Rated Hold-In Test (MCCB)
Purpose
• Verify
the breaker does NOT trip during normal operation.
• This
confirms the breaker can carry rated current continuously.
How it works
1.Ensure
test is conducted at room ambient temperature of 25ºC (77ºF)
2.Set
the handle of the MCCB breaker to ON.
3. Connect
all poles in series* with copper conductors not less than 4 ft (1.2 m) in
length
4. Verify
the Smart Trip Unit (STU) settings.
• Iu
= 1.0
• Ir =
1.0
• Ig
= Off
5. Inject
the breaker’s rated current (In) and maintain the current until the temperature
stabilization*
6. Monitor
the breaker temperature using a temperature sensor.
* Temperature stabilization can be confirmed when three temperature measurements taken every 10–20 minutes at the same location show little or no change. Typical stabilization time is about 2 hours for small MCCBs and 4 hours for larger MCCBs.
Results
• The
breaker should not trip during the test.
• If it
trips, reset it and continue monitoring temperature stabilization.
• If
the breaker continues to trip or the terminal temperature rises above 80K over
ambient, the breaker should not be returned to service.