# Surge Protector - Page 4

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Re: Surge Protector

That should be an *8900%* increase and dissipation per unit *volume*.

--
bud--

Re: Surge Protector

Opps - was closer before. Replace the paragraph with:

The 20mm MOV withstands 10.6 times the number of surges that would be
expected, correcting for its larger energy rating. It is not credible
that a 3% lower voltage at the MOV (and a 3%lower energy hit per event)
would cause a 960% rise in the number of surges the MOV can withstand.

But the 20mm MOV is larger diameter with about 8 times the volume. Since
a MOV dissipates the energy through the whole volume, the energy
dissipated per square centimeter in the 7mm MOV is 8 times the energy
dissipated per square centimeter in the 20mm MOV. The lower energy
dissipation per square centimeter in the 20mm MOV causes far less
heating and far less damage to the MOV and the MOV is able to withstand
more surges. A 3% lower energy per hit helps but is a minor contributor.

IMHO  w_'s latest rant is near incomprehensible.

I still agree with Franc.

--
bud--

Re: Surge Protector

This is exactly what w_tom posted repeatedly.  When energy
dissipated in a 'magic box' is less, then more energy is dissipated in
earth.  Again, this is what w_tom said.

Less energy dissipated in the MOV means better protection.  Franc
says MOVs work better by absorbing more energy.   Then w_tom
repeatedly requested numbers from datasheets.  When Franc finally
conceded, then his own numbers showed how energy consumption
decreases.  Franc only did half the work.  That reduced energy
consumption also coincided with a massive increase in life expectancy
- 40 or 50 times longer.  Why?  We want MOVs to absorb less energy.

w_tom also provided another example.    For every joule that an MOV
absorbed (a bad thing), then something like 30 times more energy was
dissipated elsewhere (a good thing).  Better shunt mode protectors
absorb less energy and are more conductive - shunt more energy and
absorb less.  Increased MOV joules is equivalent to larger gauge
wire.  Both absorb energy (a bad thing) while shunting energy to be
absorbed elsewhere (a good thing).

Franc Zabkar claims that MOVs protect better by absorbing more
energy.  That would be true for series mode protectors.  But MOVs are
shunt mode protectors.  Franc is simply wrong as demonstrated again by
two above examples - with numbers.

We can install a protector that is even better (more conductive)
but costs much more money. This protector uses avalanche diodes.   A
275 volt protector could easily limit voltage to 500 instead of 900+.
Better protection because that semiconductor protector is even more
conductive.  Better protection because only 500 volts instead of 1000
volts confronts protection inside appliances.

That is where Franc and this poster disagree.  Franc says MOVs
protect by absorbing the surge.  Even datasheets demonstrate that
better protectors absorb less energy.  Joules in an MOV do not mean it
absorbs more surge as Franc has repeatedly assumed.  More joules in an
MOV is equivalent to a heavier gauge wire - as was posted so many
times previously by whom?  For a more conductive wire or a longer
lasting MOV - we increase wire gauge or MOV joules.

MOV is a shunt mode device.  It performs even better when more surge
energy dissipates elsewhere.  Better protectors dissipated more surge
into earth - not through household appliances.  Better shunt mode
protectors absorb less surge energy; therefore cause less voltage to
confront electronics.  An MOV that absorbs more energy is an inferior
protector - as demonstrated how many times with numbers?  Franc
disagrees?  Bud agrees that more energy absorbed by an MOV means
better protection?  Where are the numbers for this claim?  Those
numbers do not exist.

Let's not forget the only reason for these numbers.  Franc claims
that MOVs work better by absorbing more surge energy.  That is the
question.  Shunt mode protectors work better by absorbing less
energy.  And this is why earth ground is so essential to effective
surge protection.  The effective MOV protector has a short (more
conductive) connection to earth ground.  Why?  Better protectors
dissipate more energy in earth. Just another in the so many reasons
why a protector is only as effective as its earth ground.

Bud cannot agree with that.  Protectors promoted by Bud have no
dedicated earthing wire.  Where is that energy dissipated?   Bud would
have us believe as Franc has claimed:  protector that absorbs more
surge energy is better.  Demonstrated by numbers provided even by
Franc: better MOV protectors (more joules) absorb less energy, last
longer, and shunt (clamp, divert, bond, connect, conduct) more surge
energy into earth.  But again, a protector is only as good as its
earth ground - where the surge must be dissipated.

