surge suppressor voltage limit

Hi Bud

Yes its a tough standard, in the UK I only know of one company that has had its products tested. The authorities responsible for enforcement only check products if someone gets injured, due to lack of funding.

Yes to both your other questions

I moved from Leeds about 35 years ago, to work in the West Midlands, hence I am in exile.

BillB

Leeds Lad in exile

Reply to
leedslad
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I now know what you are speaking of regarding the situation in the USA. Your

240 V supply is two hot wires with 120 V to ground and 240 V live to live. In Europe we have one live, a neutral and ground. The live has 230 V to Neutral and to Ground, Neutral has 0 V to ground.

For the US system I would use 3 MOVs 2 with 150V AC ratings connected live to ground and one with a 300 VAC rating, connected live to live. In Europe I would use 3 MOVs all rated 300 VAC, one connected live to ground, one live to neutral and one neutral to ground. With the US system the MOVs will provide a clamping voltage of about 400 V live to ground and 800 V live to live. While the European version will give

800V live to ground, live to neutral and neutral to ground.

The situation is even more complex in Europe as we have to limit the leakage to ground, normally by the use of a Gas Discharge Tube, GDT. The GDT is installed between live , the live to ground MOV and ground and neutral, its MOV and ground. The GDT has negotiable leakage at line voltage, but during a surge it will conduct, but it responds slowly increasing the peak clamping voltage due to its slow response.

So if you use a European surge suppression unit in the US it will work fine, but will not give the same protection live to ground that a unit designed for your supply would, but should be electrically safe.

BillB

Leeds Lad in exile

Reply to
leedslad

On Fri, 19 Sep 2008 23:18:47 GMT snipped-for-privacy@nospam.tesco.net wrote: | I now know what you are speaking of regarding the situation in the USA. Your | 240 V supply is two hot wires with 120 V to ground and 240 V live to live. | In Europe we have one live, a neutral and ground. The live has 230 V to | Neutral and to Ground, Neutral has 0 V to ground. | | For the US system I would use 3 MOVs 2 with 150V AC ratings connected live | to ground and one with a 300 VAC rating, connected live to live. In Europe I | would use 3 MOVs all rated 300 VAC, one connected live to ground, one live | to neutral and one neutral to ground. | With the US system the MOVs will provide a clamping voltage of about 400 V | live to ground and 800 V live to live. While the European version will give | 800V live to ground, live to neutral and neutral to ground. | | The situation is even more complex in Europe as we have to limit the leakage | to ground, normally by the use of a Gas Discharge Tube, GDT. The GDT is | installed between live , the live to ground MOV and ground and neutral, its | MOV and ground. The GDT has negotiable leakage at line voltage, but during a | surge it will conduct, but it responds slowly increasing the peak clamping | voltage due to its slow response. | | So if you use a European surge suppression unit in the US it will work fine, | but will not give the same protection live to ground that a unit designed | for your supply would, but should be electrically safe.

However, I believe it would get at least as good a protection level as the proposed doubling of the clamp voltage. The proposed 120V protection design would have 800 V on all pairs, L-G, L-N, and N-G. But maybe the European devices would be better with regard to leakage.

Reply to
phil-news-nospam

Hi Phil

The so called European devices are the same as the ones as the US version, made in the same plant in China, tested to the same standard as a component.

Yes I agree you would get less leakage to ground using a higher voltage MOV, but you would also get 800V live to ground clamping voltage instead of 400V live to ground when using the 150V MOV. The reason you fit a surge suppression device is to limit the value of any surges on the line to the lowest value economically possible to get the best protection for your money. If reducing the leakage is the prime requirement you should investigate other solutions to the problem eg GDTs.

What we have been discussing above is only half of the requirement, in addition you need to consider thermal protection for the MOVs, plus short circuit protection. An MOV without the protection can produce quite a good explosion when it fails, which all will do eventually if subjected to repeat surges. If a MOV fails you also need to know it has failed, in other words you need some form of indication. The simplest is that when you plug the device in all the circuits are dead, but this is not always possible the achieve easily. Otherwise you will continue using it, but not have the protection you think you have.

