Inspection and Testing

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Inspection and Testing REV4.1

1

Inspection

And Testing

Learner Work Book

Name:

Group:

Tutor:

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Inspection and Testing REV4.1 3

Foreword

In this unit you will learn about Inspection and testing. Inspection and testing is an immensely important subject to grasp and is relevant to every electrical installation. It is carried out during the erection of an installation and forms its completion.

Inspection and testing is also carried out periodically to ensure a system is still in compliance with the latest edition of BS7671. The results of testing are documented as proof that the installation is safe to use.

It is a legal requirement that the statutory document Electricity at Work Regulations 1989 is adhered to and that installations are safe to use and do not cause any

danger. The non-statutory documents; BS7671, the Onsite Guide and Guidance Note 3 (Inspection and Testing) are not legal requirements but by following them we are deemed to be complying with the Electricity at Work Act.

This unit examines the requirements for inspecting and testing of an installation when it is brand new, when additions or alterations have been made to it and when it has been in use for some time.

This workbook is to be accompanied by PowerPoint “Inspection and Testing”

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Inspection and Testing Unit Overview

Practical skills you will need to demonstrate

To achieve the learning outcome the candidate must be able to: Carry out an initial inspection of an installation

Select correct instruments to carry out tests Complete the correct sequence of tests Record the test results obtained

Carry out functional testing of an installation Fill in recognised certificates of completion

Knowledge Requirements

To achieve the learning outcome the candidate must know: How to carry out an initial inspection

How to correct any deviations found during inspection How to use various test instruments

The importance of the sequence of tests How to carry out functional testing How to document inspection and testing

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Purpose of Inspection and Testing

Inspection and testing is not just carried out because it is someone’s job or that it is what the client wants. It is a legal requirement in the domestic sector. In the

commercial and industrial sector it falls under the Electricity at Work Act and is

harnessed by most companies who have the legal obligation to protect their premises and personnel.

The purpose of inspection and testing is to provide, so far as is reasonably practicable, for:

The safety of persons and livestock against the effects of electric shock and burns

Protection against damage to property by fire and heat arising from an installation defect, and

Confirmation that the installation is not damaged or deteriorated so far as to impair safety, and

The identification of installation defects and non-compliance with the requirements of the Regulations which may give rise to danger.

Building Regulations

Part P of the Building Regulations (England and Wales) was introduced by the Government on January 1st 2005. It is designed to reduce accidents caused by faulty electrical installations and to prevent incompetent installers from leaving electrical installations in an unsafe condition. Part P applies to the following situations:

Dwelling houses and flats

Dwellings and business premises that have a common supply eg shops that have a flat above

Common access areas in blocks of flats such as corridors or staircases Shared amenities in blocks of flats such as laundries or gyms

In or on land associated with dwellings – such as fixed lighting or pond pumps in gardens

Outbuildings such as sheds, detached garages and greenhouses

Approved Document P is called ‘Electrical Safety’ and will be complied with if the standard of electrical work meets the ‘Fundamental Requirements of Chapter 13 of BS7671:2008’.

Inspection and testing is carried out:

• During and or on completion of a new installation.

• When minor works such as additions or alterations are carried out • To satisfy the periodic inspection of a companies’ premises. • To satisfy the requirements of Part P of the building regulations.

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Inspection and Testing REV4.1 7 Section P1 of Part P states: ‘Reasonable provision shall be made in the design, installation, inspection and testing of electrical installations in order to protect persons from fire and injury’.

Section P2 of Part P states: ‘Sufficient information shall be provided so that persons wishing to operate, maintain or alter an electrical installation can do so with

reasonable safety.

In your own words describe how people are protected from fire and injury whilst using an electrical installation.

In your own words describe what information relating to safety can be provided to persons wishing to use an electrical installation.

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Electrician and bathroom fitter prosecuted for breach

of Part P of the building regulations

A

n electrician in

Newcastle and a bathroom fitter from bath and

Somerset are to be the first to be successfully prosecuted for offences under Part P of the building regulations. Able Electrical based in Newcastle and the company’s director John Waugh, an electrician with 28 years experience, admitted 23 counts of breaching building regulations and was fined total of £16,000.

Able Electrical carried out rewiring on a property that, according to Newcastle magistrates' court, could have resulted in death or serious injury. Waugh admitted to 23 offences including falsely claiming to be registered with the NICEIC, failing to notify work to Building Control, installing cables under the landing floor in a poor manner, using old wires which are no longer covered by current regulations and not using Residual Circuit Breakers for sockets.

Newcastle Council Building Control brought charges against Able Electrical after the householder called in an NICEIC registered

electrician to inspect Able’s work and found that the property needed a complete rewire and tests could not be carried out for safety reasons.

Jim Speirs, director general of the NICEIC said: “It is unacceptable for an electrician with this level of experience to have carried out work to such a poor standard that lives are put at risk.

“A professional and competent electrician or installer would have no problem in becoming registered with a competent person scheme, and would therefore have no reason to falsify their status. The NICEIC takes misuse of its name and logo seriously and we will always prosecute any persons falsely claiming registration with our schemes.”

In a second incident, Bath & North East Somerset Council Building Control brought charges against bathroom fitter Roger Martin Drinkwater for contravening Building Regulations with regard to the installation of an electric shower in a replacement bathroom at a private property.

The defendant pleaded guilty to charges that included using a method of wiring not in accordance with the British Standard, and failing to advise the complainant that the incomplete shower should not be used and that it was awaiting checking. He was fined £1,000 for the Part P offence and £250 each for the remaining offences of failing to give a Building Notice to Building Control prior to

commencement of the work, and failing to give notice of commencement and completion of certain stages of the work. The court also ordered the defendant to pay £1,066 in costs.

Jim Speirs continued: “It is vital that anyone carrying out electrical installations are qualified to do so, and have a practical

understanding of current wiring and building regulations. These prosecutions under Part P are evidence that building control bodies and scheme operators are taking compliance with Part P seriously, and will not tolerate false claims of competent scheme registration and sub-standard, dangerous working practices.”

