surge suppressor voltage limit

You mean use a TVSS built for 120V and apply it at 240V? I worry it would be bleeding catastrophic amounts of current with double nominal voltage applied. Plus, a terminal intended for neutral (0V) would not be insulated for the 120V applied if the 240V is +-120 V. If the 240V is 240V and neutral, the 240 V terminal may only be good for 120 V nominal. Also I doubt it is 'acceptable' to apply a device intended for 120 V at 240 V.

The clamping voltage statement doesn't sound right. I'd go back and reread the information and pay particular attention to the knee voltage and the current rank just prior to it. I'm not saying it's a bad idea; just that it might have a lot of leakage on 240 that surpasses the component's temp ratings.

You don't give enough info on how you plan to use these, but I do know that the UK style 230Vac 50Hz does have accomodating surge suppressors. Their grid is configured differently than here in the US where I am of course.

HTH

MOVs used in surge suppression circuit for 240VAC are normally selected based on 240 +10% and then + 10% again. This allow for a 10% increase in the nominal supply voltage to 264 VAC and for the 10% manufacturing tolerance on the AC rating of the MOV. Therefore for 240VAC you would normally select a MOV with a nominal AC rating of at least 290 VAC. The standard rating for an MOV is either 300 VAC or 320 VAC depending on the manufacturer. These normally clamp the surge at about 800V.

In your posting you talk about 660 V, I would guess that this is the clamping voltage, not the AC rating. If you use a surge suppressor rated at

120VAC these normally use a MOV rated at 150 VAC. These will fail very quickly if are used at 240VAC, due the high leakage current.

Best regards

BillB

Those voltages are ball park numbers. Actual voltage curve is not a step function or 'knee voltage' as so many want to believe. A protector rated at 330 volts will conduct current even at 130 V RMS. How much current determines how quickly an MOV degrades. Yes, degrades because MOVs inside protectors must fail only by degrading; a change in its threshold voltage. A 10% change means the MOV has failed.

Typically, MOVs for 330 volts will also conduct at 180 volts AND will increase voltage to greater than 800 volts as a surge current increases. So what is its voltage? That would be the MOV inside a 330 volt protector. 330 or 660 volt numbers are ballpark - arbitrary. See MOV datasheets for the V-I charts.

An MOV used in 120 volt operation must conduct less than acceptable current at 185 volts. Idea is to select an MOV that conducts under a minimum acceptable current constantly. How do we measure MOV threshold voltage? One standard is to push a constant 1 milliamp through the MOV and read its voltage. If that voltage changes by 10%, then the MOV has degraded - failed. IOW that 1 milliamp voltage should be sufficiently above 185 for 120 VAC operation and above 370 for 240 VAC operation. These would also be 330 volt and 660 volt let- through voltages.

In Europe the standard for surge suppression devices is EN 61643-11. Voltage limiting devices a listed as Class 3 devices. This is a harmonised standard listed in the Official Journal of the EU. This mean it is a means of demonstrating compliance with the European Low voltage Directive. We have been testing to this standard for the last 3 years and have not yet had a first time pass. It has recently been revised and this makes compliance even more difficult to achieve.

BillB

Leeds Lad in exile

|> Originally, I thought that was a bad idea. But now I think maybe |> that will |> be useful. How I came to that conclusion was finding that |> suppressors were |> not readily available for 240VAC power systems. With such a change |> in the |> clamping voltage, I could use these more common suppressors as part |> of the |> changeover from 120V to 240V for my computers. |>

|> -- |> |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to |> ignorance | |> | by the abuse department, bellsouth.net is blocked. If you |> post to | |> | Usenet from these places, find another Usenet provider |> ASAP. | |> | Phil Howard KA9WGN (email for humans: first name in lower case at |> ipal.net) | | | You mean use a TVSS built for 120V and apply it at 240V? I worry it | would be bleeding catastrophic amounts of current with double nominal | voltage applied. Plus, a terminal intended for neutral (0V) would not | be insulated for the 120V applied if the 240V is +-120 V. If the 240V | is 240V and neutral, the 240 V terminal may only be good for 120 V

If 330V clamping level works on 120VAC, then 660V clamping level should work on

240VAC. The disadvantage would be that the L1-G and L2-G paths would be 660V as well, and those potentials are 120VAC each on a North American 240V system.

I have disassembled power strips, including a nice TrippLite one that became unusable due to water damage. These things are wired symmetrically.

| nominal. Also I doubt it is 'acceptable' to apply a device intended | for 120 V at 240 V.

I find it not 'acceptable' that the manufacturers don't make decent 240V ones in the first place. If they did, I'd buy one.

I did find one on the TrippLite web site for 240V. But it has NEMA 5-15 plug and outlets. There's something wrong with that concept. And it has a poor level of protection.

