The assumed OCPD clearing time should normally be taken as 0.5 seconds for a location at the service equipment or as close to the service equipment as possible.However, if a generator is dragged up to the building and connected to the electrical service, the reduced short-circuit current at the service may result in an increased OCPD clearing time. This is because the reduced short-circuit current will cause the tap conductors to heat up more slowly, which will allow the OCPD to take longer to trip.In this case, the OCPD clearing time should be calculated using the following formula:

Clearing time = (OCPD rating in amperes) / (Short-circuit current at the service in amperes)

For example, if the OCPD rating is 200 amperes and the short-circuit current at the service is 10,000 amperes, the OCPD clearing time would be:

Clearing time = 200 amperes / 10,000 amperes = 0.02 seconds

This clearing time is significantly less than the assumed clearing time of 0.5 seconds, which means that the OCPD would trip very quickly in the event of a short circuit.It is important to note that the OCPD clearing time is just an assumption, and the actual clearing time may vary depending on the specific circumstances. Flag for review