In example after numerical example, a better protector (MOV with
more joules) means less energy absorbed by the protector AND more
energy shunted to and absorbed by earth.  Just another reason why
better protectors have that short connection to earth ground.  As
usual, examples with numbers demonstrate validity - what an effective
protector does.  It shunts - absorbs less energy - dissipates more
energy in earth (if that superior earthing connection exists).

Re: Surge Protector

Return to what Franc Zabkar did not grasp.  Bud must say anything to
have everyone confused as to what an MOV does.  Profits are at risk.

A better protector absorbs less energy.  That is the point.  As MOV
joules increase, then energy dissipated by MOVs decreases (and life
expectancy increases).  Franc Zabkar repeatedly claims that an MOV
provided protection by absorbing the surge.  That is not an MOV's
purpose as even demonstrated by numbers for better MOVs.  As MOV
joules increase, then energy absorption decreases.  We want shunt mode
protectors to absorb less energy.  A better MOV absorbs less energy.
AND better protectors using other technologies to absorb even less
energy.  Why?  In every case, the better shunt mode protector absorbs
less energy - in direct contradiction to what Franc Zabkar has posted.

MOVs are shunt mode devices.  MOVs are effective when surge energy
is shunted (diverted, connected, clamped, conducted, bonded)
elsewhere.  That elsewhere is earth ground.  What makes a conductive
MOV so effective?  A short path to earth ground also called a 'whole
house' protector.

MOVs are for shunting energy elsewhere; not for absorbing surge
energy.   Franc Zabkar does not grasp that concept.  All this other
stuff remains completely irrelevant to what Franc Zabkar denies.   In
every example of a superior shunt mode protector, the protector
absorbs less energy.  Shunting is why MOV based protectors require a
conductive (short) path to earth ground - where surge energy is
dissipated.  A shunt mode protector without that conductive path to
earth may shunt that surge destructively elsewhere - such as through
household appliances.

Franc - your posts erroneously define MOVs doing the task of a
series mode protector.  Series mode protectors protect by absorbing
energy.  Shunt mode protectors operate by shunting (diverting) energy
elsewhere.  MOVs are shunt mode protectors.  Less energy absorbed by a
shunt mode protector means better protection.  Shunt mode protectors
must connect to something that non-destructively absorbs that energy -
ie earth ground.

Bud fears others might learn this technology.  Plug-in protectors
(shunt mode protectors) don't have that short earthing connection.  No
earth ground means nothing to absorb the energy.   Bud must post
incessantly to confuse the concept.   Better MOVs not only absorb less
energy.  Better MOV protectors also need that short connection to
earth ground.  If you learn that, then you will learn why a plug-in
protector with no dedicated earthing wire is a poor protectors.  With
no earth to absorb the surge, then where does it shunt to?  Bud will
say anything to obfuscate that question.

Re: Surge Protector

Franc did not grasp that I must say anything .....???

Ho hum - repeating:
“To quote the all-knowing w_ ‘it is an old political trick.  When facts
cannot be challenged technically, then attack the messenger.’ "

As Franc and I have both explained, decrease in energy absorption is
trivial, and makes a trivial contribution to the increase in the
cumulative energy absorption of a MOV. It is idiotic for w_ to argue
this point because it is irrelevant to his major agenda.

Bullcrap. Franc repeatedly points out that MOVs *intrinsically* absorb
energy, not that they protect by absorbing energy.

w_ thinks a “perfect’ MOV would not absorb energy - reflecting the
physics in the alternate universe where he lives.

In some applications, like a MOV across relay coil, the total protection
is by absorbing. In other applications absorbing is incidental to
protection.

MOVs are for clamping. That may or may not result in shunting energy. Or
MOVs may just absorb.

With a MOV across a relay coil where is the energy shunted?

w_ can not grasp what Franc is saying.

If you want reliable information on surges and surge protection read:
http://omegaps.com/Lightning%20Guide_FINALpublishedversion_May051.pdf
- the title is "How to protect your house and its contents from
lightning: IEEE guide for surge protection of equipment connected to AC
IEEE is the dominant organization of electrical and electronic engineers
in the US).
And also:
http://www.nist.gov/public_affairs/practiceguides/surgesfnl.pdf
- this is the "NIST recommended practice guide: Surges Happen!: how to
Institute of Standards and Technology in 2001

The IEEE guide is aimed at those with some technical background. The
NIST guide is aimed at the unwashed masses. There are minor adjustments
for Australia because people stand upside down. But Australia uses the
same physics and is not in  w_'s  alternate universe.

w_ does not grasp what either guide is says. Both say plug-in
suppressors are effective.

