introduction - legh richardson electrical services · · 2015-08-01guidance note 3 inspection and...

March 10 Legh Richardson

Introduction


Purpose of this course:To help people who want to become electriciansDevelop skills required to practice as an

electricianAllied trades and defined scope Aid progression onto the 2391 level 3 ?(should gain a few years experience before attempting 2391)


Glossary of terms and acronymsBS British Standard IN Rating of residual current

BS EN Harmonised European Standard Ipf Prospective fault current

BS7671 Wiring Regulations LV Low Voltage

CPC Circuit Protective Conductor MEIWC Minor works certificate

CSA Cross Sectional Area MCB Miniuture circuit breaker

EIC Electrical Installation Certificate MET Main Earthing Terminal

ELV Extra Low Voltage PE Protective Earth

ESQCR Elec. Safety Quality Continuity Regs PIR Periodic Inspection Report

EWR Electricity at Work Regs PME Protective Multiple Earthing

GN3 Guidance note 3 I&T RCBO Residual Current Breaker with overload/overcurrent

IEC International Electro-technical Commission RCD Residual Current Device

IEE Institute of Electrical Engineers


The Fundamentals of Initial Verification of Electrical Installations


Initial Verification - introduction

A good understanding of the following is required:What is ‘Verification’ and ‘Initial Verification’The purpose of Initial Verification1. Competency and responsibilities of the person carrying out

initial Verification2. Statutory and non-statutory documentation relating to

inspection and testing 3. Information required prior to inspection and testing4. Safe working procedures


The Purpose of initial VerificationVerify that the installation is:1. Safe2. defects and omissions can be corrected before being put into

service3. Correctly wired for function4. Provide records for further developments


Initial verification includes:1. New installation2. Rewires3. Additions and major alterations4. Consumer Unit changes5. Changes in maximum demand


Persons carrying out InspectionsMust be competentApplies to Sole traders and others working on their ownLarge companies have 3rd party inspectors usually employed full time by the

company. 3rd party Inspections not allowed for sole tradersUnless PIR for building control purposes

1. Have sufficient Electrical knowledge2. Be familiar with BS76713. Sound Knowledge of particular Installation to be inspected4. Have sufficient information about the installation5. Experience of the inspection and testing process6. Access to necessary resource documentation


Reference DocumentationStatutory 1. EWR 19892. HASAWA 19743. ESQCR 2002And Non-statutory1. Memorandum of guidance on EAWR 19892. Electricity at work safe working practices HSG853. Safety in electrical testing at work INDG3544. Electrical test equipment used by electricians GS385. BS76716. Guidance note 3 Inspection and testing GN37. Guidance on safe isolation procedures for Low Voltage installations


Statutory Documents1. EAWR 19892. HASAWA 19743. ESQCR 2002


Non-Statutory Documents1. Memorandum of guidance on EAWR 1989 – explanation of the

EAWR in simple language2. Electricity at work safe working practices HSG853. Safety in electrical testing at work INDG3544. Electrical test equipment used by electricians GS38 – H&S

guide to the correct type of equipment and condition of instruments and leads and probes for voltage indication

5. BS76716. Guidance note 3 Inspection and testing GN37. Guidance on safe isolation procedures for Low Voltage

installations


Safe Working Procedures


Risk Assessment

Management of Health and Safety 1999 requires that a Risk assessment is produced for all working conditions appropriate to the work involved.

Health and safety at Work Act 1974Electricity at Work Regulations 1989All require that the work undertaken is done safelyHow do you measure Safety?


Work on or near live conductorsEAWR 1989 Regulation 14No person shall be engaged in any work activity on or so

near any live conductor (other than one covered with insulating material so as to prevent danger) that danger may arise unless:

(a) It is unreasonable in all circumstances for it to be dead

(b) it is unreasonable for a person to be at work on or near it while it is alive

(c) Suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury


Regulation 13

Can the normal policy of dead working be carried out?

Dead Working is necessary ?

