Electrical Systems / Electrical Safety

Electrical safety surges ahead

Changes to UL 1449 safety standards for surge protection affect safety and terminology.

By J.T. Sheehan, Mersen

In brief:

  • Underwriters Laboratory (UL) updated standard 1449 to the 3rd Edition.
  • A surge device used to be referred to as a transient voltage surge suppressor (TVSS), and that terminology now is replaced with surge protective device (SPD).
  • Prior to UL 1449 3rd Edition, UL 96A required surge suppressors to be evaluated as secondary surge arresters. With the new revisions made to 1449, a secondary surge arrestor is now classified as a Type 1 SPD.

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:

  • New performance tests use more surge current, resulting in increased clamping voltages
  • New test results are numerically higher, thus not meeting old style specifications
  • Lost time of electrical and general contractors and distributors trying to source SPDs that cannot meet an outdated specification
  • In frustration, old or obsolete TVSS product may be submitted, which may or may not be UL Listed or supported in the future
  • Specifying engineers waste time evaluating submittals that do not meet the new standard
  • Specifying engineers may find significant industry confusion, unable to specify what is needed or receiving products with improper technology.

New terminology

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.

More rigorous test requirements

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.

Standard UL 1449
3rd Edition 2nd Edition
Test 3kA/6kV 0.5kA/6kV
Title Volt Protection Rating Suppressed Voltage Rating
Reference VPR SVR
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.

New Impact on UL 96A

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.
Figure 1. This illustrates the locations within the electrical distribution and the associated device type.

Location and type

UL 1449 3rd Edition assigns type designations to SPDs (1,2,3,4) based on the installation location within the electrical distribution system (Figure 1). Type 1 is installed on the line or load side of the main overcurrent protection (OCP). In the past this was referred to as SSA. The difference with UL 1449 3rd Edition is the new more rigorous safety testing, which was not required in the previous editions. Type 2 is installed on the load side of the main OCP. In the past, this device may have been associated with or referred to as a hardwired TVSS, and in some cases may not require external OCP. Type 3 is a point-of-utilization, direct plug-in type device. These components are similar to surge strips. They are required to be installed 10 m from the panel (rationale based on IEEE Cat. A location). Type 4 are surge suppression components, which could be basic components or complete modules. Type 4 components can be tested to Type 1 or Type 2 applications.

New test requirement

Over time, new developments and enhanced technology have driven the need for more rigorous standards.

New to UL 1449 3rd Edition standard is the nominal discharge current test (In). This new test requirement originates from the International Electrical Code (IEC) surge testing criteria, mandating that an SPD must remain functional after being subjected to 15 repetitive impulses of a specific value. During the In test, every mode of protection is tested, including any required overcurrent protection device. During this test, the unit is tested at its rated voltage or what is referred to in UL 1449 as the maximum continuous operating voltage (MCOV). The In testing is performed in conjunction with the VPR test, so it is crucial to understand the testing conditions for the SPD. The In values which a device must be tested at are 10 kA or 20 kA for a Type 1 device; and 3 kA, 5 kA, 10 kA or 20kA for a Type 2 device.

Important to note is that the manufacturer has the ability to chose which In value the device is tested at, which means that SPD products need to be investigated in detail to understand the published ratings. In the event a device cannot pass at any given value, it is permitted by UL that the SPD manufacturer can re-test at a lower level until a stable value is obtained to pass the test. This means that a manufacturer has a number of In values they are able to test to achieve compliance.

What do the changes to UL 1449 mean?

Since the effective date of September 29, 2009, all surge products that do not meet UL 1449 3rd Edition are to be considered obsolete. UL updated the standard to drive consistency and commonality to the SPD market, recognizing that it can be confusing to determine the published values of importance. It is also important to understand there are many SPDs on the market that no longer meet the standard but are still offered for sale. The simplest way to know if an SPD product is in compliance is to look for a UL holographic label on the device. If it has a UL SPD holographic label, it is in compliance, and, if it does not, it does not meet the new UL 1449 3rd Edition standard. Please keep in mind, some 2nd Edition products did incorporate a UL TVSS holographic label. Figure 2 illustrates the difference between obsolete and acceptable labels seen on products in today’s industry.

Figure 2. The holographic label with the TVSS wording is from an obsolete 2nd Edition device, while the holographic label with the SPD working is from a UL 1449 3rd Edition device and accepted in today’s industry.
Figure 2. The holographic label with the TVSS wording is from an obsolete 2nd Edition device, while the holographic label with the SPD working is from a UL 1449 3rd Edition device and accepted in today’s industry.


J.T. Sheehan is applications engineer at Mersen (www.mersen.com).