The fact that there is not a genuine decent one on the market means I have no choice but to "construct" one in some way. Feel free to advise HOW to do that. But any suggestion to not do that will be ignored since it is not a valid path to the goal.

On Tue, 16 Sep 2008 11:34:16 -0400 TWayne wrote: |> In a previous thread a reference was made to an expert recommendation |> that surge suppressors have their clamping voltage doubled from 330V |> to 660V for 120VAC suppressors. |>

|> Originally, I thought that was a bad idea. But now I think maybe |> that will be useful. How I came to that conclusion was finding that |> suppressors were not readily available for 240VAC power systems. |> With such a change in the clamping voltage, I could use these more |> common suppressors as part of the changeover from 120V to 240V for my |> computers. |>

|>> WARNING: Due to extreme spam, googlegroups.com is blocked. Due to |>> ignorance | by the abuse department, bellsouth.net is |>> blocked. If you post to | Usenet from these places, find |>> another Usenet provider ASAP. | |>> Phil Howard KA9WGN (email for humans: first name in lower case at |>> ipal.net) | | | The clamping voltage statement doesn't sound right. I'd go back and | reread the information and pay particular attention to the knee voltage | and the current rank just prior to it. I'm not saying it's a bad idea; | just that it might have a lot of leakage on 240 that surpasses the | component's temp ratings.

If you designed and constructed a real 240V protector, would you not make it have twice the clamping level?

| You don't give enough info on how you plan to use these, but I do know | that the UK style 230Vac 50Hz does have accomodating surge suppressors. | Their grid is configured differently than here in the US where I am of | course.

I would use it here in the US on the US style 240V system which is 120V to ground on each of two hot wires in opposing polarity (180 degrees in the case of genuine 240V single phase).

I have considered using a German power strip, and just make my computer wiring all based on the Schuko. The Schuko is unpolarized and symmetric, even though the electrical system it is based on is 230V L-N. But they require devices to be safe when plugged in either way. So these devices should be able to handle 230V relative to ground on either conductor, as we as between conductors.

The change of clamping voltage from 330V to 660V would means I might be able to find devices with protective components that could handle 240V L-L *AND* be able to support replacing NEMA 5-15R outlets with NEMA 6-15R outlets. I would prefer to use the NEMA 6-15's over the Schuko.

Alternatively to the Schuko, which is more common, I might use the Italian plug/outlet design.

Most of my "wall wart" power supplies are rated for 100-240 volts. But they all have NEMA 1-15P on them. So I'll still need to either put 240V on a NEMA 5-15R or just run these on 120V.

On Tue, 16 Sep 2008 19:03:19 GMT snipped-for-privacy@nospam.tesco.net wrote: | MOVs used in surge suppression circuit for 240VAC are normally selected | based on 240 +10% and then + 10% again. This allow for a 10% increase in the | nominal supply voltage to 264 VAC and for the 10% manufacturing tolerance on | the AC rating of the MOV. Therefore for 240VAC you would normally select a | MOV with a nominal AC rating of at least 290 VAC. The standard rating for an | MOV is either 300 VAC or 320 VAC depending on the manufacturer. These | normally clamp the surge at about 800V. | | In your posting you talk about 660 V, I would guess that this is the | clamping voltage, not the AC rating. If you use a surge suppressor rated at | 120VAC these normally use a MOV rated at 150 VAC. These will fail very | quickly if are used at 240VAC, due the high leakage current. | | Best regards | | BillB

Don't forget, Bill, that I am talking about 120VAC protectors based on DOUBLING their clamping level ... NOT the current crop of 120VAC protectors that perhaps still have the low clamping level.

I've read in multiple places that the common clamping voltage for 120VAC is

330V and for 240VAC is 660V. Fewer of the readings mentioned the 240VAC and 660V clamping level. But the ratio makes sense.

The PEAK voltage on 120VAC is 170V. The PEAK voltage on 240VAC is 340V. So the 330V level for protecting 120VAC, and the 660V level for protecting 240VAC, is well above the peak operating voltage.

If you DOUBLE the clamping level AND double the AC voltage, what do you think happens?

