I was looking at this surge supressor:
Tripp-Lite model HT1210SAT3
The specs say "Let through rating 330, 400, 400"
it's my understanding that is the clamping voltage, the max voltage
the supressor allows to pass thru. Why it lists 3 values instead of
just one value?
Thank you in advance,
I suspect the lower voltage is on the ground-neutral MOV where there
should normally not be any appreciable voltage.
IMO the price on that thing is exorbitant, I've seen UPS's with similar
insurance for less than that.
Reasonable, but you need to ask Tripplite to find out. You have MOVs
from H-N, H-G, N-G. Thus, presumably, 3 voltages.
The suppressor has a relatively high Joule rating, which means it is not
likely to fail (one reason it can have a protected equipment warranty).
The let through voltage is the voltage at the outlets at specified UL
test conditions (might be 500A). And the voltage is rounded up to
standard UL values. A high surge current could result in higher voltage.
That is likely mostly in service panel suppressors. The current that can
reach a point-of-use suppressor is greatly limited by the impedance of
the branch circuit wiring at the surge frequencies. A really short
branch circuit could have significantly higher currents. If the voltage
at the service panel reaches about 6,000V (US)there will be arc-over to
the enclosure, which dumps most of the surge energy to earth. When the
arc is established, the voltage is hundreds of volts. This limits the
voltage from hot to neutral and ground, which further limits the current
to the suppressor.
If you get the typical UPS that is used, if it has surge protection
added the UPS should have (in the US) the appropriate UL listing for
surge protection which is 1449. A lot of UPSs don't seem to have it.
The IEEE has a nice paper on surges and surge protection:
Still not sure about the clamping voltage, why some products have as
low as 40v, and others 330v?
Support from Phillips, APC, TrippLite, etc for surge supressors really
suck, so I ended up buying this one (TigerDirect and other retailers
have a friendlier price):
I just hope my home theater doesn't get fried some day in the middle
of an important game ;-)
If the clamp voltage is 40V it is for phone/cable circuits.
If you are looking at the unit in your link, 140V is the RMS voltage. AC
power has voltage that is constantly changing - a sine wave. The RMS
voltage is an 'average'. It compares with 120V which is also RMS. The
'peak' voltage for 120V RMS is about 170V.
The UL let through - 330V - is a peak voltage.
All interconnected equipment needs to connect to this suppressor. All
external wiring to the connected equipment - cable, satellite antenna,
phone lines, ... - needs to go through the suppressor. The major cause
of damage is likely high voltage between power and cable or phone wires.
Running all wires through the suppressor limits the voltage from the
wires to the ground at the suppressor, and thus limits the voltage
between the wires. The IEEE guide, in my other post, has an example of a
home theater type setup in an example at the end.
If the MOVs fail, UL has required since 1998 that there be a thermal
disconnect to disconnect the MOV. The IEEE guide explains how the
protected load can be wired across the MOVs, and thus be disconnected if
Or the protected load can be wired across the incoming line. If the MOVs
fail and are disconnected, the protected load is no longer protected.
This is how your suppressor is wired. You might want to check the status
lites occasionally. On the other hand, the Joule rating is very high,
and the suppressor is very unlikely to fail, in the middle of a game or
Having tested similar products for the European market, it does not matter
what the manufacturers quote the figures are very rarely correct or
meaningful. I have found in general that when testing to the European
standard EN 61643-11, quite often the models with the lowest Joule ratings
have the lowest clamping voltage. The clamping voltage is purely a function
of how you test the product and the product design, not just the MOV rating.
Most manufacturers quote the nominal clamping voltage of the MOV that they
fit. When you test the finished powerstrip to the applicable standard you
always get higher reading of clamping voltage, sometimes more that twice the
nominal rating of the MOV.
The only thing that I would add is that in some cases when I tested the
powerstrip it went into a self destruct mode, as the protection fitted to
the MOVs was not adequate and the MOV exploded.
So you pays your money and takes your chances and hope that what you buy is
better than no protection at all.
