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UPS design criteria and selection

UPS design criteria and selection

An UPS system is an alternate or backup source of power with the electric utility company being the primary source. The UPS provides protection of load against line frequency variations, elimination of power line noise and voltage transients, voltage regulation, and uninterruptible power for critical loads during failures of normal utility source. An UPS can be considered a source of standby power or emergency power depending on the nature of the critical loads. The amount of power that the UPS must supply also depends on these specific needs.

These needs can include emergency lighting for evacuation, emergency perimeter lighting for security, orderly shut down of manufacturing or computer operations, continued operation of life support or critical medical equipment, safe operation of equipment during sags and brownouts, and a combination of the preceding needs.

The UPS selection process involves several steps as discussed briefly here.

Determine need

Prior to selecting the UPS it is necessary to determine the need. The types of loads may determine whether local, state, or federal laws mandate the incorporation of an UPS. An UPS may be needed for a variety of purposes such as lighting, startup power, transportation, mechanical utility systems, heating, refrigeration, production, fire protection, space conditioning, data processing, communication, life support, or signal circuits.

Some facilities need an UPS for more than one purpose. It is important to determine the acceptable delay between loss of primary power and availability of UPS power, the length of time that emergency or backup power is required, and the criticality of the load that the UPS must bear. All of these factors play into the sizing of the UPS and the selection of the type of the UPS.

Determine safety

It must be determined if the safety of the selected UPS is acceptable. The UPS may have safety issues such as hydrogen accumulation from batteries, or noise pollution from solid-state equipment or rotating equipment. These issues may be addressed through proper precautions or may require a selection of a different UPS.

Determine availability

The availability of the selected UPS must be acceptable. The criticality of the loads will determine the necessary availability of the UPS. The availability of an UPS may be improved by using different configurations to provide redundancy. It should be noted that the C4ISR facilities require a reliability level of 99.9999 percent.

Determine maintainability

The selected UPS must be maintainable. Maintenance of the unit is important in assuring the unit’s availability. If the unit is not properly cared for, the unit will be more likely to fail. Therefore, it is necessary that the maintenance be performed as required. If the skills and resources required for the maintenance of the unit are not available, it may be necessary to select a unit requiring less maintenance.

Determine if affordable

The selected UPS must be affordable. While this is the most limiting factor in the selection process, cost cannot be identified without knowing the other parameters. The pricing of the unit consists of the equipment cost as well as the operating and maintenance costs. Disposal costs of the unit should also be considered for when the unit reaches the end of its life.

Re-evaluate steps

If these criteria are not met, another UPS system must be selected and these steps re-evaluated.


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The New ETS4: Easy, Fast, Open

The New ETS4: Easy, Fast, Open

Singapore, Los Angeles, Johannesburg, London, Berlin, Moscow – building automation engineers from all over the world, use ETS as product and manufacturer independent programming tool in order to increase energy efficiency of buildings. This standardised tool is currently available in 15 languages, and supports KNX installations for all media: twisted pair, radio frequency, Ethernet/IP and power line.

To meet the latest technical and economic requirements and globalisation demands, KNX Association has now completely redesigned its Engineering Tool Software (ETS) including a set of many new functions. ETS4 makes it possible to implement KNX projects in a easy and fast way. Moreover, the use of the platform-independent universal standard XML makes it possible to access all KNX project related information in text form. The ETS4 is available from October 2010.

With the new ETS4, KNX Association has responded to new, tougher requirements in terms of handling, technical features, and economy – after all, the range of applications for which bus technology is used has recently tremendously increased. The average KNX installation has now also become quit larger. The functionality that non-residential buildings and intelligent residential buildings need to offer has also become more diverse.

KNX solutions need to handle current challenges like making buildings as energy-efficient as possible.

The demands from a technical and economic point of view for Electricians and system integrators designing, installing,
commissioning and supervising KNX systems, have increased.

Practical focus

It was essential that the new ETS4 would offer a clearly-structured, intuitive user interface meeting these increased demands. A new design for its user interface design was simply a top priority in its further development. A market leader from this sector was consulted in order to accomplish this requirement – which indicates the importance that KNX Association attaches to its device and manufacturer independent standard tool for home and building automation.

An international investigation was set up in order to optimise this new user interface, not only KNX professionals but also beginners with little or no KNX knowledge were consulted. System integrators with ETS3 expertise had the opportunity to try out the usefulness of the new features and at the same time the chance to give feedback based on their daily experience.


The tests with beginners were conducted to determine how intuitive the restructured work flows really are. In workshops held around the world, both professionals and beginners tested the tool on its daily usefulness in respect to maintaining projects quickly and offering highly demanding services.

The result of all of this research work is a stateof-the-art tool that meets the needs of a modern home and building control technology.

Highly visual interface

The tool’s new user interface is characterised by an up-todate, highly visual design. A new feature is for example an overview page, where users can view projects and access further information such as KNX news and the current ETS4 configuration. The project administration view, which shows project data and properties, is clearer than the ones from its predecessor.

