IT3 U12 - Testing

CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

Testing Unit Aims By the end of the unit participants should be able to: describe the requirements of testing with reference to a) types of test equipment b) sequence and procedures for tests c) application of BS:7671 (Syllabus Reference: 2.2.10) describe how to carry out tests for a) continuity b) insulation resistance c) polarity d) earth fault loop impedance e) earth electrode resistance f) operation of RCD g) functional testing (Syllabus Reference: 2.2.07) explain the need to comply with test values and state the actions to take in the event of unsatisfactory results (Syllabus Reference: 2.2.08)

Testing Tests should be carried out in the following sequence: Before the supply is connected: i) Continuity of protective conductors, including main and supplementary bonding ii) Continuity of ring final circuit conductors, including protective conductors iii) Insulation resistance iv) Polarity (by continuity methods) v) Earth electrode resistance, when using an earth electrode resistance tester (see vii also) With supply connected: vi) Check polarity of supply, using an approved voltage indicator vii) Earth electrode resistance, using a loop impedance tester viii) Earth fault loop impedance ix) Prospective fault current measurement, if not determined by enquiry of the distributor x) Functional testing, including RCDs and switchgear.

Suitable methods of testing are described in the ‘On-Site Guide’ Section 10. The use of other methods of testing is not precluded provided that they will give results that are no less effective.

If a test indicates a failure to comply, that test, and the preceding tests (whose results may have been affected by the fault) must be repeated after rectification of the fault.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

Safety and Equipment Electrical testing involves danger. It is the tester's duty to ensure his or her own safety, and the safety of others, in the performance of the test procedures. When using test instruments, this is best achieved by precautions such as: (i)

an understanding of the correct application and use of the test instrumentation, leads, probes and accessories to be employed;

(ii)

checking that the test instrumentation is made in accordance with the appropriate safety standards such as BS EN 61243-3 for two-pole voltage detectors and BS EN 61010 or BS EN 61557 for instruments;

(iii)

checking before use that all leads, probes, accessories (including all devices such as crocodile clips used to attach conductors) and instruments are clean, undamaged and functioning;

(iv) observing the safety measures and procedures set out in the Health and Safety Executive Guidance Note GS 38 ‘Electrical test equipment for use by electricians’ for all instruments, leads, probes and accessories. In particular this recommends that the testing equipment be fuse protected against accidental connection to high energy live wiring when used on any range. This is primarily aimed at reducing the risk associated with arcing under fault conditions;

Test Instruments Test instruments should be regularly checked and re-calibrated to ensure accuracy. The serial number of the instrument should be recorded with the test results, to avoid unnecessary re-testing if one of a number of instruments is found to be inaccurate. For operation, use and care of test instruments, refer to the manufacturers’ handbook.

Results obtained during various tests should be recorded in the Test Result Schedule for future reference (Section 631); an example from the ‘BS 7671’ is shown on the following page.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

Continuity of Protective Conductors (IET Regulation 612.2.1) The initial tests applied to every protective conductor, including main earthing conductor, main and supplementary bonding conductors, are carried out for two purposes: 

To verify that the conductors are both correctly connected and electrically sound;



To provide a measure of (R1+R2) to verify that the overall earth fault loop impedance of the circuits is of a suitable value. This will allow the circuit to be disconnected from the supply in the event of an earth fault, within the disconnection times selected to meet the requirements of IET Regulation 411.3.1.1.

Use an ohmmeter capable of measuring a low resistance for these tests. It is recommended that the test be carried out with a supply having a no-load voltage between 4 volts and 24 volts, d.c. or a.c., and a short-circuit current of not less than 200 mA (Regulation 612.2.1).

Test Method 1 Bridge the line conductor to the protective conductor at the fuse-board and test between line and earth terminals at every appropriate point in the circuit under test as shown below:

Record the reading at the furthest point of the circuit. The resistance measured by the above method includes the resistance of the line conductor as well as that of the circuit protective conductor and is therefore the circuit’s (R1+R2) value, which will allow verification of the calculated value of line earth loop impedance, Zs. The approximate resistance of the line conductor can be found by linking the line and neutral conductors at the fuse-board and measuring between these two at the point of test (furthest point of circuit). Divide this value by 2 and subtract it from the value of (R 1+R2) to give the earth continuity conductor resistance value. This test should be done before connecting supplementary bonds to the protective conductors.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Test Method 2 Connect one terminal of the continuity tester to a long test lead and connect this to the consumer’s main earthing terminal as shown below. Connect the other terminal of the instrument to another test lead and use this to make contact with the protective conductor at various points on the circuit. The resistance of the protective conductor R 2 is recorded on the Schedule of Test Results.