Look inside any well know surge strip and you will find all these feature. Also have at look at

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BillB

Leeds Lad in exile

Reply to
leedslad

On Sat, 20 Sep 2008 07:55:42 GMT snipped-for-privacy@nospam.tesco.net wrote: | Hi Phil | | The so called European devices are the same as the ones as the US version, | made in the same plant in China, tested to the same standard as a component. | | Yes I agree you would get less leakage to ground using a higher voltage MOV, | but you would also get 800V live to ground clamping voltage instead of 400V | live to ground when using the 150V MOV. The reason you fit a surge | suppression device is to limit the value of any surges on the line to the | lowest value economically possible to get the best protection for your | money. If reducing the leakage is the prime requirement you should | investigate other solutions to the problem eg GDTs.

Is there any reason the 800V level of clamping would be bad? This is for a

240VAC circuit.

If course there is the argument I _can_ use a lower clamping voltage between either of the two live wires, and the grounding wire (there being no neutral in this case). My counter to that argument is that there is a suggestion being made to double the clamping level for 120VAC devices. If that is valid science then how would it apply to the North American 240V configuration?

| What we have been discussing above is only half of the requirement, in | addition you need to consider thermal protection for the MOVs, plus short | circuit protection. An MOV without the protection can produce quite a good | explosion when it fails, which all will do eventually if subjected to repeat | surges. If a MOV fails you also need to know it has failed, in other words | you need some form of indication. The simplest is that when you plug the | device in all the circuits are dead, but this is not always possible the | achieve easily. Otherwise you will continue using it, but not have the | protection you think you have.

Presumably some circuit within the device will test if the MOV is completely open, or sufficiently open to not offer the protection. Some implication in an earlier post is that the leakage itself might be a means to do this aspect of the test.

For cases of the MOV being fused closed, being behind a fuse or circuit breaker would be expected to achieve that test.

| Look inside any well know surge strip and you will find all these feature. | Also have at look at |

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| and
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| and
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In what percentage of power strip type point of use protectors do you see these features?

Reply to
phil-news-nospam

Hi again Phil

All the surge protected power strip from the major suppliers use circuits similar to those I described, most use more MOVs. The cheaper no name ones have only one MOV and no working protection circuits.

I cannot see any valid reason for doubling the live to ground clamping voltage, it the same as saying why bother to fit surge suppression in the first place. The lower the clamping voltage the less likely it is to damage the connected equipment. One perceived advantage of using higher voltage MOVs is the transient energy rating, for example a 20mm 150 VAC MOV typically has a rating of 120J, while a 20mm, 300V MOV has a rating of 250J. Therefore the higher voltage device can withstand a larger surge energy level before failure, but against this you will have the higher clamping voltage that is more likely to damage the connected equipment. Energy ratings are used as a marketing tool by some manufactures. Finally it is the connected equipment that we are trying to protect not the MOVs from failure. The simple answer is use a large diameter MOV, which gives the best of the both, a similar clamping voltage and a higher energy rating. Some manufactures attempt to increase this by the use of MOVs in parallel, unfortunately this does not normally work. For it to work it requires matched MOVs, without this the lowest rated MOV takes all the surge energy, while the other does very little.

The basic circuits we have been discussing, do provide reasonable levels of protection, but do have limitation, in relation to the energy they can absorb.

BillB

Leeds Lad in exile

Reply to
leedslad

| I cannot see any valid reason for doubling the live to ground clamping | voltage, it the same as saying why bother to fit surge suppression in the | first place. The lower the clamping voltage the less likely it is to damage | the connected equipment.

I do agree with this concept. But my point is something else.

If *they* go ahead and change the surge protector designs so that the clamping voltage is doubled for the 120V protectors, then maybe that creates a device that could be used on twice the voltage.

If the clamping voltage in the USA is doubled, but this does not happen in Europe, then the devices in both would end up being about the same, right?

I'm looking for devices to protect against surges at point of use for 240V as wired in the USA. I could use a protective device from Europe, but it would not be optimal. But my big point is, if they double the clamping voltage of protective devices from USA, they would basically be the same and this gives me another choice to find a device that should work be will be less than optimal.

The optimal design would be one that considers the voltage to be 240V L1-L2,

120V L1-G, and 120V L2-G. The less that optimal designs have one advantage over the optimal designs: they are available.

