Emergency and standby power systems provide electric power to critical loads in commercial, industrial, and institutional buildings. Personnel who test and maintain these systems for occupancies such as health care facilities, systems such as fire alarm systems, and equipment such as data processing systems should know requirements beyond the general ones. The local authority having jurisdiction (AHJ), other governmental entities having authority over the installation, insurance companies, installation-specific industry codes, standards, recommended practices, or manufacturers may impose these requirements.

Emergency power systems defined

The Institute of Electrical and Electronics Engineers (IEEE) defines an emergency power system as “an independent reserve source of electric energy that, upon failure or outage of the normal source, automatically provides reliable electric power within a specified time to critical devices and equipment whose failure to operate satisfactorily would jeopardize the health and safety of personnel or result in damage to property.”

National Electrical Code (NEC) Section 700-1 defines an emergency power system as any that is intended to provide illumination and power necessary for the safety of human life when the normal source of power to a building or portion of a building is interrupted. This corresponds to the National Fire Protection Association (NFPA) 110 definition of a Level 1 emergency power system, which is the Standard for Emergency and Standby Power Systems. The NEC is actually NFPA 70, and NFPA publishes both the NEC and NFPA 110, which are meant to be complementary.

Emergency power systems are typically installed where lighting is required for safe exiting and panic control. Other loads the NEC and NFPA 110 noted as potentially essential to protecting human life and served by the emergency power system include life safety and security systems, emergency communications systems, elevators, and others.

NEC Section 701-2 defines a legally required standby power system as one that provides power to building loads that could result in hazards to human life or hamper firefighting or rescue operations when the normal source of power is interrupted. The NEC’s legally required standby power system is equivalent to NFPA 110’s Level 2 emergency power system. Both the NEC and NFPA 110 list a number of loads such as ventilation and smoke removal systems, communication systems, and others as examples of the types of loads that could impact emergency operations if power is interrupted.

Standby power systems defined

IEEE’s definition in Standard 446 corresponds to NEC 702-2’s definition as one that is intended to protect loads that are critical to the owner’s business, but do not impact life safety. Such loads can include communication and data processing systems and manufacturing and process operations, among others.

Required testing

Acceptance testing is required in NEC Paragraphs 700-4(a) and 701-5(a) for emergency and legally required standby systems, respectively. According to the NEC, the local AHJ should perform or witness such testing. Acceptance testing is performed after system installation and before the emergency and standby systems are put into full operation.

Frequency of testing

Neither NEC Paragraphs 700-4(b) nor 701-5(b) give the required schedule for testing emergency and legally required standby power systems. The only requirement is that testing be performed regularly at a frequency acceptable to the local AHJ. Normally, manufacturers’ testing recommendations will satisfy the local AHJ.

Manufacturer recommendations for testing emergency and standby power systems should be viewed as a minimum. NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, addresses the frequency of inspecting and testing electrical equipment in Paragraph 4-4.4.7, which notes that the needed inspection and testing schedule for the same electrical equipment may vary greatly depending on its physical environment and operational demands. For example, a generator serving typical building emergency loads can probably be tested monthly. However, a generator serving loads where a power loss may endanger production workers should be tested before each shift. Similarly, IEEE Standard 446-1995, IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications, suggests that the manufacturer’s recommended maintenance schedule be used to establish a test and maintenance program, then modified.

NFPA 110, Section 6.4 provides requirements for frequency of operational inspections and testing for both emergency (Level 1) and legally required standby systems (Level 2). In general, NFPA 110 requires weekly inspection and monthly testing under load. NFPA 110, Appendix A provides a suggested maintenance schedule.

Required full-load testing

NEC Paragraph 700-4(e) requires that the means must be provided to test emergency lighting and power systems under the maximum load anticipated. The requirements for load testing legally required standby power systems are not as stringent as those for load testing emergency power systems. In accordance with NEC Paragraph 701-5(e), legally required standby systems only have to be tested under load and not for the maximum load anticipated. Since both emergency and legally required standby systems are usually combined into a single emergency system in most buildings, the distinction between the load that each must be tested under is moot, and the combined system must be tested in accordance with the more stringent load requirements for emergency systems.