Regulation 4

Identify the equipment or circuit to be worked on

Dead Working

Live Working permitted

Regulation 14C Para.21

Decide whether suitable precautions can be taken to prevent injury

Regulation 14A para.18

Is it unreasonable for work to be done dead?

Regulation 14A para.19

Identify the risks and the methods of controlling them?

Regulation 14B Para.20

Decide whether it is reasonable to work live

NO

NO

NOYes

Yes

Yes

Yes


Safe IsolationBefore Visual Inspection can take place a consistent

method for preventing the possibility of electric shock to yourself and to others must be undertaken

1/ use approved voltage tester2/ prove instrument against a known supply or proving

instrument3/ Identify what you want to isolate4/ Test for voltage5/ Isolate, Lock off and apply warning label or remove

fuses and place in your pocket


Safe Isolation6/ Retest ‘isolated’ circuits

(check all phases across (a) live conductors, (b) Live to Neutral, (c) Live to Earth

(d) Neutral to Earth! ) 7/ Recheck voltage tester against proving unit8/ Carry, removed circuit fuses, lock-off keys, voltage

tester with you when uncovering accessories and test before touching (It sounds pedantic and time wasting but there may come a time when it will save your life!


Electrical Test Equipment for use by Electricians

GS 381. Leads and casing not damaged2. Fused probes3. Finger guards4. Non-detachable probes5. Probe tips 2mm fixed6. Or/and 4mm sprung loaded


Electrical Test Equipment used By ElectriciansVoltage Indicators


Safety Isolation and Locking-off kits


Test Instrument – General RequirementsBS EN 61010Basic electrical safety of electrical/electronic instruments

BS EN 61557Electrical Safety, ranges and tolerances when measuring electrical

quantities

BS EN 61243-3Live working Voltage detectors


Requirements for Electrical Certification for New Installations, Alterations, and Additions


Reasons for Certification1. Provide a record of the inspectors involvement2. Verify that the installation has been carried out to the

regulations and is safe for operation3. Demonstrate that inspection has been carried out in the event

of fire or injury4. Provide records for subsequent inspections reducing costly

exploratory work later on


Types of Electrical Certificates1. Electrical Installation Certificate2. Minor Works Certificate3. Periodic Inspection Report

Schedule of TestsSchedule of Inspections

Warning noticesDiagrams, charts, SchematicsCircuit Labelling

Note: At present no type of certificate is a statutory requirement but should contain all the necessary information to aid understanding of the methods of protection, supply characteristics and limitations of work completed


Completing an Electrical Installation CertificateApplicable to:New BuildRewiresAdditions of new circuitsMajor AlterationsConsumer Unit changes


New Install, Additions and alterations are checked here

Departures does not mean defects but solutions used that might be ambiguous if

not detailed

Much of this is standard and will be duplicated on most certificates. The

method of earthing has to be verified and can cause confusion.

Number and type of wires is Single phase 2-wire AC. The supply protective device is usually a

BS1361 100A (max) Cartridge fuse


Supply characteristics: Earthing

CONSUMER UNIT(Fuse Box)

METER

MAIN EARTHTERMINAL

SUPPLY TAILS(25mm )2

EARTH CONDUCTOR(16mm )2

BONDING TO OTHERSERVICES (10mm )2

SUPPLYTRANSFORMER

PHASECONDUCTOR

GASWATER

FINAL CIRCUITS

TN-SEarth via supply cable

metallic sheath or armour

SUPPLYCUT-OUT


Supply Characteristics: Earthing:


METER

MAIN EARTHTERMINAL


NEUTRAL-EARTHCONDUCTOR


SUPPLYTRANSFORMER

PHASECONDUCTOR

GASWATER

FINAL CIRCUITS

TN-C-SEarth via combined earth

and neutral conductor(PME System)

SUPPLYCUT-OUT


Supply Characteristics: Earthing:


METER

MAIN EARTHTERMINAL



SUPPLYTRANSFORMER

PHASECONDUCTOR

GASWATER

FINAL CIRCUITS

TTEarth via general

mass of earth

EARTHCONDUCTOR

POLE

OVERHEADSUPPLY RCD

GENERAL MASSOF EARTH

TESTINGLINK

SUPPLYCUT-OUT


Supply Characteristics: Live conductors

400V across phases

230V across each

phase

Light Industrial & Commercial

Single Phase Domestic

Secondary windings of distribution transformer


Supply Characteristics: Ipfc and ZeZe is the external loop impedanceI pfc is the maximum fault current capability

Both of these can be ascertained by 1. Enquiry2. Measurement3. Calculation

Methods of measurement will be looked at later


Supply Characteristics: Typical service head with metering

AC, Single phase, 2-wire supply BS 1361 100A Service fuseTT earthing


Maximum demand can be calculated from the tables in OSG but this can lead to an unrealistically high value. As a rule of thumb use 66% of service fuse

Most cases are copper at 16mm2 and 10mm2 and must be verified

for connection and size

Sw Gear = BS EN 60947-2Number of live terminations = 2-pole

Rating = 125AVoltage rating = 230 or 400V

Fuse rating = main submain fuseRROC = 30,or 100 and time for

1*Idn

Use this box to describe the existing installation if additions or alterations are being carried out


Completing a Minor Works CertificateApplicable to:Additions of lights and sockets to existing circuitsChanges in accessories – like for likeWhere no large changes in maximum demand have taken

placeWhere no new circuits have been added.Note: notification to Building Control applies to all work done in bathrooms,

kitchens and outside regardless


Client information

Supply information and comments about the original installation

Test results of specific circuit worked on.

Contractors information


Initial Inspection


Purpose of Initial Inspection

1. Comply with appropriate British, European Standards2. Comply with the product standards3. (This is often tricky since we once knew ‘CE’ to be Compatible Electromagnetic

which appears to have been transformed into Chinese Export)4. Comply with the appropriate Manufacturers requirement5. Are not visibly damaged, defective or deteriorated such that

safety is impaired


The Inspection Process

All the boxes must be filled in with either

Indicates that an inspection has been carried out and the results are satisfactory

Or

Indicates that the inspection is not applicable to a particular item or system of protection

√

N/A


Inspecting New Installation Work5 Main headings• Methods of protection against electric shock• Prevention of mutual detrimental influences• Identification• Cables and conductors• General


Schedule of Inspections: methods of protectionProvision for both basic and fault protectionNot usually encountered as a single method of protection in

domestic installations (old lighting ccts)• SELV• Class II insulationBasic Protection• Insulation and/or Class II accessories and fittings• Barriers and enclosures IP 2X, 4X, X4, X5, X7, X8Fault protection• Automatic Disconnection of Supply (ADC)Additional Protection• RCDs• Supplementary Equipotential Bonding


Prevention of mutual detrimental influences• Proximity of non-electrical services and other

influences• (Gas, water and Oil)

• Segregation of Band 1 and Band 2• ( insulated to the highest voltage present)

• Electromagnetic Interference from electrical/electronic equipment (EMI)

• Insulated screened, compartmentalized, ROT=100mm

• Segregation of safety services• (Earthed screen either concentric or enclosed)


Identification– Presence of diagrams, instructions, circuit charts

and similar information– Presence of danger notices and other warning

notices– Labelling of protective devices, switches and

terminals– Identification of conductors


Cables and Conductors• Selection and erection for current carrying capacity• Erection methods• Routing of cables in prescribed zones• Adequately protected conductors• Additional protection with RCD where cables are

buried in the fabric of the building• Connection of conductors• Fire barriers


General – all other areas• Location of switches• Access to switchgear• Protective measures for special locations• Polarity of single pole switches• Correct connections• Under-voltage protection• Accessories and switchgear for external influences• Appropriate functional switching devices


Check List• Main intake• Consumer Unit/ distribution board• Bathroom requirements• Kitchen• Inspection of individual accessories for:1. terminations, 2. Identification and CPC sleaving3. polarity, 4. solid fitting, 5. IP ratings


Test Instruments – Operation and expected accuracy


Ongoing AccuracyInstrument measurements need to fall within a

tolerance range to provide a level of confidence that the measurement is within acceptable levels

