The presence and build-up of FAW in a particular area can be detected by using pheromone traps. Pheromones are natural compounds that. Guidance Note 3: Inspection & Testing (17th Edition, BS . EDIS Certificate PDF, includes the text from the Additional Comments field. This[j1]Guidance Note 3 corresponds to Performance Standard 3. text of this Guidance Note can be found in the References Section section at http://www. caite.info
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Inspection & Testing GUIDANCE NOTE 3 IEE Wiring Regulations 3 BS Requirements for Electrical Installati Author: Institution DOWNLOAD PDF. items Wiring Regulations Digital: Online is a web-based e-book solution for multi-user access to BS and associated guidance. items The IET has launched a new version of the Wiring Regulations e-books. Wiring Regulations Digital: Online is a web-based e-book solution for.
Where, during erection, an enclosure or barrier is provided to afford protection from direct contact, a degree of protection not less than IP2X or IPXXB is required. Resistance readings obtained should be not less than the minimum values referred to in Table 2. Where it is desired to indicate phase rotation or a different function for cables of the same colour, numbered or lettered sleeves are permitted. Some Guidance Notes also contain material not included in BS Requirements for Electrical Installations but which was included in earlier editions. Where items of stationary equipment having a protective conductor current exceeding 3.
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Views Total views. These characteristics should also be available for safety services such as UPS and generators. Diagrams, charts or tables The information below regarding the basis of the design must be made available. This is also a non-specific requirement of the Health and Safety at Work etc Act: This should include the Installation Method shown in Appendix 4 paragraph 8 of BS xi the method used for compliance with the requirements for protection against indirect contact and, where appropriate, the conditions required for automatic disconnection xii the information necessary for the identification of each device performing the functions of protection, isolation and switching, and its location xiii any circuit or equipment vulnerable to a particular test.
This should be recorded on the Certificate. This interval is required to be noted on the Electrical Installation Certificate and on a notice to be fixed in a prominent position at or near the origin of the installation.
The information and tables in Section 3 of this Guidance Note have been prepared to provide guidance. A model Schedule of Inspections is shown in Section 5.
Requirements for the enclosure of and accessibility of connections must be considered. It should be checked that each core or bare conductor is identified as necessary. Busbar and pole colour should also comply with Table 51A.
The single colour green or the single colour yellow must not be used. Only the colour combination green-and-yellow is permitted and is only to be used for protective conductors.
Where it is desired to indicate phase rotation or a different function for cables of the same colour, numbered or lettered sleeves are permitted.
Table 55A of BS is a schedule of types of plug and socket-outlet available, the ratings, and the associated British Standards.
Particular attention should be paid to the requirements for cable couplers. This may be impossible without dismantling the system and it is essential, therefore, that inspection should be carried out at the appropriate stage of the work, and that this is recorded at the time for incorporation in the inspection and test documents. The many requirements include: If this method is used the area shall be accessible only to skilled persons or to instructed persons under supervision.
This method of protection is not to be used in some installations and locations of increased shock risk. See Part 6 of BS Out of reach Placing out of reach protects also against direct contact.
Increased distances are necessary where long or bulky conducting objects are likely to be handled in the vicinity. PELV The requirements for PELV are as for SELV except that the secondary circuits are earthed and exposed-conductive-parts may have connections with earth, exposed-conductive-parts or protective conductors of other systems. Where equivalent insulation is used, the designer should be consulted for guidance. Methods ii iii and iv are specialised protection systems.
It is essential that inspection of such systems be carried out by persons competent in the discipline and having adequate information on the design of the system. For these specialised systems, the designer and client will advise of and agree, the necessary effective and continuing supervision. The earthing system must be determined, e. The earth impedance must be appropriate for the protective device i.
RCD or overcurrent device. A warning notice complying with Section must be fixed in a prominent position adjacent to every point of access to the location concerned. In special situations, under effective supervision, when specified by a suitably qualified engineer, it may be used to supply several items of equipment from the same source.
Compatibility, and in Section Mutual Detrimental Influence. Another aspect which should be taken into consideration during inspection is Section Proximity to other Services. All switch utilization categories must be appropriate for the nature of the load — see Table 2. Checking of utilization category may need to be carried out during construction, if the label is obscured during erection. Switchgear to BS EN if suitable for isolation will be marked with the symbol: This may be endorsed with a symbol advising of function, e.