To test the continuity of main and supplementary bonding conductors test method 2 must be used. Ensure that readings from either method are not affected by parallel earth paths.

Therefore, it is advisable to do these tests with the protective conductors disconnected from the general mass of earth.

Continuity of Ring Final Circuit Conductors (IET Regulation 612.2.2) A test will be made to verify the continuity of all live and protective conductors in every ring final circuit.

One purpose of the test is obviously to verify the continuity of the line, neutral and protective conductors, i.e. that they actually form a ring. Additionally, it is also necessary to establish that the ring has not been ‘interconnected’ to create an apparently continuous ring circuit where an actual break exists as shown below (one core shown for clarity):

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing NB: For each of the following tests use a low resistance reading ohmmeter.

Step 1 - Ring Continuity): Mark up the ends of the ring final circuit conductors as L1, N1, E1, L2, N2 and E2 as shown right.

Measure the end-to-end resistance of each ring separately.

The resistances for L1-L2, N1-N2 and E1-E2 loops are referred to respectively as r1, rn and r2.

A finite reading confirms that there is no open circuit on the ring conductors under test. The resistance values should be substantially the same (within 0.05Ί) if the conductors are the same size.

If the protective conductor has a reduced csa the resistance r2 of the protective conductor will be proportionally higher than that of the line and neutral loops, e.g.

1.67 times for 2.5/1.5mm2 cable.

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.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Step 2 - Socket neutral):

Outlets

(line-

Link together N1 to L2, N2 to L1 as shown right and test between line and neutral at each socket outlet, noting the readings in each case.

The readings obtained from all those sockets wired into the ring will be substantially the same (within 0.05Ω) and will represent (R1 + Rn). Any sockets wired as spurs will have a proportionally higher resistance value corresponding to the length of the spur cable.

Step 3 - Ring Continuity R1+R2 Value: Link together E1 to L2, E2 to L1 as shown right and test between line and cpc at each socket outlet, noting the readings in each case.

The readings at each socket outlet should be substantially the same (within 0.05Ω) value. Any sockets wired as spurs will have a proportionally higher resistance value corresponding to the length of the spur cable.

This value will be approximately one-quarter of the resistance of the line plus cpc loop resistances, i.e. (r1 + r2)/4. This reading will also be the value of R1+R2 needed to verify the calculated value of line earth loop impedance, Zs. The highest value recorded represents the maximum (R1 + R2) of the circuit and is recorded on test result schedule and can be used to determine the earth loop impedance Zs of the circuit to verify compliance with the loop impedance requirements of BS 7671 (see Appendix 9).

This sequence of tests verifies the polarity of each socket and dispenses with the need for a separate protective conductor continuity test.

Visual Inspection of the Ring Final Circuit Conductors An alternative to the above methods for verifying that no interconnection multiple loops have been made in a ring final circuit is for the installer to inspect each conductor throughout its entire length.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

Insulation Resistance (IET Regulation 612.3) These tests are to verify that for compliance with BS 7671 the insulation of conductors and electrical accessories ad equipment is satisfactory and that live conductors or protective conductors are not short-circuited, or do not show a low insulation resistance (which would indicate defective insulation conductors).

Type of Test Instrument An insulation resistance tester should be used which is capable of providing a d.c. voltage as specified in Table 61 below and this Table also specifies the minimum permitted value of insulation resistance: BS 7671 Table 61: Minimum values of insulation Resistance Circuit nominal voltage Test voltage d.c.

(V) SELV and PELV Up to and including 500 V exception of the above systems Above 500 V

with

the

(V) 250 500

Minimum insulation Resistance (M ) 0.5 1.0

1000

1.0

Notes: 1.

In locations exposed to fire hazard, a measurement of the insulation resistance between the live conductors should be applied. In practice, it may be necessary to carry out this measurement during erection of the installation and before connection of the equipment.

2.

