MOTOR TESTING PROCEDURE

1. JAVID IQBAL SODAGAR
DGM ELECTRICAL
Three-Phase Motor
Testing Procedure

2. Types of Testing For 3-Phase Motors
If a three-phase motor is exhibiting problems, such as failure to start, overheating and
inconsistent supply, there are several diagnostic tools and methods at your disposal.
These tools and methods are discussed below. Before testing, however, be sure to take
appropriate safety precautions. These include:
Wearing protective safety gear: This safety gear may include grounding straps, gloves,
and any other relevant protective gear for the environment.
Having all tools readily available: Some common diagnostic tools include ubiquitous
multimeters, clamp-on ammeters, temperature sensors and oscilloscopes. Having these
tools available will help you avoid leaving the motor unattended.
Disconnecting the motor from power: When you are ready, move the transformer’s
motor disconnect switch to take it off of power. Be careful to make sure that the power is
actually turned off — on some motors, the disconnect switch is the same as the on/off
switch, so switching the disconnect switch to the on position will power the motor.
Also, be sure to disconnect all equipment and wiring that is not going to be included in
the testing process.
Discharge before and after testing: Before beginning testing and after each electrical
test, be sure to discharge the motor, as it has an inherent amount of capacitance. This
can be accomplished by shunting conductors to ground and each other before
reconnecting.
Check the nameplate: The nameplate or motor specifications provide valuable
information about the motor, such as the intended amperage of the motor. This
information can be used to assess the health of the motor compared to its intended
design.

3. 1. General Inspections
The most basic inspection is a visual inspection. Once the motor is removed from
power and you are prepared to begin inspection, remove the cover of the motor.
Once this is removed, you can start to check the motor for visual indications of
damage. Some things to look for during this process include:
General Damage: General damage tends to be easy to spot. This may appear in the
form of burn marks or indentations. Check all over the motor for any indications of
heat or environmental damage.
Shaft Condition: Manually rotate the motor shaft to assess its condition. This should
be easy unless the motor is especially large. The shaft should rotate smoothly, with
no catches or loose parts. Newer motors may have some difficulty turning due to
tight tolerances, disuse or ambient moisture, which will need to be addressed with
oiling and further inspection. However, older motors may have more serious
obstructions that need repair or replacing.
Connection Quality: Look at all the connections within the motor for indications of
wear or damage, and assess any wires outside of the motor for potential breaks. Any
broken wires should be handled and replaced with care. Once the motor has
undergone a general inspection, double-check your inspection tools and start
troubleshooting the electrical properties of the motor.

4. 2. Continuity Tests
Continuity testing tests the resistance between two points. If there is low
resistance, the two points are electrically connected. If there is higher resistance,
the circuit is open. The earth continuity test determines whether the motor is
connected to ground.
To complete the earth continuity test, set the multimeter to continuity mode.
Once this is done, place one point on the frame of the motor and the other point
on a known connection to the earth, preferably an area close to the motor
installation. A good motor should result in a reading that is less than 0.5 ohms. If
the value is greater than 0.5 ohms, however, this indicates that the motor’s
insulation is failing and has the potential to cause an electric shock. Determining
the causes of this failure may require further testing.
3. Power Supply Test
The next test that should be completed is the power supply test. This checks that the
incoming power supply is as expected and meets the design specifications of the
motor. The power supply test can be done by checking the voltage being applied to
the motor with a multimeter. Compare this with the specifications as noted on the
nameplate. If the applied voltage is significantly lower or higher than specified, this
may be one source of your problems.
In addition to this test, check that the terminal for the power supply is in good
condition. Damage and poor connections may also be at fault for any variances or
performance issues.

5. 4. AC Motor Winding Continuity Test
Next, examine the inside of the motor and the wires involved in the three-
phase current. Set and calibrate your multimeter for voltage and find the six
wires of the three-phase motor.
When looking at the box, you should see six wires, three on each side. There
should be terminals on each side of the box that these wires are connected to.
One side will have terminals labeled L1, L2 and L3 or Line 1, Line 2 and Line
3. The other side will have terminals labeled T1, T2 and T3 or Load 1, Load 2
and Load 3. L terminals indicate line wires with incoming current, while T
terminals indicate outgoing wires. The exception is European motors, which
will have the designations U, V and W. These wires should be tested to
determine the health of the motor’s power supply.
This can be tested using the following methods:
No Power Incoming Test: To test the incoming voltage, place the multimeter
probes on different permutations of the L terminals while the box is powered
down. Take a reading for the L1 to L2 connection, the L1 to L3 connection
and the L2 to L3 connection. These readings should be the same if the motor
is working properly. For a 230/400V system, the expected voltage should
be 400V between each of the three-phase supply lines.

6. Line to Neutral Test: If there is an available neutral terminal, place one
multimeter probe on that and the other on each of the line terminals. The
voltage reading should be half of whatever voltage reading was received
during the previous test.
No Power Outgoing Test: This test is similar to the test above, but tests
the outgoing voltage. While the box is still off, take a reading between the
T1 and T2 leads, the T1 and T3 leads and T2 and T3 leads. In this case, the
voltage reading should be zero for each test.
Power Outgoing Test: Carefully power up the box and repeat the same
tests as above, testing each permutation of the T leads. There should be
little to no variation between each lead combination.
If the readings differ from the expected results and the power supply test
showed no issues, this may indicate problems with the health of the three-
phase AC motor. Most often, this indicates that the motor is burned out.

7. 5. Insulation Resistance Test
The insulation resistance test is the next test that must be done to determine
the overall health of the motor. This is done by comparing the resistance
between each pair of motor phases and between each motor phase and the
frame. This can be done with an insulation tester or Megger. The tests must be
completed as follows:
Phase Resistance: Take the insulation tester and set it to 500V. Take each end
and place it on different permutations of L1, L2 and L3 and record each
reading.
Phase to Earth Resistance: Take the insulation tester, using the same setting,
and check each lead from phase to the frame of the motor. The minimum
value of insulation resistance should be 1 Mega ohm. If the value is less than
0.2 Megaohms, replace the motor.
Any errors during this round of testing could indicate problems with
insulation, which is a problem when it comes to the safety and functionality of
the motor.

8. .6. Running Amps Test
This final test determines how much energy is drawn to drive the motor. More
powerful motors will draw more current, measured in amps. Before testing, it is
important to check the amperage draw your motor requires — this will usually be on
the nameplate.
When you are ready, use the following steps, which guide you through how to
measure three-phase current:
Prepare for Test: Set your multimeter to measure amperes and set it to the correct
ampere range for your motor per the specifications listed on the nameplate. You
should also be sure to wear rubber gloves during the test to protect yourself from
electric shock.
Turn On the Motor: Turn on the motor and locate the terminals. The positive
terminal will be labeled with a plus sign and have a red wire connected to it. The
negative terminal will be labeled with a minus sign and have a connected black wire.
Place the Sensors: Place the negative sensor of the multimeter to the negative
terminal of the motor, then place the positive sensor to the positive terminal. Be sure
to keep your hands clear of moving parts at all times to avoid injury.
When the sensors are connected, take the ampere reading and turn off the motor. The
ampere reading should be within range if it is operating correctly. The ampere
reading will not exceed the manufacturer’s specification but should be at or slightly
below the given amperage draw. If the ampere reading is well below specification or
out of range, this may indicate problems with the motor.