Methods of guaranteeing accuracy are:• Calibration• Regular checking against a known value whether it be at home or

on-site these include:• Propriety check boxes• Cross-checking methods• In-house instrument checks


Methods of checking Ongoing Accuracy – instruments and leads• Meter temperature.• Contact resistance of probes and clips.• Probe pressure will give variable readings.• Lead resistance.• Mains born noise variations in supply voltage. Some meter compensate

for this and use nominal voltages depending on the voltage applied.• Intrinsic accuracy for the particular meter.• Battery Voltage,.• Supply cable temperature. • No two instruments with or without different leads will give

consistent readings. Megger advise taking 3 readings and averaging them with their loop tester.

• Zeroing Instrument leads for continuity when using Crocodile clips should be connected so that the measurement does not use the crocodile clip springs.

• Never rely just on the measured Zs but use this as verification of Ze– measured with R1 + R2 measured.

It may sound obvious but are you measuring the single phase PSC and doubling it for 3 phase systems? Be careful some instruments (Robin) do not like testing Zs across two phases and if done will damage the instrument


CalibrationUKAS accredited servicesAccreditation by UKAS means that evaluators

i.e. testing and calibration laboratories, certification and inspection bodies have been assessed against internationally recognised standards to demonstrate their competence, impartiality and performance capability.

Similar to MOT testing for vehiclesCalibration instruments are much

more sensitive than the standard test instruments (approximately 10 times more accurate)


Proprietary Check-boxCheck that the continuity and insulation

readings are within the manufactured tolerance specifications.

17th edition instruments are within the tolerance requirements of BS7671 2008

BS EN 61557 is the British /European standard to which all electrical test instruments are designed


Cross CheckingUsing more than one instrument and checking the

readings of one against the readings of anotherRecords must be kept to validate your resultsUsing a spare set of instruments that are kept in house

to use as a standardA roll of cable will test the accuracy of continuity.


In-house instrument checkingA resistance test box but preferably high quality small

tolerance resistors made up to provide a test bench facility fro both continuity and Insulation resistance measurements

RCD testing on a known supplyLoop testing for both high current and non- trip.


Maintaining Records of checksTest instruments to be identifiable against records of

testsBasic tests include:Continuity at 0.5Ω, 1.0Ω, 10ΩInsulation resistance at 0.5MΩ, 1.0MΩ, 2.0MΩ, 50MΩ.Loop Test on designated socketRCD Test on designated RCD

Practical sessionUsing different instrument to measure known

resistancesMegger 1552Robin Cont/IR testerMultimeter100m 2.5mm2 single cable


Sequence of tests for initial verificationBS 7671 regulation 612.1 all tests performed in sequence if any

test fails then the fault is corrected and the tests are repeatedDead Tests• Continuity of protective conductors• CPCs, Main protective bonding• Ring Final Circuit continuity• Insulation Resistance• Protection by separation• Basic protection by barriers, enclosures and insulation• Polarity• Earth electrode reistance


Sequence of tests for initial verificationLive – with the supply on• Live polarity• Earth Fault loop impedance• RCD tests fore additional protection• Prospective Fault current• Verification of phase sequence• RCDs• Functional Tests• Verification of volt drop


Selecting the correct instrument and rangeMust meet the relevant performance and safety parts of BS EN

61557 and BS EN 61010, respectively

BS EN 61557: Electrical safety in low voltage distribution systems up to 1000V ac and 1500V dc. Equipment for testing, measuring or monitoring of protective measures

BS EN 61010: Safety requirements for electrical equipment for measurement control and laboratory use is the basic safety standard for electrical test instruments

BS EN 61243-3: Live working – voltage detectors – two pole low voltage types

Serial No.

Serial No.