This should include, where appropriate, locking-off and inspection or testing to verify that the circuit is dead and no other source of supply is present.
Normally such a requirement concerns only motor circuits; if it is required it will have been specified by the designer. Protective devices The choice and setting of each protective device including monitoring devices should be compared with the design.
Labelling of protective devices, switches and terminals 43 A protective device must be arranged and identified so that the circuit protected may be easily recognised. Selection of equipment and protective measures appropriate to external influences Equipment must be selected with regard to its suitability for the environment — ambient temperature, heat, water, foreign bodies, corrosion, impact, vibration, flora, fauna, radiation, building use and structure.
Isolation where live parts are not capable of being isolated by a single device. Periodic Inspection and Testing the wording of the notice is given in Regulation Erection methods Part 5 Chapter 52 contains detailed requirements on selection and erection.
Fixings of switchgear, cables, conduit, fittings, etc must be adequate for the environment. Listed below are requirements to be checked when carrying out an installation inspection. The list is not exhaustive. General 1. Complies with requirements i - iii in Section 2.
Fire Alarms BS Environmental IP requirements accounted for BS EN Means of isolation suitably labelled , Provision for disconnecting the neutral Main switches to single-phase installations, intended for use by an ordinary person, e.
Overcurrent protection provided where applicable Sect and Sect Segregation of circuits Sect and Sect Retest notice provided Sealing of the wiring system including fire barriers Switchgear 1. Suitable for the purpose intended Chap 53 Meets requirements of BS EN , BS EN , BS EN , BS EN or BS EN where applicable, or equivalent standards Securely fixed and suitably labelled Non-conductive finishes on switchgear removed at protective conductor connections and if necessary made good after connecting Suitable cable glands and gland plates used Correctly earthed Chap 54 Conditions likely to be encountered taken account of i.
Box or other enclosure securely fixed 3. Metal box or other enclosure earthed and Chap 54 4. Edge of flush boxes not projecting above wall surface 5. No sharp edges on cable entries, screw heads, etc which could cause damage to cables 6.
Non-sheathed cables, and cores of cable from which sheath has been removed, not exposed outside the enclosure 7. Conductors correctly identified , 8. Bare protective conductors sleeved green-and-yellow , 9. Terminals tight and containing all strands of the conductors Sect Cord grip correctly used or clips fitted to cables to prevent strain on the terminals Adequate current rating Suitable for the conditions likely to be encountered Sect Lighting controls 1.
Correct colour coding or marking of conductors 5. Earthing of exposed metalwork, e. Complies with the requirements for locations containing a bath or shower Sect 7. Adequate current rating 8. Suitable for inductive circuits or de-rated where necessary 9. Switch labelled to indicate purpose, where this is not obvious Track systems comply with BS EN Appropriate controls suitable for the luminaires Lighting points 1. Suitable for the mass suspended 9.
Luminaire couplers comply with BS or BS Socket-outlets 1. Mounting height above the floor or working surface suitable 3. Correct polarity and 4. Not installed in a bathroom or shower room unless shaver or SELV 5. Outside the zones in a room other than a bathroom or shower room and RCD protected 6. Controlled by a switch, where the supply is direct current 7. Protected where mounted in a floor Sect 8. Not used to supply a water heater having uninsulated elements 9. Circuit protective conductor connected directly to the earthing terminal of the socket-outlet, on a sheathed wiring installation Earthing tail from the earthed metal box, on a conduit installation to the earthing terminal of the socket-outlet Joint box 1.
Joints accessible for inspection Joints protected against mechanical damage All conductors correctly connected Complies with BS or BS vi. Fused connection unit 1. Complies with the requirements for locations containing a bath or shower Sect Correct rating and fuse Cooker control unit 1.
Securely fixed, covers in place and adequately protected against mechanical damage 2. Inspection fittings accessible 3. Number of cables for easy draw not exceeded 4.
Solid elbows and tees used only as permitted and 5. Ends of conduit reamed and bushed 6. Adequate boxes 7. Unused entries blanked off where necessary 8. Not containing unsuitable non-electrical pipes or tubes Sect 9. Provided with drainage holes and gaskets as necessary Radius of bends such that cables are not damaged Joints, scratches etc in metal conduit protected by painting , Rigid metal conduit 1.
