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Unfortunately there is no UL or NEMA standard that addresses this issue. There is no guideline to help you select the proper device for your particular site, until now.

Intermatic Inc., a maker of surge devices, offers a complimentary, limited edition CD-ROM that will assess surge suppression needs for facility managers.

The easy-to-use CD-ROM asks users a series of eleven questions — the very same questions Intermatic’s experienced applications specialists would ask when helping customers select a surge suppression product.

The CD-ROM features an interactive isokeuronic map to help customers determine their facility’s susceptibility to lightning strikes. Also featured is a full list of Intermatic surge suppressors and model specifications, including full details on the industry’s most advanced surge suppressors, the Intermatic Panel Guard 3000-5000 series.

There are several factors to compare when selecting a TVSS  system. To name a few:

1. Surge current capacity
2. Clamping or let-through voltage
3. Modes of protection
4. EMI/RFI filtration
5. Desired features like integral disconnect, integral fusing, LEDs, audible alarm, surge counter, and Form C contacts.

Surge current capacity is the maximum 8x20 micosecond pulse the unit can withstand. This is like a horsepower rating for the TVSS unit. You want this rating to be tested, not just a theoretical addition of the components in the box. It is amazing that over 75 % of TVSS manufacturers do not have the test data to back up the claims they make on their data sheets.

Clamping voltage is often misunderstood. Since almost all manufacturers are using a similarly-rated MOV technology, clamping voltages are all pretty much the same. A difference of 30 to 40V in clamp voltage does not make one unit ineffective, and in fact the difference is usually in the test setup not the actual devices being tested. CBEMA (Computer and Business Equipment Manafucturer’s Assoc) recommends a let-through of less than five times the voltage of the system, so for a 120/208Vt system that would be less than 5 x 170 Vpeak or 850 Vpeak. For a 277/480V system that would be less than 5 x 391 or 1,955 Vpeak. Remember that this is the installed clamping voltage though, and every foot you add to the installation increases the clamp voltage by about 50V (based on the 500A UL test waveform). Still, virtually all MOV devices on the market will clamp well within this range.

Modes of protection are critical considerations. Since we do not know what mode a transient might be coupled on, it is important to provide a path for the event to go in all modes (i.e. line to neutral, line to ground, line to line and neutral to ground) for a wye derived system. In a delta system there would only be six modes applicable which would be line to ground and line to line, since there is no neutral in a delta derived system.

EMI/RFI filtration is an option, not a necessity. In general, the EMI/RFI filter will attenuate lower level pulses which may not create immediate damage, but may cause system upset or "electronic rust" or latent degradation.

"Desired features" is a class of options that vary according to what you are trying to accomplish. You may want an integral disconnect so that you do not have to feed the device via a breaker, or you may want a surge counter that would show when the device turns on, or you may want form c contacts to tie the device status into a building management system. These options are all popular features which are available in Intermatic surge suppression devices. You should also evaluate what the manafacturer’s warranty is and whether it covers parts only, or includes labor. In addition, is the device still covered if it fails due to a lightning strike? These are things that should be spelled out in the manufacturer’s warranty statement.

To obtain the free CD-ROM, simply send an e-mail to mboyd@intermatic.com or call Intermatic toll-free at 1-800-391-4555.

An Intermatic applications specialist will be available to answer questions and offer advice on any surge suppression system, as well as provide specialized expertise in constructing a customized multi-tier protection system for your facility.

For additional information on the full range of Intermatic Surge Suppression products or to request a 2002 Intermatic Surge Suppression Product Catalog (item 300IG10127), contact: Intermatic Surge Protection Devices, Intermatic Plaza, Spring Grove, IL 60081-9698, register on the Web site at www.Intermatic.com or call 1-800-391-4555. You can also subscribe to their email newsletter at www.Intermatic.com\update