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Generators – Standby vs. Prime

A reliable generator, also known as a generator set or gen set, is one of the most important pieces of equipment that a commercial business, healthcare organization, educational institution or any organization that serves a large number of people can purchase. After all, a loss of power for even a short period of time can severely impact the organization’s ability to function. In the case of a hospital, a power outage could jeopardize the safety and even the lives of its patients. Before purchasing a generator for your organization, however, it is essential to have at least a basic understanding of its power rating, particularly in terms of standby vs. prime generators.

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What Are Generator Power Ratings?

Generator ratings are established by gen set manufacturers to guide purchasers and end-users in the generator selection process. Essentially, ratings are defined in terms of factors such as hours of usage on an annual basis, maximum available power, average load factors and the type of applications that best suit the generator’s capabilities. ISO 8528 is the international standard that was developed to ensure consistency among gas and diesel generator gen set ratings; although, the manufacturers have the final say in determining the ratings for their particular products.

Gen Set Rating Classifications

ISO 8528 identifies four different generator rating classifications: continuous, prime, limited-time power, and emergency standby. Caterpillar® employs two additional classifications to further define the ratings for its generator products.

Continuous – As the term implies, continuous power generators are designed to provide power on an ongoing basis throughout the year. The average output of a continuous power gen set is 70 to 100 percent of the rating and is designed to provide 100-percent power for every operating hour during the year. Continuous power gen sets are best used in situations where a limited amount of power load fluctuation occurs.

Prime – Prime gen sets also provide ongoing power, but unlike continuous generators that are designed for limited load fluctuations, prime generators can accommodate varying loads on an unlimited basis throughout the year. However, the average load factor cannot exceed 70 percent of the prime rating.

Limited-Time – Gen sets with a limited-time power rating are designed to operate at a maximum of 500 hours per year, although they can effectively manage an average load factor of up to 100 percent.

Mission Critical Standby – This Caterpillar-specific rating is intended to comply with the higher standby power requirements that apply to entities such as data centers. Cat® MSP gen sets provide an average load factor of 85 percent, as opposed to the 70 percent offered by ESP generators.

Emergency Standby – ESP gen sets are designed to provide a short-term power solution when an unexpected loss of a continuous or prime power source occurs. ESP-rated generators are generally intended to operate at a maximum of 200 hours per year at an average load factor of 70 percent. Additionally, the average power output should not exceed 70 percent in any 24-hour period.

Standby – Cat standby gen sets differ from ESP units in that they are designed to provide emergency power for the duration of an outage. The average load factor of these gen sets is 70 percent, with a maximum operating time of 500 hours per year.

Comparing Standby vs. Prime Generators

As you can see, a significant difference in standby vs. prime generators is that the former are intended to provide emergency power on a short-term basis, while the latter can meet an organization’s year round power needs.

Contact Alban CAT to Learn More About Standby vs. Prime Generators

Alban CAT Power Systems can provide reliable answers to your questions about standby vs. prime generators.

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