How MET Group Technical Services Carry Out Professional ACB Servicing and Testing

MET Group engineer servicing an ACB

Air Circuit Breakers (ACBs) are one of the most critical protection devices in a building’s electrical infrastructure — yet they’re often ignored until something goes wrong. At MET Group Technical Services, we specialise in planned ACB servicing and live testing to ensure your electrical system remains safe, compliant, and fully operational.

Why ACB Servicing Matters

An ACB protects your building from overloads, short circuits, and equipment faults. When an ACB fails to operate correctly, the consequences can be severe:

• Unplanned power outages

• Equipment damage

• Fire risk

• Loss of critical services

• Non‑compliance with electrical safety standards

Regular servicing ensures your ACB will operate exactly as designed when it’s needed most.

How MET Group Perform ACB Service and Testing

1. Initial Condition Assessment

We begin with a full visual and mechanical inspection of the ACB:

• Checking for wear, contamination, and mechanical damage

• Inspecting arc chutes, shutters, and interlocks

• Verifying correct alignment and operation of moving parts

This gives us a baseline understanding of the breaker’s condition before deeper testing begins.

2. Mechanical Cleaning & Lubrication

Dust, carbon deposits, and dried lubrication are common causes of ACB failure. MET Group Technical Services engineers:

• Clean all mechanical components

• Remove carbon build up from arc chutes

• Apply manufacturer‑approved lubricants

• Ensure smooth operation of the opening and closing mechanisms

This step alone can dramatically extend the life of the breaker.

3. Electrical Testing & Calibration

This is where MET Group’s expertise really stands out. We carry out a full suite of electrical tests to verify the ACB’s performance:

Primary Injection Testing

We inject controlled current through the breaker to confirm:

• Trip times

• Protection curves

• Overload and short‑circuit response

• Correct operation of protection relays

This ensures the ACB will trip exactly when it should — not too early, not too late.

Secondary Injection Testing

We test the electronic trip unit independently to verify:

• Long‑time, short‑time, and instantaneous settings

• Earth fault protection

• Relay accuracy and stability

This confirms the intelligence of the breaker is functioning correctly.

4. Contact Resistance Testing

High resistance at the contacts can cause overheating and catastrophic failure. MET Group measure:

• Millivolt drop across each pole

• Contact wear

• Thermal performance

If resistance is too high, we can refurbish or replace the contacts before they become a problem.

5. Functional & Safety Checks

We verify:

• Manual and motorised open/close functions

• Interlocks and safety shutters

• Spring charging mechanisms

• Remote operation (if fitted)

This ensures the breaker is safe for operators and ready for emergency use.

6. Detailed Reporting & Recommendations

Every service concludes with a comprehensive report including:

• Test results

• Condition grading

• Photos of defects

• Compliance notes

• Recommendations for repairs or upgrades

This gives building managers clear, actionable information — and peace of mind.