R1 = 0.8 ohms/100m x length/100 R2 = 1.25 ohms/100m x length/100 R1 + R2 = (0.8 x 25/100) + (1.25 x 15/100) = 0.2 + 0.1875 = 0.3975 ohms b) Zs = R1 + R2 + Ze Ze (earth loop impedance) = 0.2 ohms (typical value) Zs = 0.3975 + 0.2 = 0.5975 ohms c) Polarity test

1. Inspection and Testing
Module 5
Testing Methodology
Live Tests

2. Earth Loop Testing
Loop Tester 20kA
2000A
200A
TEST
2000Ω
200Ω
20Ω

3. Earth Loop Testing
Loop Tester 20kA
2000A
200A
TEST
2000Ω
200Ω
20Ω

4. Direct measurement of Zs
1.15Ω
ON

5. Direct measurement of Zs
0.35Ω
ON

6. Direct measurement of Zs
0.55Ω
ON

7. Direct measurement of Zs
0.65Ω
ON

8. Direct measurement of Zs
0.85Ω
ON
Record the highest value i.e 0.85Ώ

9. Measurement of Ze
Earthing conductor must be
disconnected for this test and
the installation turned off
0.25Ω

10. Measurement of Ze (three phase)
Fuses must be
removed to
disconnect the
installation for this
test
0.25Ω
ON
OFF

11. Measurement of Ze (three phase)
Fuses must be
removed to
disconnect the
installation for this
test
0.26Ω
ON
OFF

12. Measurement of Ze (three phase)
Fuses must be
removed to
disconnect the
installation for this
test
0.25Ω
ON
OFF

13. Fault Current Testing
0.865
Loop Tester 20kA
2000A
200A
TEST
2000Ω
200Ω
20Ω

14. Fault Current Testing
865
Loop Tester 20kA
2000A
200A
TEST
2000Ω
200Ω
20Ω

15. Measurement of Prospective Short Circuit Current
Note: The Earth lead is
connected to the neutral
terminal
1.25kA

16. Measurement of Prospective Earth Fault Current
1.25kA

17. Measurement of Prospective Short Circuit Current 3ph
Note: The Earth lead is
connected to the neutral
terminal
2.25kA
ON
OFF

18. Measurement of Prospective Short Circuit Current 3ph
Note: The Earth lead is
connected to the neutral
terminal
2.28kA
ON
OFF

19. Measurement of Prospective Short Circuit Current 3ph
Note: The Earth lead is
connected to the neutral
terminal
2.25kA
ON
OFF

20. 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

21. RCD Testing
mA
00 1800 30 100 X 1
20 200
X 1/2 X 5
10 300
TEST

22. RCD Testing
mA
00 1800 30 100 X 1
20 200
X 1/2 X 5
10 300
TEST

23. No Trip Test ½ current (15mA)
Load must be disconnected
ON
32A OFF
30mA
OR 1
0 180
30
1
1/2 5

24. Full Current Test (30mA)
Must trip within:-
ON 200ms BS4293
300ms BSEN61008-1
32A OFF
30mA
26ms
0 180
30
1
1/2 5

25. Full Current Test (30mA)
Change half cycle
ON Record highest
value i.e 26ms
32A OFF
30mA
18ms
0 180
30
1
1/2 5

26. Fast Trip Test (150mA)
Must trip within 40ms
ON
32A OFF
30mA
15ms
0 180
30
1
1/2 5

27. Fast Trip Test (150mA)
Change half cycle
ON Record highest
value i.e 15ms
32A OFF
30mA
9ms
0 180
30
1
1/2 5

28. Earth Electrode Test
125Ω
TEST
C1 P1 P2 C2
TEST SPIKES
3m 3m
d
15m-25m 15m-25m
Minimum 10 x d
Electrode under test

29. Earth Electrode Test
127Ώ
TEST
C1 P1 P2 C2
TEST SPIKES
3m 3m
d
15m-25m 15m-25m
Minimum 10 x d
Electrode under test

30. Earth Electrode Test
122Ω
TEST
C1 P1 P2 C2
TEST SPIKES
3m 3m
d
15m-25m 15m-25m
Minimum 10 x d
Electrode under test

31. Percentage Deviation
Average Value 122 + 125 + 127
= 124.7
3
Maximum deviation
124.7 – 122 = 2.7 *
125 – 124.7 = 0.3
127 – 124.7 = 2.3
Percentage deviation
2.7
x 100 = 2.1%
124.7
2% is very good, any value above 5% should be re-tested increasing the
distance between the Electrode and the current spike.

32. T.T Systems RCD protected Electrode Test
Bonding
Earthing Conductor
145Ω To Electrode
Loop Tester
ON
RCD
OFF

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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)

39. 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)

40. 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

41. 7) For one of the lighting circuits list all components of the
earth fault loop impedance path
b c
a d
f e
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