Low-voltage circuit breaker preventative maintenance
Author: Brian Wahl
Low-voltage circuit breakers are an important part of your power distribution system. Practicing regular maintenance and inspection of your circuit breakers is the best way to counter potential problems that may arise over time due to age and wear. The following article outlines low-voltage circuit breaker preventative maintenance. For information on low-voltage replacement circuit breakers, click here. For step by step instructions, please see your instruction manual.
Warning: Prior to performing maintenance, always verify that the circuit breaker has been de-energized. Hazardous voltage will cause death, serious personal injury, or equipment damage. Turn off and lock out all power supplying the device before performing any type of work.
Recommended maintenance plan overview
Factory production tests
Manual and electrical operation tests should be performed in order to verify the proper operation of the circuit breaker. Tests should be performed to verify proper operation of the charging, closing, tripping, anti-pump, and racking interlock mechanism.
Inspection of key components
Arc splitter plates erode as the result of load breaking. This constitutes normal wear. The erosion of the arc splitter plates can manifest itself as wear of the plates, a layer of soot, or small collection spots of molten metal. In case of heavy wear (severe erosion, large deposits of molten metal, etc.), the arc chutes should be replaced. The image below illustrates the general steps taken to remove the arc chute for a Siemens WL circuit breaker. For step by step instructions for your circuit breaker, please refer to the applicable OEM instruction manual.
Internal contacts erode during load breaking and short-circuit trips. For this reason, internal contacts are recommended to be inspected on a regular basis. The circuit breakers are equipped with an easy to view contact erosion indicator for monitoring the wear of the circuit breaker’s internal contacts. If the indicator pin is no longer visible, the contact system must be replaced. Estimated wear can be transmitted via communication option.
Steps for replacing main contacts
Primary disconnect contacts should be inspected for signs of any deterioration, damage, proper cleanliness, and proper lubrication. Wear or misalignment can be seen by checking the grease wipe on the contacts.
Lubrication of key moving parts
All WL circuit breakers use the same 480V circuit breaker lube, Isoflex Topas NB 52, which is manufactured by Kluber Lubrication. The product is sold through Siemens by its catalog number (WLBGREASE) and comes in a 400 gram tube. The color of the grease is “clear” when applied and turns to a “mustard” color as it ages over time, remaining effective as it yellows. Isoflex Topas NB 52 is not to be intermixed with other lubricants. If mixed, the substance can cause hardening which will reduce conductivity and slow or even block the motion of all sliding or rotating components.
Use Isoflex Topas NB 52 by applying a thin coat to the racking cam pins / rollers and the bottom of the cradle rails. When over-applied, the substance inhibits performance and attracts dust and dirt. In order to ensure that this is avoided, it is recommended to wipe off old grease and re-apply. The operation of the mechanism is “maintenance free.” No lubrication or maintainable parts are required in order for use.
For electrical primary disconnects, apply a thin coat of Mobile 28 to primary fingers of equipment. Over-application of grease attracts dust and dirt which inhibits performance. It is recommended to annually wipe off old grease and re-apply.
Electrical tests shall be performed in accordance with NETA or circuit breaker manufacturer specifications and should include:
Primary high current testing
Digital low resistance ohm
Insulation resistance test.
A full test data sheet will accompany each circuit breaker and should be compared to as-received testing along with to-track changes over time. Data sheet tracking can better predict and plan maintenance intervals based on the environment and use. Any circuit breaker that does not pass NETA or circuit breaker manufacturer specifications shall be failed.
Replacing coils, motors, and electronic trip units (ETUs)
Coils, motors, and electronic trip units (ETUs) are easily replaced modular components in the modern Siemens WL low-voltage circuit breaker.