operated
checking the operation and function of DeviceS.
emergency switching systems.
Choice and setting for protective and
monitoring devices, overloads, etc. 3.1 Test (i) Continuity of Protective
Conductors (cpc) Figs I and 2
Presence of danger and warning notices,
labelling of switchgear, control gear and This test is required in order to verify that
equipment, and presence of distribution
schedules, diagrams, charts, instructions - protective conductors and bonding conductors
and records of the installation.
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are elecoically sound and correctly connected connections is suspect and requires checking.
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and are continuOus throughout t e r length;
- all items of equipment and accessorieS are
properly connected to the protective et
3.2 Ts (ii) Continuity o Ring C i i t
f
conductors; Conductors Fig 3
- all bonding clamps are making a good contact This test is requited to verify that ring circuits are
with the ~ssociatedpipework or shuctures. correctly wired and connected. Al conductors,
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etd
including the protective conductor, have to be t s e
The instrument used for this test is a DC continuity to ensure that the ring is continuousthroughout,that
tester p e f d l y having 0.01 ohms resolution. A the circuit is not bridged so as to creak an apparent
UhnA test current is presently acceptable but ring with points radiating from it and to ensure that
European regulations have now standardised o n a the circuit is not i-d e
nt with those. of
2WmAtestcurrent. Ifthisstandasdisadoptedby another circuit Ihe instrument that is required for
the BSI it will mean that instruments currently the t s is a low current ohm-meter that has a clear
et
beiig used in the UK will become obsolete o
resolution enabling the user t read to 0.01 ohms.
overnight thus causing a high cost burden on the
industry. The test is usually carried out at the dismbution
board but can be carried out at any point that is
In an installation that employs steel conduits, wired into the circuit. The fmt step is to
mnking or wire armouring as a protective disconnect and separate the circuit conductors and
conductor it is necessary to test further the measure the resistance of each conductor in tum.
protective conductors with a higher test current AC
ohm-meter o an impedance tester. This should
r The next step is to cross-connect the phase
only be done after low current ohm-meter testing is conductorsto the neutral conductors so t a the out-
ht
completed and it has been established that the cpc going phase connects the returning neutral and vice
has a low value of resistance. versa The instrument is then connected to the
phase and neutral of each outlet in turn and tests
The simplest method of test is to connect the circuit are made. The resistance value a each socket that
t
phase and protective conductors together at the is connected as part of the ring will be the same.
h
distribution board and then measure te combined Any sockets that are wired as spurs from the ring
resistance of the conductors a the point of
t will have a higher resistance value.
utilisation of energy (the load position) or at the
extreme points of the circuit. The resistance values The tests are then r p a e with the phase
eetd
recorded represent the R,+& of the circuit and can COndUCtOr CrosS COMeCted to the CpC. If O U t k S are
be used for determining the earth loop impedance connected to the ring then the Ph-Ntest figure will
of the circuit be approximately 50% of the phase loop resistance
and the Ph-Evalue will be approximately 25% of
etd
A l bonding conductors need to be t s e using a
l the sum of the combined phase and cpc resistances.
low current ohm-meter connected to extraneous -
Measured values should be recorded the W-E
conductive parts and the earth terminal to which measurementbeing the R, + R2value for the outleU
they are bonded. The instrument connection to the that ate COMeCted to the Mg.
extraneous conductive part should be applied so that
the test current passes through all pipe clamps, rm
The benefits that can be derived f o this test if
cable lugs, and bolted connections. Fig 2 refers. properly conducted are:
Regulation 413-02-28 states tha the resistance of W Conductors are continuous.
supplementary bonding conductors shall fulfil these
conditions: R = 50& [where 1 is the operating
. W Connections tight.
current of the protective device: (i) ,J if an RCD
(ii) the minimum current for 5 sec disconnection W Circuitcorrectlywired
time if an over-current device].
I Conductors not cross connected with another
In practice, if the resistance of the total bond circuit.
exceeds 0.05 ohms, the reliability of the
77
Neutral and cpc conductors in correct terminal The frt test is made between live conductors.
is
order at distribution board. With a SP&N system this is between the phase and
neuaal. With a TP&N system each live conductor
H Polaritycomt. has t be tested against the other three connected
o
together. The second test is made between all live
H h4axiium R,+R, value identified. conductors together and e r h
at.
