The Institute of Electrical and Electronics Engineers (IEEE) defines an uninterruptible power supply (UPS) as a system designed to provide power automatically, without delay or transients, during any period when the normal power supply is incapable of performing acceptably. UPS systems permeate modern commercial, manufacturing, and industrial facilities and provide a constant and steady source of power to your customer’s critical loads. Critical loads are those that are key to your customer’s business. These critical loads are often sensitive electronic equipment that provides data processing, communications, and control functions that are key to your customer’s business and production processes.

However, your customers also use UPS systems to protect sensitive production processes where a momentary electrical outage or transient can damage work in process and could be very costly in terms of lost product, raw material waste, delays in production, rework, and the resulting loss of customer goodwill.

Your customer’s key business and production processes must run 24¥7 and are dependent on a reliable and high-quality power supply. UPS systems provide a buffer between the protected load and the distribution system that serves that load. The primary purpose for installing a UPS system is to protect critical loads from long-term power disturbances, such as voltage sags and swells as well as outright outages. However, UPS systems also provide isolation and power conditioning that protect these same critical loads from fast transients such as surges and dips.

Unlike other electrical equipment in the building, UPS systems stand by silently until they are needed. UPS systems are built to be very reliable but, like any piece of electrical equipment, can fail when needed due to misapplication, abuse, age, or neglect. UPS systems must be maintained and tested regularly to ensure that they will be available when needed.

Who should perform UPS maintenance?

Only qualified persons should perform maintenance work on a UPS system. The National Electrical Code (NEC) defines “qualified person” in Article 100 as one that is familiar with the construction and operation of the equipment and the hazards involved. This simple definition is appropriate for determining who should perform UPS maintenance and testing. Only knowledgeable service personnel that understand the UPS installation and operation should be charged with maintaining it.

Poorly performed maintenance can be worse than no maintenance, because it can prevent problems from being detected and corrected before they impact the operation of a critical load, which could be missed and lead to system failure. In addition, improperly performed maintenance can introduce problems into the system that will either result in an immediate failure when the UPS system is placed back into service or become a latent problem that will result in future system failure. Service personnel must also understand the overall operation of the customer’s system so that critical loads are either properly shut down during maintenance or transferred to an alternate power source without an unexpected forced outage or damage.

How should UPS maintenance be performed?

UPS maintenance and testing must be performed in accordance with manufacturer’s recommendations and industry standards. Personnel performing UPS testing and maintenance must thoroughly understand the customer’s power distribution and UPS systems, the nature and operation of critical loads, and how to perform the work.

UPS systems are not all the same even though they seem to have the same components and perform the same function. Different UPS systems operate differently due to the way that they are designed and built. Service personnel must be familiar with the construction and operation of the UPS system that they are working on. They should also thoroughly understand UPS manufacturer-recommended maintenance and test procedures as well as formal training and manufacturer certification where necessary.

In addition to knowledge and skills, service personnel must also have the necessary tools and equipment to perform UPS maintenance and testing and avoid damage to the UPS system and its components. When in doubt, the manufacturer should be consulted regarding the proper selection of tools and test equipment. Custom or specialized tools supplied by the UPS manufacturer for the UPS system being maintained should always be used. Service personnel should also have detailed written test procedures, technical manuals, and at least a one-line diagram of the customer’s distribution system readily available when performing preventive maintenance on the UPS system.

When should UPS maintenance be performed?

The regular maintenance and testing of UPS system is really what is routinely referred to as preventive maintenance (PM). IEEE defines PM as the practice of conducting routine inspections, tests, and servicing so that impending trouble can be detected and reduced or eliminated (IEEE 1996). Since UPS systems operate continuously, preventive maintenance is typically time based rather than use based.

In other words, electrical equipment, such as static UPS systems, are recommended to be maintained at fixed time intervals such as daily, weekly, monthly, or annually irrespective of the amount of use during the designated time period. Other electrical equipment has recommended preventive maintenance intervals based on use where maintenance intervals are determined by run time rather than time since the last maintenance. Parts of rotating machinery subject to wear and tear from use often require use-based preventive maintenance.