Test Date Calibration Date

Test Date RCD 1/2× RCD 1× RCD 5× Ramp (mA)

Earth Loop

min 0.47

max 0.52

min 1.9

max 2.1

min 0.47

max 0.52

min 1.9

max 2.1

min 47.5

max 52.5

50MW0.5W 2W 0.5MW 2MW

Make EuroTest 61557

1409871Insulation and Continutiy for use with calibration Test Box

Loop Impedance test Socket outlet location: Text Box next to CCU in Kitchen, Residual Current Device: Text Box next to CCU in Kitchen,

RCDMake EuroTest 61557

Insulation/continuityMake: Metrel Eurotest Multifunction Tester 1409871

Serial No. : 1409871Loop Impedance


The Tests


Test InstrumentsAll instruments used for inspection and testing of electrical

installations must comply with the latest BS7671 requirements as well as European harmonized documentation recognised by the BS7671 at the time of publication.

Instruments should also comply with the following:Have an up to date calibration certificateBe in good working order and not mechanically damagedLeads to GS 38 and not mechanically damaged


Test Instruments

The minimum number of test instruments and types of testers are:

Low reading OhmmeterInsulation Resistance testerEarth Fault loop impedance testerPSC / PFC TesterRCD testerVoltage tester


Test Instruments

Other instruments employed are:AC Low Reading OhmmeterCurrent Clamp meterEarth Electrode TesterApplied Voltage TesterMulti-meterContinuity Tester


Instruments

Provide the 5 basic tests

Multi-function Testers

Continuity, IR, Polarity, Zs/PSC, RCD


Continuity / Insulation Resistance Testers(Megger – do not use this term) Correct Name is:‘Low Reading Ohmmeter ‘Delivery = 4V – 24V DC >= 200mAOr AC Resistance Ohmmeter Delivery = 50V @ 1.5* Ib (25A Max)‘Insulation resistance Tester’Delivery = 500V @ 1mA Max


Earth Fault Loop Impedance MetersConforms to BS EN 61557-3Standard types allow a 2 cycle window of 25A to pass

through the meter – Ok for Ze but will cause unwanted tripping of RCD and 6-10A MCBs

17th ed type must not trip RCDs whilst loop testingResolution = 0.01W down to 0.2W


Earth Electrode testersProprietary test instrument generating 30V

Switching DC voltage at 128Hz 3-lead and 4-lead instruments can be used


PSC Test Meterstandard PSC/PFC testers have a range of 0 – 20kA(>20kA instruments are used on larger installations)Conforms to BS EN 61557-3Note: PSC - line (phase) to neutral

PFC – Line (phase) to Earth


RCD TesterProvide ranges of IN (1,2,5 times)Operate to BS EN 61557-6Maximum Time < 2secsOperate in both polarities (+/-)Operate within a service range of +/- 10%At 5 * IN Must operate for 50ms


Voltage Testers / IndicatorsComplies to GS38

• Fixed probes• Insulated leads• 2mm-4mm probe length• Finger guards

Indicates voltage levelBy light, sound and / or vibration


Continuity of Protective Conductors


Test instrument requirementsContinuity / Insulation Resistance Testers(Megger – do not use this term) Correct Name is:‘Low Reading Ohmmeter ‘Delivery = 4V – 24V DC >= 200mAOr AC Resistance Ohmmeter Delivery = 50V @ 1.5* Ib (25A Max)


What must be tested?Continuity of Protective Conductors

– Main Earthing Conductor– Main Protective Earthing Conductors– Supplementary Equipotential Conductors– Method 1 used to measure each conductor– Disconnect from Main Earth Terminal– Some modern Dist. Boards have disconnecting links


Why test continuity of protective conductors?– To check that the cpc is continuous– Only time cpc is used is:– (i) when there is an Earth Fault– (ii) When used to Test continuity for R1+R2


R1 + R2 methodSelect correct rangeZero instrumentTest at each outletTest at furthest point and record value as R1+R2

Ohms

Furthest PointCircuit Protective Conductor (cpc)Outlets

Consumer Unit

Earth Bar Phase

Link wire


Wander lead methodUsually used to test Protective earth bonding but can

be used to test R2 of final circuitsDisconnect earth bonding at CCU using the long lead

connected to the test instrument either:1/ Zero long lead2/ Measure long lead and deduct the value from the

measurement of R2

Ohms

Furthest PointCircuit Protective Conductor (cpc)