Class discussion. Firstly read and then discuss the above article and consider the people involved. Should these workmen be prosecuted? Why lie about being part of the NICEIC? Write down the key points below.

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Inspection and Testing REV4.1 9 Test frequency

Initial inspection and testing is necessary on all newly completed installations. In addition, because all electrical installations deteriorate due to a number of factors such as damage, wear and tear, corrosion, excessive electrical loading, ageing and environmental influences, periodic inspection and testing must be carried out at regular intervals determined by the following:

Legislation requires that all installations must be maintained in a safe condition and therefore must be periodically inspected and tested. Licensing authorities, public bodies, insurance companies and other

authorities may require public inspection and testing of electrical installations. The installation must be checked to ensure that it complies with BS 7671. It is also recommended that inspection and testing of installations should

occur when:

There is a change of use of the premises

Any alterations or additions to the original installation

Any significant change in the electrical loading of the installation Where there is reason to believe that damage may have been caused

to the installation.

The table below details the maximum period between inspections of various types of installation.

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Inspection and Testing REV4.1 10 Now answer the questions below

1 In you own words state the four purposes of inspection and testing

2. When and why should inspection and testing be carried out?

3. State the main aim of Part P of the building Regulations

4. Explain why installations need to be periodically re-tested

5. When is it recommended that electrical testing of installations be carried out?

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Inspection and Testing REV4.1 11 Calibration label

Electrical test instruments

BS EN 61010 covers basic safety requirements

for electrical test instruments, and all instruments should be checked for conformance with this standard before use. Older instruments may have been manufactured in accordance with BS 5458 but, provided these are in good condition and have been recently calibrated, there is no reason why they cannot be used. Guidance note GS38 stipulates test leads, including probes and clips, must be in good order and have no cracked or broken insulation. Fused test leads are

recommended to reduce the risk of arcing under fault conditions.

Instruments may be analogue (i.e. fitted with a needle that gives a direct reading on a fixed scale) or digital, where the instrument provides a numeric digital visual display of the actual measurement being taken. Insulation and continuity testers can be obtained in either format whilst earth-fault loop impedance testers and RCD testers are digital only.

Calibration and instrument accuracy

To ensure that the reading being taken is reasonably accurate, all instruments should have a basic

measurement accuracy of at least 5 per cent. In the case of analogue instruments a basic accuracy of 2 per cent of full-scale deflection should ensure the required accuracy of measured values over most of the scale.

All electrical test instruments should be calibrated on a regular basis. The time between calibrations will depend on the amount of usage that the instrument receives, although this should not exceed 12 months in any circumstances.

Instruments have to be calibrated in laboratory conditions against standards that can be traced back to national standards; therefore this usually means returning the instrument to a specialist test laboratory.

On being calibrated the instrument will have a calibration label attached to it stating the date the calibration took place and the date the next calibration is due. It will also be issued with a calibration certificate detailing the tests that have been carried out and a reference to the equipment used.

The user of the instrument should always check to ensure that the instrument is within calibration before being put to use.

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0.50Ω

A further adhesive label is often placed over the joint in the instrument casing stating that the calibration is void should the seal be broken. A broken seal will indicate whether anyone has deliberately opened the

instrument and possibly tampered with the internal circuitry.

Instruments that are subject to any electrical or mechanical misuse (e.g. if the

instrument is subject to an electrical short circuit or is dropped) should be returned for re-calibration before being used again. Electrical test instruments are relatively

delicate and expensive items of equipment and should be handled in a careful manner.

When not in use they should be stored in clean, dry conditions at normal room temperature. Care should also be taken of instrument leads and probes to prevent damage to their insulation and to maintain them in a good, safe working condition.

Instrument types

Low resistance Ohmmeters

This may be a specialised low-reading ohmmeter or the continuity scale of a

combined insulation and continuity tester. Whichever type is used it is recommended that the test current should be derived from a source of supply not less than 4 V and no greater than 24 V with a short circuit current not less than 200 mA and give a reading to two decimal places. Instruments manufactured to BS EN 61557 will meet the above requirements.

Errors in the reading obtained can be introduced by contact resistance or by lead resistance. Although the effects of contact resistance cannot be eliminated entirely and may introduce errors of 0.01 ohm or greater, lead resistance can be eliminated either by clipping the leads together and zeroing the instrument before use, where this facility is provided, or alternatively measuring the resistance of the leads and subtracting this from the reading obtained.

When using an instrument out on site, the accuracy of the instrument will probably not be as good as the accuracy obtained under laboratory conditions. Operating accuracy is always worse than basic accuracy and

can be affected by battery condition, generator cranking speed, ambient temperature, instrument alignment or loss of calibration

Where low resistance measurements are required when testing earth continuity, ring circuit continuity and

polarity, then a low reading ohmmeter is required. They are only

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>200MΩ

0.50Ω

Insulation resistance Ohmmeters

Insulation resistance should have a high value and therefore insulation resistance meters must have the ability to measure high resistance readings (typically 200MΩ). The test voltage required for measuring insulation resistance is given in BS 7671 Table 71A as shown below.

Circuit Nominal Voltage to earth Test Voltage dc

v

Minimum Insulation Resistance (MΩΩΩΩ)

SELV & PELV 250 V 0.25

Up to and including 500 v with the

exception of the above supplies 500 V 1.0

Above 500 V 1000 V 1.0

SELV = Separated extra low voltage - Not exceeding 50V A.C. or 120V Ripple Free D.C. PELV = Protective extra-low voltage

The photograph above shows a typical modern insulation and continuity tester that will measure both low values of resistance for use when carrying out continuity and polarity tests and also high values of resistance when used for insulation resistance tests. This type of instrument and test is only ever carried out on an isolated circuit Instruments of this type are usually enclosed in a fully insulated case for safety reasons and have a range of switches to set the instrument correctly for the type of test being carried out i.e. continuity or insulation. The instrument also has a means of selecting the voltage range required e.g. 250 V, 500 V, 1000 V.

Other features of this particular type of instrument are the ability to lock the instrument in the ‘on’ position for hands-free operation and an automatic nulling device for taking account of the resistance of the test leads.

