Escape Danger and Damage With Preventative Maintenance and Testing for Molded Case Circuit Breakers

Escape Danger and Damage With Preventative Maintenance and Testing for Molded Case Circuit Breakers

July 25, 2017

One of the simplest and most effective ways to save money is preventative maintenance, and this is particularly true of circuit breaker maintenance. Companies rely on circuit breakers to protect technologies and systems from overcurrents and short circuits that would otherwise cause significant damage.

Circuit breakers come in a variety of types that are appropriate to the equipment they’re intended to protect. Maintenance will need to be customized to the type of circuit breaker. This article will focus on molded case circuit breakers, which are used in residential, commercial, and industrial applications. It’s also a good idea to have a professional electrician inspect the circuit breaker, since he or she will be most knowledgeable and best equipped to detect issues.


When there’s an overload or short circuit, you want the closest circuit breaker to interrupt the overload or short circuit as quickly as possible — any delays could cause significant increases in the arc flash. Even just a few tenths of a second can significantly increase the arc flash energy.

While anyone who is operating or around the equipment will be wearing personal protective equipment (PPE), the type of PPE is selected based on an arc flash analysis that assumes the circuit breakers are working correctly. Preventative maintenance and testing will protect not only your equipment but also the lives of your workers.


Molded case circuit breakers need the least maintenance of all the circuit breaker types, but there are a few maintenance items you’ll want to conduct regularly.

Lubrication is essential for proper functioning, and since many molded case circuit breakers are sealed, you can’t get inside to re-lubricate. You’ll need to exercise the breaker to evenly distribute all the lubrication contained inside throughout the moving parts.

The biggest risk comes from dust on the latch surfaces, so the circuit breakers should be cleaned regularly as well. Clean with a vacuum, and then wipe down the breaker with cotton rags. You’ll want to make sure you’re particularly diligent with the insulation.

Finally, you should visually inspect the breaker for signs of damage like cracked insulation, bent linkages, cracked tracking, overheating, etc. Again, if the breaker is sealed, you’ll be limited on what you can see, but check out whatever is available to you.


Because most breakers are sealed and inspection is limited, regular testing will ensure that the circuit breaker is operating as it should. There are several tests you should run periodically:

  • Mechanical Operation Tests
  • Insulation Resistance Tests
  • Individual Pole Resistance Test (Millivolt Drop Test)
  • Inverse Time Overcurrent Trip Test
  • Instantaneous Overcurrent Trip Test
  • Rated Hold-In Test (Full Load Injection Test)
  • Accessory Device Tests
    • Shunt Trip Release
    • Under-Voltage Trip Release
    • Electrical Operator Breaker Assembly
    • Auxiliary Switch
    • Alarm Switch

The National Electrical Manufacturers Association offers an excellent resource on molded case circuit breakers that outlines the procedures for each of these tests that you can access here.

Maintenance and testing are essential to safe operation of circuit breakers, particularly for molded case circuit breakers that don’t reveal problems easily. Basic cleaning, lubrication, and visual inspection are a good start, but you’ll need to conduct the recommended tests to have confidence that you won’t experience a dangerous and costly malfunction. Always have a professional electrician conduct tests for preventative maintenance. Safety is always the number one priority.

If you’re looking for a molded case circuit breaker or other type of circuit breaker, see what we have in stock. If you have questions, feel free to give us a call at 864.249.0943.

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