Complies with BS 31, or BS Parts 1 and 2 Sect Connected to the main earth terminal Phase and neutral cables contained in the same conduit Conduit suitable for damp and corrosive situations and Maximum span between buildings without intermediate support and see Guidance Note 1 and On-Site Guide Rigid non-metallic conduit 1. Complies with BS , BS EN and BS EN Ambient and working temperatures within permitted limits and Provision for expansion and contraction Boxes and fixings suitable for mass of luminaire suspended at expected temperature , Flexible metal conduit 1.
Trunking General 1. Internal sealing provided where necessary Holes surrounding trunking made good Band I circuits partitioned from Band II circuits or insulated for the highest voltage present 8. Circuits partitioned from Band I circuits or wired in mineral-insulated metal-sheathed cables 9.
Cables supported for vertical runs Metal trunking 1. Phase and neutral cables contained in the same metal trunking Protected against damp or corrosion and Earthed Joints mechanically sound, and of adequate continuity with links fitted Insulated Cables Non-flexible cables 1. Correct type Correct current rating Protected against mechanical damage and abrasion Cables suitable for high or low ambient temperature as necessary Non-sheathed cables protected by enclosure in conduit, duct or trunking Sheathed cables routed in allowed zones or mechanical protection provided Where exposed to direct sunlight, of a suitable type Not run in lift shaft unless part of the lift installation and of the permitted type and BS Correctly selected and installed for use e.
Joints and connections mechanically sound and accessible for inspection, except as permitted otherwise Earthed concentric wiring including cne cables to be used only as permitted and Electricity Supply Regulations as amended.
Flexible cables and cords 1. Correct type Correct current rating Sect Protected where exposed to mechanical damage and Suitably sheathed where exposed to contact with water and corrosive substances Protected where used for final connections to fixed apparatus etc and Selected for resistance to damage by heat Segregation of Band I and Band II circuits BS and Sect Fire alarm and emergency lighting circuits segregated BS , BS and Section Cores correctly identified throughout Prohibited core colours not used Joints to be made using cable couplers Where used as fixed wiring relevant requirements met Final connections to portable equipment a convenient length and connected as stated Final connections to other current-using equipment properly secured or arranged to prevent strain on connections Sect Mass supported by pendants not exceeding values stated Protective conductors 1.
Cables incorporating protective conductors comply with the relevant BS Sect 2. Joints in metal conduit, duct or trunking comply with Regulations 3.
Flexible conduit to be supplemented by a protective conductor 4. Minimum cross-sectional area of copper conductors 5. Copper conductors, other than strip, of 6 mm2 or less protected by insulation 6. Circuit protective conductor at termination of sheathed cables insulated with sleeving 7.
Bare circuit protective conductor protected against mechanical damage and corrosion and 8. Insulation, sleeving and terminations identified by colour combination green-and-yellow 9. Joints sound Separate circuit protective conductors not less than 4 mm2 if not protected against mechanical damage Enclosures General 1. A model Schedule of Test Result is shown in Section 5. Section requires that: These schedules shall be based upon the models given in Appendix 6 of BS ii the Schedule of Test Results shall identify every circuit, including its related protective device s , and shall record the results of the appropriate tests and measurements detailed in Chapter 71 iii the Electrical Installation Certificate shall be signed by a competent person or persons stating that to the best of their knowledge and belief the installation has been designed, constructed, inspected and tested in accordance with BS , any permissible deviations being listed iv any defects or omissions revealed by the Inspector shall be made good and inspected and tested again before the Electrical Installation Certificate is issued.
An exception is made for a lampholder having no exposed-conductive-parts and suspended from such a point. Every protective conductor, including circuit protective conductors, the earthing conductor and main and supplementary equipotential bonding conductors, should be tested to verify that the conductors are electrically sound and correctly connected.
Similarly, luminaires fitted in grid ceilings and suspended from steel structures in buildings will create parallel paths. Under these circumstances some of the requirements may have to be visually inspected after the test has been completed. This consideration requires tests to be performed during the erection of an installation, in addition to tests at the completion stage.
Instrument — Use a low-resistance ohmmeter for these tests.
Refer to Section 4. The resistance of the test leads should be measured and deducted from all resistance readings obtained unless the instrument can auto-null.
Test method 1 Connect the phase conductor to the protective conductor at the distribution board or consumer unit so as to include all the circuit. Then test between phase and earth terminals at each outlet in the circuit.
