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Maintenance and Inspection
Troubleshooting
and Maintenance
6–10
Megger Test
The megger is a piece of test equipment that uses a high voltage to determine if an
insulation degradation has occurred. For inverters, it is important that the power termi-
nals be isolated from the Earth GND terminal via the proper amount of insulation.
The circuit diagram below shows the inverter wiring for performing the megger test. Just
follow the steps to perform the test:
1. Remove power from the inverter and wait at least 5 minutes before proceeding.
2. Open the front housing panel to access the power wiring.
3. Remove all wires to terminals [R, S, T, +1, +, –, U, V, and W]. Most importantly, the
input power and motor wires will be disconnected from the inverter.
4. Use a bare wire and short terminals [R, S, T, +1, +, –, U, V, and W] together as shown
in the diagram.
5. Connect the megger to the inverter Earth GND and to the shorted power terminals as
shown. Then perform the megger test at 500 VDC and verify 5MΩ or greater resis-
tance.
6. After completing the test, disconnect the megger from the inverter.
7. Reconnect the original wires to terminals [R, S, T, +1, +, –, U, V, and W].
CAUTION: Do not connect the megger to any control circuit terminals such as intelli-
gent I/O, analog terminals, etc. Doing so could cause damage to the inverter.
CAUTION: Never test the withstand voltage (HIPOT) on the inverter. The inverter has
a surge protector between the main circuit terminals above and the chassis ground.
Megger, 500VDC
L100
Disconnect
power source
R
S
T
U
V
W
Disconnect
motor wires
Motor
Earth
GND
+1
+
–
Add test jumper wire