Emergency power generators are an integral component in many fire and life safety systems. For this reason, NFPA 110, Standard for Emergency and Standby Power Systems, is referenced by many of the most widely used codes and standards.
NFPA 110 addresses performance requirements for emergency and standby power systems. These systems provide an alternate source of electrical power in buildings when the normal electrical power source fails. Emergency power systems are made up of several components that need to work together to make sure electrical power is restored. These include power sources, transfer equipment, controls, supervisory equipment, and accessory equipment needed to supply electrical power to the selected circuits.
This blog is meant to give an overview of the standard and its key chapters, but it’s not a replacement for reading and knowing the exact requirements of NFPA 110.
What is an emergency and standby power system?
In NFPA 110, there are two main terms used for emergency power or standby power. Those terms are emergency power supply and emergency power supply system.
The emergency power supply is the source of the electrical power and includes everything necessary to generate the power. This includes the fuel supply (energy source), the equipment used to convert the fuel to electrical energy (energy converter), as well as the necessary accessories, such as the starting system and batteries.
An emergency power supply system is a system that includes the emergency power supply as well as a system of conductors, disconnecting means, overcurrent protective devices, transfer switches, and all control, supervisory, and support devices up to and including the load terminals of the transfer equipment needed for the system to operate as a safe and reliable source of electric power.
Chapter 4 – Classification of Emergency Power Supply Systems
Emergency power supply systems are used in many different applications. Requirements that fit one situation might not be appropriate for another situation. When other codes or standards require an emergency power supply system, they typically call out the class, type, and level of system that is required. NFPA 110 contains the information for what these classes, types, and levels mean. Ultimately, these terms describe the capabilities of the system.
Class – The class describes the minimum time that the emergency power supply system is designed to operate at its rated load without being refueled or recharged. It’s measured in hours, so a Class 0.25 needs to be able to provide power for 15 minutes and a Class 6 needs to provide power for 6 hours. The only class that falls outside of these rules is a Class X, which needs to provide power for “other time, in hours, as required by the application, code or user.”
Type – The type describes the maximum time between when power is lost and when power is restored. This is measured in seconds, so a Type 10 needs to restore power within 10 seconds. There are two unique types that don’t follow this format. Type U, which needs to be basically uninterruptible—similar to an uninterruptible power supply system—and a Type M, which has no time limit and can be manually activated.
Level – The level has to do with whether or not failure of the equipment could result in the loss of life or serious injury. It’s pretty straightforward. If failure of the equipment could result in the loss of life or serious injury. then it’s a Level 1. Otherwise, the emergency power supply system is a Level 2.
The following table includes more information about classes, types, and levels.
Chapter 5 – Emergency Power Supply: Energy Sources, Converters, and Accessories
There are several different types of sources, or fuels, that can be used as an energy source, including liquified petroleum, liquified petroleum gas, natural gas, synthetic gas, and hydrogen gas. The most common is diesel fuel, which falls under the liquified petroleum category. Regardless of the type of fuel, it needs to be sized to 133 percent of the fuel required to run the generator for the time required by the class of the system.
An energy source can’t do much without being converted into electrical energy. This can be done through a variety of means that are categorized into two groups: rotating equipment (generators) and fuel cells.
Since reliability is one of the biggest concerns for an emergency power supply system, there are many requirements for equipment to be listed, designed, assembled, and tested to ensure it will function under emergency conditions.
Chapter 6 – Transfer Switch Equipment
A transfer switch does exactly what its name implies. It is a switch that, once activated, transfers the electrical load from one power source (normal power) to another (emergency power). They can be classified as an automatic transfer switch, a delayed automatic transfer switch, or a manual transfer switch, depending on the load being served and the required type of emergency power supply system.
Automatic transfer switches, as well as delayed automatic, constantly monitor the source of normal power so, in the event of a power failure, the transfer switch moves the electrical load to the emergency power supply system. Chapter 6 of NFPA 110 contains performance requirements for transfer switches and their associated equipment.
Chapter 7 – Installation and Environmental Considerations
There are a lot of factors that can affect the performance of an emergency power supply system, one of which is the correct initial installation. Chapter 7 addresses the location and environmental considerations of installation that are essential for successful startup and performance, as well as safe operation and utilization of the emergency power supply system. This includes the following considerations:
- Location
- Lighting
- Mounting
- Vibration
- Noise
- HVAC
- Cooling system
- Fuel system
- Exhaust system
- Protection
- Distribution
It is also crucial to know that the installed system will perform as expected without waiting for the initial operation to occur during the first power outage. Acceptance testing is required in order to confirm that the system will perform as required.
Chapter 8 – Routine Maintenance and Operational Testing
Emergency power supply systems are made of many components and subassemblies, all of which are required for reliable operation in order to provide emergency power in the event that primary power to a building is lost. The failure of one or more of these subsystems could compromise the ability of the emergency power system to deliver electricity in an emergency. For example, if the batteries in a diesel generator fail, then the entire system will not operate; in fact, battery failure is the most common cause of generator failure. Diligent maintenance of a building’s emergency power supply system, including routine inspections, system testing, and frequent maintenance, helps ensure proper operation.
Some of the key considerations for the inspection, testing, and maintenance of emergency power supply systems are discussed in this blog. In general, the emergency power supply system needs to be inspected weekly, exercised monthly, and tested at least once every 36 months.
NFPA 110 is a very commonly referenced standard and contains performance requirements for emergency power supply systems, most commonly generators. Hopefully this blog helped shed some light on the requirements and layout of the standard. For more information and training on NFPA 110, check out our online training as well as related certifications on the topic.