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By J.T. Sheehan, Mersen
Since 1985, the UL 1449 standard has been providing safety guidelines for surge suppression, a topic found in the past to have very little structure or commonality across the standard. Originally titled “The Standard for Safety for Transient Voltage Surge Suppressor,” this standard was initially created to provide structure to a rapidly developing and growing industry and was largely based on waveforms and testing methods from IEEE C62.41. Over time, new developments and enhanced technology have driven the need for more rigorous standards. As a result of these advances, UL responded on September 29, 2009 by making significant revisions to standard 1449, updating it to the 3rd Edition. Most notably impacted are the terminology, test program and specifying requirements.
Some key facts about UL 1449 3rd Edition which have an impact on specifiers and the supply chain include:
Along with new test methods, terminology has been added to UL 1449 3rd Edition. In the past, a surge device was referred to as a transient voltage surge suppressor (TVSS). This old terminology has been replaced with surge protective device (SPD), reflecting the changes made to the NEC and international standards terminology. Along with TVSS, the 2nd Edition secondary surge arrestors (SSAs) have been consolidated into the new 3rd Edition. Most 3rd Edition Type 1 devices will replace obsolete old secondary surge arresters on the market. Having this new terminology creates an industry umbrella for all surge categories together under one common test criteria.
When specifying a surge product in today’s industry, there is often confusion with the significant number of previously used terminologies to address surge protection. However, there are a few critical concepts to understand to sort through the values of importance when selecting an SPD. Previously, UL 1449 2nd Edition referred to the clamp voltage test as the suppressed voltage rating (SVR), which consisted of a 500 A, 6,000 V surge. Updated in UL 1449 3rd Edition, the clamp voltage test is referred to as the voltage protection rating (VPR) and consists of a 3,000 A, 6,000 V surge — more than six times more surge current required than that of the previous 2nd Edition test requirements. This means the VPR for an SPD will be higher than the SVR of an identical SPD. Higher current levels equal higher clamp voltages.
|3rd Edition||2nd Edition|
|Title||Volt Protection Rating||Suppressed Voltage Rating|
Table 1: The above table shows the comparison between VPR and SVR test requirements.
The change from SVR to VPR is the single most important change in the UL 1449 3rd Edition relating to specifiers. The SVR listed in current specifications will be obsolete since comparing a VPR rating to an SVR rating would provide no information of value. To be sure, there is an accurate performance comparison, the VPR of one device must be compared with the VPR of another device.
Prior to UL 1449 3rd Edition, UL 96A required surge suppressors to be evaluated as secondary surge arresters. However, with new revisions made to 1449, secondary arrestors are now classified as a Type 1 SPD. This means that UL 96A will now accept Type 1 or Type 2 SPDs having 20 kA nominal discharge current (In) ratings.
Figure 1. This illustrates the locations within the electrical distribution and the associated device type.