Insulation resistance measurements are usually much higher than those of Table 61A

Pre-Test Checks Before commencing with insulation resistance tests, a number of checks should be made with precautions taken as follows: (a)

pilot or indicator lamps and capacitors are disconnected from circuits to avoid misleading test values from being obtained.

(b)

if a circuit includes voltage-sensitive electronic devices such as RCCBs, RCBOs, surge protection devices or SRCDs incorporating electronic amplifiers, dimmer switches, touch switches, delay timers, power controllers, electronic starters or control gear for fluorescent lamps etc either: 1)

the devices must be temporarily disconnected, or

2)

a measurement should be made between the live conductors (line and neutral) connected together and the protective earth only.

The tests should be made at the distribution board with the main switch off, all fuses in place, switches and circuit-breakers closed, lamps removed and other current-using equipment disconnected. Where the removal of lamps and/or the disconnection of current-using equipment are impracticable, the local switches controlling such lamps and/or equipment should be open.

Where a circuit contains two-way switching, the two-way switches must be operated one at a time and further insulation resistance tests carried out to ensure that all the circuit wiring is tested.

For an installation operating at 230/400V, although an insulation resistance value of only 1MΩ complies with BS 7671, where an insulation resistance of less than, say, 2MΩ is obtained the possibility of a latent defect exists. In these circumstances, each circuit should be tested separately.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Where surge protective equipment devices (SPDs) or other equipment such as electronic devices or RCDs with amplifiers are likely to influence the results of the test or may suffer damage from the test voltage, such equipment must be disconnected before carrying out the insulation resistance test. (BS 7671 Regulation 612.3.2) Where it is not reasonably practicable to disconnect such equipment, the test voltage for the particular circuit may be reduced to 250V d.c. but the insulation resistance must be at least 1MΩ.

Where the circuit includes electronic devices which are likely to influence the results or be damaged, only a measurement between the live conductors connected together and earth should be made and the value should be not less than the value stated in Table 61A. (BS 7671 Regulation 612.3.3) Insulation Resistance Between Live Conductors Single-phase and three-phase Test between all the live (line and neutral) conductors at the distribution board (see diagram below): Resistance readings obtained should be not less than the minimum value referred to in Table 61A. Insulation resistance test of the whole installation

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Insulation resistance test between live conductors of a circuit

Insulation Resistance Test To Earth For a circuit containing two-way switching or two-way and intermediate switching, the switches must be operated one at a time and the circuit subjected to additional insulation resistance tests.

Notes: 1.

The test may initially be carried out on the completed installation.

2. earthing and bonding connections are in place.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Three-phase Test to earth from all live conductors (including the neutral) connected together. Where a low reading is obtained it is necessary to test each conductor separately to earth, after disconnecting all equipment.

Resistance readings obtained should be not less than the minimum value referred to in Table 61A.

SELV and PELV Circuits Test between SELV and PELV circuits 250V d.c. (BS 7671 Regulation 612.4.1)

and

live

parts of

other

circuits at

Test between SELV or PELV conductors at 250V d.c. and between PELV conductors and protective conductors of the PELV circuit at 250V d.c. (BS 7671 Regulation 612.4.2) FELV Circuits FELV circuits are tested as LV circuits at 500V d.c. (BS 7671 Regulation 612.4.4)

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

Polarity (IET Regulation 612.6) This test must be carried out to verify that: (i)

every fuse and single-pole control and protective device is connected in the line conductor only, and

(ii)

except for E14 and E27 lampholders to BS EN 60238, in circuits having an earthed neutral conductor, centre contact bayonet and Edison screw lampholders have the outer or screwed contacts connected to the neutral conductor, and

(iii)

wiring has been correctly connected to socket-outlets and similar accessories.

This test is carried out before connection of the supply and uses the same test as Method 1 of the Continuity of Protective Conductors test and can thus be done simultaneously.

After connection of the supply, polarity must be checked using a voltage indicator or a test lamp (in either case with leads complying with the recommendations of HSE Guidance Note GS 38).

It is only necessary to confirm polarity; there is no necessity to record a value. In other words, it is a ‘GO’ or ‘NO-GO’ test.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

Earth Electrode Resistance (IET Regulation 612.7) NB: This test must be carried out with the main earth conductor disconnected from the earth electrode under test. Ensure that safety of the installation and those using it are compromised by the disconnection of the earthing conductor.

NB: Where a measurement of RA is not practicable the measured value of external earth fault loop impedance may be used.

