Application Example - PCE Instruments PCE-ITM 20 User Manual

3.15

Application Example

Power tools and small appliances
This test would also apply to other similar equipment that has a line cord. For double insulated
power tools, the megohmmeter lead shown connected to the housing would be connected to
some metal part of the tool (e. g. chuck, blade).
Note: The switch of the device must be in the "ON" position and the main power should be
disconnected.
Motors
AC-Disconnect the motor from the line by disconnecting the wires at the motor terminals or by
opening the main switch. If the main switch is used and the motor also has a starter then the
starter must be held, by some means, in the "ON" position. In the latter case, the measured
resistance will include the resistance of the motor, wire and all other components between the
motor and the main switch. If a weakness is indicated, the motor and other components should
be checked individually. If the motor is disconnected at the motor terminals, connect one
megohmmeter lead to the grounded motor housing and the other lead to one of the motor leads.
DC-Disconnect the motor from the line. To test the brush rigging, field coils and armature, connect
one megohmmeter lead to the grounded motor housing and the other lead to the brush on the
commutator. If the resistance measurement indicates a weakness, raise the brushes off the
commutator and separately test the armature, field coils and brush rigging by connecting one
megohmmeter lead to each of them individually, leaving the other connected to the grounded
motor housing. The above also applies to DC generators.
Connect
to housing
(GND)
© PCE Instruments
15
Motor
Line
Connect
to motor
side of
switch
switch
Starter
(must
be
"ON")
Main
switch