See Fig 1a for Test method connections.
Fig 1a: Bonding conductor continuity can be checked using this test method. One end of the bonding conductor and any intermediate connections with services may need to be disconnected to avoid parallel paths. Where indirect shock protection is provided by limiting the resistance of the circuit protective conductor to that given in Table 41C of BS i. Fig 1b: Use a low-resistance ohmmeter for this test. The test results show if the ring has been inter-connected to create an apparently continuous ring circuit which is in fact broken.
Use a low-resistance ohmmeter for these tests. Step 1: The phase, neutral and protective conductors are identified and the end-to-end resistance of each is measured separately see Fig 2a.
These resistances are r1, rn and r2 respectively. A finite reading confirms that there is no open circuit on the ring conductors under test. The resistance values obtained should be the same within 0. If the protective conductor has a reduced csa the resistance r2 of the protective conductor loop will be proportionally higher than that of the phase or neutral loop e.
If these relationships are not achieved then either the conductors are incorrectly identified or there is something wrong at one or more of the accessories. Step 2: The phase and neutral conductors are then connected together so that the outgoing phase conductor is connected to the returning neutral conductor and vice-versa see Fig 2b. The resistance between phase and neutral conductors is measured at each socket-outlet. The readings at each of the sockets wired into the ring will be substantially the same and the value will be approximately one quarter of the resistance of the phase plus the neutral loop resistances, i.
Any sockets wired as spurs will give a higher resistance value due to the resistance of the spur conductors. Where single-core cables are used, care should be taken to verify that the phase and neutral conductors of opposite ends of the ring circuit are connected together. An error in this respect will be apparent from the readings taken at the socket-outlets, progressively increasing in value as readings are taken towards the midpoint of the ring, then decreasing again towards the other end of the ring.
Step 3: The above step is then repeated but with the phase and cpc crossconnected see Fig 2c. The readings obtained at each of the sockets wired into the ring will be substantially the same and the value will be approximately one quarter of the resistance of the phase plus cpc loop resistances, i.
As before, a higher resistance value will be recorded at any sockets wired as spurs. The value can be used to determine the earth loop impedance ZS of the circuit to verify compliance with the loop impedance requirements of the Regulations See Section 2.
This sequence of tests also verifies the polarity of each socket, except that if the testing has been carried out at the terminals on the reverse of the accessories a visual inspection is required to confirm correct polarity connections. Connections for testing continuity of ring final circuit conductors Fig 2a: If circuits contain voltage sensitive devices, Test 2, from protective earth to phase and neutral connected together, may be appropriate if vulnerable equipment is not to be disconnected.
Further precautions may also be necessary to avoid damage to some electronic devices, and it may be necessary to consult the manufacturer of the equipment to identify necessary precautions. Use an insulation resistance tester for these tests. The installation will be deemed to conform with the Regulations if the main switchboard, and each distribution circuit tested separately with all its final circuits connected, but with current-using equipment disconnected, has an insulation resistance not less than that specified in Table 71A, which is reproduced here as Table 2.
Simple installations that contain no distribution circuits should be tested as a whole. The tests should be carried out with the main switch off, all fuses in place, switches and circuit-breakers closed, lamps removed, and fluorescent and discharge luminaires and other equipment disconnected.
TABLE 2. Although an insulation resistance value of not less than 0. In these circumstances, each circuit should be tested separately. This will help identify i whether one particular circuit in the installation has a lower insulation resistance value possibly indicating a latent defect that should be rectified or ii whether the low insulation resistance represents, for example, the summation of individual circuit insulation resistance and as such may not be a cause for concern.
Test 1, Insulation resistance between live conductors Test between the live conductors at the appropriate distribution board. Resistance readings obtained should be not less than the minimum values referred to in Table 2. See Fig 3a for Test method connections. For circuits containing two-way switching or two-way and intermediate switching the switches must be operated one at a time and the circuits subjected to additional insulation resistance tests.
See Fig 3b for Test method connections. They are not applied when type-tested switchgear is assembled on site. The tests involve the use of high voltages and great care is necessary to avoid danger. The test voltage and duration must accord with the appropriate British Standard specification. Where there is no such British Standard, the test may be applied using a test voltage of V a.
This test voltage should be at supply frequency, and should be applied to the insulation for a duration of 1 minute. The insulation can be deemed to be satisfactory if no breakdown or flashover occurs during the period of test.