Drive to auxiliary test spikes into the ground at intervals shown in the diagram below and connect the test leads between the main electrode/tests spikes and the earth electrode test instrument.

WARNING The instrument produces a voltage of approximately 50 volts between the E and C or the E and P terminals depending on the setting of the range switch. DO NOT TOUCH THE TEST LEADS DURING TESTING. If the earth into which the auxiliary spikes have been driven is not already moist, make it so by watering. If it is impossible to drive the auxiliary spikes into the ground (e.g. if the area concerned is concreted) a good reading can often be taken when the spikes are laid in the correct positions on the surface and well watered; this does not work on an asphalted surface.

CAUTION Make sure that the connections to the earth electrode and the two auxiliary electrodes are separated during measurement. If the leads are twisted or touching, the reading may be affected by induced voltages. Also ensure that connections to the electrode under test, the auxiliary electrodes and the instrument are firmly made. Poor connections can also affect the accuracy of readings.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Earth Resistance Measurement Set the range switch to the 2 000Ω position and press the test button to display the earth resistance measurement. If the reading is below 200Ω set the range switch to 200Ω and retest for a more accurate reading. If the reading is below 20Ω set the range switch to 20Ω and retest for a more accurate reading.

NOTE: If the display reads "...", this indicates that the earth resistance measurement exceeds 2000Ω. This may be due to: 1.

excessive resistance to earth from the auxiliary electrodes. This can be reduced by watering them, or driving them more firmly into the ground.

2.

very high resistance to earth from the electrode under test. This can be reduced by using a longer electrode driven deeper into the ground, by driving extra electrodes close to the first and Interconnecting them, or by burying a conducting plate. DO NOT try to obtain a lower reading by watering the earth electrode, as its resistance will increase again as it dries out, possibly affecting the operation of protective devices.

Check for Overlapping Resistance Areas If the resistance areas of the auxiliary and main electrodes overlap, a false reading will result. The presence of overlapping resistance areas can be checked by the following procedure (this procedure is shown in the diagram below): 1.

Move the central auxiliary electrode (connected by the yellow lead to the terminal marked "P" on the instrument) 3m nearer to the electrode under test than its original position. Take a further resistance reading.

2.

Move the central auxiliary electrode (connected by the yellow lead to the terminal marked "P" on the instrument) 3m further from the electrode under test than its original position. Take a further resistance reading.

3.

If the original resistance reading and the subsequent readings differ by more than 5% (one part in 20) there is an overlap of resistance areas. In this case, the main auxiliary spike (connected by the red lead to the "C" terminal of the instrument) must be moved further away from the electrode under test.

NB: Where a measurement of RA is not practicable the measured value of external earth fault loop impedance may be used.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

Re-checking Polarity – Supply Connected Using an approved voltage indicator or test lamp and probes which comply with the HSE Guidance Note GS 38, again carry out a polarity test to verify that all fuses, circuit breakers and switches are connected in the live conductor. Test from the common terminal of switches to earth, the line pin of each socket outlet to earth and the centre pin of any Edison screw lampholders to earth. In each case the voltmeter or test lamp should indicate the supply voltage for a satisfactory result.

Determining Ze The reasons that Ze is required to be measured are twofold: To verify that there is an earth connection.

To verify that the Ze value is equal to or less than the value determined by the designer and used in design calculations.

Ze is measured using an earth fault loop impedance tester at the origin of the installation.

The impedance measurement is made between the line 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. ENSURE THAT THE EARTH CONNECTION HAS BEEN REPLACED BEFORE RECLOSING THE MAIN SWITCH.

Prospective Fault Current (IET Regulation 612.11) The prospective short-circuit current (PSC) and the prospective earth fault current (PFC) shall be measured, calculated or determined by another method, at the origin and at other relevant points in the installation.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Prospective Earth Fault Current (PFC)

Prospective Short-Circuit Current (PSC)

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing

Earth Fault Loop Impedance (IET Regulation 612.9) Where protective measures are used which require a knowledge of earth fault loop impedance, the relevant impedances shall be measured, or determined by an alternative method.

The earth fault current path for a TN-S system is shown in the diagram below:

The loop comprises the following parts, starting at the point of the fault: circuit protective conductor; the main earthing terminal and earthing conductor; for TN systems the metallic return path or, in the case of TT and IT systems, the earth return path; the path through the earthed neutral point of the supply transformer; the source line winding, and the line conductor from the source to the point of the fault.

