ACB Testing, Inspection and Maintenance Requirements

The Air Circuit Breaker (ACB) is an electrical device used to provide overcurrent and short-circuit protection for electric circuits over 800 Amps to 10K Amps. These are usually used in low voltage applications below 450V. We usually see them in Main Distribution Boards (MDBs) as the incoming breaker. The ACB 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.

An ACB is a circuit operation breaker that operates in the air as an arc extinguishing medium, at a given atmospheric pressure. The ACB can remain in an ‘On’ or ‘Closed’ position for months and years and without being activated and without regular maintenance it can fail to operate without warning and can lead to major consequences.

Cornerstone’s inspections are based on BS 6423 & IET standards and our experience involves different industry types – oil and gas, factories, hotels, healthcare, schools, residential and commercial real-estate across UAE, Qatar, Kuwait & Saudi Arabia.

The below is an overview of the different tasks involved in the testing of an ACB:

General Inspection & functional test:

• Check for type of ACB
• Check for withdrawing racking handle and mechanism
• Check for closing and opening, on/off manually in open position
• Check for charging the storage spring mechanism pumping the storage handle
• Check the ON/OFF/trip push button
• Check and verify spring charged/discharged/ok to close
• Check and verify the ACB position disconnect/test/connect
• Check operation of the protection release
• Check the control wiring
• Check for closing coil, shunt coil, U/V coil
• Check for motor operating mechanism
• Check the operations of interlock & check its mechanical operation, lock and switch on & off
• Visual inspection and servicing of moving and fixed parts
• Check racking-in and out operation
• Prepare and submit the test report with condition report to client

Mechanical cradle:

• Check the physical condition of the ACB & mechanical cradle
• Check and clean arc chute & cubicles
• Check and clean the arc chutes chambers of each pole
• Clean and grease contacts – remove dust and traces of excess oil or grease
• Check connection screws of cables to verify tightness of terminal boards
• Check draw out guide rails
• Check shutter – power terminals
• Locking device for shutter
• Shutter operating device

Electronic trip by using test kit & ETU settings.

• Overload (l) ampere rating+ time.
• Short circuit(S) short time delay.
• Instantaneous(I) short circuit protection.
• Neutral (N) conductor.
• Ground (G) earth fault protection.

Specialized tests:

• Secondary injection Test.
• Insulation resistance Test.
• Electrical/Functional Test.

Cornerstone has vast experience working with all ACB brand types including ABB, Merlin Gerin, Schneider Electric, GEC, Mitsubishi, Moeller & Federal providing standalone testing to full maintenance services.

We bring value to our clients by designing custom maintenance programmes and inspections as per their need and priorities, maximizing productivity and profit.