Use an applied voltage tester for this test. Where protection against indirect contact is provided by supplementary insulation applied to equipment during erection, a test should be made to verify that: For details of test methods refer to Section 2.
If the voltage exceeds 25 V a. This may be by either: The live conductors of any adjacent higher voltage circuit in contact with or in the same enclosure as SELV separated extra-low voltage circuits must be tested to verify electrical separation in accordance with BS Testing of SELV circuits The first test applied to this arrangement is an insulation resistance test in accordance with Table 2.
Table 71A Where the circuit is supplied from a safety source complying with BS , the test is made at V d. In practice readings less than 5 megohms require investigation.
Use an insulation resistance tester for this test. The insulation resistance must not be less than 0. In practice a reading less than 5 megohms requires investigation. Compliance with Regulation will have been verified by the inspection required by Regulation iii. This should be confirmed. The exposed-conductive-parts should be inspected compliance with Regulation Protection against indirect contact in the secondary circuit is dependent upon the primary circuit protection.
In addition, should any doubt exist, the voltage should be measured to verify it does not exceed V. Where the source of supply does not comply with Regulation i , compliance with Regulation must be verified. This test should be performed at a voltage of V d. The live parts of the separated circuit must be tested to ensure that they are electrically separate from other circuits. This is achieved by testing between the live conductors of the separated circuit connected together and the conductors of any other adjacent circuit strapped together.
The insulation resistance should be not less than 0. A separate wiring system is preferred for electrical separation. If multicore cables or insulated cables in insulated conduit are used, all cables must be insulated to the highest voltage present and each conductor must be protected against overcurrent.
This equipotential bonding is then subjected to a V d. If protection is provided by overcurrent devices, the appropriate value of loop impedance given by Regulation Tables 41B, 41C and 41D for V systems shall be determined.
Table 41A Table 41B Instrument: Use a loop impedance tester for this test. Where, during erection, an enclosure or barrier is provided to afford protection from direct contact, a degree of protection not less than IP2X or IPXXB is required.
Readily accessible horizontal top surfaces shall have a degree of protection of at least IP4X. The test is made with a metallic standard test finger test finger 1 to BS The finger is pushed without undue force not more than 10 N against any openings in the enclosure and, if it enters, it is placed in every possible position.
A SELV supply, not exceeding 50 V, in series with a suitable lamp is connected between the test finger and the live parts inside the enclosure. Conducting parts covered only with varnish or paint or protected by oxidation or by a similar process, shall be covered with a metal foil electrically connected to those parts which are normally live in service.
The protection is satisfactory if the lamp does not light. The end of the wire shall be free from burrs, and at a right angle to its length. The protection is satisfactory if the wire cannot enter the enclosure.
Reference should be made to the appropriate product standard or BS EN for a fuller description of the degrees of protection, details of the standard test finger and other aspects of the tests.
Consult HS G This testing is done by applying metallic foil closely around all the insulation, and then firstly applying 2 kV a. The insulation can be deemed to be satisfactory if no breakdown or flashover occurs during the test. This test is then followed by an insulation resistance test at V d. Use a high output applied voltage tester for the high voltage test.
Measuring insulation resistance of floors and walls A magneto-ohmmeter or battery-powered insulation tester providing a no-load voltage of approximately V or V if the rated voltage of the installation exceeds V is used as a d. The test electrodes may be either of the following types.
In case of dispute, the use of test electrode 1 is the reference method. It is recommended that the test be made before the application of the surface treatment varnishes, paints and similar products.
Test electrode 1 The electrode see Fig 4a is a mm square metallic plate with a mm square of damped water absorbent paper or cloth from which surplus water has been removed, placed between the metal plate and the surface being tested.
During the measurement a force of approximately N 12 stone or 75 kg in weight in the case of floors or N in the case of walls is applied on the plate. Fig 4a: Test electrode 1 N I wooden plate metal plate damp cloth P UX floor covering sub-floor PE Test electrode 2 The test electrode see Fig 4b comprises a metallic tripod of which the parts resting on the floor form the points of an equilateral triangle.
Before measurements are made, the surface being tested is moistened or covered with a damp cloth. While measurements of the floors and walls are being made a force of approximately N floors or N walls , is applied to the tripod.