Many times, recommended preventive maintenance for electrical equipment can be a hybrid time- and use-based program, depending on the subsystems and components involved. A rotary UPS system might be an example of electrical equipment that has a hybrid preventive maintenance program because rotary UPS systems include both static and mechanical subsystems.

What preventive maintenance should be performed?

As noted above, PM for a particular UPS system should always be performed in accordance with the manufacturer’s recommendations and specified procedures. This ensures that the manufacturer’s warranty on the equipment remains intact as well and that the unique aspects of the UPS system are addressed. Based on the operating characteristics of the components used in the UPS system, the design, and field experience, the manufacturer understands what needs to be monitored and what PM actions should be taken to avoid possible failure.

In addition to manufacturer recommendations for UPS system preventive maintenance, two industry-recommended practices can provide guidance to service personnel maintaining UPS systems. These recommended practices should be viewed as the minimum PM required and manufacturer recommendations should always take precedence. If there appears to be a conflict between the generic recommended practices and UPS manufacturer recommendations, the manufacturer should be contacted to determine the appropriate PM practice for the particular UPS system being maintained.

What two industry-recommended practices address UPS preventive maintenance?

* NFPA 70B, the Recommended Practice for Electrical Equipment Maintenance, is published by the National Fire Protection Association. The 1998 edition is the current one. Its purpose is to reduce hazards to life and property that can result from failure of industrial-type electrical systems and equipment (NFPA 1998). NFPA 70B is not intended to supersede manufacturer recommendations and the systems and equipment covered are intended to be those that are typically installed in commercial, industrial, and institutional facilities.

Chapter 22 of NFPA 70B is dedicated to the testing and maintenance of UPS systems and addresses general UPS maintenance procedures, UPS component testing, and UPS system testing. Maintenance and test recommendations and intervals for a variety of UPS components and subsystems are covered including disconnecting means, bypass switches, transfer switches, circuit breakers, batteries and chargers, rectifiers and inverters, motors, and generators, among others.

Where the maintenance and testing of UPS subsystems and components are addressed in other parts of NFPA 70B, Chapter 22 refers the reader to the applicable section. For example, the maintenance and testing of lead acid batteries and chargers is covered in Chapter 6 of NFPA 70B and the maintenance and testing of rotating machinery, such as motors and generators, is covered in NFPA 70B, Chapter 14. Recommended administrative practices such as coordination with users of critical equipment served by the UPS and keeping a maintenance log are also covered.

* IEEE Standard 446, the Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications, is a part of the IEEE’s Color Book Series that addresses various aspects of commercial and industrial power systems. Therefore, it is often referred to as the Orange Book. The 1995 edition is the latest one of this standard. The purpose of IEEE Standard 446 is to present recommended engineering principles, practices, and guidelines for the selection, design, installation, application, operation, and maintenance of emergency and standby power systems.

Recommended maintenance procedures and intervals for both static and rotary UPS systems are provided in Section 8.5 of IEEE Standard 446. Typical maintenance schedules and recommended weekly, monthly, quarterly, and annual tests and inspection lists are provided for these UPS systems. As noted in IEEE Standard 446, however, the typical maintenance schedules are only intended to be a guide and may be incomplete. The actual maintenance schedule used to maintain a specific UPS system should account for manufacturer recommendations, the critical systems that it serves, the physical environment in which it operates, the frequency that it is required to operate at, and ongoing operational experience.

NEC-required UPS preventive maintenance

In general, the NEC is focused on the installation of electrical equipment and conductors for safety and not the ongoing maintenance and testing of electrical systems. However, NEC Paragraph 90-1(b) states that both compliance with the NEC on the initial electrical installation and proper maintenance throughout the electrical installation’s life will keep it essentially free from hazard. Since one of the purposes of a UPS system is to keep critical loads in operation during the failure of the normal power supply, UPS systems may be covered under either NEC Article 700, 701, or 702, depending on the critical load supplied.