Earth-loop impedance testers

Earth-loop impedance testers of the type shown in the photograph have the capability to measure both earth-loop impedance and also prospective short-circuit current, depending on which function is selected on the range selection switch.

The instrument also has a series of LED warning lights to indicate whether the polarity of the circuit under test is correct or

not. The instrument gives a direct digital read-out in Ohms of the value of the measurement being taken at an accuracy of plus or minus 2 per cent and to two decimal places.

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40mS

RCD testers

Instruments for testing residual current devices, such as the one shown in the photograph have two selection switches. One switch that should be set to the rated tripping current of the RCD (e.g. 30 mA, 100 mA etc.) and the other set to the test current required i.e. 50 per cent or 100 per cent of the rated tripping current or 150 mA for testing 30 mA RCDs when being used for supplementary protection. Half cycle tests can be selected to ensure full protection. All-in-one tester

A modern innovation by manufacturers is the production of an ‘all in one’ instrument that has the ability to carry out the most common tests required by the Regulations. These are:

Continuity tests (including polarity tests) Insulation resistance tests

Earth-loop impedance tests RCD tests

Measurement of prospective short circuit current.

The photograph below shows an example of this type of instrument, which by manipulation of the function and range switches will perform, all of the above tests.

Testing your meter

In order to carry out effective testing it is not just a case of unpacking your meters and carrying on with the tests. It is important that you regularly check your

instruments to make sure they are in good and safe working order.

Before using any of your instruments make sure that all test probes and conductors to be tested are scrupulously clean to avoid incorrect test results Check the leads for damage

Check the battery levels by zeroing or nulling the lead resistance

Ensure you get visual confirmation of the expected test values. (Open leads display a high resistance value. Closed leads display a low resistance)

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1 Describe the general aim of the standard BS EN 61010.

2. Describe what is meant by instrument calibration

3. What is the recommended calibration period and how can we check if an instrument is calibrated?

4. Name three tests we carry out with a low reading Ohmmeter and how accurate must the meter reading be?

5. What three voltage settings are available on an insulation resistance tester?

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Inspection and Testing REV4.1 16 Incorrectly terminated SWA

Initial Verification

The following notes provide a detailed description of the procedures required to carry out an initial inspection of an electrical installation. Substantial reference has been made to the lEE Wiring Regulations (BS7671), the On Site Guide and lEE Guidance Note No.3 and it is recommended that wherever possible these documents are referred to should clarification be required.

The most important considerations prior to carrying out any inspection and test procedure are that:

All the required information about the installation is available The person carrying out the procedure is competent to do so That all safety requirements have been met

Forward planning is also a major consideration and it is essential that suitable inspection checklists have been prepared and that appropriate certification is available for completion.

It is also important to realize that a large proportion of any new installation will be hidden from view once the building fabric has been completed and

therefore it is preferable to carry out a certain amount of visual inspection throughout the installation process: e.g. conduit, cable tray or trunking is often installed either above the ceiling or below the floor and once the ceiling or floor tiles have been fitted it is difficult and often expensive to gain access for inspection purposes. The same applies to testing and it may be advisable to carry out tests such as earth continuity during construction rather than after the building has been completed.

It must be remembered however that when visual inspection and / or tests are carried out during the construction line, the results must be recorded on the appropriate checklists or test certificates.

It is also worth noting that although the major part of any inspection will be visual other human senses may be employed: e.g. a piece of equipment with moving parts may generate an usual noise if it is not working correctly or an electrical device which overheats will be hot to touch as well as giving off a

distinctive smell. The senses of hearing touch and smell will assist in detecting these.

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Inspection and Testing REV4.1 17 The importance of paperwork

When an installation is complete the persons responsible for the work must report to the owner that it is complete and ready for service. This is presented in the form of an electrical installation certificate that must be separately signed to verify the design, the construction and the inspection and test aspects to confirm that the installation complies with BS7671.

The installer should also compile an operational manual for the installation, which will include all the relevant data, including:

A full set of circuit and schematic drawings,

All design calculations for cable sizes, cable volt drop, earth-loop impedance, etc.

Leaflets or manufacturers' details for all the equipment installed, As fitted' drawings of the completed work where applicable, A full specification,

Copies of the electrical installation certificate, together with any other commissioning records,

A schedule of dates for periodic inspection and testing,

The names, addresses and telephone numbers of the designer, the installer, and the inspector / tester.

The certificate could be used in a court of law to prove the competence of the electrical tester should anything happen at a later date. If we were to certify an electrical installation that would later result in damage or harm to persons or property we would require proof that we carried out a full inspection and test in accordance with BS7671 which would satisfy the Electricity at Work Act. The legalities of our responsibilities are that we are guilty until proven innocent. So having correct paper work and test records could save your neck!

The certificate we will take a look at is the NICEIC’s (National Inspection Council for Electrical Installation Contracting) domestic installer form. This

would be supplied to a client who had requested work to be done on domestic premises

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19 Information needed

Before carrying out the initial inspection (and test) of an installation it is essential that the person carrying out the work be provided with the following information:

1. The maximum demand of the installation expressed in amperes per line together with details of the number and type of live

conductors both for the source of energy and for each circuit to be used within the installation, (e.g. single-line two-wire a.c. or three line four-wire a.c. etc).

2. The general characteristics of the supply such as: The nominal voltage (Uo)

The nature of the current ( I ) and its frequency (Hz)

The prospective short circuit current at the origin of the installation (kA) The earth fault loop impedance (Ze) of that part of the system external to the

installation.

The type and rating of the over current device acting at the origin of the installation.

If this information is not known it must be established either by calculation, measurement, inquiry or inspection.

3. The type of earthing arrangement used for the installation e.g. TN-S, TN-C-S, TT etc.

4. The type and composition of each circuit (i.e. details of each sub-circuit, what it is feeding, the number and size of conductors and the type of wiring used).

5. The location and description of all devices installed for the purposes of protection, isolation and switching (e.g. fuses/circuit breakers etc).

6. Details of the method selected to prevent danger from shock in the event of an earth fault (This will invariably be protection by earthed equipotential bonding and automatic disconnection of the supply).

