Continuity Testing; Guard Terminal - Megger MJ10 Guide De L'utilisateur

Operation
the two farther ends of the test leads together and carry
out a check on the leads. A zero reading should result,
which double checks that the leads are not disconnected
or broken and therefore, the insulation resistance
readings are correct.
Note:- BM12 readings are taken after pressing the
'Test' button, there is no other control to operate.
Automatic Discharge
Capacitive circuits automatically discharge through the
tester when the 'Test' button is released. The approximate
discharge voltage will be indicated on the voltage scale.
Wait a few moments for the voltage to fall to zero before
disconnecting the test leads.

Continuity Testing

With the leads connected to the instrument, and having
tested them and the fuse as described in the Preliminary
Checks, set the selector switch to the 'Ω+' position. With
the circuit under test isolated connect the leads across
the appropriate points. Press the 'Test' button and whilst
keeping it pressed turn the generator handle (MJ10 only).
The resistance will be indicated on the 'Ω' scale.
Note:- The resistance of the test leads is allowed for in
the calibration of the instrument. It is for this
reason that only the test leads supplied, or identical
replacement leads, should be used.
8
If necessary repeat the continuity test with the selector
switch set to the 'Ω–' position. The effects of any stray
e.m.fs. in the sample under test may then be negated by
taking the average of the reading when the 'Ω+' position
was used with that when the 'Ω–' position was used.

Guard Terminal

For basic insulation tests and where there is little possibility of
surface leakage affecting the measurement, it is unnecessary
to use the guard terminal. i.e. if the insulator is clean and
there are unlikely to be any adverse current paths. However
in cable testing, there may be surface leakage paths across
the insulation between the bare cable and the external
sheathing due to the presence of moisture or dirt. Where it
is required to remove the effect of this leakage, particularly
at high testing voltages, a bare wire may be bound tightly
around the insulation and connected via the third test lead
to the guard terminal 'G'.
Leakage path
to '+'ve
terminal
Tightly bound bare wire
to '-'ve
to 'G'
terminal
terminal