Emergency systems. NEC Article 700 covers the installation, operation, and maintenance of emergency systems. In accordance with NEC Section 700-1, emergency systems are intended to provide illumination and power necessary for the safety of human life when the normal power source fails. The requirements for using UPS systems to provide emergency power are provided in NEC Paragraph 700-12(c). If a UPS system is used to provide emergency power, then it will be subject to the testing and maintenance requirements specified in NEC Section 700-4, which requires acceptance testing when the UPS system is installed, in addition to ongoing operational testing throughout the installation’s life. NEC Section 700-4 requires that the UPS system be tested periodically, that written records of all tests and maintenance be kept, and that there is a provision for testing the UPS system under load.

Legally required standby systems. The installation, operation, and maintenance of legally required standby systems are covered in NEC Article 701. The purpose of a legally required standby system is to provide power to assist in fire fighting and rescue operations as well as to control health hazards during the loss of the normal power source. In most facilities, the required emergency and legally required standby systems are combined into a single system that meets the more stringent requirements of NEC Article 700 for emergency systems. NEC Paragraph 701-12(c) provides the requirements for using a UPS system as a source of power for a legally required standby system. The requirements for acceptance and operational testing of legally-required standby systems are similar to those for emergency systems and are specified in NEC Section 700-5. Like emergency systems, UPS systems used as legally required standby systems must be tested periodically, written records of all tests and maintenance be kept, and there must be a provision for testing the UPS system under load.

Optional standby systems. Most UPS systems installed in commercial, industrial, and institutional facilities would be categorized as optional standby systems as defined by NEC Article 702. An optional standby system is intended to provide an alternate source of power to loads that are not critical to life safety. Optional standby systems protect against economic loss that could result from a disruption of the normal supply of power. Power disruptions can cause business interruption or damage to the customer’s production equipment, work in process, or stored finished product. Since life safety is not an issue with optional standby systems, the NEC does not have any mandatory requirements for acceptance and operational testing of UPS systems installed as optional standby systems.

Manufacturing and testing standards

NFPA- and IEEE-recommended practices deal with the maintenance and testing of UPS systems after they have been installed. Both the National Electrical Manufacturers Association (NEMA) and Underwriters Laboratories Inc. (UL) publish standards that cover the design, manufacture, and testing of UPS systems. NEMA Standard PE 1-1992 is entitled Uninterruptible Power Systems and provides information about the types and arrangements of UPS systems, usual and unusual service conditions, rated values and performance parameters, and manufacturing testing specifications and methods, among other things.

Similarly, UL Standard 1778, entitled Uninterruptible Power Supply Equipment, provides the UL test requirements for static UPS systems installed in accordance with the NEC but not used as emergency or legally required standby systems. While these standards are primarily for the UPS system’s manufacturer, they provide information about how, and under what conditions, conforming UPS systems should operate.

Assisting your customers

UPS systems stand by silently until needed. However, unless they are maintained and tested regularly, there is no way to know that the system will be capable of performing its vital function when needed. Many customers have UPS systems protecting critical communication, data processing, and production equipment that their businesses depend on. These customers may not understand the importance or need for a preventive maintenance program for their UPS systems. Further, these customers may not have the necessary test equipment and expertise to properly test and maintain their UPS systems.

The electrical contracting company can better serve its customers by alerting them to the need for regular testing and maintenance of the UPS system when it is installed and providing them with manufacturer- and industry-recommended preventive maintenance practices. The company can also assist the customer in developing and implementing a preventive maintenance program tailored to the customer’s installation and in maintaining the UPS system throughout its life if the customer does not have the staff, skills, or expertise in house to do the job.

Acknowledgement

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

Dr. GLAVINICH is Chair and Associate Professor of Architectural Engineering at the University of Kansas. He can be reached at (785) 864-3435 or tglavinich@ukans.edu.