7. The presence of any sensitive electronic devices which may be susceptible to damage by the application of 500 volts d.c when carrying out insulation resistance tests.

The above information may be gained from a variety of sources such as the project specification, contract drawings, as fitted drawings or distribution

board schedules. If such documents are not available, then the person ordering the testing should be approached

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20

Sample taken from an NICEIC certificate

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21 Scope of the inspection

BS 7671 states that as far as reasonably practicable, an inspection shall be carried out to verify that:

All equipment and materials used in the installation are of the correct type and comply with the appropriate British Standards or acceptable equivalent

All parts of the installation have been correctly selected and installed No part of the installation is visibly damaged or otherwise defective The installation is suitable for the surrounding environmental conditions.

Initial inspection checklist

The visual inspection shall include the checking of the following items where relevant to the installation and where necessary, during erection of the equipment. This means that some of the visual inspections can be carried out during erection of the equipment and therefore need not be re-inspected.

.

Remember, if any of the initial verification checks require you to remove covers then you will need to carry out safe isolation, otherwise you will contravene the Electricity at Work Act 1989. The key point with all electrical work is that you maintain yours and everyone’s safety when carrying out such work.

Initial Inspection at a glance:

1. Connection of conductors 2. Identification of conductors

3. Routing of cables within mechanical protection

4. Selection of conductors for current carrying capacity and volt drop.

5. Connection of single – pole devices in the line conductor only

6. Correct connection of equipment 7. Presence of fire barriers and suitable

seals

8. Methods of protection against electric shock (earthing)

9. Prevention of detrimental influences 10. Presence of appropriate devices for

isolation and switching

11. Presence of under – voltage protective devices

12. Choice of setting of protective devices

13. Labeling of protective devices, switches and terminals

14. Selection of equipment

appropriate to external influences 15. Adequacy of access to switchgear

and equipment

16. Presence of warning signs and danger notices

17. Presence of diagrams, charts, instructions and similar information

18. Erection methods

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Inspection and Testing REV4.1 22 1. Connection of conductors

Every connection between conductors or between conductors and equipment must be electrically continuous and mechanically sound. We must also make sure that all connections are adequately enclosed but accessible as required by the regulations. Loose connections can lead to many dangerous events from electric shock to fire.

Note: Before attempting to re-secure any electrical accessory you must ensure that the supply has been isolated.

Questions to ask ourselves:

• Are terminations electrically and mechanically sound?

• Is insulation and sheathing removed only to a minimum to allow

satisfactory termination?

Dangers:

Movement of the socket outlet may dislodge circuit connections and contact exposed conductors. Work to this standard generally means connections are also loose. Can lead to arcing; overheating; electric shock; fire. Remedy:

Dangers:

Constant use of this main isolator with a loose supply connection can catch fire through arcing and overheating.

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Inspection and Testing REV4.1 23 2. Identification of conductors

A check should be made that each conductor is identified in accordance with the requirements of BS7671 Table 51A and Table 51B. Although numbered sleeves or discs may be used in special circumstances, the most common form of identification is by means of coloured insulation or sleeving. It should be noted in particular that only protective conductors should be identified by a combination of the colours green and yellow.

• Are conductors correctly identified in accordance with BS7671? • Are switch wires identified as live at both terminations?

Harmonised colours of conductors to BS7671:2008

Dangers:

Old switch wire colours not

identified as live at two way switch so could present a danger when switch is replaced.

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Inspection and Testing REV4.1 24 3. Routing of cables within mechanical protection

Cables should be routed out of harms way and protected against mechanical damage where necessary. Permitted cable routes are clearly defined in the 'on site guide' or alternatively cables should be installed in earthed metal conduit or trunking.

• Are cables installed so that external influences from mechanical

damage, corrosion or heat etc have been considered?

• Are covers and lids in place to prevent unauthorised access?

Danger:

Remedy:

Install cables away from

terminations and ensure they are protected from mechanical damage

Dangers:

Unprotected single insulated conductors may get snagged or damaged by persons or

equipment. Remedy:

Single core insulated cables should only be installed where they are afforded mechanical protection. Name five types different types of installation where they are properly protected.

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Inspection and Testing REV4.1 25 4. Selection of conductors for current carrying capacity and volt drop

Where practicable the size of cable used at the consumer unit should be checked for current carrying capacity and voltage drop based upon information provided by the installation designer. Incorrect ratings can lead to equipment failure and overheating of conductors.

The maximum permitted voltage drop allowable from the nominal voltage is 3% for lighting and 5% for power. This value is from the origin of the installation to the furthest point of utilisation. At 230V that is 6.9V for lighting and 11.5V for power. If we know the conductor size the procedure to measure voltage drop is simple. 1. For each circuit - when isolated – the L and N conductors are joined at the

furthest point and the resistance of the loop measured at the distribution board. 2. We then calculate the approximate length of the circuit.

Circuit length in metres = 29.4 x R x S

Where R = loop resistance value and S = cable cross sectional area in mm² Example: the loop resistance of a lighting circuit, shorted out at the furthest point is found to be 0.7Ω. If the c.s.a of the cable is 1.0 mm², what is the circuit length?

L = 29.4 x 0.7 x 1 = 20.6 metres.

The voltage drop may then be determined by reference to appendix 4 of BS 7671. 1.0 mm² is listed as dropping 44mV/a/m

Therefore if the above circuit is carrying a current when fully loaded of 5A, the voltage drop will be:

Vd = Ib x L x mV/a/m = 5 x 20.6 x 44 = 4.53 Volts 1 000 1 000

• Are conductors selected for current carrying capacity and voltage

drop in accordance with the design requirements?

How can we determine that the size of the conductor is correct for the intended use of the circuit?

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Inspection and Testing REV4.1 26 5. Connection of single pole devices in the line conductor only

This is verification of polarity. A check must be made that all single pole devices are connected in the line conductor only. Where neutrals are used to switch devices the equipment or circuit remains live when the circuit is seemingly isolated.

Note: Before attempting to re-secure any electrical accessory you must ensure that the supply has been isolated.

• Are single pole devices and switching devices connected in the live

conductor only?