One method of test is as described for Test method 1 paragraph 2.
Therefore, if the testing has been to the terminals on the reverse of the accessories and not to the socket tubes, a visual inspection is required. The phase connection in socket-outlets and similar accessories is connected to the phase conductor. See Fig 5 for Test method connections. After connection of the supply, polarity should be confirmed using an approved voltage indicator.
The test may be carried out either at lighting points or switches. Use an earth electrode resistance tester for this test.
Test method 1 Before this test is undertaken, the earthing conductor to the earth electrode must be disconnected either at the electrode or at the main earthing terminal to ensure that all the test current passes through the earth electrode alone. This will leave the installation unprotected against earth faults. The test should be carried out when the ground conditions are least favourable, such as during dry weather.
Connection to the earth electrode is made using terminals C1 and P1 of a four-terminal earth tester. To exclude the resistance of the test leads from the resistance reading, individual leads should be taken from these terminals and connected separately to the electrode. If the test lead resistance is insignificant, the two terminals may be short-circuited at the tester and connection made with a single test lead, the same being true if using a three-terminal tester.
Connection to the temporary spikes is made as shown in Fig 6. The distance between the test spikes is important. If they are too close together, their resistance areas will overlap. In general, reliable results may be expected if the distance between the electrode under test and the current spike is at least ten times the maximum dimension of the electrode system, e. Three readings are taken: By comparing the three readings, a percentage deviation can be determined. This is calculated by taking the average of the three readings, finding the maximum deviation of the readings from this average in ohms, and expressing this as a percentage of the average.
The accuracy of the measurement using this technique is typically 1. It is difficult to achieve a measurement accuracy better than 2 per cent, and inadvisable to accept readings that differ by more than 5 per cent. Fig 6: Because these testers employ phase-sensitive detectors psd , the errors associated with stray currents are eliminated.
The instrument should be capable of checking that the resistance of the temporary spikes used for testing are within the accuracy limits stated in the instrument specification. This may be achieved by an indicator provided on the instrument, or the instrument should have a sufficiently high upper range to enable a discrete test to be performed on the spikes. If the temporary spike resistance is too high, measures to reduce the resistance will be necessary, such as driving the spikes deeper into the ground or watering with brine to improve contact resistance.
In no circumstances should these techniques be used to temporarily reduce the resistance of the earth electrode under test. In these circumstances, where the electrical resistances to earth are relatively high and precision is not required, an earth fault loop impedance tester may be used.
Test method 2 alternative for RCD protected TT installations Before this test is undertaken, the earthing conductor to the earth electrode should be disconnected at the main earthing terminal to ensure that all the test current passes through the earth electrode alone.
A loop impedance tester is connected between the phase conductor at the source of the TT installation and the earth electrode, and a test performed. The impedance reading taken is treated as the electrode resistance. BS requires: Maximum values of RA for the basic standard ratings of residual current devices are given in the following table, unless the manufacturer declares alternative values. In practice, however, values above ohms will require further investigation.
Where items of stationary equipment having a protective conductor current exceeding 3. Earth fault loop impedance Zs may be determined by: Determining Ze Measurement The reasons that Ze is required to be measured are twofold: The impedance measurement is made between the phase of the supply and the means of earthing with the main switch open or with all the circuits isolated. The means of earthing must be disconnected from the installation earthed equipotential bonding for the duration of the test to remove parallel paths.
Care should be taken to avoid any shock hazard to the testing personnel and other persons on the site both whilst establishing contact, and performing the test. Refer to Part 4. Direct measurement of Zs Direct measurement of Zs can only be made on a live installation.
Neither the connection with earth nor bonding conductors are disconnected. This must be taken into account when comparing the results with design data. Care should be taken during the tests to avoid any shock hazard to the testing personnel, other persons or livestock on site. Three-wire loop impedance testers require a connection to the neutral for the instrument to operate. Verification of test results Values of Zs should be compared with one of the following: As this is the normal temperature range to be expected, then correction for temperature is not usually required.
Appendix 2 also provides a means of correcting these values for other test temperatures. Examples of how these formulae may be used are given in Appendix 2. The threequarters figure allows for a reduced cross-section protective conductor and errs on the side of safety. Earth fault loop impedance test voltage The normal method of test employed by a phase earth loop tester is to compare the unloaded loop circuit voltage with the circuit voltage when loaded with a low resistance, typically 10 ohms.
