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Measurements - General
Live - Earth loop impedance measurement can be made via installation
sockets using the plug terminated test lead, or at any other convenient
point on the installation using the optional dual lead test set. The optional
dual lead test can also be used to carry out Live - Neutral loop impedance
measurement.
Refer to Safety Warnings before using the instrument
Switching 'On'and testing
Turning the rotary switch will activate the instrument. Alternatively, pressing
the Retest button will re-activate the instrument after 'Auto shut off'. The
activated instrument will momentarily display all screen segments, followed
by the software version number. When connected to mains voltage of the
correct polarity the L - PE 'neon'indicator activates and supply voltage
is displayed. If out of voltage range, VOL flashes alternately with the actual
measured voltage.The word ' null' is then displayed as an 11 second self
calibration check ('Auto' range only) is completed. The instrument then
proceeds to automatically take a measurement. Two pin plug terminated
test leads should be reversed if only the N - PE voltage indicator is
activated. Repeat measurements can be made either by disconnecting
and then reconnecting the instrument (e.g. when using test probes) or by
pressing the Retest button. When operational, the LT7 will carry out a self
calibration every 5 minutes.
Circuit condition Indication
Testing is inhibited if:
1 )
Phase and Neutral supply connections are reversed. (N - PE ' n e o n ' activated).
2)
Neutral - Earth voltage >50 V when performing a 3 wire test (L-PE
and N - PE 'neons'activated).
3)
Electrical 'noise'exceeds rejection level on low current range.
(
displayed).
4)
Voltage is out of range. Flashing 'VOL' and actual Voltage
displayed.
5)
Supply frequency out of limits (flashing 'HZ' displayed).
6 )
Thermal protection device operates on h i g h current range ( and
d i s p l a y e d ) .
Low Current (Auto) measurement (0,1
This mode measures Live to Earth loop impedance via installation
sockets. Live to Earth or Live to Neutral loop impedance can also be
measured using the optional dual lead test set. The measurement
sequence takes
will not trip.
LT7 is supplied as standard with a display resolution of 0,1 Ω. In areas of
exceptional electrical noise, and where improved repeatability may be
desired, it is possible to change the display resolution to 1 Ω in the
following manner:-
1)
Turn rotary switch to the ' OFF' position.
2)
Press and hold the Retest push button whilst turning the rotary
selector switch to any other position.
Still holding the Retest button, the display will cycle between 1 Ω and
3)
0,1 Ω resolution.
4)
Release the Retest button when the desired resolution is displayed.
To operate LT7:-
1)
Turn rotary switch to 'Auto'.
2)
Connect LT7 by mains cord, or using the dual test lead firmly
connect red test probe to Live and the black test probe to Neutral
or to Protective Earth (ground). Mains (line) voltage is displayed.
3)
Test progress is indicated by a sequential display of vertical bars.
OPERATION
11 seconds. Residual Current Devices (R.C.D.s) ≥30mA
or 1
resolution)
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