Bud hopes people will read reputable sources, like the IEEE and/or NIST
guides.

w_ has a religious belief (immune from challenge) that surge protection
must use earthing. Thus in his view plug-in suppressors (which are not
well earthed) can not possibly work. The IEEE guide explains plug-in
suppressors work by CLAMPING the voltage on all wires (signal and power)
to the common ground at the suppressor. Plug-in suppressors do not work
primarily by earthing (or absorbing).  The guide explains earthing
occurs elsewhere. (Read the guide starting pdf page 40).

Note that all interconnected equipment needs to be connected to the same
plug-in suppressor, or interconnecting wires need to go through the
suppressor. External connections, like phone, also need to go through
the suppressor. Connecting all wiring through the suppressor prevents
damaging voltages between power and signal wires. These multiport
suppressors are described in both guides.

w_ must post incessantly because his religious belief has been
challenged. Just like arguing with a Jehovah’s Witness.

w_ can’t figure what both Franc and I have been saying.
And w_ can’t figure out how plug-in suppressors work even though it is
explained in the IEEE guide.

For excellent information on surges and surge protection read the IEEE
and NIST guides. Both say plug-in suppressors are effective.

There are 98,615,938 other web sites, including 13,843,032 by
lunatics, and w_ can't find another lunatic that says plug-in
suppressors are NOT effective. All you have is  w_'s opinions based on
his religious belief in earthing.

--
bud--

Re: Surge Protector

to keyboard and composed:

Sorry, you're right. Nevertheless, my conclusions are unaffected. In
fact you've just demonstrated how little the voltage changes in
response to large changes in current, ie 1.35:1 V/V as opposed to
1000:1 A/A.

You cannot seriously claim that a figure of 3% or 5% is significant.
It amounts to *nothing*. It is certainly not a valid reason to choose
a higher energy MOV over a lower energy one. It makes about as much
sense as choosing a 5W zener over a 400mW zener when the circuit
dissipation calls for 100mW. The benefits of a larger MOV are an
ability to withstand a larger surge, and an ability to withstand more
surges in the same time. The latter is reflected in the average power
rating.

In fact the difference of 5% is a consequence of the fact that MOVs
are imperfect. If a MOV had a perfectly sharp IV characteristic, then
there would be no difference in the absorbed energy in the above
example.

E = Vp x 400A x 30us = 12J  (if Vp = 1000V)

The resistance of a 20mm MOV hit by a 1000V 1000A surge is 1.00 ohms.

The resistance of a 7mm MOV hit by a 1050V 1000A surge is 1.05 ohms.

A 10W 1 ohm resistor and a 250mW 1 ohm resistor both have the same
resistance.

A figure of 3% is *insignificant*. A MOV doesn't last longer because
it absorbs 3% less energy. A 45J MOV will be significantly degraded by
a 12J surge simply because it is rated to handle 45J. OTOH a 382J MOV
will not be greatly affected by the same surge because it is rated for
382J, not because its IV characteristic reduces the impact to only
11.4J (12J - 5%).

Think of the larger MOV as 8 smaller MOVs in parallel. In fact, if the
energy rating of a MOV is proportional to its area (assuming equal
thickness), then we have ...

Rating of 20mm MOV = (20mm/7mm)^2 x 45J = 8.2 x 45 = 367J

The fact that 5% less energy is absorbed is of no practical
significance. It's the energy rating and average power dissipation
that are important, the latter in the case of repetitive transients.

Insignificant.

5% is insignificant.

5% less energy will have an insignificant impact on the MOV's life
span.

5% is *nothing*. Less energy absorbed in relation to a MOV's rating is
what determines its life expectancy. It's not the absolute energy
figure itself which is the determinant.

For example, if a single MOV absorbs 10J, then 8 such MOVs in parallel
should experience exactly the same degradation (less 5%) when
absorbing a combined amount of 80J. Alternatively, for the same 10J
surge, each of those 8 MOVs will see only 1.25J. That's why a larger
MOV lasts longer.

You have no idea how a clamp works. Energy is absorbed as a direct
consequence of clamping action. The MOV mitigates the affect of the
surge by reducing the surge voltage. In so doing it diverts the
majority of the surge current through itself, and absorbs an amount of
energy given by ...

