When an electric motor is malfunctioning (or the system that it’s running is not performing as expected) electrical tests can be used to gain considerable insight as to what might be causing problems. Using a multifunction electrical tester to check resistance, amps, capacitance, and insulation resistance can be highly effective in troubleshooting most problems. However, with an electrical tester in-hand, it becomes easier to overlook many other potential sources of problems. As a technician, you must never put down your common sense; your multi-meter and your megger don’t replace your brain.
Video Synopsis
Amps: An amp meter is arguably the most effective tool to use for electrical troubleshooting. If a motor is not drawing its usual amount of amps, there is definitely a problem. For example, you have a pump rated at 30 amps, it will usually draw 30 amps under its normal operating condition. If you test a 30-amp pump and it is drawing fewer than 30 amps, something in system is almost definitely stopping the flow of water to the pump. If an electric motor is pulling more than its rated amount, turn the motor off to prevent damage and examine the operating environment to determine why the motor is drawing more amps than it is rated for. Remember, when doing electrical tests, check the amps first! David repeatedly tells the class, “Amps tell you everything.”
Capacitance: Capacitors are not necessarily prone to failure, but they do fail more often than some of the other components used in electric motors. When testing capacitors, David advises students to (safely) short them with a screwdriver because they retain electric charge.
Tests with a Megger: A megger is used to measure insulation resistance. When testing a motor’s insulation resistance, a higher resistance reading is better. Resistance to ground of one million or higher is desirable, but a reading of infinity is ideal. Lower numbers are indicative of insulation failure, and are often caused by moisture inside the insulation. Also, if insulation resistance reads low on the motor while idle, running the motor for a few minutes may change the result. If the test result improves while the motor is hot, it should be safe to operate, but maintenance should be scheduled soon.
Use Your Senses: Electrical tests are very useful, but always check the basics first. Very often, a failing electric motor will display symptoms that anyone can easily observe with their five senses. Smoke, fumes, and excess heat are all common symptoms, as well as loud and abnormal sounds. Always take note of these symptoms before delving into more advanced. David also tells a story about a failed installation of a pump that our shop repaired – when it was reinstalled after the repair, a concrete block was in the way of the impeller, but the symptoms all indicated that the pump motor had failed. There are always possibilities that may not be obvious, whether they’re related to the motor itself or the operating environment.
Control Panels: Being able to test a control panel is a vital skill because control panel issues are as common as electric motor issues, and often cause similar symptoms. If control panels are not taken into account when attempting to troubleshoot issues, unnecessary repairs might be performed on the motor, wasting valuable time, money, and human resources.