T&i live tests

Inspection and Testing

Module 5

Testing Methodology

Live Tests

20kA2000A

200A

20Ω200Ω

2000Ω

TEST

Earth Loop Testing

Loop Tester

1.15Ω

Direct measurement of Zs

ON


ON

0.35Ω


ON

0.55Ω


ON

0.65Ω


ON

0.85Ω

Record the highest value i.e 0.85Ώ

0.25Ω

Measurement of Ze

Earthing conductor must be disconnected for this test and the installation turned off

ON

OFF

0.25Ω

Measurement of Ze (three phase)

Fuses must be removed to disconnect the installation for this test

ON

OFF

0.26Ω



ON

OFF

0.25Ω



20kA2000A

200A

20Ω200Ω

2000Ω

TEST

Fault Current Testing

Loop Tester

0.865

20kA2000A

200A

20Ω200Ω

2000Ω

TEST

Loop Tester

865

Fault Current Testing

1.25kA

Measurement of Prospective Short Circuit Current

Note: The Earth lead is connected to the neutral terminal

1.25kA

Measurement of Prospective Earth Fault Current

ON

OFF

2.25kA


Measurement of Prospective Short Circuit Current 3ph

ON

OFF

2.28kA



ON

OFF

2.25kA



Determination of 3phase fault current

Highest single phase value measured = 2.28kA

2.28 X 3 = 3.95kA

An approximation can be done as 2 x the reading i.e.2 x 2.28 = 4.56kA

Note:- The minimum breaking capacity for

protective devices is 4kA

RCD Testing

TEST

00 1800

10

2030 100

200

300X 1/2

X 1X 5

mA

ON

OFF

0 18030

1/21

5

OR 1

No Trip Test ½ current (15mA)

32A

30mA

Load must be disconnected

ON

OFF

030

1/21

5

32A

30mA

Full Current Test (30mA)

Must trip within:-

200ms BS4293

300ms BSEN61008-1

26ms180

ON

OFF

030

1/21

5

32A

30mA

Full Current Test (30mA)

Change half cycle

18ms

Record highest value i.e 26ms

180

ON

OFF

030

1/21

5

32A

30mA

Fast Trip Test (150mA)

Must trip within 40ms

15ms180

ON

OFF

030

1/21

5

32A

30mA

Fast Trip Test (150mA)

9ms

Change half cycle

Record highest value i.e 15ms

180

C1 P1 P2 C2

125Ω

TEST

d

Earth Electrode Test

Electrode under test

TEST SPIKES

Minimum 10 x d15m-25m 15m-25m

3m 3m

C1 P1 P2 C2

127Ώ

TEST

d



TEST SPIKES


3m 3m

C1 P1 P2 C2

122Ω

TEST

d



TEST SPIKES


3m 3m

Percentage Deviation

Average Value 122 + 125 + 127

3= 124.7

Maximum deviation

124.7 – 122 = 2.7 *

125 – 124.7 = 0.3

127 – 124.7 = 2.3

Percentage deviation2.7

124.7 x 100 = 2.1%

2% is very good, any value above 5% should be re-tested increasing the distance between the Electrode and the current spike.

145Ω

Bonding

Earthing Conductor

To ElectrodeLoop Tester

T.T Systems RCD protected Electrode Test

ON

RCD

OFF

Section B School Nursery

1) a) Which type of verification is required for this installation

b) What documentation/information is required

c) State two statutory regulations that govern the inspection and test

d) What documentation will need to be completed

1)a) As a new installation it will require an Initial Verification

b) The results of the assessment regarding maximum demand, methods of earthing etc and charts or diagrams regarding the type of circuit, number of points

served, location of control, methods of protection and equipment vulnerable to damage by the test equipment

c) State two statutory regulations that govern the inspection and test

c) The Health and Safety at Work Act and the Electricity at Work Regulations

d) What documentation will need to be completed

d) The Electrical Installation Certificate and

i) schedule of test results

ii) schedule of inspection

2) List the test instruments required for this installation

Voltage proving unit

Low reading Ohm meter and insulation resistance meter (contained in a combined Insulation/Continuity tester)

Earth loop impedance and Prospective Short-circuit current meter

There are no RCDs in the installation, therefore no test equipment is required for these tests

3) List in the correct sequence the tests that are required

i) Continuity of protective conductors including bonding

ii) Ring final circuit continuity

iii) Insulation resistance

iv) Polarity

v) Earth loop impedance

vi) Prospective fault current

vii)Functional testing

4)a) Calculate the approximate value of R1 + R2 of the ring final circuit in rooms 1 and 2

b)Calculate the approximate Zs value for the above ring

c) What other test is automatically carried out when carrying out the ring final circuit continuity test

a) 2.5mm2 + 1.5mm2 = 7.41 + 12.1 = 19.51mΩ/m

R1 + R2 = 0.25(19.51/1000 x 30) = 0.15Ω

b) Zs = Ze + (R1 + R2)

Zs = 0.4 + 0.15 = 0.55Ω (measured at 200 C)

c) This test proves, continuity of the live conductors as a ring, continuity of the cpc and proves polarity

5) The following insulation resistance values have been recorded for 3 circuits supplied from the distribution board:-

2MΩ, 7MΩ and 50MΩ, all other circuits are > 200MΩ

Calculate the overall insulation resistance value and determine if this value is acceptable or unacceptable (give reasons)

1/RT = 1/R1 + 1/R2 + 1/R3 + 1/R4

1/RT = 1/2 + 1/7 + 1/50 + 1/200

1/RT = 0.5 + 0.143 + 0.02 + 0.005 = 0.668

RT = 1/0.668 = 1.5MΩ

This is greater than the minimum of 0.5MΩ (acceptable)

6)a) Calculate the Zs value of the air conditioning unit

b) What factors need to be applied when correcting measured Zs values

c) What other method can be used to verify the measured Zs value

d) Apply the method given in c) above and confirm of the measured Zs value is acceptable or unacceptable

e) If unacceptable give two methods of overcoming this unacceptable reading

a)Zs = Ze + (R1 +R2)

(4.0mm2 + 1.5mm2 = 4.61 + 12.1 = 16.71mΩ/m)

Zs = 0.4 + (16.71/1000 x 15) = 0.65Ω (measured at 200 C)

b) Factors which need to be applied are:-

i) Ambient temperature when the test is conducted

ii) Cable operating temperature (usually 700C)

c) The rule of thumb (0.75 x max Zs)

d) Max Zs = 1.5Ω (1.5 x 0.75 = 1.125Ω > 0.65Ω measured

The circuit is acceptable

e) The two methods recognised in BS7671 are:-

i) Provide the circuit with an RCD

ii) Provide local supplementary bonding complying with the max resistance value of 413-02-27/8

7) For one of the lighting circuits list all components of the earth fault loop impedance path

a

b c

e

d

f

a) Supply phase, b) supply phase conductor, c) circuit phase conductor, d) exposed-conductive-part of the light, e) c.p.c of the lighting circuit, f) return path (armour/sheath) of the supply cable

T&i live tests

Education

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