Energy = Volts x Amps x time

I have no idea what you are talking about. Are you saying that these
extra joules pass mysteriously through the MOV on their way to earth?

True, but 5% less energy will have no significant impact.

A *perfect* MOV will *always* absorb energy. That's how it is intended
to work.

For example, a perfect MOV installed in a 240VAC appliance should have
a breakover voltage rating of 275V, say. Above this voltage the MOV
should clamp any surge to 275V, but below this voltage the MOV should
remain open circuit. Let's say the DC rating of this perfect MOV is
380VDC. Then *any* DC surge clamped/diverted by this perfect MOV will
cause the MOV to absorb E = 380 x Isurge x dt joules.

A perfect MOV will never absorb 0J. For this to be possible, the MOV
would need to clamp the surge to Vp = 0V, which would mean that it
would be shorting the mains supply.

- Franc Zabkar
--

Re: Surge Protector

I agree with Franc's posts.  w_  is totally off in this branch of the
discussion.

I would only add that actual measurements by the US-NIST guru on
surges found that light bulbs would burn out on a surge (maybe 100
microsecond duration) at about 1500V (US - 120V bulbs). Typically only
a single light bulb would burn out (it would bypass enough of the
surge to protect the others). Another tidbit - in the US there is arc--
over at panels or receptacles at about 6000V limiting the voltage
between power wires. Both voltages are likely to be higher on 230V
systems.

--
bud--

Re: Surge Protector

Various and routine insults posted by Bud are removed from the
quote.  Bud promotes for plug-in protector manufacturers.  Truth
concerning things not provided by his products such as earth ground
must be negated by insults.

In developing standards for surge testing, one waveform (numbers no
longer remembered- maybe 100/10000 usec) was proposed and rejected.
That test waveform was rejected because it caused incandescent light
bulb failure.  Lightning strike does not cause light bulb failure
meaning that test waveform was not a valid testing standard.  Other
test waveforms that were acceptable are now listed as IEEE/ANSI C62.xx
standards.

Some protectors would even claim to meet C62.xx standards.  They
were playing games with the naivety of many who never bothered to ask
embarrassing questions.  How does a protector conform to a test
waveform?  It does not.  But IEEE/ANSI C62.42 means a protector must
be better?

Test waveform was rejected as a standard because it did something to
light bulbs that lightning does not - damage the bulb.

Re: Surge Protector

w_ is hallucinating again. There were no insults in my post.

To quote the all-knowing w_ "it is an old political trick.  When facts
cannot be challenged technically, then attack the messenger."
And there was nothing in my post about surge protection.

Further hallucinations and completely unrelated to anything in my post.

Geez - something on-topic.

Looking at the relevant technical paper, arcing started in a lamp at
about 30 microseconds of a 50 microsecond surge. (My post recollected a
100 microsecond surge.) Both are far from w_’s 10,000 microseconds.

The paper says for 120V 100W bulbs, the bulb may fail with an 800V
surge; few bulbs survive 1500V.
For 230V European systems, a bulb may fail at 1800V.

In any case, surges can certainly cause burnout of incandescent light
bulbs, which is what I said.

Totally irrelevant to anything.

The technical paper was written by Francois Martzloff and others.
Martzloff was the US—NIST guru on surges, did much research and had many
published peer-reviewed technical papers on surges.

So who should I believe -  w_ or Martzloff?  Gee, its a tough call.

--
bud--

Re: Surge Protector

Again the point is being avoided - a point directly traceable to
Tim's original question.  Franc claims shunt mode protectors work by
absorbing surges.  In each case, a better protector absorbs less
energy.  MOVs with more joules absorb less energy.  Replacing MOVs
with avalanche diodes absorb even less energy. Using a gas discharge
tube (as was the standard solution almost 100 years ago) absorbs even
less energy,  Absorbing less energy is what a shunt mode protector
does - equivalent to what a wire does.  Energy is shunted (diverted,
clamped, connected) elsewhere.  That 'elsewhere' is earth ground.

Bud so dislikes this reality because his protectors don't have a low
impedance earthing connection.   Why is earthing THE most critical
component in a shunt mode 'system'?  An MOV, et al  becomes as
conductive as possible.  A surge is shunted (clamped, diverted) to
earth ground.  Earth dissipates the surge - not a protector.  An MOV
that shunts 20 or 30 times more energy to earth (than is absorbed) is
a best protector for the dollar.

