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NFPA 110: An Introduction

What is NFPA 110?

Planning around preventing or lowering the impact of power outages is a standard consideration for the resilience of a power grid. However, for some locations and grids, such as those serving critical health or safety functions, power outages for any length of time can put human lives at risk.

For this reason, the National Fire Prevention Association (NFPA) Standard 110, the Standard for Emergency and Standby Power Systems, was created. It outlines the requirements for designing and installing backup power systems for critical applications and covers emergency power systems' ongoing performance and maintenance.

In this blog, we’ll define some of the most important NFPA 110 terms, what it covers, major considerations, and how you can ensure compliance of your backup power systems with the standard.

Key Terms in the NFPA 110

EPS: The emergency power supply (EPS) provides the electrical power supply in your backup system. This is most often a generator, which is completely separate from your main power supply.

EPSS: The emergency power supply system includes everything that allows the EPS to function as a backup power source, including transfer switches, load terminals, conductors, supervisory equipment, and disconnecting and overcurrent protective devices.

AHJ: The “authority having jurisdiction” refers to whichever boards or agencies are responsible for applying construction codes and standards in your area (county, city, or state level).

Level: In the NFPA 110, two levels determine how critical your EPSS loads are for human life and safety. Level 1 is when a loss of power would result in "loss of life or serious injuries," and Level 2 is when the load is "less critical to human life and safety." Examples of a Level 1 NFPA 110 application would be ventilation equipment, fire pumps, and life safety illumination, while examples of Level 2 applications would be sewage disposal or heating and ventilation systems.

Class: Class in the NFPA 110 determines how long the EPSS must be able to run, without refueling, at its fully rated load. For example, a Class 6 EPSS would have to be able to run for six hours without being refueled, while a Class 24 would need to be able to go for 24 hours.

Type: This refers to how long, in seconds, it takes for all the Level 1 and Level 2 loads to be transferred to the EPSS. For example, for Level 1 loads, the standard is 10 seconds, so these EPSS are called Type 10. For less critical loads, a restoration time of 120 seconds, or Type 120, might be acceptable. There are also classifications of Type U for uninterruptible power systems and Type M for manual stationary (i.e., non-automatic) EPSS.

The Scope of NFPA 110

The NFPA 110 applies to the entire EPSS covering Level 1 and 2 loads, namely the power source (generator) and the equipment (controls, switchgear, conductors, circuit breakers etc.) that supply that power to the required circuits. Within the scope of NFPA 110 are the requirements for the installation, inspection, maintenance, and testing of relevant EPSS up to the load terminals of the transfer switch. It is not possible for individual components to be signed off as NFPA 110 compliant, only the entire EPSS can be certified, which must be installed, maintained, tested and operated in line with NFPA 110 guidelines.

There are legal obligations to comply with NFPA 110 in situations where the protection of human life is concerned (Levels 1 and 2.) Regardless, it is also considered best practice for designing EPSS in other situations. Though Levels 1 and 2 explicitly cover applications that would affect human health and safety, there are also many other applications, such as pharmaceutical manufacturing or data centers, where power outages could result in very large financial losses. Although NFPA 110 is not obligatory in these cases, it has become an adhered-to standard for designing, installing and maintaining EPSS.

Important Considerations for NFPA 110

Fuel Storage: With the Class determining the EPSS' required running time without receiving fuel, some applications may have to plan for large quantities of stored fuel. For example, a Class 72 EPSS could require thousands of gallons of fuel stored which requires large-scale planning for maintenance, optimum storage conditions, and the major health and safety implications of the store itself.

Running Situations: As the EPSS classified under NFPA 110 are, by nature, designed to be run in less-than-optimal conditions; therefore, it is critical to design the EPSS to be run in flood, earthquake, or fire situations. Depending on the threat matrix affecting your application, these may require extensive subsidiary applications.

Room Temperature: Section 5.3.5 of the NFPA 110 gives the requirements for the room temperature for where the EPSS is stored. It outlines the need for ventilation for indoor generators, with venting for heat created by the engine radiator, alternator, and exhaust system. Under non-operational conditions, NFPA 110-19 clarified that 40°F was the optimum room temperature.

Starting Batteries: NFPA 110-19 also clarified the guidance regarding starting batteries. While generally, generators will have both a mechanically-driven charger/alternator and a separate AC-powered battery charger, previous guidance suggested the mechanical charger could be omitted in certain situations. This exception has been removed, with the redundancy of dual starting batteries as the advised approach.

How to Comply with NFPA 110

Compliance with NFPA 110 begins with your work in designing and installing the EPSS with the system manufacturer and installer. However, your EPSS is not compliant immediately after installation. This compliance must be proved to the AHJ after installation, through a program of testing. These are known as acceptance tests, and if passed are followed by two-hour load tests to ensure the EPSS is capable of operating up to its rated capacity. Upon passing these, the EPSS will then be warranted and commissioned by your AHJ.

Ongoing maintenance of your EPSS is covered in Chapter 8 of the NFPA 110, and contains recommendations for weekly, monthly, quarterly, and annual inspection and maintenance tasks. These should take into account the manufacturer’s recommendation, relevant equipment instruction manuals, the minimum requirements of Chapter 8 NFPA 110, and the requirements of your AHJ.

To find out more about installing, maintaining, testing, and inspecting emergency power supply systems for critical loads in order to gain compliance with NFPA 110 reach out to our highly experienced team.



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