What is the Emergency Standby power or ESP Rating?

Helpfully, ISO-8528-1:2018 defines basic generator set rating categories based on four operational
categories: Emergency Standby Power (ESP), Prime Power (PRP), Limited-Time Running Prime (LTP) and Continuous Power (COP). In each category, a generator set’s rating is determined by maximum allowable power output in relation to running time and the load profile.

Incorrectly using these ratings can lead to lower generator life, invalid warranties and in some instances terminal failure.

What is the load factor and running time on an Emergency Standby Power generator?

So what is Emergency Standby Power (ESP)? According to ISO-8528-1, ESP-rated generator set must provide power for the duration of an outage, but with maintenance intervals procedures being carried out as specified. The ISO standard gives no limit to run time in the event of a utility power outage, so the unit must be designed to meet individual requirements. Because the ESP rating is the maximum amount of power that the generator set is capable of delivering, no overload capacity is available for the ESP rating. ISO-8528-1 limits the 24-hour average load factor to 70 percent of the nameplate ESP rating, individual engine manufacturers can authorize a higher 24-hour average load factors if they desire.

Using the generator for more than 250hrs? Look at the other ISO 8528-1 Ratings.

What alternative ratings are there to Emergency Standby Power?

If the Emergency Standby Power Rating doesn't suit your requirements, you can consider buying a generator at an Prime Power (PRP), Limited-Time Running Prime (LTP) or Continuous Power (COP) rating.