Understand Motors

Published On: April 17, 2024By Categories: Features, Pumps and Water Systems

Knowing why motor components fail helps when troubleshooting pump systems.

By Daniel Featherstone

When it comes to pump troubleshooting, it’s easy to find ourselves working on autopilot.

We are quick to replace a pump if it’s not working. However, this quick-fix method can result in the same issues down the road. Maybe on the next pump, we will decide to replace a part this time, the capacitor or switch for example. But is that taking the time to find the root cause?

Let’s take a closer look into the motor components and see just what influence they have on the pump’s operation and why they might be failing.

Knowing Voltage

The capacitor in a single-phase motor is only needed for roughly three-tenths (0.3) of a second to start the motor. When the motor speeds up to 2500-2800 RPM, the governor or relay in a submersible three-wire application activates and takes the start capacitor out of the circuit.

Figure 1. The allowable variance of microfarads (MFD) is usually printed on a motor.

In the case of an above-ground pump with dual voltage, it is important to note that unless otherwise specified, the pump is likely wired for 230 volts. Connecting the pump to 115 volts when the motor is set to 230 volts may result in insufficient RPM for the capacitor to be removed from the circuit, causing the overload to heat up and trip.

If a new installation exhibits rapid cycling right out of the gate, it is advisable to verify the voltage. Conversely, if the above-ground pump is configured for 115 volts and connected to 230 volts, the motor windings may quickly burn out and smoke.

When encountering a three-wire control box with a chattering relay, voltage-related issues are commonly the cause. Using a voltmeter is recommended to confirm the correct voltage.

Additionally, voltage drop may be a contributing factor, particularly during pump start-up. A voltage drop could indicate breaker size or wire gauge problems, as the pump’s inrush current is often significant and inversely related to amperage and voltage.

When troubleshooting a three-wire submersible motor, it’s important to consider the various components that could cause issues. After disconnecting the power and ensuring the capacitor is discharged, the first step is to inspect the capacitor.

Start capacitors are equipped with a relief mechanism that allows for the release of oil if the capacitor overheats, indicating a potentially weak capacitor or prolonged usage. If this is ruptured, it’s a clear sign that a heat event occurred from a weak or worn-out capacitor.

Another way to check the capacitor is to use a capacitance meter. This is often a function of a good multimeter. For a start capacitor, the microfarads (MFD) are usually printed on it with an allowable variance (Figure 1). The variance is usually in the range of 0 to +20%.

If a run capacitor is present, a visual inspection works as well. However, checking with a capacitance meter, the variance may now be +5% to –5%. It is important to remember a start capacitor will quickly fail if below its minimum. It is recommended to not start the motor in these situations and replace the capacitor.

Troubleshooting a submersible motor requires a comprehensive approach.

If the capacitor appears in good condition, it’s time to investigate further. Let’s look at the governor or relay’s influence on the start capacitor. Check the condition of the start switch points to make sure there is no sign of carbon buildup or damage, which would indicate rapid cycling or voltage issues.

Next, assess the pressure tank and switch, as they play a significant role in controlling and limiting the pump’s cycling. Consider the wire gauge and ensure it aligns with the pump’s requirements, as stated in the owner’s manual. Upsizing the pump horsepower without adequately considering wire size can lead to operational issues.

That’s a lot, isn’t it? I hope you see how the capacitor and the start components work together. I’m sure you also see that troubleshooting a submersible motor requires a comprehensive approach.

You need to account for various factors, including the condition of components such as the capacitor, governor/relay, start switch points, pressure tank, pressure switch, wire gauge, and breaker or fuse sizing. Systematically addressing these aspects can effectively identify and resolve issues, ensuring optimal water well system performance.

Testing the Overload

An additional thought on troubleshooting a motor is the overload, which has two essential parts: the heater and a disc that reacts to the motor’s condition. When the heater gets hot, it can trip the overload, taking the motor offline. Once it cools down, the overload will automatically reset.

To test the overload, measure points one to two and point two to three with the power off and the capacitor discharged. Set your meter to the lowest ohm setting; the reading should be one or less. Worn thermal overloads are uncommon, but neglecting the pump could cause it to occur.

When it comes to inspecting the windings of an above-ground motor, there is a distinct odor often found if the windings have been damaged. Open drip-proof motors will have an ozone-like burnt smell if the windings are damaged. You can also visually inspect the condition of the motor windings with an open drip-proof motor. However, the testing procedures for above-ground single-phase motors and submersible motors vary by manufacturer, so it’s best to get the exact test procedure from the manufacturer.

In my years of experience, the primary test is the smell and visual inspection of the windings. Another reason for the windings failing could be the motor’s location or environment. Are there any “foreign objects” like an insect or small animal that could have crawled in? Is there enough airflow to cool the motor properly? Is the motor in direct sunlight, creating more heat? Setting the pump location up for success against potential risks like these is critical.


In summary, thoroughly investigating how a pump failed is a valuable proficiency that can help you better service your customer.

Understanding how the capacitor and starting components work to engage the motor and the overload’s role in protecting the motor is fundamental to the examination process. Additionally, check to make sure the requirements in the owner’s manual match the systematic setup for the pump, as it can vary by manufacturer.

If you are the service person who identifies and resolves the issue while educating the customer, you may gain a customer for life. Lastly, remember that many customers will happily provide positive feedback online.

Daniel Featherstone is a technical training leader for Pentair Flow Technologies. He has been with Pentair for more than 23 years and training for more than 20. His experience includes a variety of pumps from standard centrifugal and submersibles to vertical multistage and vertical line shaft turbines, and more.

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