Building Services Engineering 5th Edition Handbook

Electrical installations 311
13.12 Electrical power measurement logger (reproduced by courtesy of Mobile Architecture and Built
Environment Laboratory, Deakin University, Geelong).
with additional cables and attachment clips. Both useful power in kW and apparent power in
kVA are measured. All work on live electrical wiring is only done by a registered electrician.
Verification of correct polarity
A visual inspection is carried out of all fuses and switches to check that they are fitted into a
line conductor. The centre contact of each screw lamp holder is connected to the line conductor.
Plugs and sockets must be correctly connected and wire rigidly held.
Tests of effective earthing
There are four separate tests:
Test of the protective conductor: A 40 V 50 Hz supply of up to 25 A is injected into the earth
conductor. Its resistance is not to exceed 1 . An impedance test meter is used.
Earth loop impedance test: A line-earth loop impedance test meter is attached to a 13 A
three-pin plug. This is plugged into each power socket and the meter injects a current into the
earth protective conductor. The current flows along the supply authority’s cable sheath to the
local transformer and back to the power socket along the line conductor.
Test of residual current devices: A test transformer providing 45 V is connected to a socket
outlet. A short-circuit current is passed from the neutral to the protective conductor, causing the
residual current device to trip instantaneously.
Measurement of consumer earth electrode resistance: Where this is used, a test electrode
is put into the ground and a steady 50 Hz current is passed between the electrode and the
consumer’s earth electrode to determine its circuit resistance.
Insulation resistance tests
An insulation test meter is connected between the line and protective conductors. A 500 V direct
current is applied to this circuit by the meter and an electrical resistance of 0.5 M or more must
be shown.