Example
The CPC for ring final circuit formed 1.
If, after carrying out this further test, the inspecting engineer still questions
the quality and soundness the protective conductor formed the metallic
conduit trunking then further test can done using a.5 times the design current the circuit, but not greater than 25A.
If the inspecting engineer has grounds question the soundness and
quality these joints then the phase–earth loop impedance test described
later this chapter should carried out. voltage not
greater than 50V the frequency the installation and current approach-
ing 1. Determine satisfactory continuity test value for the CPC using the value given in
Table the Site Guide.
Because fault currents will flow around the earth fault loop path, the
measured resistance values must low enough allow the overcurrent
protective device operate quickly.12.c. The result recorded installa-
tion schedule such that given Appendix the IEE Regulations.
Resistance/metre for a
mm Copper conductor /m
Th
1 10
2
. Ω
Table 14.526
100 100 0.1. From Table (shown Table 12.1 Chapter 12). For satisfactory test result, the resist-
ance the protective conductor should consistent with those values
calculated for line conductor similar length and cross-sectional area. The resistances some other metallic containers are
given Table 14.
Where steel conduit trunking forms the protective conductor, the stan-
dard test described above may used, but additionally the enclosure must
be visually checked along its length verify the integrity all the joints.05 less (IEE Guidance Note 3).25
25 1.
A satisfactory test result for the bonding conductors will the order of
0.5mm2
copper conductor 50m approximate
length.14
32 0.
Values resistance per metre for copper and aluminium conductors are
shown Table 12.337
.949
75 0.Electrical installations and wiring systems
353
The resistance the long test lead subtracted from these readings to
give the resistance value the CPC.12 Resistance Values Some Metallic Containers
Metallic sheath Size (mm) Resistance 20°C (mΩ/m)
Conduit 1. Ω
e
erefore,
the resistance mm
50 10
0 605
3
.85
Trunking 0.
This test can done using low-voltage transformer and suitably con-
nected ammeters and voltmeters, but number commercial instruments
are available such the Clare tester, which give direct reading ohms.
