Earth Resistance Measurement
The CM500 can rapidly measure the earth electrode resistance
and earth resistance (from 0.01 Ω to 3.00 kΩ) of a TT installation
using the earth test spike and the plug terminated test lead, or at
any other convenient point on the installation using the 2-wire
lead set. If
Setting A is selected when using the plug terminated
lead set, the polarity of the mains socket is immaterial. Line and
Neutral will be swapped if necessary, and an indication given on
the display.
Setting b requires Line and Neutral to be fixed.
Inserting the Earth Test spike
A test spike must be inserted into the ground well away (>20 m)
from the main earth electrode(s) or anything connected to the earth
electrode(s). Buried earthed metal pipes, fences, etc. near to the
spike could give a misleading low reading. The
CM500 may
display ‘
E32’ or a very low resistance if the spike is incorrectly
positioned.To check the result, reposition the spike and verify the
readings. Suitable test spikes and leads are contained in the
accessory Earth Test Kit.
Earth resistance measurement - Power plug method
The earth resistance of an installation will include the effects of
any parallel resistance paths from the
PE conductor to earth e.g.
cross bonded metal service pipes.
1. Insert the test spike.
2. Connect the 20 m earth test lead to the
CM500 [4 mm
socket (S)] first and then to the test spike.
3. Select
Re.
4. Insert the power plug into an installation socket.
5. Supply voltage and polarity are displayed.
6. Press the
TEST key.
7. Measured earth resistance value is displayed.
Earth resistance measurement - 2- wire lead set method
1. Insert the Test spike.
2. Connect the 20 m earth test lead to the
CM500 [4 mm
socket (S)] first and then to the test spike.
3. Select
Re.
4. Connect the red lead to phase and the black lead to earth.
No connection to neutral is necessary.
5. Supply voltage is displayed.
Note:- Though displayed,
polarity indications are invalid when using the 2-wire test
lead set, and should be ignored.
6. Press the TEST key
7. Measured earth resistance value is displayed.
Earth Electrode Resistance Measurement
To measure the earth electrode resistance, the earth electrode
must be disconnected from the
PE conductor of the installation
under test. To do this safely, the installation must be switched Off
and isolated from the supply.
1. Insert the test spike.
2. Connect the 20 m earth test lead to the
CM500 [4 mm
socket (
S)] first and then to the test spike.
Operation (Contd.)
24
CM500 is calibrated to give the resistance from the
supply ends of the test leads. Test results may be
adversely affected by supply voltage fluctuations or
electrical ‘noise’ during measurement. It is
recommended that tests are repeated and the results
verified, when measurement results are considered
abnormal. Connect the test lead to the instrument first
and then to the earth spike.
To Next Page
Loading...