H Socket outlets have not been over-heating. The minimum permissable insulation resistance
value must be not less than the values in Table 71A
of the Regulations.
Regulation 713-04-04 relates these to an individual
3.3 Test (ii) Insulation Resistance distribution board with is submain, main protection
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and Bssociatedfinal circuits all connected and with
This test is required before the installation is f x d equipment disconnected.
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connected to the supply to ensure t a there are no
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short circuitsbetween conductors or low insulation Regulation 713-04-05 requires the test instrumentto
resistance due to defective insulation or dampness, be able to maintain a 1mA test c m n t when loaded
as these may cause earth faults in the system or on with the minimim acceptable insulation resistance ;
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equipment. Either will allow leakage o high fault eg for a 24OV system the instrument must maintain
c m n t s to flow which could damage the cables and 1mA when loaded with 0.5 megohms at a test
the equipment. Table 71A in Regulation 713-04-05 voltage of 5OOV.
indicates the test voltages and m i n i u m insulation
resistance values for various nominal voltages of
installations. The instrument required is an
insulation resistance tester with test voltage ranges 3.4 Test (iv)
suitable for the nominal voltage of the system. Site Applied Insulation
Before commencing the tests it is necessary to Test (v)
check that there are no pilot lights or capacitors Protection by Separation of
connected into the system as these can give a low Circuits
resistance reading which will be misleading. Also Test (vi)
electronic devices forming part of the installation Protection against Direct
ht
t a may be damaged by the test voltage and should Contact by Barriers or
be diSCOMeCted. Enclosures applied during
erection
Care must be taken whilst carrying out these tests Test(vii)
to ensm that cables that are charged during the test Insulation o Non-Conducting
f
are given adequate time to discharge before the al
Floors and Wls
instrument is disconnected, otherwise a cable could
be left charged a 500V or lOOOV and this may
t
cause an electric shock resulting in an accident These tests apply generally to where the method of
and/or subsequent injury. protection against indirect contact is other than
earth equipotential bonding. They are specialised
The tests are conducted on one section of the test and are very rarely needed.
installation at a time. Each section comprises a
distribution board with its submain, main switch
and all f d circuits incorporated in the system.
Usually testing is done at the distributionboard but,
if it is more convenient, it can be done at the 3.5 oaiy
Test (viii) P l r t
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supply end of the submain. A l fuses should be in
place, switches and circuit breakefi closed and, It is essential that polarity is correct throughout the
where practical, all lamps and tubes removed and installation and that single pole devices are
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all f x d equipment disconnected. Where it is not COMeCted to phase COndUCtorS Ody. MO that S
practical to remove lamps or disconnect equipment, socket outlets are correctly connected and centre
local switches and isolators should be open. contact lampholders have the centre contact
connected to the phase conductor. For TP&N
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circuits it is essential that the neutral conductor is z, + (z, +zJsubmain + (z, + a circuit.
6nal
confinned to be in the neutral connecto~ tenninal. The continuity of the protective conductor still has
In some installations it may be important to verify to be determined prior to energising the system. If
phase roration by establishing that the phases are an AC ohmmeter has been used for this purpose.
connected in the c o m t order. the Z, + Z of the circuit will have already been
,
measured. This, added to the &, will determine the
The instrumentrequired for the test is the same low s s e 2,. Alternatively, if a low current DC
ytm
current ohm-meter used on the previous tests and inshument is used to measure R, + &, then a
the m t o of ts is the same as described for
ehd et measurement o the circuit earth fault loop
f
protective conductor continuity. impedance has to be made with a loop tester after
the circuit has been energised.
It appears that measuring Earth Fault Loop
3.6 Test (ix) Earth Fault Loop Impedance Impedances may have a limited future. Discussions
Fig 4 in the Euuropean are centring around
measurements of protective conductor resistance
The Regulations require that where a knowledge of only, making the assumption that the extemal earth
earth fault loop impedance of a circuit is r e q u i d loop impedance of a system is going to be
it shalJbe measuredordetamined. There isa need negligible. The philosophy behind this appears to
to ascertain the earth loop impedance of every f d be that if the touch voltage under fault conditions is
circuit, submain and distributm of an installation in limited to 50V - o whatever voltage is considered
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order to verify that the circuit protection device will -
safe in a particular environment then the fault is
operate within the required disconnection times. permitted to stand for a longer period. If this is
adapted by the B S W . then installations in the
The earth fault loop impedance (z,) of a f d UK are going to be less safe than under the present
circuit c m r s s
opie: Standards.
