Test instruments and recommended

testing sequence

1

C&G 2395-01

Level 3 Award in the

Periodic Inspection, Testing and

Certification of Electrical Installations

describe the different types of test instrument required

explain the requirements regarding periodic testing sequence

describe the importance of comparing test results with relevant

criteria

explain the requirements for safety when testing

state the requirements for circuits in prescribed special

installations and locations, in terms of identifying the installations

and locations to which special requirements apply, demonstrating

the ability to make reference to the appropriate requirements in

each case and, from given information, be able to identify the

requirements in relation to specific areas and installations.

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Outcomes of this Session

The person carrying out inspection and testing must be

competent.

The inspector must therefore be, skilled, experienced,

and have sufficient knowledge of the type of installation

to be inspected and tested to ensure that no danger

arises to any person, livestock or property.

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Requirements of testing

Know the instrument, its uses and limitations

Follow all the safety procedures

Check that the equipment meets current standards

Check that the test leads meet with the requirements of GS 38

Check that the test equipment is calibrated correctly.

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Test Instruments

Testing should be carried out in such a manner that

`no danger to person livestock or property arises’

There are certain tests that can cause damage to equipment

Before testing can take place, the correct instruments must be selected.

The type of instrument chosen depends on the test being done.

You should be aware of certain criteria that need to be considered.

When using test instruments, the precautions to take are:

BS 7671 lays out the minimum requirements for

the test instruments used to test in accordance

with BS EN 61557

All the differing test instruments are listed and

although two of them are the most common, it is

necessary for you to know the requirements of

all of each.

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Requirements of Test Instruments

A low resistance ohmmeter or

continuity scale on a combined

insulation/continuity tester.

Four characteristics:

1. The measuring range should have a

resolution of at least 0.01 Ω.

2. A test current derived from a source

with no-load voltage between 4 V-24 V.

3. A short-circuit test current of not less

than 200 mA.

Instruments to BS EN 61557-4 will meet

these requirements.

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Low-resistance ohmmeter

(continuity test instrument) 4.3 p.82

Zero reading on the display shows that the

resistance of the leads have been nulled.

Calibration label

showing date

Leads

connected

together

The person carrying out the tests, should also be aware that the accuracy of

any results will depend on the way in which a particular test instrument is used.

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Accuracy of results

You should check that:

you know how to ‘null’ or ‘zero’,

where necessary, the test

instrument

where applicable, the crocodile

clips are connected the right way

round

you are aware of the limits of the

test instrument

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Insulation Resistance Tester (High resistance ohmmeter)

An Insulation Resistance Tester is a small d.c. generator.

(This instrument is often, incorrectly, called a `megger’!)

The instrument should comply with BS EN

61557-2.

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Insulation Resistance Tester/Ohmmeter O.S.G. 10.3.3 p.95 (GN3 4.4 p.83)

1. 250V d.c. for SELV and PELV

circuits/SPDs (O.S.G Table 10.3.3 p.96)

2. 500V d.c. for all circuits ≤ 500V a.c.

3. 1000V d.c. for circuits > 500V < 1000V

The test voltages required are:

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Insulation Resistance Test

The insulation resistance test

is the electrician’s ‘pressure

test’.

We ‘pressurise’ the system

by applying a voltage, and

we can see where the

current ‘leaks’ .

We are testing for current

‘leakage’ between conductors.

We are making sure that the

current passes through the

load and not between the live

conductors, or between live

conductors to earth.

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Earth Fault Loop Impedance Tester

This should operate in less than 40

ms (about 2 cycles of alternating

current), with a test current of

between 20-25 A.

The resolution on the scale is

adequate at 0.01 Ω.

This instrument should comply

with BS EN 61557-3.

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Earth Electrode Test Instrument O.S.G 10.3.5.2 p.101 (GN3 2.7.12 p.46-47)

There are two types of instrument that can be

used for carrying out an earth electrode

resistance test.

Test method 1 (DEAD testing)

Earth electrode test instrument which has three or

four terminals (C1,P1/P2,T2/C2,T1),

Test method 2 (LIVE testing)

An earth fault loop impedance test instrument

when there is an RCD protecting the TT

installation.