The selective lists for opening databases, opening projects, importing data and viewing the most recently opened projects are together with the central toolbar, very useful features.

Initially ETS users – when working on projects – might miss the ‘old’ overview, because it’s no longer divided into three parts – topology view, group address view and building view. But professionals will quickly appreciate the simplified navigation and larger overviews of the “single window interface”. This is because of integrating various system views into one, crucial information is always visible and this without the need for additional menus.

In the topology overview for example, it only takes a mouse click via the line and device menu to quickly and easily reach communication objects, device details and comments. Important information can always be called via a sidebar. There is also a special Favourites window which can be personalised in order to quickly access customer-specific elements such as preconfigured devices or entire lines.


pic4Another advantage of the new ETS4 user interface is the “guided workflow” – a step by-step tutorial for creating bus configurations. Especially the topic-based Help features and the possibility to undo and repeat actions are very convenient.

System checks can be carried out at any time – this allows possible configuration errors to be detected quickly and in time. Drag & drop for e.g. assigning group addresses to communication objects, makes working with ETS4 yet even more intuitive. Thanks to the free-configurable views (dynamic folders), professionals can put together their own
interfaces in order to suit them to the way they work.


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Arc-resistant low voltage switchgear

Arc-resistant low voltage switchgear

For years, electrical equipment has been designed to withstand and deal with the issue of bolted faults, where the current spikes to a dangerously high level but is safely interrupted by the protective devices contained in the equipment (breakers, fuses and relays). However, these devices typically do not detect and interrupt dangerous internal arcing faults, which have a lower current level, but can generate a far more dangerous scenario for operating personnel.

Arc faults can be caused by a breakdown of insulation materials, objects coming into close proximity with the energized bus assembly, even entry of rodents or other animals into the equipment. The thermal energy created by these events can get as high as 35,000ºF, melting materials and clothing from several feet away. Also consider that the arc blast produced by a lineup of 480 Vac switchgear rated at 85 kA can be equivalent to 20.7 lbs of TNT!


So, what is the solution?

Eaton’s solution: arc-resistant low voltage switchgear

Eaton introduces the addition of an ANSI Type 2 arc-resistant low voltage switchgear offering to its current product line. This is the latest release in arc-safe equipment from Eaton’s Electrical Sector. The arc-resistant low voltage switchgear protects operating and maintenance personnel from dangerous arcing faults
by redirecting or channeling the arc energy out the top of the switchgear, regardless of the origination location of the arc.

Eaton’s arc-resistant low voltage switchgear has been successfully tested to ANSI C37.20.7 at KEMA-Powertest, and has been ULT witnessed and certified.

Standard features
  • Ratings:
    • Up to 100 kA short circuit at 508 Vac maximum and up to 85 kA short circuit at 635 Vac maximum
    • Up to 10 kA horizontal main bus continuous current
    • Up to 5 kA vertical bus continuous current
    • MagnumE DS power circuit breaker frame ratings between 800A and 6000A
  • ANSI Type 2 arc-resistant design protects the operator around the entire perimeter of the equipment
  • Floor-to-ceiling height of 10 feet required whether exhausting into a room or through an arc plenum
  • Strengthened one-piece breaker door and latches
  • Dynamic flap system on rear ventilation openings that remain open under normal operating conditions, but close during an arcing event to prevent dangerous gasses from escaping
  • Patented bellows design allowing drawout of breaker into the disconnected position with the door closed, while simultaneously protecting the operator from any dangerous gasses during an arc event
  • Patented venting system that directs arc gasses out the top of the enclosure, regardless of the arc origination location
  • Up to four-high breaker configuration with no additional layout restrictions
  • Strengthened side and rear panels with standard split rear covers for cable access
  • NEMAT 1 enclosure, with either top or bottom cable or bus duct entry
  • Cable compartment floor plates


Optional features
  • Zone selective interlocking protection
  • ANSI Type 2B arc-resistant design protects the operator even with the low voltage instrument compartment door open
  • Arcflash Reduction Maintenance SystemE
  • Safety shutters
  • One-piece hinged and bolted rear panel
  • Insulated bus
  • Vented bus/cable compartment barrier
  • Cable compartment segregation barrier



  • Superior protection against arcs in breaker, bus or cable compartments
  • No increase in footprint over regular Magnum DS switchgear
  • Closed door racking
  • UL 1558 and UL 891
  • ANSI C37.20.1, ANSI C37.13, ANSI C37.51 and ANSI C37.20.7
  • CSAT standard—CSA C22.2 No. 31-04
  • Third-party (UL/CSA) witness tested
  • Seismic certification 2006-IBC

Testing procedures were completed per ANSI C37.20.7 standards with arcs initiated in:

  • Breaker compartment
  • Vertical and horizontal bus
  • Cable termination compartments

Additionally, the tested arc duration was up to the full 0.5 seconds recommended by ANSI C37.20.7, with no dependence on the tripping speed of an upstream breaker.

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