When using Design Master Electrical or Electrical RT to calculate arc-flash values, you must specify the trip time for the breakers.
The trip times are based upon the time-current curve for the specific breakers that will be installed in your project. If you know the specific breaker, you can search for it in our breaker database using the Set Curve buttons when creating or modifying equipment.
Sometimes, you won’t know what breakers are going to be used or are unable to obtain the curves for them. Here is a general method you can use for determining the trip time in those situations.
For each piece of equipment, locate the upstream overcurrent protection (OCP). This OCP needs to be outside the equipment. For example, do not use the main breaker for the panel. Instead, use the breaker in the panel upstream.
Note the size of the OCP and the rating of the OCP.
For a breaker, multiply the rating by 10. For a fuse, multiply the rating by 5. Compare that number to the arcing current value calculated by Design Master Electrical.
If the arcing current is greater than that value, set the arcing time to 0.0167. The OCP will trip immediately in this case, which requires 1 cycle.
If the arcing current is less than that value, set the arcing time to 2. The OCP will effectively never trip. A maximum of 2 seconds is used because we assume the individual will move out of the arc in that time.