• Are there only live conductors terminated into switches and circuit

protection?

Dangers:

A fault or an overload will cause the fuse to operate but the

equipment will still remain live but not operational. Electric shock risk Remedy: L N E Load Danger: Remedy:

Disconnect the neutrals from the switch and connect the live conductors into the switch terminals

L N

E

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Inspection and Testing REV4.1 27 6. Correct connection of equipment

Accessories and equipment should be checked to ensure they have been connected correctly including correct polarity. Incorrect connection of equipment can lead to damage to the equipment or fire.

• Are all accessories and items of equipment correctly connected? • Do all terminals have the correct conductors connected into them?

Danger:

Remedy:

Isolate circuit and re-wire strappers with a three core and earth and re-connect the switch

Danger:

Remedy:

Disconnect and re-connect socket conductors into the correct

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Inspection and Testing REV4.1 28 7. Presence of fire barriers and suitable seals

A check must be made (preferably during construction) that fire barriers, suitable seals and/or other means of protection against thermal effects have been provided as necessary to meet the requirements of the regulations.

Suitable fire barriers need to be installed where cables pass through floors and walls. Due to there being an entry to pass the cable through it would provide a path for fire to travel through. Expanding foam or transient blocks are the main form of seal used. Where conduit, trunking or ducting does not exceed an internal csa of 710mm² it need not be sealed internally as it passes through walls and floors. Where this dimension is exceeded it needs to be sealed against the spread of fire.

• Are fire barriers present where required and protection against

thermal effects provided?

• Where cables pass through walls and floors are the access holes

sealed?

• Are correct termination methods used for cable entries?

• Where there is a danger of overheating conductors have they been

protected by heat resistance sleeving or barriers?

Dangers:

An electrical fire within this

trunking would escape through the open cable entries. Also carries an electric shock risk.

Remedy:

Danger:

Remedy:

Disconnect and circuit conductors. Remove conduit and re-terminate using a 25 to 20mm reducer. Reconnect the conductors.

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Inspection and Testing REV4.1 29 8. Methods of protection against electric shock

A check must be made that the requirements of the regulations have been met for the method of protection used. Failure to comply with BS7671 could result in an electric shock.

Basic Protection

Basic protection is protecting from touching parts that are live under normal use. This generally corresponds to contact of persons or livestock with live parts. The

unfortunate being receives maximum shock voltage. We are granted basic protection by:

Insulation

Although protection by insulation is the usual method of protection against direct contact other methods can be used. However, where insulation should be present it should be checked to ensure that no live conductors have been left exposed.

Barriers / Enclosures

Where live parts are protected by barriers or enclosures (e.g. bare bus-bars enclosed in a metal bus-bar chamber) they should be checked to ensure that all covers have been fitted and all fixing devices are secure.

Obstacles

Protection by obstacles provides protection only against unintentional contact with live conductors. If this method is used the area should be accessible only to skilled persons or persons under supervision.

Out of reach

Placing live parts out of reach can also provide protection against direct contact although increased distances may be necessary where long or bulky conducting objects are likely to be handled in the vicinity.

• What methods have been used to provide basic and fault

protection?

• Are all live parts correctly protected from contact of persons or

livestock?

• Are all barriers in place so contact with live parts is not possible? • Are all points of earth termination on accessories and equipment

connected to earth?

• Have all exposed conductive parts been connected to earth? • Have all extraneous conductive parts been connected to earth?

BS7671 defines it as:

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Inspection and Testing REV4.1 30 Fault protection

Methods of fault protection are given in BS7671 as: Automatic disconnection of supply.

Use of class II equipment. Non-conducting location.

Earth-free local equipotential bonding Electrical separation.

Where persons or livestock come into contact with an exposed conductive part that has become live under fault conditions they should be protected by the part being earthed. Examples of exposed conductive parts include metal trunking, metal conduit or exposed metal parts of an appliance such as an electric kettle. Should the

insulation of any of the live parts within the kettle become defective then the metal casing may become live and anyone touching the kettle would be at risk of receiving a dangerous electric shock.

BS7671 defines it as:

“Protection against electric shock under single fault conditions”

Danger:

Remedy:

Isolate CU. Remove supply busbar. Replace with correct model and ensure it is shrouded

Dangers:

Access to live parts via poorly fitting terminal shroud. Electric shock

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Inspection and Testing REV4.1 31 The most commonly used method of fault protection is automatic disconnection of the supply (ADS) and it these requirements that should be checked at the initial inspection stage.

Earthing arrangements; earthing conductors; main protective bonding conductors; circuit protective conductors and supplementary bonding conductors should all be checked to ensure that they have been correctly installed and are of the correct size and are correctly labelled.

Protection against both basic and fault protection

Separated extra low voltage (SELV) is the most common method of providing protection against both. Requirements for this type of system include:

An isolated source of supply - e.g. a safety-isolating transformer to BS3535. Also numbered BS EN 60742.

Electrical separation, which means no electrical connection between the SELV circuit and higher voltage systems.

No connection with earth or the exposed conductive parts

There must be no connection to earth and precautions must he taken to ensure, as far as possible, that earth faults will not occur. Such precautions would include the use of flexible cords without metallic sheaths, using double insulation, making sure that flexible cords are visible throughout their length of run, and so on. Perhaps the most common example of a separated circuit is the bathroom transformer unit feeding an electric shaver. By breaking the link to the earthed supply system using the double wound transformer, there is no path to earth for shock current.

Danger:

Remedy:

Remove brass light switch and replace with a plastic one or use the earth terminal point on the switch cover

(32)

Inspection and Testing REV4.1 32 9. Prevention of detrimental influences

Account must be taken of the proximity of other electrical services of a different voltage band and of non-electrical services and influences. E.g. fire alarm and

emergency lighting circuits must be separated from other cables and from each other and category 1 and category 2 circuits must not be present in the same enclosure or wiring system unless they are either segregated or wired with cable insulation suitable for the highest voltage present. This is due to the magnetic influence low voltage circuits can have on extra low voltage circuits. This can appear as false signals or “noise” on telephone lines for example.

