Caterpillar Generator Set Ratings vs ISO8528-1
07 Nov 2023
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Caterpillar defines five basic generator set ratings: Emergency Standby Power (ESP), Standby, Mission Critical Standby, Prime, and Continuous.
See how Cat generator set ratings compare against those defined by the industry standard ISO8528-1 in the table below.
ISO 8528-1:2018 defines various classifications for the application, rating and performance of reciprocating internal combustion engine driven alternating current generator sets.
| ISO 8528-1 vs Caterpillar Ratings | |||
| ISO 8528-1 Rating | Caterpillar Rating | ||
| Rating | Definition | Rating | Definition |
| Emergency Standby Power (ESP) |
The maximum power available during a variable electrical power sequence, under the stated operating conditions, for which a generating set is capable of delivering in the event of a utility power outage or under test conditions for up to 200 hours of operation per year with maintenance intervals and procedures being carried out as prescribed by the manufacturer.
The permissible average power output over 24 hours of operation shall not exceed 70% of the ESP rating. |
Emergency Standby Power (ESP) |
Typical usage of 50 hours per year with a maximum of 200 hours per year with varying loads.
Average variable load factor is 70% of the ESP rating.
No overload is available.
Not for maintained utility paralleling applications. |
| No ISO equivalent | Standby Power |
Typical usage of 200 hours per year, with a maximum of 500 hours per year with varying loads.
Average variable load factor is 70% of Standby rating.
No overload is available.
Not for maintained utility paralleling applications. |
|
| Mission Critical Standby |
Typical usage of 200 hours per year, with a maximum of 500 hours per year with varying loads.
Average variable load factor is 85% of Standby rating.
Typical peak demand of up to 100% of the rating for 5% of the operating time.
No overload is available. Not for maintained utility paralleling applications.Typical application is data centers and healthcare. |
||
| Limited Time Running Power (LTP) | The maximum power available under the agreed operating conditions, for which the generator set is capable of delivering for up to 500 hours of operation per year with the maintenance intervals and procedures being carried out as prescribed by the manufacturer. | Load Management Guidelines (Prime Power Rating) |
Load management is the deliberate control of loads on a generator set and/or utility to have the lowest possible electrical costs.
Maximum of 500 hours per year with varying loads.
Maximum load factor is 100%.
Typical application is peak shaving. |
| Prime Running Power (PRP) |
The maximum power which a generator set is capable of delivering continuously whilst supplying a variable electrical load when operated for an unlimited number of hours per year under the agreed operating conditions with the maintenance intervals and procedures being carried out as prescribed by the manufacturer.
The permissible average power output over 24 hours of operation shall not exceed 70% of the PRP rating. |
Prime Power |
Unlimited hours of usage.
Average variable load factor is 70% of the Prime Power rating. 10% overload available, but limited to 1 in 12 hours and not to exceed 25 hours per year. The 10% overload is available in accordance with ISO 3046-1.
Life to overhaul of the engine is dependant on operations as outlined in ISO8528-1, and time spent during operation above 70% load may affect the life to overhaul. |
| Continuous Operating Power (COP) | The maximum power which the generator set is capable of delivering continuously while supplying a constant electrical load when operated for an unlimited number of hours per year under the agreed operating conditions with the maintenance intervals and procedures being carried out as prescribed by the manufacturer. | Continuous Power |
Unlimited hours of usage.
Non-varying load factor is 70% - 100% of the published Continuous Power rating. Typical demand is 100% of the continuous rating for 100% of the operating hours. |
Read more on how Caterpillar defines the 5 different generator set ratings here.
See our full range of generator sets here.
