Air Circuit Breakers (ACBs) are used as circuit protection for a wide range of low voltage (up to 600V AC) applications, typically generators, MCCB distribution boards, UPS, small power stations, etc with sizes ranging from 400A to 6300A or larger. Protection is provided in either 3 or 4 pole configurations. Additional protective devices can be fitted such as undervoltage releases and shunt trip coils together with auxiliary contacts for remote signalling. 

ACBs are the cause of almost 20% of power distribution system failures, mainly due to lack of maintenance, dust, hardened grease, corrosion and/or frozen parts that prevent the proper operation of the trip linkage. It wasn’t long ago that ageing electrical equipment was replaced but in today’s business environment, maintenance is the preferred choice to ensure reliable operation and extend the life expectancy.


As with all electro-mechanical devices, major electrical equipment manufacturers recommend maintenance of air circuit breakers to ensure proper operation and to maintain equipment warranties. With regular service air circuit breakers can remain in service almost indefinitely as long as spare parts are readily available.

In time users will tend to add or remove electrical load from some devices. If this change is permanent, the electrical trip characteristics should be reset using a “current injection” tester and the whole device recalibrated. Service intervals depend on the age of the device, load operational environment, number of emergency operations, etc. Companies such as shentongroup Power Management normally recommend maintenance is carried out every two or three years, but an annual service may be needed if the unit is old has had a large number of emergency operations or is installed in environments with dusty or humid atmospheres. Calibration and certification should be incorporated into regular inspections and testing in accordance with the latest regulations.

Onsite Maintenance

Onsite generator maintenance or repair may include the use of new parts to return an ACB to full working order. This normally involves:

  • Visual inspection for any broken parts and replace as needed. Clean and lubricate all mechanical linkages.
  • Inspect all breakers, remove all covers and arc extinguishing shields, inspect for damage, wear and deterioration, clean and lubricate as required. Check, clean and dress (if required) the main contacts, clean all covers and arc shields.
  • Check security of all control wiring and associated fitted components, prove mechanical operations and reinstate covers and arc extinguishing shields.
  • Carry out insulation test, phase to phase and phase to earth.
  • Prove mechanical and electrical operation of the breaker by racking breaker to test position and carrying out injection test on electronic trip devices to prove operating characteristics against set points.
  • Rack breaker to connect position and return breaker to service condition.

Once maintenance has been completed, an Inspection and Test Certificate would be issued as completion and acceptance of work carried out.

Comparing Benefits

The most obvious benefits of regular servicing is the significant savings that can be made over buying new equipment and not just physical equipment but the time and labour involved in specification, procurement, installation, testing and commissioning. Regular servicing can mean reduced downtime and improve equipment reliability because damaged or worn components are usually identified before they cause premature failure. Cable and copper busbar installation, the conversion of ACBs from fixed to withdrawable pattern and the rebuilding and refurbishment of switchboards all enable engineers to modernise existing equipment at a fraction of the cost of procuring and fitting of new devices.

Electrical equipment manufacturers normally offer only new equipment to a customer seeking to upgrade an electrical system. However, before buying any new switchgear, consider the service options and your company may just save a lot of money and downtime.

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