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Mechanical Considerations for Capacitor Mounting

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Over the last 30 years in the plastic-dielectric capacitor business, I’ve seen many electrical failures resulting from mechanical issues. Stressing electrical connections can lead to ESR increases over time, arcing at contact planes, and hot terminations from improper contact. Plastic-dielectric capacitors, especially polypropylene dielectrics preferred in the power applications, expand much more than metals. Transportation and installation of large systems can result in large mechanical stresses transmitted to the terminations. Over time, temperature excursions along with mechanical shock and vibration, affect the connections leading to potential thermal runaway.

As time goes on, and new engineers enter the field, it can be beneficial to restate some of the lessons learned. Sometimes what’s old becomes new again. Here’s just a few basic notes to consider when planning the mounting and installation of power capacitors.

Although these may seem obvious upon first glance, I still see systems where these basic precautions are overlooked, and come back with a vengeance. The capacitor life is shortened, and the potential for catastrophic failure (most often fires in AC applications) increases with time as the capacitor losses increase to thermal runaway. Taking a little extra time to insure proper stress relief will provide safer operation and higher reliability in your power applications.

J. Bond – June 2015