Unless a product is tested independently to a recognised standard (UL or EN)
and an APPROVED (Listed in the USA) by the test body, you can not compare
products in a meaningful manner.
Leeds Lad in exile
Interesting what you run across. How do I get a job blowing things up?
In this case the unit says it is listed under UL1449 - the appropriate
standard for power line surges (plus a standard for phone protectors).
The test includes measuring the UL "let through voltage", hitting it
with a specified series of surges (not huge, but the surge available on
US branch circuits is limited as explained in another post). The UL "let
through voltage" is measured again and compared to the first value.
There are additional tests that may cause the suppressor to fail, but it
must fail safely. If it passes the UL standard, the suppressor should
have at least a minimum functionality. The "let through voltage" is
determined by a defined test (rounded up to the next standard UL value).
This suppressor has a rating of 3570 Joules, which is quite high. There
is no specified way of measuring the energy rating, so the value may not
be comparable. I know of no definition for "clamping voltage (RMS)",
which is in the product spec.
Like I said if its "listed" that means it has been tested by an independent
lab, like UL and is marked with an approval mark (CSA, TUV or UL in the
states, etc), not just the claims of the manufacturer.
The quoted values for let-through voltage should therefore be OK with no
risk of it starting a fire under normal use.
It is when there is not listing or approval that things get risky.
I just wish that in Europe, more products were tested and approved by
European Certification Bodies, particularly those from Asia.
Leeds Lad in exile
| Like I said if its "listed" that means it has been tested by an independent
| lab, like UL and is marked with an approval mark (CSA, TUV or UL in the
| states, etc), not just the claims of the manufacturer.
| The quoted values for let-through voltage should therefore be OK with no
| risk of it starting a fire under normal use.
| It is when there is not listing or approval that things get risky.
| I just wish that in Europe, more products were tested and approved by
| European Certification Bodies, particularly those from Asia.
But just what does the testing certification/approval really mean?
1. That the device is effective and will provide proper surge protection
to connected devices?
2. That the device is safe and won't explode or catch fire under normal
surge protection operations, and thus not result in injury or death?
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
Tested and approved means that the product has been tested to the applicable
standard(s) and found to meet all the applicable requirement within the
standard(s). The place where the product is manufactured is then inspected
1. That safety related component purchased for use in the product are
checked on delivery to ensure that they are identical to those used in the
model tested and that they are marked with the required certification marks.
2. That the components are stored and then kited to ensure that only the
correct components are release for production of the product.
3. That suitable build instructions and information is available to guide
the operator during the product assembly and final test.
4. That the product is been tested at the end of the production line as
required by the standard and that the test equipment is calibrated and is
check for correct operation at least once per day.
5. That the operators and quality personnel on production are suitability
trained and training record exist.
6. That the manufacturer has in place a quality system that will ensure that
before any change is made to the product that will effect the safety related
components or the product safety, the approval of the certification body is
obtained before the change is made.
7. That the manufacturer's quality system has a effective customer complaint
procedure and that the complaints are auctioned within a reasonable time.
The above are the major requirements that the manufacturer must meet before
a certificate is issued. The inspection is then repeated 4 times per year
for a NRTL approval for the USA, twice per year for a Canadian approval and
once per year for a European approval.
If a major change is made to the standard(s) the product must be reassessed
to the new requirements and a revised certificate issued. Major changes are
usually only made when a deficiency is found in the standard.
In the end after all the above, what does it all really mean, hopefully the
product is safe within the conditions specified within the scope of the
standard and will not pose a risk of electrical shock or fire when used as
intended. Unfortunately no one can write a standard that can cover all
eventualities, in Europe we have to consider all foreseeable miss use, this
is not the case in the USA as far as I know.
Leeds Lad in exile
I'm glade to see that you both understand the logic, the problem is not
In Europe the Governments seem to think that just because someone put the CE
mark on a product that they have tested it and its safe.
I sometimes think CE now stands for China export only, as it gives no
guarrentee that a product has been tested and certainly not that it's safe.
Leeds Lad in exile
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