Extech Instruments 380260 User Manual page 5

Applications
Measuring Power Tools and Small Appliances
This section applies to any device under test that uses a line
cord. For double insulated power tools, the meter's leads
should be connected to the device's housing (chuck, blade,
etc.) and the lines of the power cord.
Testing AC Motors
Disconnect the motor from the line by disconnecting the wires from the motor terminals or
opening the mains switch.
If the mains switch is opened, and the motor also has a motor-starter, then the starter must
be held in the ON position. With the mains switch opened, 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
meter lead to the grounded motor housing and the other lead to one of the motor leads.
Refer to diagram at below.
Motor
GND
Testing DC Motors
1. Disconnect the motor from the line.
2. To test the brush rigging, field coils and armature, connect one meter lead to the
grounded motor housing and the other lead to the brush on the commutator.
3. If the resistance measurement indicates a weakness, raise the brushes off of the
commutator and separately test the armature, field coils and brush rigging (one at a
time). Leave one lead connected to the grounded motor housing while testing the
motor components. This also applies to DC Generators.
Mains
Starter
Switch
Notes:
1. The STARTER must be in the ON position during the
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Model 380260 Version 2.2 1/08