OutletsConsumer Unit

Earth Bar Long Lead


Continuity testing metal enclosures


Evaluating continuity test resultsEvaluation of a test must take place to verify that the test

complies and the requirements of BS7671 have been met.Methods that could be employed are:1. Law of Resistivity – calculations based on the physical

properties of the conductor

2. From tabulated values given for copper conductors (OSG. App 9 table 9a,b,c, GN3 AppA table 1a,b)

areationalseccrosA,conductortheoflengththeL

conductorgivenaofsisitivityReTheWhereAL.R


Effects of temperature on the resistance of conductorsIncreasing the temperature increases the resistance of

conductors therefore the ambient temperature needs to be known

Useful methods of adjusting the resistance for temperature are:

• Law of Temperature coefficient of resistance

• Tabulated values given in OSG App9 table 9b

12iF .1RR


Continuity of Ring Final Circuits


Test Instrument requirementsLow Reading OhmmeterDelivers 4-24V output Voltage and >=200mA

short circuit current,Multimeters do not provide enough voltage and

current output.


What should be tested?1. Main Protective Earth Bonding2. Supplementary Bonding3. Circuit Protective Conductors4. Exposed conductive parts

– Trunking– Conduit– Cable Tray– M/C Switch Gear


Ring final circuit continuity requirementsEach conductor forms a complete loopNo of skts on the ring is unlimitedNo of SFCU is unlimitedNo of unfused spurs is limited to the no of skts on the ringArea covered is <100m2


RFC test procedure Stage 1

Spur from FCU

Spur from Socket on RingSpur from JB (must be accessible for inspection)

Spur from Origin

Value = RW

RFC Quick verificationP-P, N-N, should be within 0.05W, this indicates that the lengths

are the sameAn example might be:P-P = 0.4W and N-N = 0.4WThen PE – PE = 1.67 0.4W = 0.67WRFC can be assumed to be:R1 + R2 = 0.4/4 + 0.67/4 = 0.1+ 0.168 = 0.25W - 0.3W

Note: 1.67 comes from the ratio between the CSAs of the phase and the cpc which is: 2.5mm2 / 1.5mm2

The theory of this method relates to the laws of resistivity

where R = resistance of the conductor, L = the length of conductor and A = the cross sectional area of the conductor.

The resistivity of copper () is not shown but is always a constant value so will be added into the formula

materialgivenaforALR

Stage 2Interconnect P1 – N2 and P2 – N1Test between P-N rings interconnected

at each socket outletTest values should be the same 0.01WR1+Rn / 4

Stage 3aInterconnect P1-PE2 and measure at P2-PE1

Value = 2RW

Stage 3Complete the interconnection with P2-PE1Measure at each outlet – the results will beSubstantially the same (0.01W)

Value = 2RW / 4

Ring Final Circuit problems – broken rings

Broken Rings creates 2 radials2.5mm2 cable = 27A max. 2.5mm2 cable not protected by 32A MCB

Either upgrade cable to 4.0mm2 or change MCB for 20ADetected when P-P, N-N, PE-PE are measured

Ring Final Circuit problems – Interconnecting loopsMultiple LoopsUneven ring final path where the volt drop under load will be significantly different in different parts of the ring

Kitchen rings are the most susceptible – it is unlikely that this fault will be detected unless the circuit is tested thoroughly


Example of RFC measurementsThe conductors are measured end to end at the

consumer unit on a ring final circuit to be;P-P = 0.25Ω, N-N = 0.24Ω, E-E = 0.4ΩCalculate the Values that you would expect to get when

interconnecting R1+Rn and R1+R2Verify that R1+R2 are correct.Estimate the value of Zs if Ze = 0.2Ω


Finding R1+R2 by alternative methodNot acceptable !:Measure Ze, Measure Zs

Zs is measured with parallel paths in place and could be smaller than Ze

ZeZs2R1R


Insulation Resistance Testing


Reasons for Insulation Resistance testingThis is an important test which ensures the

consistency and stability of an electrical installation and the final circuits

Conductors carry current which if they come into momentary contact will cause sparking and arcing – this in turn causes fire.