The impedance of this fault path, the ‘earth fault loop impedance’, is denoted by the symbol ZS.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Earth Fault Loop Impedance Testing The earth fault loop impedance (ZS) is required to be determined for the furthest point of each circuit. It may be determined by: 1.

measurement of R1 + R2 during continuity testing (see earlier notes) and adding to Ze, i.e.

ZS = Ze + (R1 + R2) Ze is determined by:   

2.

Measurement (see below), or Enquiry of the electricity supplier, or Calculation, or

direct measurement using and earth fault loop impedance tester (see page 15).

Measurement of (R1 + R2) to add to Ze Whilst testing the continuity of protective conductors of radial circuits, or whilst testing the continuity of ring final circuits, the value of (R1 + R2)test is measured (at the test ambient temperature).

The measured value of (R1 + R2)test for the final circuit should be added to the value of (R1 + R2)test for any distribution circuit supplying the final circuit, to give the total (R1 + R2)test from the origin of the installation.

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. Readings given by the loop impedance tester may be less than Ze + (R1 + R2) because of parallel earth return paths provided by any bonded extraneous-conductive-parts. This must be taken into account when comparing the results with design data.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Care should be taken during the tests to avoid any shock hazard to the testing personnel, other persons or livestock on site.

Verification of test results Values of ZS should be compared with one of the following: 1.

For standard thermoplastic (PVC) circuits, the values in Appendix B of Guidance Note 3.

2.

Earth fault loop impedance figures provided by the designer.

3.

Tabulated values in BS 7671 (Tables 41.2, 41.3 and 41.3), corrected for temperature.

4.

Rule-of-thumb figures.

Rule-of-thumb figures As a rule of thumb, the measured value of earth fault loop impedance for each circuit at the most remote outlet should not exceed 0.8 of the relevant value in BS 7671 tables. This takes into account the increase of resistance of the conductors with the increase in temperature due to load current and errs on the side of safety.

Test for Earth Electrode Resistance – Supply Connected This test is carried out in the same manner as the test for Z e but with the tester leads connected to the earth electrode, with the main earthing conductor disconnected from the main earth terminal, and the line conductor at the source of the installation. All the precautions taken for testing for Ze must be employed for this test.

Prospective Fault Current (PFC) (612.11) It is not recommended that installation designs are based on measured values of prospective fault current, as changes to the distribution network subsequent to the completion of the installation may increase fault levels. Designs should be based on the maximum fault current provided by the distributor.

If it is desired to measure prospective fault levels this should be done with all main bonding in place. Measurements are made at the distribution board between live conductors and between line conductors and earth.

For three-phase supplies the maximum possible fault level will be approximately twice the single-phase to neutral value. (For three-phase to earth faults, neutral and earth path impedances have no influence.)

Functional testing of RCD - supply connected (612.8 and 612.13.1) The object of the test is to verify the effectiveness of the residual current device, that is, it is operating with the correct sensitivity and proving the integrity of the electrical and mechanical elements. The test must simulate an appropriate fault condition and be independent of any test facility incorporated in the device.

The tests are made on the load side of the RCD, as near as practicable to its point of installation and between the line conductor of the protected circuit and the associated circuit protective conductor. The load supplied should be disconnected during the test.

These tests must completed in both the positive going part of the cycle (0°) and the negative going part of the cycle (180°).

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing General purpose RCCBs to BS 4293 1.

With a leakage current flowing equivalent to 50% of the rated tripping current (I∆n), the device should not open (½ x current test).

2.

With a leakage current flowing equivalent to 100% of the rated tripping current of the RCD (I∆n), the device should open in less than 200 ms (1 x current test). Where the RCD incorporates an intentional time delay it should trip within a time range from ‘50% of the rated time delay plus 200 ms’ to ‘100% of the rated time delay plus 200 ms’.

General purpose RCCBs to BS EN 61008 or RCBOs to BS EN 61009 1.

With a leakage current flowing equivalent to 50% of the rated tripping current (I∆n), the device should not open (½ x current test).

2.