So the remaining question is, if they do double the clamping voltage on the the models for the 120V market, are they usable on 240V? Would there be any difference between these "doubled for 120V" compared to the "normal for 240V" models in UK (not considering the NEMA vs. BS outlets and plugs, fusing requirements, etc).

| One perceived advantage of using higher voltage MOVs is the transient energy | rating, for example a 20mm 150 VAC MOV typically has a rating of 120J, while | a 20mm, 300V MOV has a rating of 250J. Therefore the higher voltage device | can withstand a larger surge energy level before failure, but against this | you will have the higher clamping voltage that is more likely to damage the | connected equipment. Energy ratings are used as a marketing tool by some | manufactures. Finally it is the connected equipment that we are trying to | protect not the MOVs from failure. The simple answer is use a large diameter | MOV, which gives the best of the both, a similar clamping voltage and a | higher energy rating. Some manufactures attempt to increase this by the use | of MOVs in parallel, unfortunately this does not normally work. For it to | work it requires matched MOVs, without this the lowest rated MOV takes all | the surge energy, while the other does very little.

Apparently some "experts" think that today's home appliances can withstand some higher surge levels, and that the MOVs are being destroyed more often than desireable in the protectors.

When I look at my computer SMPSUs and see "100-240V 50/60Hz" on them, should I assume these units can withstand the surge levels that would not be clamped by a 240V protector device in UK, when used in the USA whether on 120V or 240V?

Surges that originate upstream on the power utility distribution lines might well have twice the voltage on a 240V connection compared to a 120V connection. But surges that originate after the utility transformer steps the voltage down to the utilization voltage, are going to be the same.

The only reason I see to have any more protection in the USA compared to the UK is that we have areas of the country with more frequent lightning.

| The basic circuits we have been discussing, do provide reasonable levels of | protection, but do have limitation, in relation to the energy they can | absorb.

  1. So maybe we don't need a lower clamping voltage in the USA, given that more and more appliances (especially computers) handle all of 100-240V.

  1. So maybe there is an advantage in the ability to handle more energy with the clamping voltage doubled. That and being destroyed less often.

1+2 = maybe the "experts" are right.

  1. I want to use 240V, even though that means a different system configuration in the USA (compared to UK).

1+2+3 = more devices available (but I have to be very careful to choose units that have this doubled clamping voltage else the MOVs will give up their magic smoke as soon as I plug them in).
Reply to
phil-news-nospam

Hi Phil

Lets try and answer your questi> If *they* go ahead and change the surge protector designs so that the > clamping

The answer is no, you could not use it at twice the voltage. Only the ratings of the MOVs between Live and Ground have been increased in voltage rating. The MOV between live and live is still the same (300VAC). If you tried to use the unit on a higher rated supply the MOV between live and live would fail, as it is only rated for a 240 VAC supply.

Yes the MOVs would be the same.

If the device is a power strip the would it could have the same protection circuit, but it would not meet US or Canadian requirements due to the sockets been European and not meeting US or Canadian standards.

The answer should be yes if you ignore the differences in the standard requirements. Most counties other than the US base their standard on IEC 60884-1 for the electrical safety of the basic power strip and on IEC 61643-1 for surge suppression. So what is designed for Germany can also be sold in Holland, Spain etc. and what is designed for the UK can be sold in Hong Kong, Cyprus, Malta etc. Although Japan use the same socket as Japan it must be tested to Japanese standard and have a PSE approval before it can be sold there.

They can, but they will last longer with the lower clampng voltage, It is the marketing department like to use the higher energy rating as a marketing tool, the engineer still prefer the lower clamping voltage.

Yes, but they will last longer with the lower clamping voltage level between live and ground.

No it depends on the source of the surge.

Not true some area of the UK have similar lighting strikes frequency as the US.

As I have already said the lower the clamping voltage the longer the life of the protected device will be.

No a lower clamping voltage should always be the prime objective, the life of the MOVs can always be improved by using a larger more expensive device if cost is not the limiting factor.

The choice is yours.

NO any device rated for 240 VAC should give acceptable life both for your equipment and the protection device itself, if purchased from one of the major manufacturers. Do not be tempted to buy a cheap no name unit, irrespective of the manufacturers claims.

BillB

Reply to
leedslad

Doubling a varistor's voltage does nothing to double its surge energy handling abilities. That energy number is more related to current - not voltage. Voltage is a symptom of that current. Increasing a varistor's voltage mean a varistor absorbs more energy which means the varistor fails (degrades) faster.

