Megger WM6, User Manual

FUSE REPLACEMENT

The fuse is held in a screw-type holder. To change a
fuse, use a screwdriver to release the centre part of
the holder containing the fuse. Replace with a 1 A 
20 x 5 mm ceramic fuse part no. 25413-286. An
alternative fuse should not be used as the fuse
resistance will affect the lower continuity readings.

INSULATION TESTING

After connecting the test leads to the instrument and
making the preliminary checks as detailed above, set
the slider switch to ‘M

Ω

’. With the circuit to be tested

isolated, connect the test leads as follows:—
(a) for insulation tests to earth —

connect the red lead to earth or frame of the
equipment, and the black lead to that part of the
circuit to be tested.

(b) for insulation tests between wires —

connect a lead to the core of each of the wires.

Turn the generator handle at between 160 r.p.m. and
240 r.p.m. The meter pointer will indicate the value of
insulation resistance on the ‘M

Ω

’ scale. (If a capacitive

circuit is tested the pointer will initially deflect towards
zero and then gradually rise to its final steady value as
the capacitance is charged up to the output voltage of
the tester.)

If several successive readings of ‘

∞

’ are obtained,

connect the two further ends of the test leads together
and turn the generator handle. A zero reading should
result which double checks that the leads are not
disconnected or broken and therefore the insulation
resistance readings are correct.

Capacitive circuits automatically discharge through
the tester when the generator handle stops rotating.
The meter pointer will deflect beyond the ‘

∞

’  position

on the scale and then return to its normal rest position
at ‘

∞

’  when the circuit has discharged. Wait a few

moments for this to happen before disconnecting the
test leads. The discharge time (to 0 V) is approx. 8
seconds per microfarad.

CONTINUITY TESTING

With the test leads connected to the instrument, and
having checked them and the fuse as described
above, set the slider switch to the ‘

Ω

’ position. With the

circuit under test isolated, connect the test leads
across the appropriate points and turn the generator
handle at between 160 r.p.m. and 240 r.p.m. The
resistance will be indicated on the ‘

Ω

’ scale. This

resistance includes that of the test leads which should
be measured separately, (by performing a test with
the clips joined together), and the result deducted
from the total.

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