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Home / Technical Articles / Electrical Preventive Maintenance of Air Circuit Breakers
Electrical Preventive Maintenance of Air Circuit Breakers
Electrical Preventive Maintenance of Air Circuit Breakers

Recommended minimum practice for preventive maintenance

Insulation //

Remove and clean interphase barriers. Clean all insulating materials with vacuum and/or clean lint free rags. If it is necessary to use cleaning solvents, use only solvents recommended by the manufacturer.

Inspect for (early) signs of corona, tracking, arcing, or thermal or physical damage.

Insulation barriers (left: Interface barrier; right: Earth barrier)
Insulation barriers (left: Interface barrier; right: Earth barrier)

Ensure that insulation is left clean and dry.


Ensure that all contacts are clean, smooth, and in proper alignment. Ensure that spring pressures are maintained according to manufacturer’s specifications. On silver contacts, discoloration is not usually harmful unless caused by insulating deposits. Clean silver contacts with alcohol or silver cleaner using non-abrasive cloths.

Contact resistance tests using micro-ohmmeter
Contact resistance tests using micro-ohmmeter (photo credit:

Manually close breaker to check for proper wipe, contact pressure, contact alignment, and to ensure that all contacts make at approximately the same time.

If possible, a contact resistance test should be performed to determine the quality of the contacts. Micro-ohmmeters, which are used to perform contact resistance tests, apply a DC current through the entire closed circuit breaker current path, including the contacts, pivot point, and stab connections of the circuit breaker. The test set read-out displays the contact resistance directly in micro-ohms.

Older breakers equipped with carbon contactors generally require very little maintenance. Examine for proper pressure, deterioration, or excessive dressing which may interfere with their proper operation.

Draw-out contacts on the circuit breaker and the stationary contacts in the cubicle should be cleaned and inspected for overheating, alignment, and broken or weak springs. Coat contact surfaces with contact lubricant to ease mating (see manufacturer’s recommendations).

Arc Interrupters

Clean all ceramic materials of loose dirt and examine for signs of moisture, make sure the assemblies are clean and dry. Examine for cracked or broken pieces. Dirt and arcing deposits may be removed by light sanding — do not use emery cloth or wire brushes which may leave conductive residue behind. Repair or replace as necessary.

Examine arc chutes for dirt and/or dust accumulations and clean as necessary. Dielectric testing of arc shields may be recommended by the manufacturer. Check air puffer for proper operation.

Operating Mechanism

Inspect for loose, broken, worn, or missing parts (consult manufacturer’s schematics for required parts). Examine for excessive wear of moving parts. Observe that operating mechanisms function properly without binding, hanging, or without delayed action.

Ensure any lubrication is done according to the manufacturer’s specifications.

Figure 1 - Cutaway view of the molded case circuit breaker
Figure 1 – Cutaway view of the molded case circuit breaker

Ensure mechanisms are clean, properly lubricated, and all bolts and screws are properly secured. Repair or replace as necessary.

Auxiliary Devices

Inspect operating devices for proper operation and general condition. Ensure all indicating devices are fully functional and properly set.

Auxiliary devices (aux. switch, alarm switch, shunt trip and unrevoltage trip device)
Auxiliary devices (aux. switch, alarm switch, shunt trip and unrevoltage trip device)

Protective relays and circuit breaker trip devices should be inspected and tested according to manufacturers’ specifications and applicable industry standards such as those issued by the Institute of Electrical and Electronics Engineers (IEEE) and the National Fire Protection Association (NFPA).

  • Standard for and electrical preventive maintenance (EPM) program – The Hartford Steam Boiler Inspection and Insurance Company
  • Fuji Electric FA Components & Systems Catalogue

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More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Naushad Ahmed
    Apr 04, 2023

    sir, i need training in Transformers and all types of breaker

  2. Kemboi
    Sep 13, 2020

    I would like to receive training on mv maintenance and transformer protection relay.

  3. francis
    May 25, 2017

    hi sir is the air circuit breaker400A can manually push by hand? because its tripping without anu load or power supply what is the cause hope to subscribe soon thanks in advance

  4. Clark
    Mar 18, 2016

    Lint-free rags should be used when cleaning a breaker because?

    *lint attracts dust, which can cause tracking?
    please let me know the correct answer please.

  5. anil
    Nov 30, 2015

    sir which is the best method for arc extingused at the high load

  6. Larsen & Toubro
    Nov 06, 2015

    Thanks for sharing your blog with us.This blog shared all the functions of Circuit Breaker and its rated charachteristics.This blog has cleared all the concept of Air Circuit Breaker.L&T Electrical & Automation has some registered product.You may visit L&T Electrical & Automation

    May 02, 2015


    • Clarance
      Jul 06, 2020

      Please check your main moving mechanism parts. Some time it just need to regreasing or some oiling. See your environment. If dusty sure this will happened.

  8. moulay najim
    Nov 16, 2014

    Yes, i am satisfy.

  9. Sen
    Nov 03, 2014

    Hello Sir

    My ACB now one terminal have been burn and it occur tree time , so how can i solve it ?

    • Clarance
      Jul 06, 2020

      Some ACB the main moving contact or main fix contact can be replaced. If yes please do replace it. Easily you can see the damage. If there was some melted mark mean the damage is already there. If it just carbonise just clean it.

      • Dhananjaya
        Dec 08, 2020

        No only abb make only we changing opposition fixed and moving contact s

  10. sachin s
    Aug 13, 2014

    Hello Sir..What is function of the micrologic control.?

  11. karim pourmosa
    Jul 11, 2014


  12. akhtar
    Mar 30, 2014



  13. michael k kudahor
    Mar 25, 2014

    Better still what to consider in other to improve the power factor of a plant .

    • vijay
      Nov 03, 2014

      Most of the plants were fitted with synchronous condenser or generator to cop up with power factor issue. Also, condensers are fitted at various places where inductive loads are located. While installing a new inductive machinery it is advisable to take its pf into consideration.

  14. michael k kudahor
    Mar 25, 2014

    it educative to know you share such a deep insight, i would love to know what are the best and affordable ways of improving power factor of a plant?

    Feb 07, 2014

    Hello Sir,
    Can we control kvar ratings of a power factor capacitor by varying voltage supplied to it, by varying the triggering of thyristors and thus control power factor in a more significant manner?

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