Inverse-Time Overcurrent Trip Test (MCCB)

Inverse-Time Overcurrent Trip Test (MCCB)

Purpose


•Verify the long-time protection function.
•This confirms the breaker trips according to its inverse time curve.

How it works

  1. Connect two poles *in series* with copper conductors not less than 4 ft (1.2 m) in length

  2. Check Trip Unit Dial Settings
  3. Set MCCB handle to ON position
  4. Inject 300% of rated current (3 × In)
  5. Measure time to trip
  6. Compare to trip curve limits
  7. Repeat the test once each, changing the R-S, S-T, and R-T phases

Example:
  1. Breaker rated current = 800A
  2. Test current:
  3. 3 × 800A = 2400A

The breaker should trip within the maximum allowable time defined by standards.