NFPA Today - September 18, 2020

Maintaining Your Emergency Power Supply System is Critical, Particularly during Hurricane Season

According to the U.S. Energy Information Agency, nearly all electrical customers experience at least one electrical utility outage each year. On average, each outage lasts 60 minutes or more. As we are in the peak of hurricane season that seems to worsen year after year and some grids imposing rolling blackouts due to a strain on the grid and to reduce the risk of wild fires, it is more important than ever that we prepare for a loss of power in our buildings. Emergency and standby power systems are an integral part of the fire and life safety approach within a building because they provide reliable backup to the utility and deliver electricity to critical building systems such as fire pumps, emergency lighting, elevators, fire alarm systems, and other critical equipment during a utility interruption.

Emergency power supply system

Each emergency power supply system comprises complex subsystems with many internal components, 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. Diligent maintenance of a building's emergency power supply system, including routine inspections, system testing, and frequent maintenance helps ensure proper operation.

Emergency power supply

The emergency power supply is what provides the emergency power in the system. Power supplies are designed to ensure that they can provide enough power to all of the systems in the building requiring emergency power. The most common form of emergency power is a generator that is fueled by diesel, natural gas, propane, or gasoline.

Am I required to complete inspection, testing, and maintenance?

The requirements of NFPA 110, Standard for Emergency and Standby Power Systems cover installation, operation, maintenance, and testing for the proper performance of the emergency power supply system. The requirements from this standard are invoked by direct reference in several major codes and standards, including NFPA 101, NFPA 99, the NEC, and the International Building Code.

What does the inspection, testing, and maintenance of my emergency power supply system entail?

First of all, it is important to note that all inspection, testing, and maintenance (ITM) needs to be performed by a qualified person.  This is a person who has skills and knowledge related to the operation, maintenance, repair, and testing of the EPSS equipment and installations and has received safety training to recognize and avoid the hazards involved. That being said, some of these tests can be completed by a competent owner or facility management with the proper training, or a separate contractor can be hired.

ITM on the emergency power supply system it is important to follow all the manufacturers recommendations and instructions as well as any specific requirements from the Authority Having Jurisdiction. Here the focus will be on the major ITM requirements found in Chapter 8 of NFPA 110.

Some of the key considerations for ITM are discussed below in detail, but, in general, the emergency power supply system needs to be inspected weekly, exercised monthly, and tested at least once every 36 months.

Transfer switches and paralleling gear

Transfer switches and paralleling gear needs to be inspected, maintained, and tested including checking connections, looking for signs of overheating, removal of dirt and dust, and replacement of contacts where required and verifying that the system controls will operate as intended.

Storage batteries

Storage batteries need to be inspected weekly (including the electrolyte levels and battery voltage) and maintained in compliance with the manufacturer's specifications. A battery load test should be conducted quarterly, and a monthly recording of the electrolyte specific gravity needs to be taken.


A Fuel quality test needs be completed at least annually to ensure that the fuel is not degrading.  

Monthly exercise

A monthly exercise under load needs to be conducted to ensure the system remains operational. The generator set should never be idled for periods of time because a condition known as wet stacking can occur in generator sets (specifically diesel) that are not run under load. Wet stacking occurs when unburnt fuel is able to pass through the combustion chamber and build up within the exhaust of the engine. The following procedure should be used to help record each monthly exercise:

  1. Record run time on run time meter
  2. Simulate normal power failure from test switch on the automatic transfer switch, or by opening normal power supply
  3. Observe and record time delay on start
  4. Record cranking time
  5. Transfer the load to the generator
  6. Record ac voltage, frequency, amperage, and kW
  7. Record initial oil pressure and battery charging rate
  8. Record oil pressure, battery charging rate, and water or air temp after 15 minutes of running
  9. Return test switch to normal or reestablish normal power supply after a minimum run time of 30 minutes
  10. Record prime mover and ac instruments just prior to transfer
  11. Record time delay on re-transfer
  12. Record time delay on shutdown for units so equipped
  13. Place unit in automatic operation mode

When you are performing the test, it is important to pay attention to the maximum ambient temperature in the generator room and ensure that it does not go above the maximum specified by the manufacturer as well as ensure that any shutters (if provided for combustion and ventilation air) are working properly and are not blocked.

36-month test

Level 1 Emergency Power Supply Systems (EPSS) (Level 1 means the failure of the EPSS could result in loss of human life or serious injury, Level 2 systems are those that a failure is less critical to human and life safety) need to be tested at least once every 36 months for the duration of its assigned class but is not required to exceed 4 hours. The intent of this requirement is to provide reasonable assurance that the EPSS with all of its auxiliary subsystems is capable of running for the duration of its assigned class with its running load. The class rating of an emergency power supply system indicates the duration it is designed to run for without refueling, for example a Class 2 is designed to run for 2 hours without being refueled, and a class 48 is designed to run 48 hours without being refueled.


As with all ITM that is performed on fire and life safety systems, records need to be created and maintained for all inspections, operational tests, exercising, repairs, and modifications.


The EPSS needs to be maintained in accordance with the manufacturers instructions to ensure that the system is capable of supplying power within the time specified for the type (see table below) and for the time duration required by the class. If any maintenance is performed on any portion of the emergency power supply system, a 30 minute operational test needs to be performed after maintenance or repair has been performed to ensure that they system is still operational.

Are you performing all of the required ITM on your Emergency Power Supply System? Do you have a time in which you lost power in your building and utilized Emergency Power? Let me know in the comments below.

Want to learn more about inspecting, testing, and maintaining emergency lighting? Check out an article I wrote in NFPA Journal on verifying the emergency lighting and exit marking when reopening a building.

If you found this article helpful, subscribe to the NFPA Network Newsletter for monthly, personalized content related to the world of fire, electrical, and building & life safety

Sign up for the NFPA Network Newsletter
Shawn Mahoney
Technical Services Engineer with a masters degree and PE in fire protection supporting subjects throughout the association

Related Articles