MOV does not protect by absorbing surge energy.  MOV protects by
shunting that energy elsewhere - into earth.

The bottom line about surge protection:
Only component required in a surge protection system is earth ground.
Either a surge is connected directly to earth OR we install an MOV
type protector to make a temporary earthing connection.   Earthing
electrode is the 'protection'.   'Protector' is either a hard wire
(cable TV or satellite dish) or a 'whole house' type protector (for
telephone or AC electric).

MOV and wire only absorb energy because each is not perfect.  Both
absorb trivial energy to shunt massive energy elsewhere.  Both become
even better protectors when they absorb less energy.  Franc - that is
the point.  Better protectors in every case absorb less energy.  More
joules in an MOV means it absorbs less energy - especially when the
MOV is so grossly undersized as to operate at the end of that hock
stick upswing.  Why do you keep trying to claim a better protector
will absorb more surge energy?  Why do you keep arguing irrelevance?

Tim asked whether a surge protector was recommended.  Yes, but one
that earths surges.   One that is sufficiently size so as to be a
better conductor - not create these scary pictures:
http://www.hanford.gov/rl/?page55%6&parent55%4
http://www.westwhitelandfire.com/Articles/Surge%20Protectors.pdf
http://www.ddxg.net/old/surge_protectors.htm
http://www.zerosurge.com/HTML/movs.html

Since an MOV operates by shunting (absorbing less energy), then the
protector will only be as effective as its earth ground.  Earth is
where energy is absorbed.  No earth ground means an MOV has nothing to
shunt to - provides no effective protection.  Tim should install a
protector that actually earths surges - by becoming as conductive as
is practicable.

Re: Surge Protector

to keyboard and composed:

A reduction of 3% (your numbers) is insignificant.

E = Vp x Ip x dt   for *all* shunt mode protectors.

What will happen if you place a wire across a mains supply?

This is the IV characteristic of a perfect shunt mode protector:

I
| +I           ^
|              |
|              |
-V ______0_____| +V           ---> V
|
|
|
| -I

Nowhere is the resistance (R=V/I) of the protector equal to zero.

This is the IV characteristic of a perfect wire, ie one with zero
resistance:

I
| +I            ^
|               |
|               |
|V=0            ---> V
|
|
|
| -I

Earthing is irrelevant to a shunt mode system, unless the surge/spike
is being shunted to earth.

Energy does *not* pass mysteriously through a MOV on its way to earth.

Explain how a shunt mode protector (eg transorb) connected across the
generator terminals in an airplane utilises an earth connection?

A two-wire appliance has no earth ground other than the earth-neutral
bond in a MEN system. A surge suppressor between A-N is required
because only one end of a common mode surge entering the premises is
shunted to ground at the meter box.

A *perfect* shunt mode protector *always* absorbs energy. That's in
the nature of its design. Please place an X on the IV characteristic
curve that I have drawn above, showing any point where the absorbed
energy is zero.

Yes, a better shunt mode protector will have a vertical IV
characteristic, not one shaped like an ice hockey stick. And yes, it
will absorb less energy. But a 20mm MOV will only absorb 3% less
energy (your numbers) than a 7mm MOV.

I have *never* claimed that. I have always said that a bigger MOV will
only absorb about 3-5% less energy than a smaller one. The bigger MOV
is better because it will sustain larger surges without damage, and
because it can sustain more surges, not because it can reduce the
impact of the same surge current by a mere 5%.

A MOV is only interested in the potential between its two terminals.
It doesn't care where the surge current goes - it just attempts to
maintain its terminal voltage as low as possible.

- Franc Zabkar
--

Re: Surge Protector

I will try not to repeat what Franc has just posted - I agree with him
completely.

The elephant in the room is  w_’s  religious belief in earthing.
Apparently  w_  can not consider that the intrinsic action of a MOV is
*clamping*, because it threatens his religious belief in earthing, which
requires shunting.

But the IEEE guide explains plug-in suppressors work by CLAMPING the
voltage on all wires (signal and power) to the common ground at the
suppressor. Plug-in suppressors do not work primarily by earthing (or
shunting or absorbing).  The guide explains earthing occurs elsewhere.
(Read the guide starting pdf page 40).
http://omegaps.com/Lightning%20Guide_FINALpublishedversion_May051.pdf

Religious belief in earthing #2.