Protector does not work by absorbing surges. It works by acting more like wire during a surge. A protector that absorbs less energy is more effective and lasts longer.

How does a varistor absorb less energy? Increase its joules rating.

Doubling voltage is about getting a varistor to absorb no energy - conduct near zero current during normal operation. For example, a 185 volt varistor for 120 VAC operation will conduct 800 volts during a more destructive surges. Increase varistor voltage to 370 volts for

240 VAC operation and that varistor may conduct at 1500 volts. The resulting higher voltage for same current means the varistor absorbs more energy during that surge which is not desirable. See varistor manufacturer datasheets for V-I charts.
Reply to
w_tom

Hi Tom

Regarding your comments, varistor do not conduct voltage, they conduct current, the voltage is the resistance produce by the flow of current through the device.

As I have said previously manufacturers sell there power strips using the Energy rating as a mean of trying to say their unit is better than the competitor, as it has a high energy rating whereas in real life this makes no difference to the actual protection they provide to the connected equipment, as it is the clamping voltage that makes the difference.

MOV only fail in a correctly designed power strip if they are subject to repeated high energy surges, this is rarely true in real life conditions.

Try reading the MOV manufacturers literature it explains the basic principles of how an MOV works, see

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BillB

Leeds Lad in exile

Reply to
leedslad

Correct about a surge; it is current. References to conducting voltage are a misnomer used only to explain a concept - not an accurate engineering term.

In North America, joules must be listed per safety standards. Meanwhile, many protectors only use 1/3rd and never more than 2/3rd of their joules when doing protection. Number of joules actually used may be even lower depending on what surge is where. IOW joules number on a power strip protector really provides no useful information for engineering purposes - at best only provides a ballpark absolute maximum that will never be achieved. Joules is a number that must be published per North American standards.

Many also see the word 'joules'; then assume those joules will absorb all of a surge. Again, a conclusion based only on assumptions; not based in learning what joules actually measure.

Surges are current - as stated by both authors. Voltage is only a symptom of that current. A surge properly diverted (by a protectors or other methods) means a massive current creates 'near to zero' voltage.

Another way to reduce voltage during a surge? Increase varistor joules. More joules means less voltage and less energy gets absorbed. A concept that many have difficulty grasping.

Reply to
w_tom

On Sun, 21 Sep 2008 20:50:05 GMT snipped-for-privacy@nospam.tesco.net wrote: | Hi Phil | | Lets try and answer your questions. | | On 21-Sep-2008, snipped-for-privacy@ipal.net wrote: | |> If *they* go ahead and change the surge protector designs so that the |> clamping |> voltage is doubled for the 120V protectors, then maybe that creates a |> device |> that could be used on twice the voltage. | | The answer is no, you could not use it at twice the voltage. Only the | ratings of the MOVs between Live and Ground have been increased in voltage | rating. The MOV between live and live is still the same (300VAC). If you | tried to use the unit on a higher rated supply the MOV between live and live | would fail, as it is only rated for a 240 VAC supply.

Your reference to "The MOV between live and live is still the same (300VAC)" isn't making any sense here. If you are talking about a device intended for

120V as in USA, then there is no "live and live". There is only one live, and a neutral, and a ground.

Unless you are referring to balanced power as in NEC 647. And that is quite a different beast.

If the voltage of ALL the MOVs on a 120V power strip are doubled, then that means the L-N are doubled, the L-G are doubled, and the N-G are doubled. So then if I use that device on 240V (USA style) then we change L to L1, and N to L2. So are yoy trying to say that when the voltage of a surge suppressor is doubled, it's not really doubled on the L-N pairing (which becomes L1-L2 when used for 240V)?

|> If the clamping voltage in the USA is doubled, but this does not happen in |> Europe, then the devices in both would end up being about the same, right? | | Yes the MOVs would be the same.

So why could the be used on 240V in Europe but not in USA?

|> I'm looking for devices to protect against surges at point of use for 240V |> as wired in the USA. I could use a protective device from Europe, but it |> would not be optimal. But my big point is, if they double the clamping |> voltage of protective devices from USA, they would basically be the same |> and this gives me another choice to find a device that should work be will |> be less than optimal. | | If the device is a power strip the would it could have the same protection | circuit, but it would not meet US or Canadian requirements due to the | sockets been European and not meeting US or Canadian standards.

