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On a vessel of at least 1,000 HP, or in a laboratory or workshop,
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the candidate troubleshoots a malfunctioning motor controller.
All
The assessment is required for all OICEW endorsements regardless of any limitations for propulsion mode and/or vessel equipment.
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The candidate:
Obtains the necessary schematics and wiring diagrams; Verifies that any necessary circuit breakers and disconnects switches supplying power to the motor and associated control equipment are closed as appropriate; Using a voltmeter, checks for power available at the service entrance of the controller and verifies that all supply voltages are within accepted parameters; Tests power and control fuses using on-line testing techniques with a voltmeter - to verify the results, tests the fuses off-line with an ohmmeter; If fuses are blown, visually checks for obvious signs of electrical shorts and grounds; Visually checks the interior of the controller enclosure for any signs of overheating, burning of contacts, weak contactor springs, corroded magnetic contactor armature faces, discoloration of terminals and conductors, broken conductors, loose fuses, and loose terminal connections; also uses sense of smell to check for burned insulation; Restores power and attempts to restart the motor while observing the motor controller to determine what relays and contactors are pulling in, if any; If the motor contactor is pulling in:
a. Listens for any buzzing or chattering noises;
b. Using a voltmeter, checks for voltage drops and imbalances; and
c. Using a clamp-on ammeter, checks for current draws and imbalances in the power circuit lines; verifies normal current by checking the motor nameplate data; If the motor contactor is not pulling in:
a. Determines what actions in terms of motor controller load energization (such as relays, timers, contactors, indicator lights, etc., if any, do take place; and
b. Using the control schematic, determines what specific operating contacts are necessary for energizing specific operating contactor and relay coils for normal motor startup; After closing any required operating contacts, checks to see if normal voltage is applied to the operating coil. If:
a. Normal voltage is being applied to the operating coil, tests the coil resistance with an ohmmeter, ensuring first that power is secured to the controller and coil is properly isolated;
b. No voltage at all is being applied to the operating coil, determines the location of the open in the control circuit;
c. An unacceptably low voltage is being applied to the operating coil, determines the location of the partial open in the control circuit.; and Verifies on-line results for low or no voltage by testing operating contacts for continuity using off-line testing with an ohmmeter. Ensures that power is secured to the controller and operating contacts are properly isolated before testing.
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