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Understanding Emergency & Standby Power for Commercial Facilities and Buildings

Generators have a wide range of options, come in different shapes and sizes, and are used for all kinds of applications in commercial facilities around the world. Almost every large building has one installed or the facility manager is thinking about how to get one. Understanding all these variables and how they factor into your operation can be a major challenge. Generator Source has been working with large generator sales and service for many decades. This article expands on some common generator features and attempts to explain the primary differences in rating types, how to obtain redundancy in your system, and also discusses the typical power configuration most businesses and buildings utilize such as UPS and automatic transfer switches.

Generator Rating BasicsCummins Generators used in Parallel Operation

Most generators are manufactured in four basic ratings. These ratings define the amount of time the generator is designed to operate. Ratings are clearly stamped on the generator identification tag. It is important to understand the ratings when understanding the setup of a facility. Cummins generator ratings are featured below:
  • Emergency Standby Power (ESP) - Used to supply power to a varying electrical load during a utility interruption
  • Limited-Time Running Power (LTP) - Used to supply power to a constant electrical load for limited operation
  • Prime Power (PRP) - Used to supply power to a varying electrical load for unlimited hours of operation
  • Base Load (Continuous) Power (COP) -Used to supply power to a constant load for unlimited hours of operation
The lion's share of industrial buildings that require emergency or standby power is on the utility power grid. Generators with the ESP ratings are used in these facilities. These generators can be paralleled for multiple generator use. Remote communities in Canada depend totally on diesel generators for power. An ESP generator can be used as a backup when a primary generator is down for maintenance or repairs.

The use of the building or complex determines if it falls under an emergency or standby classification. An ESP rated generator is rated to assume the load when utility power fails. The generator is the main component in both classifications. However, the electrical/electronic equipment is different.

The terms emergency and standby are often switched with one another causing confusion. The National Fire Protection Association (NFPA) maintains standards for all buildings. NFPA 110 is the Standard for Emergency and Standby Power Systems. Go to NFPA 110 to subscribe or purchase complete document. This article will supply some definitions and examples featuring both emergency and standby power.

Emergency Power and Building Redundancy

Generator Automatic Transfer Switch
Both emergency and standby power systems are classified as Emergency Power Supply Systems (EPSS) by the NFPA. They divide the supply systems into two levels. Emergency power is often considered a Level 2 system. "Level 2 systems shall be installed where failure of the EPSS to perform is less critical to human life," and is defined in NFPA 110, 4.4.2.

Local authorities, such as building inspectors and/or fire marshals, should always be consulted to determine if the building is in compliance with all regulations. Level 2 or Emergency Power systems are installed in facilities that require minimal power during utility outages. Systems such as elevators, emergency lighting (egress & design dependent), fire and alarm monitoring are normally powered during outages. 

Buildings that employ emergency power systems are considered among the most basic in the equipment line up. However, correct operation is vital to ensure human safety during utility failure. Some of the equipment used in emergency power systems is:
  • Generator (EPS rating) - Generator commonly fueled by diesel or natural gas. Can be indoor or outdoor style.
  • Automatic Transfer Switch (ATS) - Transfers load from utility power to generator power when utility power fails. When utility power is restored, transfers load back.
  • Distribution Panel - Often has switching and circuit protection capabilities. Connected to circuits in the emergency power network. Individual cable routings can be required.


An industrial bearing manufacturer has an automated plant with many pieces of equipment and supporting auxiliary systems. The business plan dictates total plant shutdown during a utility power failure. A basic equipment array supplies power to emergency lighting and safety systems to ensure personal egress. A diesel generator is fueled by natural gas and team main rooms are on emergency lighting for extended utility outages. 

When utility power fails, all production equipment and supporting auxiliary systems shut down. Production personnel exit factory. Remote auxiliary spaces have battery backup lighting for personal egress. Main spaces are equipped with egress lighting. Skeleton crew stays in team rooms with emergency lighting. When utility power is restored, skeleton crew starts auxiliary systems and production equipment. The production staff is notified of power restoration.

Standby Power, UPS & Automatic Transfer SwitchesAdvanced Control Room Nuclear Power Plant

Hospitals, Airport Control Towers and Power Plants are examples of buildings that are required to have a standby power system. Standby systems are more advanced and have more equipment to support facility operation. These buildings are considered a Level 1 system. "Level 1 systems shall be installed where failure of the equipment to perform could result in loss of human life," and is defined in NFPA 110, 4.4.1.

Any generator requires a short start-up time to assume the load. During this time a brief power loss occurs. Many pieces of advanced life-support and process equipment are sensitive to power loss. A standby power system must supply power to all critical systems without interruption. EPS rated generators are often connected in parallel for to assume the load. Some of the equipment that can be used in these systems is:
  • Uninterruptible Power Supply - This is a battery backup circuit that assumes the load, while the generator starts, during utility power failure. An in-circuit inverter is used to change DC to AC as the UPS assumes the load to critical equipment. UPS switches to charging mode once the generator assumes the load. Multiple UPS systems can be used in a building.
  • Master Paralleling Control Panel - Each generator is equipped with an individual control system. Paralleling control panels parallel multiple generators to assume the load. Can automatically parallel all generators, including redundant start and stop functions.
  • Distribution and Control Panels - These panels can contain, automatic switching (such as ATS), manual switching, circuit protection, alarm monitoring & systems controls to name just a few. Size and equipment list are only determined by the needs of the building power system.


A remote community in Canada is totally dependent on diesel engines from the local power company. The company operates multiple generators in parallel with a redundant backup design. During high power demand, a generator fails. This causes a temporary power failure while a redundant generator is placed on-line. UPS assumes the load in buildings with critical power requirements. Generators start, parallel, and assume the load from utility power and UPS. When power is returned, generators shut down.

Generators Provide Redundancy & Piece of Mind

For more complex backup power systems, like the ones you often see in data centers and large hospital campuses, there are a wide range of additional details to factor in. A generator is a key cog but many other factors can also be taken into consideration so you essentially build in backups for the backups. One trend being pushed towards hospitals is requiring standby generators for each backup generator they have to protect from failure of the primary backup. This sounds (and is) fairly extreme but there are times when one or more pieces in a system can fail so these high-level operators need to take all this into account and discuss with qualified engineers and planners.

Generator Source can help you understand the endless options and what kind of power generation system is ideal for your operation.  We always have a large inventory of industrial and commercial generators in-stock that are ready for immediate delivery. Contact Us with any questions.

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