TD.37H.13.S.E.Rev A
The Second Edition of UL1449 became effective August 17, 1998.  This new standard includes some important changes affecting the safety and performance of Transient Voltage Surge Suppression products.  These products are also known as Surge Protection Devices (SPDs).
Introduction
UL1449 is the standard that describes the requirements
a Transient Voltage Surge Suppressor (TVSS) must
meet in order to have the UL mark applied to the
product.  The standard applies to products connected to
50 or 60 Hz power, not to exceed 600 VAC.  These
requirements do no cover Secondary Surge Arrestors
intended for use on the line side of any main overcurrent
protection.
The first edition of UL1449 was released in August of 1986.  The primary objective of UL was to determine if a safety risk existed.  In the ten years that followed, a number of changes occurred in the implementation of the standard and the understanding behind the testing procedures.  It also became apparent that additional safety tests were required as well as the requirement to retest older products that may not have had the most
modern tests applied.
The second edition of UL1449 was released in August of
1996 with an effective date of February 16, 1998.  This required every surge suppressor manufacturer to submit their products for re-testing.  Due to number of
manufacturers, products, and limited resources at UL,this date was pushed back to August 17, 1998.  Because of this, all units manufactured after August 17, 1998must pass all test procedures outlined in the second edition of UL1449 to continue to be listed and labeled as UL1449.
TVSS Categories:
The second edition of UL1449 categorizes TVSS by one of three types:
Direct Plug-in – These devices incorporate integral
blades for connection directly to electrical outlets where point-of-use surge protection is desired.
Cord-connected – These devices incorporate a power supply cord terminating in an attachment plug for
connection to electrical outlets where point-of-use surge protection is desired.
replaceablePermanently Connected – These devices utilize
terminals or leads that are then “hard wired”  into the electrical distribution system.  These products include switchboard and panelboard mounted devices and receptacle-type products. This paper will focus on the permanently connected type of products.
The standard tests Listed products differently than Recognized products (components).  An example of a Recognized product is a “TVSS Module” used in an enclosure to complete an assembled product. Recognized products do not have enclosures, or are housed in an enclosure that is incomplete or unsuitable for field installation or direct connection to a branch circuit.
Note:  When evaluating TVSS devices, ask manufacturers utilizing replaceable modules or
recognized components for data relating to their entire assembly, not their component (modules) rating.
Testing Overview
This section contains the electrical tests for TVSS. UL1449 has basic safety tests similar to other types of electrical products. These tests include leakage current,dielectric withstand, insulation resistance, and
temperature rise.  There are also a series of mechanical integrity tests.  Here we will discuss the major tests conducted by UL.
Measured Limiting Voltage (MLV) and Duty CycleTest
This test is performed to measure the let-through voltage of a product under test and is used to assign a Measured Limiting Voltage Rating (MLVR). Part of the UL labeling requirement is to publish this value on the product nameplate.
The new standard has clarified the test method, its
details, and step by step procedures.  The purpose is to test the ability of the TVSS to suppress or limit a specific surge while the duty cycle portion tests the ability of the
T ECH N OTE #: 13
New UL1449 Safety Standard for
Transient Voltage Surge Suppressors
TD.37H.13.S.E.Rev A
TVSS to function repeatedly.  Products are tested using the ANSI/IEEE 1.2/50 µs open voltage, and 8 x 20 µs short circuit combination waveforms. Table 1 lists the changes to the peak voltage and current values.First Edition Second Edition Product Type Voltage/Current
Impulse Voltage/Current
Impulse Permanently Connected 6,000 Volts,3,000 Amps 6,000 Volts,  500 Amps Cord
connected &Direct plug-in
6,000 Volts,  500 Amps
6,000 Volts,  500 Amps
Under first edition, permanently connected products were tested and measured at different points.  On a TVSS supplied with wire leads, the device was tested and measured at the end of the leads.  If terminals were supplied, the device was tested at the terminals.  If the product was a component (replaceable module), it was tested at the connection point.
The new MLV test uses 6 inches (15cm) of wire
measured from the outside of the enclosure.  In the case of products supplied with wire leads, the leads are cut back to 6 inches.  For products with terminal
connections, wire is attached to the terminals and cut back so that 6 inches extends from the enclosure.  This 6 inches of wire is used to simulate an installed product.The testing begins by subjecting the TVSS to a single 6kV, 500A surge impulse.  The measured limiting voltage is measured and recorded.  The TVSS is then duty cycle tested using ten consecutive 6 kV, 3 kA positive impulses and 10 consecutive 6 kV, 3 kA negative
impulses at 60 second intervals.  The test is completed by subjecting the TVSS to a final 6 kV, 500A impulse that is measured and recorded.  This second measured limiting voltage must not deviate ± 10% from the initial measured limiting voltage.
Number of
Impulses Voltage (1.25 x 50µs)Amperage (8 x 20 µs)Remarks
1
6,000V 500A MLV measured & recorded 2 – 216,000V 3,000A Duty Cycle Testing
22
6,000V
500A
MLV must not deviate by ± 10%when compared to Impulse # 1
Once the MLV and duty cycle testing is completed, the TVSS is assigned a rating.  Ratings are assigned based on a performance range.  For example if the MLV is
between 0V and 330V, it will be assigned a 330V rating. If the MLV is between 331V and 400V it will receive a 400V rating.  Etc.
UL 1449 Second Edition Suppressed
Voltage Ratings (SVR)
330V 900V    (New)2500V 400V 1000V 3000V 500V 1200V 4000V
600V
1500V
5000V 700V    (New)1800V  (New)6000V
800V 2000V
Surge Current Test (New)
This test is performed to determine the ability of the device to safely withstand a high energy surge.  The TVSS is connected to AC power and subjected to two surge impulses (one positive and one negative) 6 to 20kV/10 kA at the peak of the voltage waveform.After the two large impulses are applied, the unit remains connected to the rated voltage for seven hours.  It is acceptable for the TVSS to fail the first, second, or while connected to power, but only in a manor which will not cause a fire or expose the end user to live parts.  Data is not collected on the let through voltage.
Overvoltage Test
This test is performed to determine that the TVSS can withstand 110% of the rated operating voltage  for seven hours without evidence of a risk of fire or electrical
hazard. It is not acceptable for the product to fail, without automatically resetting when normal power is applied.
Abnormal Overvoltage Test (New)
These tests are performed to determine that the TVSS can withstand the rated L-L voltage on the L-N mode (i.e.208 VAC on a 120VAC product).  This is a severe test and is likely to damage the internal components and cause a short circuit from line to neutral.
The High Current Test applies a fault current up to 25kA, while the Low Current Test applies fault current of 0.125, 0.5, 2.5, and 5 amps.  These tests are applied for seven hours and are often referred to as the “slow cook”or “slow burn” tests.  In both tests, it is acceptable for the unit to fail, but the product must do so without evidence of fire or electrical shock hazard.
Conclusion
The second edition of UL1449 is an improvement because testing procedures are now defined and
additional safety tests have been added to reduce the risk of fire and electrical hazard to the end user.  The enhanced safety tests required some manufacturers to change their designs in order to m
eet the new standard. All Cutler-Hammer products have been tested by UL and all permanently connected units passed second edition testing without modifications.  Should you have any questions or comments regarding UL1449 second
edition or TVSS products in general, please contact your local Cutler-Hammer sales engineer.

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