Insulation protects the shorting out of conductors and


The nature of Insulation Resistance

Load

Switch

Joint BoxN

P

E

OhmsMegga


How Insulation Resistance works when calculatingBased on Resistors in parallel.

When increasing the length of an insulator between two conductors the capacitance/dielectric between the two conductors increases and leaks and therefore the Insulation resistance decreases

The same is true when conductors are paralled up this is the same as extending the length of te two conductors

Rn1........

2R1

1R1

R1T

Following the examples given in most technical documentation (BSI!)

This page has been left intentionally blank


Test Instrument requirementsInsulation Resistance testers provide a test voltage of 500V DC at

1.0mAThe voltages can be adjusted dependant up the circuit and

conditions

Circuit nominal voltage (V) Test Voltage d.c. (V) Minimum I.R (MW)

SELV or PELV 250 >=0.5

≤ 500V including FELV 500 >=1.0

Above 500V ≤ 1000V a.c. 1000 >=1.0


What needs to be testedSingle PhasePhase / Neutral to Protective Earth (P/N – PE)Phase to Earth (P – PE)Neutral to Earth (N – PE)Phase to Neutral (P – N)3-PhaseAll live conductors in turnAll live conductors to Protective Earth


Precautions and preparation1. Permit to work / prior notification2. Main Isolator off3. All circuit fuses OPD on4. All switches On5. All loads removed6. Where loads cannot be removed then it is necessary

to isolate locally


Test MethodsConsiderations before testing. Most Low Voltage circuits are rated at

230V so the meter must be set to:(i) The M scale with a voltage pressure of 500V DC and a current of 1mA.(ii) All switches must be closed and fuse links in place so that the voltage is

across all of the length of the conductors, even in the switch lines(iii) All loads and appliances must be disconnected from the circuit since

this will effect the resistance. It will reduce the resistance to a few ohms because the meter is now trying to read the resistance of the load and not of the insulation.

(iv) All loads include any electronic switches and components in the circuit. These may be timer controls for boilers, dimmer switches, fluorescent/discharge lighting control gear.

(v) Some electronic components employed in control circuitry work at voltages of less than 50V and are rated for such voltage so that the cost and size are kept small. 500V across these components will damage them. Where SPD’s are fitted then the test can be 250V.


Testing SELV and PELV circuitsTest voltage at 250V

230V Primary

Secondary SELV or FELV

Switch closed for test duration

Live conductors linked out for test duration

Live conductors linked out for test duration

0.5MW+250V DC


Testing SELV and PELV circuitsTrunking and other enclosures that share cabling of

different voltages

Live conductors linked out for test durationSELV circuit


1.0MW+500V DC 1 minute

c.p.c. of highest voltage circuits present in cable groupLive conductors linked out for test durationSeparated circuit


1.0MW+500V DC 1minute

c.p.c. of highest voltage circuits present in cable group and other LV conductors


Polarity TestingTo ensure that All single pole switches are connected in the phase / line conductor

onlyAll sockets and Switched fused connection units are correctly

connectedAll phase conductors to Edison screw lamp holders are connected

to the centre pin (E14 and E27 are exempt)


Earth-Fault Loop Impedance Tests


Earth Fault loop Test - Why we need to test1. Confirm that measured Zs is less than Zs Max (table

41.2 -41.4)2. Confirm disconnection times within values given in

table 41.13. Verify that extraneous and exposed metalwork is

connected to the MET4. Confirm voltage does not rise above 50V under fault

conditions


The earth fault loop path

Supply TX

Secondary coils

Circuit Fuse

Load

Fault

Alternative Earth-Fault Path

Suppliers Earth

Earth-Fault Path

Origin of Installation

Consumers Installation

MET


Zs by calculationZs = Ze + R1 + R2 Basic formula

Zs = Actual formula

ML)1000

tab2R1R(ZeZs


Zs by measurement and adjustmentZs measured ≤ Zs max (tables 41.2 -41.4) 0.8

(Appendix 14)

OrZs measured x 1.25 ≤ Zs max (tables 41.2 – 41.4)


Testing Residual Current Devices


RCD TestingRCDs are now our main line protection for earth faultsA propriety RCD tester is required either as a

standalone unit or as part of a multifunctional testerRCDs exist by other names such as:RCCB – Residual Current Circuit BreakerRCBO – Residual Current Breaker with OverloadVOELB – Voltage operated earth Leakage Breaker – note:

this method is obsolete and has been discontinued. Part P recommends that these devices are removed


RCD – basic operation and layout Phase and Neutral conductors are contra wound round a torroid to form a transformer.