- the extemal earth loop impedance (a;
the phase/cpc impedance/resistance(R, + 37
. Test (x) Earth Electrode Resistance
RJ of the distribum, Pigs5and6
the ( , + RJ of the submain ;
R When an installation requires an earth electrode it
is necessary to measure the resistance of the
the ( , + RJ of the f n l circuit and its
R ia electmde and the surrounding earth to ensure
f n l connection.
ia sufircient fault current will flow bough the earth
to operate the circuit protective devices within the
The values (R, + RJ of each component part will required disconnection times. There are two
have already been measured separately as part of methods of testing earth electrodes:
the protective conductor continuity t s . Therefore,
et
to deteamine the earth fault loop impedance (z,) of
each circuit all that is required is a direct Method A
measurement of earth loop impedance (z3 a the t By using an earth resistance tester connected as
origin of the installation. Add (ZJ to the shown in Figure 5;
appropriate ( , + RJ values and the ( , of every
R Z)
circuit is obtained. Alternatively, the ( , of each
Z)
circuit can be m a u e separately with an earth
esrd Method B
loop impedance tester though this doubles the work By using an earth loop impedance tester (refer to
and means that there is considerabletesting required Fig 6).
after the system has be energised.
[*This method ir only suitalde where the earding system is TT
In larger instaliations incorporating cables with ond rlu main form o indirect contact protection U by means @
f
a residual current device.]
conductors greater than 35sq mm, the reactance of
the cables may have a significant effect on the total
earth loop impedance of the system. The loop
impedance formula for these circuits becomes: Z =,
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3.8 Test (xi) Operation o Residual Current
f installer and the inspector each attest that their
Devices (RCDs) mpxtive contributions t the installation comply
o
with the Regulations. It should also record the
The effectiveness of all RCDs fitted in the general characteristics of the installation and list the
installation has to be tested with an instrument that installation record documents as well as the records
simulates a fault condition. This test is carried out of the tests carried out. The Certificate must be
after all the other tests have established that the signed by competent people as previously delined
installation is properly earthed and earth loop and the person signing for the inspection and testing
impedances are below the maximum acceptable is required to advise the user that reinspection is
limits for the devices to operate. The test required periodically and recommend the intervals
requirements are: between inspections.
a) At the rated tripping current the device The Certificate and the test records should be
must operate within 200 ms; included in the installation Record Manual and
retained by the user. The Electricity a W r t ok
b) At 5 times the rating it must opexate Regulationsalso require that test records be retained
withii 40 ms; in ordex that the duty holder may monitor the
elh
condition of the installation. The Hat and Safety
c) At half the rating it must not trip; Regulations require the supplier of a system to
provide all necessary information for its safe use
d) The integral test switch must cause it to and maintenance. The RecordManual should fulfidl
O W ; these obligations.
d) A record of the tripping times should be
maintained as this will enable t condition
o
of the device to be monitored.
Having completed the tests, a check should be made ACKNOWLEDGEMENTS
to see t a the appropiate notice has been fitted at
ht
the supply position instructing the user to opemte 1. The Open College and The Institution of
Electronics and Elechical Incorporated
the test switch quarterly. This notice is most
Engineers for kind permission to reproduce
important and it should be prominently displayed. diagrams from "Applying the 16th Edition"
Experience of use and testing of RCDs i showing
s Open Learning Course.
that if they are not regularly operated, they are
liiely to fail under fault conditions which could 2. The Institution of Electrical Engineers for kind
prove fatal. permission t reprodm the Forms of
o
Completion f o the 16th Edition IEE Wiring
rm
Regulations.
4. CERTIFICATION Fig 7
When the inspection and testing has been
completed, the test records can be used to verify
certain aspects of the installation design. It is,
therefore, important that test results are accurately
documented as the work progresses. Copies of the
records should be submitted to the designer in order
that hefshe verities that the design calculations are
c o m t . The Regulationsrequire that on completion
of a new o altered installation, and following
r
verification that the installation complies with the
Regulations, a Certificate should be issued to the
person ordering the work.
The Certificate requires that the designer, the