Voltage Bands / Circuit Categories Category 1

Circuits operating at low voltages (50 to 600 volts AC) and supplied from the electrical mains.

Category 2

Any data, telecommunication, intruder alarm systems and circuits operating at extra low voltage. (not exceeding 50 volts AC and 120 volts DC)

Category 3

Any fire detection system, emergency lighting or alarm Questions to ask ourselves:

• Are wiring systems installed such that they can have no harmful

effect on non-electrical systems?

• Are systems of different voltages are segregated where necessary?

Dangers:

Circuit with different categories are in close proximity which can lead to interference or false signals

Remedy:

Dangers:

Circuits with different categories are in close proximity which can lead to interference or false signals

(33)

Inspection and Testing REV4.1 33 10. Presence of appropriate devices for isolation and switching

BS7671 requires, that effective means suitably positioned and ready to operate shall be provided so that all voltage may be cut off from every installation, every circuit within the installation and from all equipment, as may be necessary to prevent or remove danger.

This means that switches and/or isolating devices of the correct rating must be installed as

appropriate to meet the above requirements. It may be advisable, where feasible, to carry out an isolation exercise to check that effective isolation can be achieved. This should include switching off, locking-off and testing to verify that the circuit is dead and no other source of supply is present.

11. Presence of under voltage protective devices

Suitable precautions must be taken where a loss (no volt) or lowering of voltage and subsequent restoration of voltage could cause danger. The most common situation would be where a motor driven machine stops due to a loss of voltage and

unexpectedly re-starts when the voltage is restored. Precautions such as the

installation of a motor starter containing a contactor must be employed. To overcome the dangers a control circuit is employed and the use of a manual stop and start station that requires a manual input to reset the circuit once it has failed.

• Are there appropriate devices for isolations and switching correctly

located and installed?

• Are there suitable means for isolating circuits and equipment?

• Where under voltage may give rise for concern are there protective

devices present?

• Are there contactor control circuits with manual starting where

required?

State one example of where automatic re-energisation may cause danger to persons or property and explain the possible consequences.

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Inspection and Testing REV4.1 34 12. Choice of setting of protective devices

Protective devices are employed in a circuit to detect over current and fault current. Their sole purpose is to disconnect should their rating be exceeded. If a device is installed that is of insufficient rating this may lead to conductors and / or equipment over heating and resulting in damage to the circuit.

13. Labelling of protective devices, switches and terminals

A check should be carried out to ensure that labels and warning notices as required by B7671 have been fitted e.g. labelling of circuits, MCBs, RCDs fuses and isolating devices with their circuit designation. Periodic inspection notices advising of the recommended date of the next inspection and warning notices referring earthing and bonding connections.

The connection of the bonding wires to the pipes has to be made with a proper clamp to BS 951 complete with the label

“SAFETY ELECTRICAL CONNECTION - DO NOT REMOVE.” Questions to ask ourselves:

• Are protective and monitoring devices correctly chosen and set to

ensure protection against overload and faults?

Dangers:

Radial circuits incorrectly added to 32A MCB. Overloaded conductors and subsequent damage to insulation and equipment. Electrical fire Remedy:

• Are all protective devices, switches (where necessary) and terminals

correctly labelled?

• Do devices and accessories display their source or supply and duty

so we know where and what we are isolating?

Consider a domestic dwelling. What identification would you expect to see above the protective devices in the consumer unit? Give three different examples

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Inspection and Testing REV4.1 35 Keeping circuits in order

One way this can be achieved is to correctly terminate the conductors in sequence so that mistakes cannot be made when an attempt to identify a circuits’ conductors. Each protective device in a consumer unit is classified as a “way”. For example, there might be 6 ways in one consumer unit and a number in a sequence (usually from the main isolator). The neutral and earth bars in this consumer unit will also be numbered in sequence. If a lighting circuit is supplied from way 3 the neutral and earth

conductors should also be connected into way 3 on the neutral and earth bars. If the conductors are not connected in sequence this can cause confusion for the test engineer.

We can usually identify a circuit by tracing the individual conductors from each terminal to the point in the cable where the sheath is stripped to. If single core cable is used they might be wired into a conduit. However, conduit is often used for more than one circuit making identification even more difficult. Ideally the installer would apply identification on each conductor therefore making the process of removing a circuit a lot easier.

What information can we place on isolators, sockets and light switches in commercial premises?

What BS7671 says:

Regulations 314-1 (i) and (ii) state that every installation shall be divided into circuits to avoid danger and minimise inconvenience and to facilitate safe operation, inspection, testing and maintenance.

Regulation 514-1-2 “states as far as reasonably practicable, wiring shall be

arranged or marked that it can be identified for inspection, testing, repair or alteration of the installation.”

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Inspection and Testing REV4.1 36 Class activity

Read the evidence thoroughly then work through the initial numbered inspection requirements. Then use the circuit chart below to complete the task.

1. Record the way numbers of the circuits and record their description of load and rating i.e. Way 1 - Lift Motor- 20 A Type B

2. Record all of the live and circuit protective conductor sizes connected

3. How would you identify the neutrals and earths of each of the circuits and put them in the correct sequence?

We are required to inspect and test a six-way MCB consumer unit.

• Contained within it are four MCBs rated at 6A, 16A, 32A and a 45A (all type B) in sequence from left to right.

• The main switch is on the right hand side of the consumer unit.

• There is a circuit chart present that displays the information from left to right; Lighting; Immersion heater; Ring main; Shower.

• Connected into the 45A MCB is one 10mm² flat twin and earth.

• There is also a 25mm conduit carrying 9 x 2.5mm² stranded conductors, three browns, three blues and three green / yellows. Two of the browns connect into the 32A MCB.

• A brown 1.5mm² solid conductor connects into the 6 amp MCB and we trace that to a flat pvc/pvc cable.