Instruments should comply with BS EN 61557-5.

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RCD Test Instrument

The RCD test instrument needs three scales. These are ×½; ×1 and ×5.

In each of the tests required for the RCD, the

test voltage must not rise above 50 V a.c. rms.

The accuracy of the instrument must be ± 10%

to allow for voltage variations and have a timing

accuracy of ± 5%.

Additionally, they should allow for positive and

negative half-cycles to be tested, as well as

allowing for time delayed RCDs.

fit for use

used properly

appropriate for the task

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Checking of Test Instruments

Test instruments require regular testing and calibration where required. The

instrument should have a current test certificate!

The normal time span between calibration checks should not be more than 1

year.

As far as the EAWR is concerned, test instruments should be:

The accuracy of a test instrument can be judged in one of two ways:

1. regular accuracy checks using resistors/calibration check unit, etc.

2. regular (at least annual) calibration of the test instrument.

15

Visual Inspection

Check for any obvious mechanical damage

or deterioration of materials and equipment,

exposed cables and live parts, missing

covers, fixings, labels and notices etc.

Inspection and Testing Procedure

16

Visual Inspection

The main switchgear and all distribution boards. These

should be inspected for the following:

Fuses and MCBs are correctly rated for over-current and

fault current

Fuse and switch contacts are clean and have not been

over-heating

Conductor terminations are tight and correctly lugged (if

possible)

Busbar connections are properly made and clamps are

tight.

Inspection and Testing Procedure

17

Cables - whenever possible cables should be

inspected to ascertain:

The suitability for the load and operating

environment

The condition of the insulation and protection

Adequacy of fixings and mechanical protection

Suitability of glands and shrouds

Proper use of earthing clamps and earth

connections

Any signs of over-heating and damage

Inspection and Testing Procedure

18

Equipment, accessories and lighting fittings should be

inspected for:

Deterioration due to the atmosphere

Mechanical damage

Over-heating and adequate fixings

Connections of conductors and condition of flexes -

This should include removing light fitting covers, switch

plates, socket outlets and covers of equipment.

A sample of approximately 10% of all parts and areas of

the installation should be inspected.

Inspection and Testing Procedure

Inspection and Testing Procedure

19

Testing

Continuity of circuit protective conductors (CPCs) at all

metal accessories and equipment within a height of 3.5

metres from floor level, and at 10% of all lighting fittings.

Continuity of all bonding conductors and earth clamps.

Continuity of all ring circuit conductors, including CPCs.

R1 + R2 continuity test or R2 test on every final circuit.

Inspection and Testing Procedure

20

Testing

Insulation resistance between live conductors and earth of

all circuits collectively, excepting any circuits supplying

electronic equipment which may be damaged by the test.

These shall be listed separately as not having been

tested.

An electrical separation test on all electrically separated

circuits.

Polarity at the board and at a 10% sample of all lighting

switches and equipment to ensure that switches interrupt

only phase conductors.

Inspection and Testing Procedure

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Testing

Earth fault loop impedance (Ze) at the main intake position.

Earth fault loop impedance (Zs) at each distribution board.

Earth fault loop impedance (Zs) test on every final circuit and every

socket outlet.

Test all Residual Current Devices.

The resistance of every earth electrode.

Prospective fault current at the main intake position and at every

distribution board.

A manual operation test on all MCBs, RCDs, switch fuses and

isolators.

Exhibitions, shows and stands - Regulation 711.6 requires inspection

and testing to be carried out each time the installation is assembled. No

additional tests are called for.

Electrical installations in caravans and motor caravans - Fig 721 requires

that a periodic inspection is to be carried out not less than once every

three years and annually if the caravan is used frequently.

Temporary electrical installations for structures, amusement devices and

booths at fairgrounds, amusement parks and circuses - Regulation 740.6

requires the electrical installation between its origin and any electrical

equipment to be inspected and tested after each assembly on site. No

additional tests are called for.

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Inspection and testing of special

installations and locations

Part 7 of BS 7671 details the particular requirements for special installations

and locations, such as swimming pools, saunas, caravan parks etc. There

are occasional instances where a special location makes mention of

inspection and testing.

End