Still not explained by w_  - for a MOV connected across a relay coil,
where is energy shunted to. (And then there is Franc’s airplane.)

And of course, plug-in suppressors do not work primarily by shunting - a
major violation for  w_ (but not for the IEEE or anyone else). They do
not work primarily by absorbing either.

The religious belief in earthing - #3.

w_ can't understand his own hanford link.  It is about "some older
model" power strips and says overheating was fixed in the US with a
revision to UL1449 that requires thermal disconnects. That was 1998.
Perhaps  w_  thinks you are not as smart in Australia?

Religious belief in earthing #4?

Because  w_   is evangelical in his belief in earthing, he uses google
groups to search for “surge” to spread his beliefs. Among his primary
beliefs is that plug-in suppressors can’t possibly work.
Perhaps  w_’s  nonsense about MOVs is an attempt at a ‘scientific’
attack on plug-in suppressors.  w_ knows that in a direct attack he will
get hammered.

Tim should read reliable sources for information, like the IEEE and NIST
guides.

Both guides say plug-in suppressors are effective.

w_ has never produced a link to a source that says plug-in suppressors
are NOT effective. Or that agrees with his nonsense about MOVs.

Never explained by w_:
- Why do the only 2 examples of protection in the IEEE guide use plug-
in suppressors?
- Why does the NIST guide says plug-in suppressors are "the easiest
solution"?
- Where is energy shunted to for a MOV connected across a relay coil?

--
bud--

Re: Surge Protector

to keyboard and composed:

Here is the datasheet for Littlefuse's ZA Varistor Series:
http://www.littelfuse.com/data/en/Data_Sheets/ZA.pdf

Notice the references to *average* power as opposed to *instantaneous*
power.

For example, note 1 on page 4 states ...

"Average power dissipation of transients not to exceed 0.2W, 0.25W,
0.4W, 0.6W or 1W for model sizes 5mm, 7mm, 10mm, 14mm and 20mm,
respectively."

Page 5 talks about "Power Dissipation Ratings":

====================================================================
Should transients occur in rapid succession, the average power
dissipation required is simply the energy (watt-seconds) per pulse
times the number of pulses per second. The power so developed must be
within the specifications shown on the Device Ratings and
Specifications table for the specific device. Furthermore, the
operating values need to be derated at high temperatures as shown in
Figure 1. Because varistors can only dissipate a relatively small
amount of average power they are, therefore, not suitable for
repetitive applications that involve substantial amounts of average
power dissipation.
====================================================================

- Franc Zabkar
--

Re: Surge Protector

Exactly.  Now you are starting to grasp why lightning surges
typically don't explode light bulbs.  Why a 70 joule MOV dissipates so
few watts.  And why a surge so large to stress an MOV to maximum
results in 10 or more times energy absorbed elsewhere.  Dissipating
most of the energy eslewhere is why MOVs are so effective shunt mode
protectors.  More energy is absorbed elsewhere (in earth) and less
energy is absorbed in inside MOVs.

Joules consumed by a light bulb determines things such as light
efficiency.  Light bulbs are designed to absorb joules.  But absorbing
more joules is bad for MOVs.  How to reduce the joules consumed by a
shunt mode protector?   Increase MOV joules rating (same reason we
increase wire size).  An MOV with more joules means that MOV absorbs
less energy  - which is exactly what we want for surge protection.

Until you grasp that fact from datasheet charts, then you will not
understand what MOVs do.  MOV does not provide better protection by
absorbing more energy.  MOV provides better protection by absorbing
less energy AND when shunting more energy to earth.  What makes a
better protector?  More MOV joules means it absorbs less energy.
More MOV joules means a better conductive connection (shunt) to earth.
What makes a better protection 'system'?  Better earthing.

You formulas are correct.  But assumed is that (for example) voltage
is a mathematically independent variable.  What happens when an MOV
has higher joules?  Then its Vp decreases resulting in more energy
shunted to earth and less energy absorbed by the MOV.

In simple terms, MOVs perform a job more like a switch.  A more
conductive switch, means a better protector.  That means more MOV
joules so that less energy is absorbed by the MOV.

Series mode protectors operate better by absorbing more energy.
Shunt mode protectors operate better by absorbing less energy.  MOV is
a shunt mode protector.  Again, study charts in those manufacturer
datasheets.  The numbers that confirm the above concepts are in those
manufacturer datasheet charts.