A smaller ‘sense coil is wound round the torroid.

Under normal operation, the current flowing through the live conductors maintains the magnetic flux at an equilibrium.

The current flow bypassing the live conductors, such as an earth fault will cause an imbalance in the magnetic field and allowing the MF to rotate.

The rotating magnetic cuts across the sense coil conductors generating a small emf which is connected to a solenoid disconnecting the supply


RCD Test method:The tests to show that the RCD correctly operates is:For RCDs and RCCBs used for the protection of Fire

then½ * IN

1 * IN

For RCDs and RCBOs used for additional protection then:

½ * IN

1 * IN

5 * IN


½ -1 IλN +200>30N/A<= 30>25BS 4392 (S) (old)

>30

>30

>30

IλN (mA)

130 -500N/A<= 30>25BS EN 61008 (S)

< 300< 40<= 30>6BS EN 61008 (G)

< 200< 40<= 30>25BS 4293 (G) (old)

T (mS)T (mS)IλN (mA)In(A)Type

< 300>30< 40<= 30>6BS EN 61009 RCBO

RCD disconnection times


Testing Functional Switching


Functional Testing– RCDs – mechanical operation– MCBs and MCCBs – check mechanical operation– Switches for Isolation– Switches for Mechanical Maintenance– Switches for emergency stopping– Remote and auxiliary Control – Contactors– Motor Control Starters, overload settings– Automated Switching, PIRs, motor overruns– Central Heating systems where installed by the

electrican


Prospective Fault Current Tests


I pfc = maximum prospective earth fault current (phase to earth)

I psc = maximum short circuit current (phase to neutral or/and phase to phase)

Test instrument used (in both cases) = loop tester


Single phase <100A service fuseMaximum pfc of installationIsolate supply to Distribution boardDisconnect earthing conductorSet instrument to ‘pfc’ or ‘Ze’Press start button (dependant on instrument)

Read results Pfc =x.xx kA, Ze = x.xxΩ


Schedule of Test Results

Documentation and Labelling– Completion Certificate– Periodic Inspection and Test Certificate– Minor Works Certificate– Inspection Checklist– Schedule of Test Results– Manufacturers Data and instructions– Circuit Diagrams and ‘As-Fitted’ Drawings

Documentation 2Schedule of Test ResultsCharacteristics of Supply (Earthing and PSC)Overcurrent Protection and Short-circuit capacityContinuity, Insulation Resistance, PolarityEarth Loop ImpedanceRCDs and functional testsRemarks (Codes of compliance)

Documentation and Labelling(i) Warning Notices (voltages over 250V)(ii) Identification of Protective Devices(iii) Earth Bonding Connection Labels (BS951)(iv) RCD Functional Testing

(Mechanical operation only)(v) Date of next test(vi) Circuit diagrams and schedules

(adjacent to main Dist. Board)

BS EN60898 and BS3871 Instantaneous tripping currents

≤ 20.0 IN> 10 IND

≤ 10.0 IN> 5 INC

≤ 5.0 IN> 3 INB

≤ 50.0 IN> 10 IN4

≤ 10.0 IN> 7.0 IN3

≤ 7.0 IN> 4.0 IN2

≤ 4.0 IN> 2.7 IN1

AmperesType

12.525

10.0209000M9

7.5156000M6

7.5104500M4.5

6.06.03000M3

3.03.01500M1.5

1.51.51000M1

kAkA

ICSICNProspective current (A)

Category of Duty

Circuit Breakers BS EN 60898MCB to BS3871


Appendices