Full-load testing shows if an emergency or standby system will function properly when needed. Full-load testing of emergency and legally required power sources can be accomplished by installing a load bank that is equal to the anticipated maximum load or, better yet, to the power source rating. This protects sensitive electronic equipment from possible damage and downtime from transfer between the normal and emergency power sources. However, even if a load bank is provided, the emergency or legally mandated standby power system should be tested using the actual load to ensure whole-system operation.

NFPA 110, Section 6.4 provides specific requirements for how emergency and legally required standby power systems are to be tested under load. These systems are to be tested monthly for at least 30 minutes under specified loads, as described in Section 6.4. In addition, generator load tests are to include cold starts. When developing a testing and maintenance program for emergency and standby generators, NFPA 110 Section 6.4 should be used.

Testing and maintaining system components

Automatic transfer switch. NFPA 110 requires that automatic transfer switches (ATSs) be maintained in Paragraph 6-3.5. It should include at least:

* Checking all connections for proper tightness

* Inspecting for overheating

* Inspecting for contact erosion or other damage

* Cleaning and removing dust or dirt

NFPA 110, Paragraph 6-4.5, also requires that ATSs associated with emergency (Level 1) and legally required standby (Level 2) power systems be operated at least monthly. This test requires that the ATS be electrically operated from the normal position to the backup position and then back to the normal position. If this test is not carried out under normal load, both the normal and emergency power source must be scheduled for shut down. Otherwise, a bypass switch can be installed to isolate the ATS switch while maintaining power to the critical load during the test.

A generic maintenance plan for an engine-generator set and its associated systems is provided in Appendix A of NFPA 110.

NFPA does not specify how to perform these inspections and tests, so consult the manufacturer’s operation and maintenance (O&M) manuals. IEEE Standard 446 also discusses operating factors that affect engine-generator maintenance and includes a typical maintenance schedule in Section 8.4.

Circuit breakers. NFPA 110 Paragraph 6-4.6 requires low-voltage circuit breakers between the engine-generator set and the load terminals of the ATS to be manually operated at least annually under no-load conditions for emergency (Level 1) power systems. Further, Appendix A of NFPA 110 recommends testing circuit breakers under simulated overload conditions every two years. Section 18-10.2 of NFPA 70B provides additional information.

Battery systems. In addition to NFPA 110 requirements, NEC Paragraphs 700-4(c) and 701-5(c) require that batteries used as part of an emergency or legally required standby power system are maintained.

Unit equipment. In too-small buildings for a central system, battery-operated units connected to the lighting branch circuit serving the space provide the required emergency lighting and exit signage. These units contain an integral battery, charging system, and transfer device. The NEC calls this “unit equipment,” and the required installation and operation requirements for this type of emergency lighting is provided in NEC Paragraph 700-12(e). Unit equipment includes emergency ballasts incorporated into standard lighting fixtures. NFPA 101, Paragraph 5-9.3 requires that unit equipment be individually tested every 30 days for at least 30 seconds and annually for 11/2 hours. The only exception is self-testing unit equipment that automatically performs the required test and indicates test failure.

Required record keeping

Written records must be kept for all emergency and legally required standby power system inspections, tests, and maintenance and made available to the local authority having jurisdiction for review. NEC Paragraphs 700-12(d) and 701-5(d) require them for emergency and legally required standby power systems, respectively. NFPA 110, Paragraph 6-3.4, however, specifies the information to include:

* Date of the inspection, test, or maintenance

* Service personnel performing the inspection, test, or maintenance

* Record of any problems encountered, repairs made, and parts replaced

* Record of testing the repair as recommended by the manufacturer

In addition, generic forms for logging routine maintenance, operation, and testing are provided in Appendix A of NFPA. Similarly, Figure F-11 in Appendix F of NFPA 70B provides a wet-cell battery record that can be used to record weekly and quarterly cell readings.

NFPA 101, Paragraph 5-9.3 requires written records to be kept for all inspections, tests, and maintenance carried out on battery-powered emergency lighting.


This article is the result of ongoing research into the development of service contracting business by electrical contracting firms sponsored by the Electrical Contracting Foundation, Inc. The author would like to thank the foundation for its continuing support.

GLAVINICH is Chair and Associate Professor of Architectural Engineering at The University of Kansas. He can be reached at
(913) 268-8442 or tglavinich@ukans.edu.