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INSP_TEST_VERIFY Powered By Docstoc



    H.R. Lovegrove

    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
    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.
                                                                 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
    inspected and t s e as the work proceeds,ie during
                    etd                                                                    ra
                                                                 voltage t be available. G e t care should be talcen
    erection and before being put into service, in order         by the inspector to ensure t a the site personnel are
    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
    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.
                                                                 The minimum number of items that require

checking as part of the inspection process are:              From these it becomes obvious t a the inspection
                                                             procedure is on-going throughout t e constnrction
         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
         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
         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.


         are elecoically sound and correctly connected           connections is suspect and requires checking.
         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
        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,
                                                                 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
    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-
    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
    phase and protective conductors together at the              is connected as part of the ring will be the same.
    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
    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
    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

     Neutral and cpc conductors in correct terminal           The frt test is made between live conductors.
     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
                                                              together. The second test is made between all live
H h4axiium R,+R, value identified.                            conductors together and e r h

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
                                                              and Bssociatedfinal circuits all connected and with
This test is required before the installation is              f x d equipment disconnected.
connected to the supply to ensure t a there are no
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 ;
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
t a may be damaged by the test voltage and should                               Contact by Barriers or
be diSCOMeCted.                                                                 Enclosures applied during
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
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
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
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
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

circuits it is essential that the neutral conductor is         z, + (z, +zJsubmain + (z, + a circuit.
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
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
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
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,
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
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 @
                                                               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 =,

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
                                                             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
                                                             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
         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
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
                                                                      Completion f o the 16th Edition IEE Wiring

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
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

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