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STATE OF THE
ART TECHNOLOGY AND
THE IMPACT OF
UL1449 2ND EDITION
INTRODUCTION
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)
ADVANTAGE
When UL applies the abnormal voltage, the surge protector does not
fail.
DISADVANTAGE
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.
ADVANTAGE
When UL applies the abnormal voltage, the surge protector fails, AC
fault current flows and the fuse clears the fault before the unit
explodes.
DISADVANTAGE
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.
ADVANTAGE
Passes UL abnormal overvoltage test by disconnecting the failed surge
components. Does not limit the maximum surge capacity of the protector
DISADVANTAGE
Significant design and testing time required to perfect the fuse link.
CFC designs are already patented.
TEST 2. LIMITED CURRENT ABNORMAL OVERVOLTAGE TEST
DESIGN OPTION A
Same as Test 1
ADVANTAGE
Same as test 1
DISADVANTAGE
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.
ADVANTAGE
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.
DISADVANTAGE
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.
ADVANTAGE
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.
DISADVANTAGE
Significant design and testing time required to perfect the thermal
fuse link. CFC designs are already patented.
CONCLUSION
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 |