As an MOV joule rating increases, then MOV absorbs less energy.
Less energy absorbed means longer life expectancy.  Effective
protectors also shunt surges and remain functional - another fact from
those charts.  A protectors joules rating must be high enough as to
absorb less energy, shunt more energy to earth, and therefore remain
functional after direct lightning strikes.

Install protectors to make direct lightning strikes irrelevant.  A
properly sized (sufficient joules) and earthed protector means
protection inside appliances is not overwhelmed and homeowner should
never even know the surge existed.  Too few MOV joules means the
protector absorbs more energy, vaporizes, and may even result in these
scary pictures:
http://www.hanford.gov/rl/?page55%6&parent55%4
http://www.westwhitelandfire.com/Articles/Surge%20Protectors.pdf
http://www.ddxg.net/old/surge_protectors.htm
http://www.zerosurge.com/HTML/movs.html

Re: Surge Protector

to keyboard and composed:

Elsewhere in this thread it was shown that a 1800V transient is enough
take out a 240V 100W bulb.

By my calculation, the energy involved would be only ...

E = 1800V x 1800V / 60 ohms x 20us = 1.1J

You still don't understand. The transient power dissipation can be 1MW
(1000V x 1000A). A MOV doesn't need to dissipate a lot of *average*
power.

This was shown to be insignificant on numerous occasions. A 5%
reduction in energy absorption is not a design criterion for surge
protectors.

MOVs are shunt mode protectors. They don't care about earthing. All
they need to do is to *shunt* the surge away from the parallel
attached appliance. That's why two-wire appliances often have a MOV
between active and neutral.

5% is insignificant.

A MOV is not a switch, it is a *clamp*. A *perfect* MOV cannot *ever*
have a zero resistance. If it did, then it would short out the mains
supply.

5% is insignificant.

A MOV that absorbs 9.95J rather than 10J will not last significantly
longer.

5% is insignificant.

I agree that one should opt for higher rated protectors/MOVs. I don't
agree that higher rated MOVs absorb significantly less energy. That is
demonstrably false, even by your own analyses.

- Franc Zabkar
--

Re: Surge Protector

Exactly.  Now you are starting to grasp why lightning surges
typically don't explode light bulbs.  Why a 70 joule MOV dissipates so
few watts.  And why a surge so large to stress an MOV to maximum
results in 10 or more times energy absorbed elsewhere.  That is what
we want.  More energy absorbed elsewhere (in earth) and less energy
absorbed in the MOV.

Joules consumed by a light bulb determines things such as light
efficiency.  Light bulbs are designed to consume joules.  But
absorbing more joules is bad for MOVs.  How to reduce the joules
consumed by a shunt mode protector?   Increase MOV joules rating.  An
MOV with more joules means that MOV absorbs less energy  - which is
exactly what we want for surge protection.

Until you grasp that fact from those datasheet charts, then you will
not understand what MOVs do.  MOV does not provide better protection
by absorbing more energy.  MOV provides better protection by absorbing
less energy AND when shunting more energy to earth.  What makes a
better protector?  More MOV joules means it absorbs less energy.
More MOV joules means a better conductive connection (shunt) to earth.
What makes a better protection 'system'?  Better earthing.

Your formulas are correct.  But assumed is that (for example)
voltage is a mathematically independent variable.  Not true.  Study
the charts.  What happens when an MOV has higher joules?  Then its Vp
decreases resulting in more energy shunted to earth and less energy
absorbed by the MOV.

In simple terms, MOVs perform a job more like a switch.  A more
conductive switch, means a better protector.  That means more MOV
joules so that less energy is absorbed by the MOV.

Series mode protectors operate better by absorbing more energy.
Shunt mode protectors operate better by absorbing less energy.  MOV is
a shunt mode protector.  Again, study charts in those manufacturer
datasheets.  The numbers that confirm the above concepts are in those
manufacturer datasheet charts.

As an MOV joule rating increases, then MOV absorbs less energy.
Less energy absorbed means longer life expectancy.  Effective
protectors also shunt surges and remain functional - another fact from
those charts.  A protectors joules rating must be high enough as to
absorb less energy, shunt more energy to earth, and therefore remain
functional after direct lightning strikes.

Install protectors to make direct lightning strikes irrelevant.
Properly sized (sufficient joules) and earthed protector means
protection inside appliances is not overwhelmed and homeowner should
never even know the surge existed.