This method of test can create an electric shock hazard if the phase earth loop impedance is high and the test duration is not limited. In these circumstances the potential of the protective conductor could approach phase voltage for the duration of the test see paragraph 4.
Residual current devices The test measuring current of earth fault loop impedance testers may trip any RCD protecting the circuit. This will prevent a measurement being taken and may result in an unwanted disconnection of supply to the circuit under test. There are two common techniques: This should mean that RCDs with a rated residual operating current of 30 mA and greater will not trip. Type A RCDs - tripping is ensured for residual sinusoidal alternating currents and for pulsating direct currents Type AC RCDs - tripping is ensured for residual sinusoidal alternating currents.
The designer is required to determine the prospective fault current, under both short-circuit and earth fault conditions, at every relevant point of the installation.
This may be done by calculation, ascertained by enquiry or by measurement. The term prospective fault current includes the prospective short-circuit current and the prospective earth fault current. It is the greater of these two prospective fault currents which should be determined and compared with the breaking capacity of the device.
Measurement of prospective short-circuit current L N E G Where a 3-lead instrument is used, both the neutral and earth leads are connected to the neutral. B R test instrument With the power on, the maximum value of the prospective shortcircuit current can be obtained by direct measurement between live conductors at the protective device at the origin of the installation as shown in Fig 8. With many instruments, the voltage between phases can not be measured directly.
For three-phase supplies, the maximum balanced prospective short-circuit level will be, as a rule of thumb, approximately twice the single-phase value.
This figure errs on the side of safety. Measurement of prospective earth fault current L N E G B R test instrument The prospective earth fault current may be measured with the same instrument, as indicated in Fig 9. Use a prospective fault current tester for this test. The larger of the two values Ipf should be recorded on the Schedule of Test Results. For a three-phase system, the prospective short-circuit current will always be larger than the earth fault current.
Rated short-circuit breaking capacities of protective devices The rated short-circuit capacities of fuses, and circuit-breakers to BS now withdrawn and BS EN - are shown in Table 2.
Icn is the maximum fault current the breaker can interrupt safely, although the breaker may no longer be usable. Ics is the maximum fault current the breaker can interrupt safely without loss of performance. The Icn value is marked on the device in a rectangle e. For domestic installations the prospective fault current is unlikely to exceed 6 kA up to which value the Icn Where a service cut-out containing a cartridge fuse to BS type 2 supplies a consumer unit which complies with BS or BS EN , then the short-circuit capacity of the overcurrent protective devices within consumer units may be taken to be 16 kA.
Fault currents up to 16 kA Except for London and some other major city centres, the maximum fault current for V single-phase supplies up to A will not exceed 16 kA. The short-circuit capacity of overcurrent protective devices incorporated within consumer units may be taken to be 16 kA where: The value to be recorded is the greater of either the short-circuit current between live conductors or the earth fault current between phase conductor s and the main earthing terminal.
If it is considered necessary to record values at other relevant points, they can be recorded on the Schedule of Test Results. Where the protective devices used at the origin have the necessary rated breaking capacity and similar devices are used throughout the installation, it can be assumed that the Regulations are satisfied in this respect for all distribution boards. This test sequence will be in addition to proving that the test button is operational.
The effectiveness of the test button should be checked after the test sequence. For each of the tests readings should be taken on both positive and negative half cycles and the longer operating time recorded. Prior to these RCD tests it is essential, for safety reasons, that the earth loop impedance is tested to check the requirements have been met. Use an RCD tester for these tests. Test method The test is made on the load side of the RCD between the phase conductor of the protected circuit and the associated cpc.
The load should be disconnected during the test. RCD testers require a few milliamperes to operate the instrument, and this is normally obtained from the phase and neutral of the circuit under test. This means that the test current will be increased by the instrument supply current and will cause some devices to operate during the 50 per cent test at a time when they should not operate. Under this circumstance it is necessary to check the operating parameters of the RCD with the manufacturer before failing the device.
Precautions must therefore be taken to prevent contact of persons or livestock with such parts. Because of the variability of the time delay it is not possible to specify a maximum test time. It is suggested that in practice a 2 s maximum test time is sufficient. The maximum test time must not be longer than 40 ms, unless the protective conductor potential rises by less than 50 V. The instrument supplier will advise on compliance.
