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Standards and classifications help in UPS selection Raising the Standard for UPS Reliability

By Jorma Mannerkoski
Director of Product Marketing Powerware EMEA
May 13 -19, 2002

When choosing UPS equipment how can you ensure that it will perform as expected and the information provided by different vendors is comparable will be reliable? One way is to look at the European Union wide standards which govern UPSs.

UPS standards in Europe are created and maintained by an organisation called the European Committee for Electrotechnical Standardisation (CENELEC). This body is composed of members from each EU country as well as members from many other Eastern and Central European countries. UPS manufacturers normally follow the CENELEC standards in order to comply with the relevant European Directives.

The UPS standard, EN50091, has three parts. Part one deals with safety requirements for UPSs and is compulsory for all UPSs sold in the EU. Part two is also compulsory and deals with electro magnetic compatibility (EMC). It has two parts emissions and immunity. Emissions govern what levels of noise and disturbances the UPS is permitted to emit into the environment. The immunity section specifies what levels of disturbance the UPS must be able to tolerate from outside sources. The final part of the standard specifies performance. This section, which is not mandatory, provides benchmark data and a methodology on how to measure the performance and functionality of different types of UPSs and states specification methods for UPS values.

The performance standard is intended to aid buyers and users of UPS equipment in the selection process. The standard categorises the different UPS topologies:


Stand-by UPS supplies power to the load directly from utility until a utility power failure occurs. The UPS then turns on the inverter and supplies load from the battery. These UPSs are also called Off-line. These units meet CENECLEC Class VDF or VI


Line interactive UPS compensates for deficiencies in utility voltage by running the UPS inverter parallel to utility voltage when needed. The UPS output is therefore partly dependent of the quality of the utility power. Several marketing names are used for these UPSs, Single Conversion, Parallel On-line and Delta Conversion to name a few. These units meet CENELEC Class VI.


Double conversion UPS regenerates the electricity constantly. The output power is completely independent of the input power. These units are most often called On-Line UPSs. These units meet CENELEC Class VFI.

The CELELEC performance standard is an excellent aid in UPS selection, but using it does require some knowledge of UPSs and electrical systems. It is therefore most beneficial to buyers and users that who are professionally involved in electrical power either as consultants, electrical contractors or facility managers.

For most UPS users, especially when those buying in small and mid-range UPSs, it is not justifiable cannot afford to spend a lot of time thinking about different UPS topologies and UPS performance characteristics. Powerware has therefore taken an extra step to help in their selection procedure.

Powerware has further developed the UPS classification based on the CENELEC standard. It is based on the UPS's ability to solve different power problems. There are nine common power problems in any electrical environment. Powerware offers Series 3, Series 5 and Series 9 to address the various protection needs.


The UPSs are able to correct 3 out of the 9 power problems (Power failure, Surge and Sag). These UPSs are intended for protection of PCs and desktop workstation protection in the home and office environment. They are the most economical UPSs and due to their small size and virtually no noiseless operation are ideally suited for desktop use. Series 3 corresponds to Stand-By in CENELEC classification


These UPSs are able to correct 5 out of the 9 power problems (Power failure, Surge, Sag, and Undervoltage). These UPSs are designed to be used with Servers in an office environment. As servers are more critical than individual workstations, the higher protection level is also justified required. Series 5 corresponds to Stand-by and Line-interactive in CENELEC classification


These UPSs are able to correct all 9 power problems (Power failure, Sag, Surge, Undervoltage, Line noise, Overvoltage, Frequency variation, Switching transient and Harmonic distortion). These UPSs are used with all mission critical electrical equipment that is not allowed which cannot afford to go down (servers, communication equipment etc.). Any equipment installed outside office environment Mission critical equipment both inside and outside the office environment should always be protected by Series 9 UPS. These UPSs also feature possibility for extending the battery back up time up to several hours. Series 9 corresponds to Double-Conversion in CENELEC classification.

Both CENELEC Performance standard and Powerware 3-5-9 classifications are aimed at helping in the UPS selection. The CENELEC standard is intended for power professionals and whilst the Powerware 3-5-9 can be very helpful for a more casual the less experienced UPS buyer. As a customer you should always make sure the UPS vendor can provide information about the UPSs CENELEC class and it's ability to correct the nine power problems.

Another indication of reliability is the CE mark. This is the manufacturer's declaration that the UPS complies with the EU requirements. Testing of product compliance with CE regulations is normally carried out by an independent laboratory. In addition, many UPS manufacturers, such as Powerware, adhere to the international quality standards (ISO9000 series) giving customers and users further assurance of reliability.


Invensys Powerware is a global leader in the power solutions industry. Offering the broadest range of product and services available today, Invensys Powerware integrates a full line of AC and DC power systems, power conversion products, standby batteries, telephone line surge suppression, power management software, remote monitoring, turnkey integration services and site support, providing a seamless solution. Powerware systems and services increase enterprise-wide systems availability and are utilised in local and wide area networking, data and voice over IP, co-location facilities, fixed-line and wireless communication networks, and industrial manufacturing. Invensys Powerware is headquartered in Raleigh, NC, and is part of Invensys plc. Invensys plc is a global leader in the automation and controls industry, with headquarters located in London, England. Invensys operates in all regions of the world through four focused divisions Software Systems, Automation Systems, Powerware and Control Systems.


GemNet is the authorized distributor for Powerware Corporation (an Invensys company), and offers a large range of specialized power related products and services. The company has local offices in Pakistan (GemNet Private Limited) and Jebel Ali, Dubai, U.A.E. (GemNet Gulf).