That's a different issue. I might swap out the receptacle parts, plus other components that can only handle 120V.

|> So the remaining question is, if they do double the clamping voltage on |> the |> the models for the 120V market, are they usable on 240V? Would there be |> any |> difference between these "doubled for 120V" compared to the "normal for |> 240V" models in UK (not considering the NEMA vs. BS outlets and plugs, |> fusing requirements, etc). | | The answer should be yes if you ignore the differences in the standard | requirements. | Most counties other than the US base their standard on IEC 60884-1 for the | electrical safety of the basic power strip and on IEC 61643-1 for surge | suppression. So what is designed for Germany can also be sold in Holland, | Spain etc. and what is designed for the UK can be sold in Hong Kong, Cyprus, | Malta etc. Although Japan use the same socket as Japan it must be tested to | Japanese standard and have a PSE approval before it can be sold there.

I have some "wall warts" that are rated for 100-240V 50/60Hz, but the plugs are NEMA 1-15 (e.g. standard for 120V w/o ground pin).

|> Apparently some "experts" think that today's home appliances can withstand |> some higher surge levels, and that the MOVs are being destroyed more often |> than desirable in the protectors. | | They can, but they will last longer with the lower clampng voltage, It is | the marketing department like to use the higher energy rating as a marketing | tool, the engineer still prefer the lower clamping voltage.

But on 240V, the clamping voltage would be "just right" (doubled from 120V).

|> The only reason I see to have any more protection in the USA compared to |> the UK |> is that we have areas of the country with more frequent lightning. | | Not true some area of the UK have similar lighting strikes frequency as the | US.

Some areas of the US have substantially more than most of the US. How does the UK compare to say, Florida?

|> 1. So maybe we don't need a lower clamping voltage in the USA, given that |> more and more appliances (especially computers) handle all of |> 100-240V. | | As I have already said the lower the clamping voltage the longer the life of | the protected device will be.

Of course. But I want to run the device at 240V for power efficiency.

|> 1+2+3 = more devices available (but I have to be very careful to choose |> units |> that have this doubled clamping voltage else the MOVs will give up their |> magic |> smoke as soon as I plug them in). | | NO any device rated for 240 VAC should give acceptable life both for your | equipment and the protection device itself, if purchased from one of the | major manufacturers. Do not be tempted to buy a cheap no name unit, | irrespective of the manufacturers claims.

I never do that. I always want to know who to sue (even if that would be a very unrealistic thing) :-)

Reply to
phil-news-nospam

On Mon, 22 Sep 2008 08:25:10 -0700 (PDT) w_tom wrote: | On Sep 21, 1:00 pm, snipped-for-privacy@ipal.net wrote: |> 1+2 = maybe the "experts" are right. | | Doubling a varistor's voltage does nothing to double its surge | energy handling abilities. That energy number is more related to | current - not voltage. Voltage is a symptom of that current. | Increasing a varistor's voltage mean a varistor absorbs more energy | which means the varistor fails (degrades) faster.

The surge energy handling is not the issue I am asking about.

The issue I am asking about is using double the supply voltage when the MOVs are doubled in their clamping voltage.

| Protector does not work by absorbing surges. It works by acting | more like wire during a surge. A protector that absorbs less energy | is more effective and lasts longer. | | How does a varistor absorb less energy? Increase its joules rating.

An increase of joules rating is MORE energy, not less.

| Doubling voltage is about getting a varistor to absorb no energy - | conduct near zero current during normal operation. For example, a 185 | volt varistor for 120 VAC operation will conduct 800 volts during a | more destructive surges. Increase varistor voltage to 370 volts for | 240 VAC operation and that varistor may conduct at 1500 volts. The | resulting higher voltage for same current means the varistor absorbs | more energy during that surge which is not desirable. See varistor | manufacturer datasheets for V-I charts.

