top of page

ACB Testing & Maintenance 

              Air Circuit Breaker Maintenance, Testing & Repairs

One of the components of an electrical installation that often get completely overlooked is the primary switch gear and means of isolation. In most installations, and particularly those serving larger facilities, the likelihood is that the main means of isolation and protection for the system is by means of an ‘Air Circuit Breaker’ which is a mechanical device of varying designs depending on brand and age.

This equipment can remain in an ‘On’ or ‘Closed’ position for months and years and without being activated and without regular maintenance; can fail to operate without warning with potential, major consequences.


The switchgear, be it ABB, Merlin Gerin, Schneider Electric, GEC, Mitsubishi or other manufacturers, is designed to act as the primary point of isolation and as a protection in the event of a fault or over current occurring on the system, thereby safeguarding the system up-line. Failure to operate can lead to serious consequences.

  MET Groups Air Circuit Breaker Service To Keep You Compliant & Provide Reliability

At MET Group , we can provide a full maintenance service for this primary breaker unit, as well as secondary units and those further down the installation. We can design a bespoke maintenance programme to dovetail with existing routines which might include a main shutdown, withdrawing switches, cleaning, re-torqueing (not something that is done unless it is panel maintenance), lubrication (one of the most key items with ACB maintenance), greasing, functional testing, contact service and replacement of any worn or damaged components.


In addition, over current relay/ trip units can be Secondary Injection Tested using the appropriate test equipment for each brand of equipment to ensure that tripping parameters are still within manufacturer’s tolerances and that the unit will perform as designed and protect site assets/ systems.
In addition to the maintenance of ACB’s, we can carry out similar inspections and tests on Moulded Case Circuit Breakers (MCCB) to ensure correct tripping characteristics and performance.
The individual programme agreed upon, might include a full invasive inspection and physical maintenance of the whole primary and secondary panel arrangement under a controlled shutdown process. As an additional check, we can undertake a thermographic survey of the switchgear, under full load, to ensure that there is no overheating of components or connections.


Air circuit breakers (ACBs) are critical components in electrical distribution systems, responsible for protecting circuits from overloads and short circuits. Regular testing of air circuit breakers is essential to ensure their proper functioning and reliability. Here are some key aspects of METs air circuit breaker testing:

  1. Visual Inspection:

    • Conduct a visual inspection of the circuit breaker for any signs of physical damage, corrosion, loose connections, or overheating.

    • Check for proper alignment and operation of mechanical linkages and moving parts.

  2. Contact Resistance Test:

    • Perform a contact resistance test to ensure that the electrical contacts within the circuit breaker have low resistance, minimizing power losses and ensuring efficient current interruption.

    • High contact resistance can lead to overheating and decreased performance.

  3. Insulation Resistance Test:

    • Conduct an insulation resistance test to verify the insulation integrity of the circuit breaker. This test helps identify any insulation breakdown or contamination.

    • Ensure that the insulation resistance meets the specified requirements.

  4. Overcurrent Protection Testing:

    • Test the overcurrent protection features of the circuit breaker to verify that it trips within the specified time under overload and short circuit conditions.

    • Use a test kit to simulate various fault conditions and check the response of the circuit breaker.

  5. Trip Unit Calibration:

    • If the air circuit breaker has an electronic trip unit, calibrate it to ensure that it operates within the specified parameters.

    • Verify that the trip unit settings align with the protection requirements of the connected electrical system.

  6. Secondary Injection Testing:

    • Perform secondary injection testing on the trip unit to simulate the operation of protective relays and ensure coordination with other protective devices in the system.

    • This helps validate the correct functioning of the protection scheme.

  7. Closing and Opening Time Measurement:

    • Measure the closing and opening times of the circuit breaker to ensure that it operates within the specified time limits.

    • Incorrect operating times can affect the coordination of protection devices in the system.

  8. Mechanical Operation Test:

    • Conduct a mechanical operation test to ensure smooth and proper functioning of the operating mechanism.

    • Verify that the breaker can be manually closed and opened without any issues.

  9. Dielectric Strength Test:

    • Perform a dielectric strength test to check the insulation properties of the circuit breaker under high voltage conditions.

    • This test ensures that the insulation can withstand the voltage stress without breakdown.


Talk to us

Contact us today and we can discuss your project needs.

bottom of page