MCCB ( Step by Step) Preventive Maintenance

MCCB ( Step by Step) Preventive Maintenance

1. Safety First (Mandatory)

Before touching anything:

  • Apply Lockout/Tagout (LOTO) on the feeder
  • Verify zero voltage with a calibrated meter (phase-to-phase and phase-to-ground)
  • Wear appropriate PPE (arc-rated gear if required by site)
  • Confirm downstream equipment is de-energized

 2. Visual Inspection (Panel Closed First)

With the panel still closed (if possible):

  • Check breaker position (ON/OFF/TRIPPED)
  • Look for:
    • Burn marks or discoloration on panel door or window
    • Smell of overheating
    • Dust buildup or moisture inside panel
  • Verify labeling and breaker accessibility

 3. Open Panel & Initial Internal Check

After de-energizing:

  • Inspect breaker body and surrounding area
  • Look for:
    • Cracks or deformation in casing
    • Dust, corrosion, or moisture
    • Signs of arcing or overheating

 4. Torque Check on Terminations

This is one of the most important steps:

  • Use calibrated torque wrench
  • Check:
    • Line-side and load-side terminals
  • Re-torque to manufacturer specification (do NOT over-tighten)
  • Look for:
    • Loose lugs
    • Oxidation on copper/aluminum conductors

 5. Thermal Inspection (If Available)

  • Perform infrared thermography underload (before shutdown or during normal operation)
  • Check for:
    • Hot spots on terminals
    • Uneven phase heating
  • Any significant temperature difference = warning sign

 6. Mechanical Operation Test

With breaker still de-energized:

  • Turn breaker ON → OFF manually
  • Check:
    • Smooth operation (no stiffness)
    • Positive click action
    • Handle alignment
  • Reset trip mechanism if it was previously tripped

 7. Trip Function Test (Optional but Recommended)

Depending on breaker type:

  • Use test button (if available)
  • Or secondary injection test (for advanced maintenance)
  • Confirm:
    • Trip mechanism operates correctly
    • Breaker resets properly afterward

 8. Cleaning

  • Use:
    • Dry lint-free cloth
    • Low-pressure air (dry only)
  • Clean:
    • Insulation surfaces
    • Terminal areas
    • Arc chute area (if accessible per manufacturer)
  • Do NOT use solvents unless manufacturer allows

 9. Accessory Check (If installed)

Inspect and test:

  • Shunt trip
  • UV release
  • Motor operator
  • Auxiliary contacts
  • Under-voltage release

Verify correct wiring condition and insulation integrity.

10. Insulation Resistance Test (Megger Test)

  • Test phase-to-phase and phase-to-ground
  • Typical test voltage: 500V–1000V DC (depends on system rating)
  • Compare results with previous records
  • Low insulation = moisture or degradation issue

 11. Documentation

Record:

  • Torque values
  • IR readings (thermography + megger)
  • Visual findings
  • Any corrective actions taken
  • Breaker condition status (Good / Watch / Replace)

12. Re-Energization

  • Ensure all tools removed
  • Reinstall covers properly
  • Remove LOTO per procedure
  • Energize system step-by-step
  • Monitor breaker underload for initial period

 Recommended Frequency (Typical)

  • Visual check: every 3–6 months
  • Torque check: every 6–12 months
  • Full maintenance: every 1–3 years (depending on load criticality)
  • Thermal scanning: annually or quarterly for critical systems