With the many standards and associations charged with maintaining the various standards, it is no wonder confusion arises when a piece of electrical equipment can have many uses.
By James M. Daley, PE, CCP Automatic Switch Company
The Y2K issue prompted wide spread application of standby power to important loads. This promulgated small-scale on-site generation with many of these installations for residences and small businesses. Given that cost is an important consideration, other interpretations of UL Standards and the NEC could be used since such systems were only optional standby applications. As a result, some significant confusion crept into the industry. This has left the electrical inspector wondering if the installation he is reviewing really does meet the requirements of the National Electrical Code. The discussion that follows attempts to present the issues and offer some suggestions —it remains for the Standards writing and Code enforcement agencies to resolve the issues.
The National Fire Protection Agency (NFPA) is the author and custodian of the National Electric Code (NEC), NFPA 70. In most political jurisdictions, this Code is the governing document against which electrical installations are judged for their potential hazards. Sometimes this Code is augmented with local requirements to meet the unique needs of a given political jurisdiction. Whatever the case, electrical construction is governed by Code requirements.
The Code requires all electrical equipment to be suitable for its intended use in any given application. Given the infinite number of electrical equipment configurations, it is unrealistic to expect that any individual could be sufficiently knowledgeable to assess the suitability of a piece of electrical equipment for any given application. The Code recognizes this. The assurance of suitability comes from the independent evaluation of electrical equipment with respect to acceptable standards. The Code acknowledges the suitability of electrical equipment listed by an recognized independent testing laboratory. It states that the agency having jurisdiction by the electrical inspector may accept such listing and/or labeling as evidence of suitability.
This is where the confusion surfaces. The requirement is for equipment suitable for its intended service in the specific application. The label does not always indicate the service for which the product is suitable and intended. In some cases, even the standards promulgate confusion. When this occurs, the need for clarification exists.
Y2K and the increased use of hi-tech office equipment have created a sizable market for optional standby equipment. Manufacturers have responded to this opportunity for sales by trying to fit existing products into the market opportunity. As a result, manufacturers have petitioned the standards writing agencies to modify some of the standards to allow use of their product. When unassociated groups prepare different standards, it is likely that contradicting standards will be issued. It is believed this is the case with respect to the qualification of transfer equipment.
UL 1008, Standard for safety Transfer Switch Equipment establishes the minimum qualification requirements for transfer switching equipment. A conflict has arisen in UL 67, Standard for safety Panelboards, Section 25A Transfer Equipment Panelboard Tests and UL 98, Standard for safety Enclosed and Dead-Front Switches, Section 20, Par. 20.5. The change to UL 67 becomes effective February 9, 2001. In that it is new, and likely an oversight by UL, when the issue is resolved, the indications are that transfer switching equipment will be required to be qualified to UL 1008.
Codes and standards
There are a few Codes used throughout the world. The most common are
- CEI IEC: International Electrotechnical Commission
- CSA: Canadian Standards Association
- NFPA: National Fire Protection Agency
For countries having membership in the European Economic Community, IEC standards are in force. IEC 60364-5-51 Electrical installations of buildings, Part 5: Selection and erection of electrical equipment, Chapter 51: Common rules, Article 511: Compliance with standards, Par. 511.1 states, " Every item of equipment shall comply with such IEC standards as are appropriate…"
NFPA 70 National Electric Code, Chapter 1 General, Article 110 Requirements for Electrical Installations, Paragraph 110-2 Approval, states, "The conductors and equipment required or permitted by this Code shall be acceptable only if approved." Paragraph 110-3 Examination, Identification, Installation and Use of Equipment, "…a) Examination states, "In judging equipment, considerations such as the following shall be evaluated:
- Suitability for installation and use in conformity with the provisions of this Code…"
Par. 110-3.b Installation and use states, "Listed or labeled equipment shall be installed and used in accordance with any instruction included in the listing or labeling." Article700-3 (Emergency Systems) states, "All equipment shall be approved for use on emergency systems. Article 701-4 (Legally Required Standby Systems) states, "All equipment shall be approved for the intended use." Article 702-4 (Optional Standby Systems) states, "All equipment shall be approved for the intended use." Article 90-7 Examination of equipment for safety states that "…equipment evaluation made under standard conditions will provide a basis for approval…" It is accepted that Underwriters Laboratories is a qualified testing agency. Further, it is recognized that products bearing the UL label can be considered as approved. This is where the confusion begins. The only standard for safety for Transfer Switch Equipment in the United States is UL 1008. In Canada, it is CSA 22.2-178. In countries governed by IEC standards, the applicable standard is IEC 60947-6-1.
Certain manufacturers argue that UL 67, Standard for safety for Panelboards and UL 98 Standard for safety for enclosed and dead front switches, also apply. The view taken in this discussion is that these standards do not provide an adequate basis for qualification of Transfer Switch Equipment to the needs of safety.
It is concluded that Underwriters Laboratories does not intend to issue two or more standards for any given product that are in conflict with each other. Evidence of this can be found in UL 2200 Standard for safety for Stationary engine generator assemblies. Section 10.8 states, "A transfer switch used to connect the load shall comply with the applicable requirements in the Standard for Automatic Transfer Switches, UL 1008.". If the alternate supply consists of a stationary engine generator set, the only Transfer Switch Equipment permitted is that which is qualified to UL 1008.
The designations "National Electrical Code" and "NEC" refer to the National Electrical Code, which is a registered trademark of the National Fire Protection Association.
About the author
James M. Daley, PE, CCP; Senior Member of IEEE; BSEE '72, MSEM '86, New Jersey Institute of Technology; Professional Engineer registered in New Jersey; Senior Member and Certified Cogeneration Professional of the Association of Energy Engineers; Member, Tau Beta Pi - National Engineering Honor Society.
Mr. Daley has been with Automatic Switch Co. since November 1965. In his tenure, he has served in several product oriented engineering and marketing capacities dealing with Power Control Systems, the most recent being Director of Engineering, Switchgear. Currently he holds the staff position of Division Engineer, Switch Division. In his tenure, he has made numerous contributions to the development and advancement of power switchgear and controls for engine generator power systems. He has pioneered high current switchgear designs and holds a patent on control elements. Mr. Daley has written and presented several tutorials on generation, distribution and control of on site electric power as well as other topics. He has published several papers and articles for IEEE, EGSA and industry periodicals. These include Transaction papers in both the IEEE and SAE. He is the recipient of the 1999 Prize Paper Award from the Power Systems Engineering Committee of the Industry Applications Society of the IEEE. (Back to top)