Why can't I change the breaker opening time in the arc flash spreadsheet?

Definition of the breaker opening time:

The breaker opening time is the time required for a breaker to open after receiving a signal from the trip unit to operate. The combination of the Trip/Delay time and the Breaker Opening time determines the total time required to clear the fault. For low voltage circuit breakers, the total clearing time displayed on the Manufacturer's drawing is assumed to include the breaker opening time.

For relays, the breaker opening time is dependent on the rated voltage of the breaker. These are typical breaker opening times:

1.5 cycles < 1kV molded case
3 cycles < 1kV power circuit
5 cycles 1 - 35kV
8 cycles > 35kV

From the picture below (on page 2), you will notice that the column named 'Breaker Opening Time (sec.)' has a white background. This means that it is an editable field in the arc flash spreadsheet.

There are two cases where you cannot change the breaker opening time in the arc flash evaluation:

  • 1.) The fault current contribution is coming from an induction motor set within the Options menu to clear in a specified number of cycles.
  • 2.) The maximum arcing duration has already been reached. Either because:
  • a. The protective device that is suppose to trip that portion of the arcing fault current is set above the maximum arcing duration.
  • b. You do not have a protective device to clear the arcing current.