• The neutrals and earths do not correspond with the way numbers allocated to the protective devices

Circuit Chart 2.1.3.L1

Way Description Rating Type Live mm²

CPC mm²

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Inspection and Testing REV4.1 37 14. Selection of equipment appropriate to external influences

All equipment must be selected as suitable for the environment in which it is likely to operate. Items to be considered are taken from Chapter 52 of BS7671:

Ambient temperature:

A wiring system and its components shall be selected so as to be suitable for the highest and lowest ambient temperature. Presence of external heat sources:

A wiring system shall be selected and erected so as to avoid harm from heat sources such as the sun or hot pipe work. This shall be achieved by shielding; selecting a system suitable for such conditions; placing sufficiently away from the heat source. Presence of water and subsequent corrosion:

A wiring system shall be selected and erected so that no damage will be caused by condensation or moisture. This may be overcome by selecting accessories using the IP chart. Ingress of foreign bodies:

A wiring system shall be selected and erected to minimize the ingress of dust and other matter. This may be overcome by selecting accessories using the IP chart shown in the Tables from BS7671 and the On Site Guide or on the next page. Impact:

A wiring system shall be selected and erected so as to minimise mechanical damage from impact, abrasion, penetration, compression or tension. This shall be afforded by the mechanical characteristics of the wiring system or the use of extra mechanical protection.

Vibration:

A wiring system shall be selected and erected so as to be suitable to withstand the effects of vibration. This shall be afforded by using secure fixings suitable for the situation.

Flora and Fauna:

A wiring system shall be selected and erected so suitable to withstand the effects of flora (mould growth) and fauna (insects, birds and small animals) This shall be afforded by using shielding or equipment suitable for the environment.

Radiation:

A wiring system shall be selected and erected so suitable to withstand the effects of radiation from the sun and ultraviolet rays. Using shielding or equipment suitable for the environment shall afford this.

Building use and structure:

A wiring system shall be selected and erected so as to be suitable to withstand the effects of building stresses or movement. This shall be afforded by using secure fixings suitable for the situation so that no stress is put onto the wiring system.

• Have all items of equipment and protective measures been selected in

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Inspection and Testing REV4.1 38 15. Adequacy of access to switchgear and equipment

BS7671 requires that every piece of equipment that requires operation or attention must be installed so that adequate and safe means of access and working space are provided.

16. Presence of warning signs and danger notices

A check should be carried out to ensure that warning notices as required by BS7671 have been fitted e.g. labelling of circuits, MCBs, RCDs fuses and isolating devices of the voltages present within enclosures. Notices displaying that only authorised personnel may enter switch rooms and open enclosures etc.

• Are all means of access to switchgear and equipment adequate?

Why is adequate access important with regard to switch gear and equipment?

Danger:

Remedy:

Create a cut in the ceiling to allow removal of consumer unit cover or lower the entire trunking and consumer unit installation

• Are danger notices and warning signs present where required?

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Inspection and Testing REV4.1 39 17. Presence of diagrams, charts, instructions and similar information

All distribution boards should be provided with a distribution board schedule that provides information regarding types of circuits, number and size of conductors, type of wiring etc. This should be attached within or adjacent to each distribution board.

By displaying a circuit chart, usually mounted inside the door, it would display information about the circuit such as:

• The consumer unit designation • Zs at the consumer unit

• Where this consumer unit is supplied from and the size of its protective device/s.

• Size of the supply cable

• Way reference for each final circuit

• Circuit description • Type of wiring

• Over current protection type and rating • Circuit cable sizes

• Number of points served Questions to ask ourselves:

• Are diagrams, instructions and similar information relating to the

installation available?

Dangers:

No chart or identification is

present. Isolating a specific circuit for testing and inspection or maintenance is not an easy task. Unintentional isolation of supplies. Remedy:

Other information might relate to the operation of specific equipment. An operator in a factory may benefit from the information supplied to minimise

(40)

Inspection and Testing REV4.1 40 18. Erection methods

Correct methods of installation should be checked, in particular fixings of switchgear, cables, conduit etc, which must be adequate and suitable for the environment.

• Have all wiring systems, accessories and equipment been selected

and installed in accordance with the requirements of BS7671, and are fixings for equipment adequate for the environment?

Danger:

Remedy:

Assuming there is enough slack on the cable ensure the sheath enters the enclosure and secure it in place so it will not fall out.

Chapter 52 of BS7671 deals with the selection and erection of wiring systems. Below are the main points.

• Non-sheathed cables to be enclosed in conduit, ducting or

trunking.

• Prevention of damage by condensation or water ingress, and

drainage points if necessary.

• Ingress of solid foreign bodies to be minimised.

• Wiring systems to be selected and erected to minimise

mechanical damage.

• Wiring systems buried in floors to be sufficiently protected

against damage.

• Cables under floors or above ceilings and cables concealed within

walls or partitions should be no less than the 50mm minimum requirement from the surface.

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1 List seven items of information needed prior to commencing an initial verification

2. Give a brief description of the scope of an initial verification

3. What are the main objectives when inspecting the connection of conductors?

4. Why is it important to ensure single pole devices are only connected in the live conductor?

5. Where do fire barriers need to be installed in an electrical installation?

(42)

Sequence of Tests

Testing can be hazardous, both to the tester and to others who are within the area of the installation during the test. The danger is compounded if tests are not carried out in the correct sequence. Some tests require the supply to be on. Some tests will prove the operation of the circuit. The person designated to do the testing carries a huge responsibility to verify that the circuits will not cause danger to property, persons or livestock therefore BS7671 states the order we should carry out the tests.

For example, it is of great importance that the continuity of protective conductors is confirmed before the insulation resistance test is carried out. A continuity test confirms the circuit under test is correctly identified whilst the high voltage used for insulation testing could appear on a circuit still being installed and could result in an electrician receiving an electric shock whilst up a ladder.

Again, an earth-fault loop impedance test cannot be conducted before an installation is connected to the supply, and the danger associated with such a test before

verifying polarity or insulation resistance will be obvious.

Recording circuit details

To aid the testing process a record must be made first of the final circuits. See the left half of the certificate part on the next page for the information that is needed prior to commencing testing. Recording these details logs on a document the installation and can this can then be used as a reference of “as installed” circuits.

Recording the test results

Not every reading we take needs to be recorded but there are specific ones that do. See the right half of the certificate part on the next page for the information that is needed to document the testing. Recording these results is written proof that the installation has been tested in accordance with BS7671.