What I have read is that the varistors used for 120VAC operation conduct at

330V and posts here have said that is 400V. I just verified that one of my surge suppressors lists 330V. The theory is, if they double that voltage to at least 660V, then these could be used on 240VAC circuits. Originally I was expecting to use German Schuko surge suppressor strips. These are designed for 230V or the full 220V-240V European range. Complications with this would be plugging in wall warts that have US plug prongs. Once it is mentioned that power strips in USA should have the voltage rating of MOVs doubled, that opens up the possibility of power strips that can run on 240V and have the right outlet type.
Reply to
phil-news-nospam

| As I have said previously manufacturers sell there power strips using the | Energy rating as a mean of trying to say their unit is better than the | competitor, as it has a high energy rating whereas in real life this makes | no difference to the actual protection they provide to the connected | equipment, as it is the clamping voltage that makes the difference.

Unless the MOVs are destroyed and go open circuit before the surge is complete.

| MOV only fail in a correctly designed power strip if they are subject to | repeated high energy surges, this is rarely true in real life conditions.

Or a substantial available current sufficient to heat the MOV to the point of vaporization.

Reply to
phil-news-nospam

On Mon, 22 Sep 2008 16:55:35 -0700 (PDT) w_tom wrote: | On Sep 22, 4:40 pm, snipped-for-privacy@nospam.tesco.net wrote: |> Regarding your comments, varistor do not conduct voltage, they conduct |> current, the voltage is the resistance produce by the flow of current |> through the device. |> As I have said previously manufacturers sell there power strips using the |> Energy rating as a mean of trying to say their unit is better than the |> competitor, ... | | Correct about a surge; it is current. References to conducting | voltage are a misnomer used only to explain a concept - not an | accurate engineering term. | | In North America, joules must be listed per safety standards. | Meanwhile, many protectors only use 1/3rd and never more than 2/3rd of | their joules when doing protection. Number of joules actually used | may be even lower depending on what surge is where. IOW joules number | on a power strip protector really provides no useful information for | engineering purposes - at best only provides a ballpark absolute | maximum that will never be achieved. Joules is a number that must be | published per North American standards.

The clamping voltage would be more useful. But it would help to also know the clamped impedance (should be very very low, but it would not be zero).

| Many also see the word 'joules'; then assume those joules will absorb | all of a surge. Again, a conclusion based only on assumptions; not | based in learning what joules actually measure. | | Surges are current - as stated by both authors. Voltage is only a | symptom of that current. A surge properly diverted (by a protectors | or other methods) means a massive current creates 'near to zero' | voltage.

Right. And we want that voltage drop to be below the supply voltage so the surge is not any greater.

| Another way to reduce voltage during a surge? Increase varistor | joules. More joules means less voltage and less energy gets | absorbed. A concept that many have difficulty grasping.

Joules _is_ energy. So that doesn't make sense UNLESS you are saying that a higher joules RATING has a lower impedance, and that results in a lower voltage drop when conducting.

Reply to
phil-news-nospam

Phil - you keep having this problem. Joules is energy. Does that mean varistors work by absorbing the surge? Of course not. A benchmark statement. More joules means less voltage and less energy gets absorbed by the varistor. A concept that so many have diffculty grasping, in part, because assumptions replace learning. Learn what joules measure before posting your assumptions.

Do the work. Learn from varistor datasheets. It's not difficult. Once you learn how varistors work, then this becomes obvious. More joules means the protector absorbs less surge energy - which is desireable in protectors. For better protection, we want varistors to absorb less energy. This is accomplished by increasing the joules.

That becomes obvious even on the V-I charts. Those datasheet V-I charts were referenced repeatedly. Did you review them yet? Then it becomes obvious: increasing joules means less energy gets absorbed.

Reply to
w_tom

If vaporization failure occurs, then a protector was grossly undersized and was a threat to human life. Vaporization is a complete violation of the manufacturer's "Absolute Maximum Ratings" which are located at the very top of every MOV datasheet. Varistor must fail only by degrading. MOVs must never get so hot as to vaporize. But vaporization gets the naive to recommend obscenely profitable and ineffective protectors.

An effective protector remains functional after a surge so that humans never even knows a surge existed.

Increasing varistor voltage is to make the MOV not conduct energy during normal operation. Varistor voltage is kept as low as possible so that MOV does not conduct during normal operation and absorbs minimal energy during a surge.

Also stated correctly before and restated again. So that a protector absorbs even less energy, increase its joules. Increased joules means a protector absorbs less energy during a surge; which is what we want from a better protector. This concept is difficult for those who know only by using assumption. This concept is obvious once numbers from MOV datasheets are learned. Increasing joules means the protector is better - absorbs less surge energy.

