Is it enough just to megger test a submersible pump (sump pump)?

An electric motor serves as a crucial device that transforms electrical power into mechanical energy, facilitating many devices and machinery in their operation. It plays an integral part in generating movement and functionality by leveraging the principles of electromagnetism. This conversion process leads to the powering of various appliances, vehicles, and industrial equipment.  Electric motors are pivotal, powering vital processes, especially in manufacturing and energy production. Their invention dates back to 1873 with the accidental discovery of the Gramme Machine, the first of its kind.  The evolution of this technology saw a major leap in 1888 when Nikola Tesla introduced the first practical AC electric motor.

Like any mechanical device, they are susceptible to wear and tear over time and operational stress. To ensure their reliable performance and durability, engineers employ a crucial diagnostic procedure called insulation testing, which is widely referred to as “megger testing”.

For numerous years, megger testing has been a trusted tool for electricians to gauge the health of motors. The term “megger” has transcended its status as a brand name to become an industry standard, much like “hoover”. megger testing is a specific type of electrical test that evaluates insulation performance within an electrical apparatus. The process involves the application of a mega-ohm meter to each phase connection of the motor leads and ground, followed by the application of voltage. This meter measures the voltage drop across the connection point between the motor leads and ground, and subsequently calculates an insulation value which is then displayed for the user. A higher resistance number typically suggests better performance. Ideally, these data points are tracked throughout the lifespan of the motor, serving as a warning system for potential failure.

Megger testing, a prevalent practice in various settings, serves as a key component of Preventive Maintenance (PM) performed at regular intervals. This method primarily measures the resistance between the motor under examination’s phase windings and the ground. Despite its widespread use, this protocol has limitations in predicting motor failures.  It is because an insulation breakdown, which negatively affects the resistance, results in a discrepancy between phases or between one measurement and a preceding one, thereby giving an understanding of motor health.  However, megger testing solely measures resistance to the ground.  It’s crucial to note that most electrical motor failures initiate with insulation breakdown – not between phases and ground, but between windings within a phase or windings of different phases. Unfortunately, megger testing in isolation is incapable of discerning this type of failure.

Resistance measurements of windings work as an additional test technique, supplementing megger testing. The logic behind this is that any variation in resistance could potentially signal an impending failure, similar to resistance to the ground. However, this approach might not always detect a winding-to-winding short. Although a turn-to-turn short does affect resistance measurements, the impact on resistance alone is typically minimal. Conversely, the impedance across the windings experiences a more significant effect. Most multimeters are designed to test resistance, not impedance (a measure of the opposition to electrical flow), which often leads to a misunderstanding with those who tend to equate resistance and impedance.

To more precisely assess the electrical health of an electric motor, it is imperative to extend the evaluation beyond megger testing.

Testing a sump pump  

Submersible pumps are a reliable method for transporting water from buildings or residences in Type C and structural waterproofing applications.  These pumps are engineered to function while completely submerged in the water they’re pumping.

The motor plays a pivotal role in the operation of a submersible pump (sump pump/packaged pumping station).  In case of any malfunction, it is beneficial to commence with motor testing for an effective diagnosis. Given the pump’s location below ground in a chamber, it is advisable to confirm the motor’s functionality before installation or by removing the submersible pump from a sump chamber.  This verification can be accomplished by measuring and assessing the winding resistance and insulation resistance, which are key indicators of a submersible pump motor’s condition. These tests are effective strategies for troubleshooting both new and used motors.

For safety reasons, it’s essential that certain activities are not attempted at home without professional guidance or supervision.

Using a megohmmeter (megger) or ohmmeter, which are connected to the motor leads, is a highly effective way to ascertain whether the motor windings are either electrically short or open, which can influence the motor’s overall performance.  The ohmmeter is particularly useful for measuring winding resistance, while the megohmmeter excels in checking insulation resistance. After obtaining the necessary measurements, these should be compared with the standard values provided by the pump manufacturer for the specific motor.

Regular Servicing

It is advised to choose a well-regarded service provider for your pump maintenance needs. This can ensure optimal performance and longevity of your equipment. Selecting a reliable service can also prevent potential issues and costly repairs in the future.

Always Happy to Help

For all your project requirements, Delta’s Technical Team is a dependable resource. Offering expert advice, comprehensive support, and timely practical assistance, we cater to your specific needs. Reach us at 01992 523 523 or drop us an email at info@deltamembranes.com.