With a leakage current flowing equivalent to 100% of the rated tripping current of the RCD (I∆n), the device should open in less than 300 ms (1 x current test) unless it is of ‘Type S’ (or selective) which incorporates an intentional time delay. In this case, it should trip within a time range from 130 ms to 500 ms.

RCD protected socket-outlets to BS 7288 1.

With a leakage current flowing equivalent to 50% of the rated tripping current (I∆n), the device should not open (½ x current test).

2.

With a leakage current flowing equivalent to 100% of the rated tripping current of the RCD (I∆n), the device should open in less than 200 ms (1 x current test).

Additional protection Where an RCD with a rated residual current rating I∆n not exceeding 30 mA is used to provide additional protection (against direct contact), with a test current of 5 x I∆n the device should open in less than 40 ms. 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).

Integrated test device An integral test device is incorporated in each RCD. This device enables the electrical and mechanical parts of the RCD to be verified, by pressing the button marked ‘T’ or ‘Test’.

Operation of the integral test device does not provide a means of checking: the continuity of the earthing conductor or the associated circuit protective conductors, any earth electrode or other means of earthing, or any other part of the associated installation earthing.

The test button will only operate the RCD is the device is energised.

Confirm that the notice to test RCDs quarterly (by pressing the test button) is fixed in a prominent position.

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CGLI 2330 Certificate in Electrotechnical Technology Level 3 Installation Technology: Unit 302/3 – Inspection & Testing and Fault Diagnosis & Rectification

Unit 12 – Testing Frequency of Inspection and Testing (from IET 17th Edition Guidance Note Number 3) Type of installation

1 General Installation Domestic Commercial Educational establishments Hospitals Industrial Residential accommodation Office Shops Laboratories Buildings Open To The Public Cinemas Churches installations Leisure complexes (excluding swimming pools) Places of public entertainment Restaurants and hotels Theatres Public houses Village halls/community centres Special installations Agricultural and horticultural Caravans Caravan parks Highway power supplies Marinas Fish farms Swimming pools Emergency lighting Fire alarms Launderettes Petrol filling stations Construction site installations

Routine check sub-clause 3.5

2 -

Maximum period between inspections and testing as necessary 3

Reference (see key below)

4

4 months 1 year 1 year At change of occupancy/1 year 1 year 1 year 1 year

At change of occupancy/10 years At change of occupancy/5 years 5 years 5 years 3 years 5 years 5 years 5 years 5 years

1 year 1 year 1 year

1 to 3 years 5 years 3 years

2, 6, 7 2 1, 2, 6

1 year 1 year 1 year 1 year 1 year

3 years 5 years 3 years 5 years 5 years

1, 2, 6 1, 2, 6 2, 6, 7 1, 2, 6 1, 2

1 year 1 year 6 months as convenient 4 months 4 months 4 months Daily/monthly Daily/weekly/monthly 1 year 1 year 3 months

3 years 3 years 1 year 6 years 1 year 1 year 1 year 3 years 1 year 1 year 1 year 3 months

1, 2 8 1, 2, 6

1 year

1, 2 1, 2 1, 2 1, 2 1 1, 2 1, 2 1, 2

1, 2 1, 2 1, 2, 6 2, 3, 4 2, 4, 5 1, 2, 6 1, 2, 6 1, 2

Reference key 1.

Particular attention must be taken to comply with SI 1988 No 1057. Electricity, Safety, Quality and Continuity Regulations 2002 (as amended).

2.

SI 1989 No 635. Electricity at Work Regulations 1989 (Regulation 4 & Memorandum).

3.

See BS 5266: Part 1: 2005 Code of Practice for the emergency lighting of premises other than cinemas and certain other specified premises used for entertainment.

4.

Other intervals are recommended for testing operation of batteries and generators.

5.

BS 5839: Part 1: 2002 Code of Practice for system design installation and servicing (fire detection and alarm systems for buildings).

6.

Local Authority Conditions of Licence.

7.

SI 1955 No 1129 (Clause 27). Cinematography (Safety) Regulations.

8.

It is recommended that a caravan is inspected and tested annually if it used frequently (see 721.514.1 and fig. 721 – instructions for electricity supply).

For more information see pages 352 - 360 and page 409 ‘Electrical Installations Level 3 2330 Technical Certificate’ – revised for the 17th Edition IET Wiring Regulations (ISBN 978 0 435401 10 8).

The College at Clacton

Unit 12 Page 21

December 2011