Reply to
w_tom

. From previous threads, w_ seems to have the idea that high joule ratings magically reduce the actual clamp voltage.

In fact, high joule ratings come with high surge current ratings. Comparing a high joule MOV with a lower joule MOV (with the same nominal clamp voltage) at the same surge currents, the high rated one will be operating at a lower percentage of its rated surge current. The current density through the MOV will be correspondingly lower. That produces a lower actual clamp voltage. There is no magic involved. And the difference isn't that great.

High current/joule rated MOVs are used because they give long life. The joule rating for a MOV is a single event rating. As the individual energy hits on a MOV become a smaller percentage of the rating, the cumulative energy rating of a MOV goes up rapidly (not linearly).

Reply to
bud--

. Francois Martzloff was the US-NIST guru on surges with many published papers. From one of them: "The fact of the matter is that nowadays, most electronic appliances have an inherent immunity level of at least 600 V to 800 V, so that the clamping voltages of 330 V widely offered by [surge suppressor] manufacturers are really not necessary. Objective assessment of the situation leads to the conclusion that the 330 V clamping level, promoted by a few manufacturers, was encouraged by the promulgation of UL Std 1449, showing that voltage as the lowest in a series of possible clamping voltages for 120 V circuits. Thus was created the downward auction of "lower is better" notwithstanding the objections raised by several researchers and well-informed manufacturers. One of the consequences of this downward auction can be premature ageing of [surge suppressors] that are called upon to carry surge currents as the result of relatively low transient voltages that would not put equipment in jeopardy."

The paper dates back to 1995. Suppressors with very high ratings are now readily and cheaply available which may make the argument less relevant.

For the 250V world, one would have to know the immunity level. It may be closer to the normal voltage than in the US, making an increase in clamp voltage less practical. .

. Matching would be better. At least you should sequentially go through the paralleled MOVs, with some sharing along the way. Or can you drive one into failure (conduction at normal voltages) before the others are 'used up'?

How do manufacturers get ratings of 1000+J for a single MOV in a plug-in suppressor? Paralleling? There seem to be high rated single MOVs that can be used in service panel suppressors. .

. Another Martzloff paper looks at the energy absorption for a MOV at the end of a branch circuit. It is surprisingly small for 2 reasons:

  1. At about 6000V (US) there is arc over from panel busses to enclosure(+neutral+ground+earthing system). After the arc is established, the voltage is hundreds of volts. That dumps most of the energy coming in on hot power wires to earth. (Receptacles (US) also arc-over at about 6kV.)
  2. The impedance of branch circuit wiring for surges greatly limits the surge current, and thus energy, that can reach a MOV.

The maximum energy dissipated in the MOV was 35 Joules for a 10 meter branch circuit. In 13 of 15 cases it was 1 Joule or less. That was with surges source currents from 2,000 to 10,000A (the maximum likely for a home). Surprisingly, the highest energies were for some of the lower surge currents because the MOV could hold the service panel voltage below arc-over.

Reply to
bud--

Hi Again Phil

My reference to L to L is based on an earlier comment that the 240V domestic supply was 120VAC-Ground-120VAC ie 240V Live to Live. If this is not the case please advise what a 240VAC domestic supply is as all my comments have been based on this assumption.

If you change the AC rated voltage of all the MOVs to 300VAC the device can work at either 120VAC live to ground or at 240VAC live to ground. In both cases the clamping voltage will be approximately 800V live to live (or neutral), live to ground and neutral to ground. Where as if the live to ground voltage is 120VAC and the neutral to ground AC voltage is either 0 or 120V and you use a 150VAC MOV, the clamping voltage to ground for both MOVs will be approximately 400V.

The answer is yes they can, but a European device will not meet US/Canadian standards and likewise the US version would not meet European standards, as the standards set different requirements.

Do these have surge protection?

What is "just right" ?

Its the same in the UK.

I have not implied that you should not use 240V, I have only tried to state that the lower the clamping voltage is the better the equipment will be protected.

In the UK I am not as concerned over who you will sue, but about trying to make sure you do not need to sue anyone.

Best regards

BillB

Reply to
leedslad

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