STATE OF THE ART TECHNOLOGY AND
THE IMPACT OF UL1449 2ND EDITION
Surge protectors, for use on the load side of the main AC disconnect, are listed to UL 1449.
This UL standard was changed in 1998 to UL1449 2nd edition.
The revised UL1449 (2nd edition), in force for products manufactured after Feb. 16, 1998, will certainly lead to improvements in the safety of surge protectors - but buyer beware!
To comply with UL 1449 2nd edition, many manufacturers have employed designs that may negatively impact the performance of their surge protectors.
WHAT CHANGES HAVE BEEN MADE TO UL 1449?
There were a lot of changes, but the two most significant ones were abnormal power simulations. The purpose of these tests is to show that the surge protector will fail gracefully in the presence of an abnormally high AC voltage. Such abnormal conditions are common in typical supply systems and can be the result of lost neutral connections or single phasing of High Voltage transformer.
1.) High current abnormal overvoltage test:
Here the surge protector is subjected to full phase voltage (e.g.240V across a surge protector designed for 120V) with the maximum available fault current limited up to 25,000 amps.
2.) Limited current abnormal overvoltage test
Again the surge protector is subjected to full phase voltage, but the available current is limited to a value between 5A and 0.125A.
HOW DO SURGE PROTECTORS RESPOND TO THESE TEST ?
In both cases the high AC voltage causes the suge protection elements to fail. However with the available fault current, test 1 can cause the surge protector to explode violently.
In case 2, the low current level causes significant heating in the failed protection elements. Fuses do not blow ( because the current is so low). With nothing to interrupt the low level current the heat builds increasing the risk of fire. Indeed cases documented by UL have shown that poorly designed surge protectors have caused building fires.
WHAT CHOICES DO MANUFACTURER'S OF SURGE PROTECTION DEVICES HAVE TO COMPLY WITH UL1449 2ND EDITION?
TEST 1. HIGH CURRENT ABNORMAL OVERVOLTAGE TEST.
DESIGN OPTIONS A:
Increase the operating voltage of the surge protector(e.g. from 120V to 240V)
When UL applies the abnormal voltage, the surge protector does not fail.
The residual transient voltage under surge conditions will increase dramatically. (e.g. from 400V let thru to 800V let thru)
DESIGN OPTION B:
Add standard cartridge fuses, typically 15-30 amp.
When UL applies the abnormal voltage, the surge protector fails, AC fault current flows and the fuse clears the fault before the unit explodes.
Standard fuses will also blow under short duration surge conditions. For example a 30A fuse will blow on a surge current of 8-20 microseconds. The addition of fuses can thus severly limit the maximum surge current rating of the surge protector.
DESIGN OPTION CFC
Design a fuse link to pass both the requirements of UL and allow full surge performance without premature operation.
Passes UL abnormal overvoltage test by disconnecting the failed surge components. Does not limit the maximum surge capacity of the protector
DISADVANTAGE TEST 2. LIMITED CURRENT ABNORMAL OVERVOLTAGE TEST
Significant design and testing time required to perfect the fuse link. CFC designs are already patented.
DESIGN OPTION A
Same as Test 1
Same as test 1
Same as test 1.
DESIGN OPTION B
Add standard thermal disconnect devices. These devices are designed to disconnect a circuit permanently when the temperature exceeds a defined value, E.G. 105 degrees C.
When UL applies the abnormal voltage, the surge protector fails, the contiuous low level current causes heat to be developed. When the temperature exceeds the operating point of the thermal disconnect, power is removed from the surge component. The unit passes the test.
Standard thermal disconnect devices incorporate fine foil contacts that allow the disconnect mechanism to work. This foil, although rated for 15AAC duty, will weld or vaporize under high amplitude surge conditions. Welding renders the thermal device useless. Even worse, should the foil vaporize, surge protection will be lost.
DESIGN OPTION C
Design a thermal fuse link to pass both requirments of UL and allow full surge performance without premature operation.
The use of eutectic alloy as a connection to the surge protection component, allows a link, held under tension, to operate at a precise temperature. The size of the connection ensures that surge currents do not cause premature operation of the link.
Significant design and testing time required to perfect the thermal fuse link. CFC designs are already patented.
Manufacturer's of surge protection devices can comply with the revised UL 1449 2nd edition requirements by adding cartridge fuses and thermal disconnects. However, these standard components are not tested for duty in a surge protector. As such the inclusion of these components can and does limit the capabilities of the surge protector.
Although the rating on the surge protector may say 300KA, the inclusion of components to pass UL 1449 2nd edition, effectively limits the performance to a much lower level - not the advertised 300KA.
The only viable solution to this problem is to use a custom fusing mechanism.
CFC Solutions, incorporates a patented thermal and short circuit fusing mechanism that has passes UL 1449 2nd edition. Further, this design has been tested to withstand the full surge capacity of the surge protector as advertised. Finally, this design is not new, the same mechanism has been used in CFC products since 1997.
To summarize, the unique thermal and short circuit mechanism used in CFC Solutions products:
1.) passes UL 1449 2nd edition
2.) does not limit the performance of the surge protector
3.) has been in use for 6 years worldwide
CFC SOLUTIONS, INC - KEY PERFORMANCE BENEFITS
1.) MASSIVE 40MM THREE TERMINAL BLOCK MOV'S PROVIDE LOWER AND FASTER SURGE RESPONSE BY CONTROLLING PARASITIC IMPEDANCE
2.) THE COMBINATION OF BLOCK MOV AND THERMAL FUSELINK ALLOWS CONTROL OF GREATER THAN 150,000A SURGE CURRENTS.
3.) FUSELINK DISCONNECTS ONLY FAULTY COMPONENTS, PROVIDING PROTECTION REDUNDANCY.
4.) STATUS INDICATION IS MECHANICALLY LINKED TO THE FUSE MECHANISM, CORRECT MONITORING IS THUS INDEPENDENT OD AC POWER.
THE BOTTOM LINE
Most TVSS manufacturers publish literature that includes very high surge suppression capacities. As mentioned before, these numbers are based soley on adding the suppression capability of their MOV'S, SAD's or selenium diodes. The problem with this is that placed before any of these surge handling components, a fuse opens up at a current level that is much less than the published tvss suppression data. For example, Manufacturer A has a model that is advertised at 350KA of surge capacity per phase. Unfortunately, before their selenuim and MOV's they place a Gould Schuwmut class J 35 amp fuse. This fuse limits the 350,000 amps of surge current they claim to have, to 6,270 amps of surge current per phase. What are you paying for ? 350,000 amps of surge current protecion per phase. What are you getting? A "heck" of a lot less.
Please understand, the purpose of this report is not to convey a negative message regarding fusing or fuse manufacturers. Proper coordination of the surge protection devices suppression components with the fuse is simply overlooked. A careful balance between providing a fuse that will clear a fault safely or take a failed component off-line quickly and a fuse sized large enough to allow the TVSS to operate at its full surge current rating, is a major design challenge