Functional checks All assemblies, including switchgear, controls and interlocks, are to be functionally tested, that is operated to confirm that they work and are properly installed, mounted and adjusted. For an installation under effective supervision in normal use, periodic inspection and testing may be replaced by an adequate regime of continuous monitoring and maintenance of the installation and all its constituent equipment by skilled persons.
Appropriate maintenance records must be kept. The records may be kept on paper or computer and should record that electrical maintenance and testing has been carried out. The results of any tests should be recorded. Reference to legislation and other documents is made below and it is vital that these requirements are ascertained before undertaking periodic inspection and testing.
As may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger. The Memorandum of Guidance published by the Health and Safety Executive advises that this regulation is concerned with the need for maintenance to ensure the safety of the system rather than being concerned with the activity of doing the maintenance in a safe manner, which is required by Regulation 4 3.
The obligation to maintain a system arises if danger would otherwise result.
There is no specific requirement to carry out a maintenance activity as such, what is required is that the system be kept in a safe condition. The frequency and nature of the maintenance must be such as to prevent danger so far as is reasonably practicable. Regular inspection of equipment including the electrical installation is an essential part of any preventive maintenance programme.
This regular inspection may be carried out as required with or without dismantling and supplemented by testing. There is no specific requirement to test the installation on every inspection. Where testing requires dismantling, the tester should consider whether that the risks associated with dismantling and re-assembling are justified. Dismantling, and particularly disconnection of cables or components, introduces a risk of unsatisfactory reassembly.
Information on the requirements for routine checks and inspections should be provided in accordance with Section 6 of the Health and Safety at Work etc Act and as required by The Construction Design and Management Regulations This is a matter of judgement for the duty holder.
In domestic premises it is presumed that the occupier will soon notice any breakages or excessive wear and arrange for precautions to be taken and repairs to be carried out. In other situations, there must be arrangements made for initiating reports of wear and tear from users of the premises. This should be supplemented by routine checks.
The frequency of these checks will depend entirely upon the nature of the premises. Routine checks would typically include: TABLE 3. This should be recorded. Enquiries should be made to the person responsible for the electrical installation with regard to the provision of diagrams, design criteria, electricity supply and earthing arrangements.
The recommended frequency of subsequent inspections may be increased or decreased at the discretion of the person carrying out the inspection and testing. As well as for domestic and commercial premises, a change in occupancy of other premises may necessitate additional inspection and testing. The formal inspections should be carried out in accordance with Chapter 73 of BS This requires an inspection comprising careful scrutiny of the installation, carried out without dismantling or with partial dismantling as required, together with the appropriate tests of Chapter Particular attention must be taken to comply with SI No The Electricity Supply Regulations as amended.
SI No See BS Part 1: Other intervals are recommended for testing operation of batteries and generators. Local Authority Conditions of Licence.
A survey may be necessary to identify switchgear, controlgear, and the circuits they control. During the inspection, the opportunity should be taken to identify dangers which might arise during the testing. Any location and equipment for which safety precautions may be necessary should be noted and the appropriate steps taken.
Where it is necessary to disconnect part or the whole of an installation in order to carry out a test, the disconnection should be made at a time agreed with the user and for the minimum period needed to carry out the test. Where more than one test necessitates a disconnection where possible they should be made during one disconnection period.
A careful check should be made of the type of equipment on site so that the necessary precautions can be taken, where conditions require, to disconnect or short-out electronic and other equipment which may be damaged by testing.
Special care must be taken where control and protective devices contain electronic components. The scope of the periodic inspection and testing must be decided by a competent person, taking into account the availability of records and the use, condition and nature of the installation. So far as is reasonably practicable, the visual inspection must verify that the safety of persons, livestock and property is not endangered.
A thorough visual inspection should be made of all electrical equipment which is not concealed, and should include the accessible internal condition of a sample of the equipment. The external condition should be noted and if damage is identified or if the degree of protection has been impaired, this should be recorded on the schedule to the Report.
The assessment of condition should take account of known changes in conditions influencing and affecting electrical safety, e. However, such sections must not be permanently excluded from inspection and testing, and a suitable programme should be devised which includes the inspection and testing of such sections.
In domestic type premises the whole installation can be readily isolated for inspection, but with most other installations it is not practicable and too disruptive to isolate the whole installation for the amount of time that is required for a comprehensive inspection.