It is preferable that the earth electrode to be tested is
first isolated from the circuit it is protecting, so that
only the earth is measured and not the complete
system. When this is done, the circuits and equipment
must be de-energised. If however this is not possible,
the earth electrode should be duplicated so that when
it is disconnected for test purposes, the other one
provides the necessary circuit protection. The
following safety precautions are essential when
working near high tension systems where any
unintentional ‘Live' earths may be encountered
between the site earth and remote earths established
for test purposes. A 'Live' earth is one that carries
current from the mains supply, or could do so under
fault conditions
.
1.
All persons involved must be trained and
competent in isolation and safety procedures for
the system to be worked on. They must be
clearly instructed not to touch the earth
electrode; test spikes; test leads, or their
terminations if any 'Live' earths may be
encountered. It is recommended that they wear
appropriate rubber gloves, rubber soled shoes,
and stand on a rubber mat.
2.
The 'P' and 'C' terminals should be connected
through a double pole isolation switch, the rating
of which will cope with the maximum fault
voltage and current. The isolation switch must
be open whilst any personal contact is made
with the remote test spikes, or the connecting
leads, e.g. when changing their position.
Fig.2 A method of disconnection where fault
conditions may occur.
Note: If a fault occurs while a test is being made the
instrument may be damaged. Incorporating fuses at the
isolation switch, rated at 100 mA, and able to cope with
the maximum fault voltage will provide some protection
for the instrument.
Live Earth Safety Precautions
9
Fault
current
Isolation
switches
Fuses
C1
P2
C2
ES
H
4 POLE
3 POLE
MEASURE R
E
P1
ES
MEGGER
MEGGER
®
DET5/4D
DET5/4D
EARTH
EARTH
TESTER
TESTER
Earth
resistance
Voltage rise of
earthing system
under fault
conditions
True earth
Remote
test spikes
Summary of Contents for DET5/4D
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