What BS 7671 says

• Regulation 711-01-01 states ‘Every installation shall, during

erection and/or on completion before being put into service, be inspected and tested to verify, so far as is reasonably practicable, that the requirements of the Regulations have been met.

Precautions shall be taken to avoid danger to persons, livestock, and to avoid damage to property and installed equipment during inspection and testing’

• Regulation 713 lists the sequence in which tests should be carried

out. If any test indicates a failure to comply, that test and any preceding test, the results of which may have been influenced by the fault indicated, must be repeated after the fault has being rectified

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(44)

44 Test sequence

Having carried out the initial inspection, the following items where relevant, must be tested in the same sequence as stated in BS7671 and shown below.

Some tests will be carried out before the supply is connected, whilst others cannot be performed until the installation is energised. The list below shows the correct

sequence of testing to reduce the possibility of accidents to the minimum.

Test Sequence at a glance:

With the supply isolated:

1. Continuity of protective conductors, including main and supplementary equipotential bonding

2. Continuity of ring final circuit conductors

3. Insulation resistance

4. **Insulation of site built assemblies 5. Protection by electrical separation 6. **Protection by barriers or enclosures

provided during erection

7. **Insulation of non-conducting floor and walls

8. Polarity

With the supply energized:

9. Earth fault loop impedance 10. Prospective fault current 11. *Earth electrode resistance 12. Operation of residual current

devices

* Using an earth loop tester only

** Specialist testing and will not

be discussed in this unit

X

Consider that the insulation resistance test failed on a ring main. Explain what would be the dangers of carrying on with the testing sequence.

(45)

Inspection and Testing REV4.1 45 Earth Continuity - Method 2 Earth Continuity - Method 1

Test 1 - Continuity of protective conductors

(Including main and supplementary protective bonding) Why do we do this test?

All protective and bonding conductors must be tested to ensure that they are electrically safe and correctly connected.

Regulations state that every protective conductor, including each bonding conductor, shall be tested to verify that it is electrically sound and correctly connected.

How do we do this test?

There are two methods for completing this test (Method 1 and Method 2) but only one of them is necessary. For this test you need a low reading ohmmeter

Method 1

Before carrying out this test the leads should be ‘nulled out’. If the test instrument does not have this facility, the resistance of the leads should be measured and deducted from the readings. The live conductor and the

protective conductor are linked together at the consumer unit or distribution board. The ohmmeter is used to test between the live and earth terminals at each outlet in the circuit.

The measurement at the circuit’s extremity should be recorded and is the value of R1 + R2 for the circuit under test. On a lighting circuit the value of R1 should include the switch wire at the luminaires. This method should be carried out before any

supplementary bonds are made. Operate switches to confirm polarity and see that they affect the reading.

Method 2

One lead of the continuity tester is connected to the consumer’s main earth terminal. The other lead is connected to a “wandering” lead, which is used to make contact with protective conductors at light fittings, switches, spur outlets etc. The resistance of the test leads will be included in the result; therefore the resistance of the test leads must be measured and subtracted from the reading obtained if the instrument does not have a nulling facility. In this

method the protective conductor only is tested and this reading R2 is recorded on the installation schedule.

This method is also used to test the main and supplementary protective bonding conductors. The ohmmeter leads are connected between the points being tested, between simultaneously accessible extraneous conductive parts i.e. pipe work, sinks etc. or between simultaneously accessible extraneous conductive parts and exposed conductive parts (metal parts of the installation).

The test method 1 described below checks the continuity of the protective conductor and will also measure R1 + R2 which, when corrected for temperature,

will enable the designer to verify the calculated earth fault loop impedance Zs. Testing the operation of switching circuits during this test will also confirms

(46)

46

Picture the test

Method 1 – Continuity of CPC, R1+R2 and Polarity

1. Isolate supply

2. Live (R1)

and earth (R2)

linked

5. Place meter

across live and

earth at each

accessory

3. Light

switch on

4. Zero lead

resistance and

set to Ω

6. Take readings and

record the highest

value

7. Operate

switch with

meter

connected to

confirm

polarity

(47)

47

Picture the test

Method 2 – Continuity of CPC (R2)

1. Isolate

main

supply

3. Zero lead

resistance and

set to Ω

2. Connect “wandering” lead to the earth bar

and one meter lead

4. Take

readings at

each earth

point and

record the

highest value

(48)

48

Picture the test

Continuity of Main Protective Bonding Conductors

1. Isolate

main

supply

3. Zero lead

resistance and

set to Ω

2. Disconnect bonding

conductors from main

earth terminal

5. Take

reading

ensuring

less than

0.05 Ω

4. Place one lead on

conductor and

other on the clamp

connection (Use

wandering lead if

necessary)

Class Discussion: Mike is obtaining values which seem too high than the expected values. What could explain higher than expected

Inspection and Testing

Inspection

And Testing

Learner Work Book

Name:

Group:

Tutor:

Table of Contents

Foreword

Inspection and Testing Unit Overview

Purpose of Inspection and Testing

Electrician and bathroom fitter prosecuted for breach

of Part P of the building regulations

A

Electrical test instruments

0.50Ω

>200MΩ

0.50Ω

40mS

Initial Verification

Initial inspection checklist

Sequence of Tests

X

Picture the test

1. Isolate supply

2. Live (R1)

and earth (R2)

linked

5. Place meter

across live and

earth at each

accessory

3. Light

switch on

4. Zero lead

resistance and

set to Ω

6. Take readings and

record the highest

value

7. Operate

switch with

meter

connected to

confirm

polarity

Picture the test

1. Isolate

main

supply

3. Zero lead

resistance and

set to Ω

2. Connect “wandering” lead to the earth bar

and one meter lead

4. Take

readings at

each earth

point and

record the

highest value

Picture the test

1. Isolate

main

supply

3. Zero lead

resistance and

set to Ω

2. Disconnect bonding

conductors from main

earth terminal

5. Take

reading

ensuring

less than

0.05 Ω

4. Place one lead on

conductor and

other on the clamp

connection (Use