On Wed, 17 Sep 2008 08:31:03 -0700 (PDT) w_tom wrote: | On Sep 15, 11:44 pm, snipped-for-privacy@ipal.net wrote: |> In a previous thread a reference was made to an expert recommendation that |> surge suppressors have their clamping voltage doubled from 330V to 660V for |> 120VAC suppressors. | | Those voltages are ball park numbers. Actual voltage curve is not a | step function or 'knee voltage' as so many want to believe. A | protector rated at 330 volts will conduct current even at 130 V RMS. | How much current determines how quickly an MOV degrades. Yes, | degrades because MOVs inside protectors must fail only by degrading; a | change in its threshold voltage. A 10% change means the MOV has | failed. | | Typically, MOVs for 330 volts will also conduct at 180 volts AND | will increase voltage to greater than 800 volts as a surge current | increases. So what is its voltage? That would be the MOV inside a 330 | volt protector. 330 or 660 volt numbers are ballpark - arbitrary. | See MOV datasheets for the V-I charts. | | An MOV used in 120 volt operation must conduct less than acceptable | current at 185 volts. Idea is to select an MOV that conducts under a | minimum acceptable current constantly. How do we measure MOV | threshold voltage? One standard is to push a constant 1 milliamp | through the MOV and read its voltage. If that voltage changes by 10%, | then the MOV has degraded - failed. IOW that 1 milliamp voltage | should be sufficiently above 185 for 120 VAC operation and above 370 | for 240 VAC operation. These would also be 330 volt and 660 volt let- | through voltages.

So you think maybe I should fall back to the old plan of using Schuko power strips protectors?

I don't know what is inside that Schuko strip to suggest it is safe. Question is whether you are doing this to learn, or doing it to make a protector. Using (and modifying) a Schuko for North American power is not acceptable for normal operation and may even violate your fire insurance. But it might be educational if used as an experiment.

No. Same standards that also define what surges an appliance must withstand without damage also define how much voltage it must see constantly. That standard then defines the maximum constant voltage a protector must remain 'inert' for. For 120 VAC operation, that protector must remain 'inert' at voltages above 185 - not 170.

What happens when AC mains goes to a completely normal 125 volts? All part of a protector design.

I have seen (older) power strips that use 3 or so ordinary duplex 5-15R recepticles in a row. If you want to make your own, try to find these and replace the outlets with 6-15R's.

What are the problems?

Please explain what you mean by doubling their clamping voltage?

All the surge suppression devices we have tested are suitable for use at

240VAC and use 300V MOVs with rated clamping voltages of around 770V. These have all had clamping voltages of around 800V when subjected to 8/20us pulses. I am talking of testing surge suppression devices not just an MOV by its self.

Similar sized MOV rated at 150VAC have rated clamping voltages of between

360 and 400V.

See Little Fuse website for details

BillB

Leeds Lad in exile

Hi Bud

Normally they do not indicate a failure after a failure has occurred, or they fail unsafe.

BillB

Leeds Lad in exile

| Please explain what you mean by doubling their clamping voltage?

Using a 660V level instead of ao 330V level.

| All the surge suppression devices we have tested are suitable for use at | 240VAC and use 300V MOVs with rated clamping voltages of around 770V. These | have all had clamping voltages of around 800V when subjected to 8/20us | pulses.

I've not tested these in labs. I'm just going on things I have read in the past. In particular someone did post here that an "expert" recommended that the levels be double.

| I am talking of testing surge suppression devices not just an MOV by its | self. | | Similar sized MOV rated at 150VAC have rated clamping voltages of between | 360 and 400V. | | See Little Fuse website for details |

I'll bookmark that to check it out.

On Thu, 18 Sep 2008 15:48:40 +0000 (UTC) Michael Moroney wrote: | snipped-for-privacy@ipal.net writes: | |>I would use it here in the US on the US style 240V system which is 120V to |>ground on each of two hot wires in opposing polarity (180 degrees in the |>case of genuine 240V single phase). | |>I have considered using a German power strip, and just make my computer |>wiring all based on the Schuko. The Schuko is unpolarized and symmetric, |>even though the electrical system it is based on is 230V L-N. But they |>require devices to be safe when plugged in either way. So these devices |>should be able to handle 230V relative to ground on either conductor, as |>we as between conductors. | | I have seen (older) power strips that use 3 or so ordinary duplex 5-15R | recepticles in a row. If you want to make your own, try to find these and | replace the outlets with 6-15R's.

That was the idea ... except in for some wall warts I'll still need 5-15R.

| On Sep 17, 8:35 pm, snipped-for-privacy@ipal.net wrote: |> So you think maybe I should fall back to the old plan of using Schuko power |> strips protectors? | | I don't know what is inside that Schuko strip to suggest it is | safe. Question is whether you are doing this to learn, or doing it to | make a protector. Using (and modifying) a Schuko for North American | power is not acceptable for normal operation and may even violate your | fire insurance. But it might be educational if used as an experiment.

Open one up and see. It's basically the same thing as used for 120V in USA, except it obviously has to be able to handle the 230V (+/- 10V) standard in Europe AND be able to handle being plugged in either way.

|> The PEAK voltage on 120VAC is 170V. | No. Same standards that also define what surges an appliance must | withstand without damage also define how much voltage it must see | constantly. That standard then defines the maximum constant voltage a | protector must remain 'inert' for. For 120 VAC operation, that | protector must remain 'inert' at voltages above 185 - not 170.

I was not saying the operative level was 170, only that the sinusoidal peak of a nominal 120VAC is 170V. Add 10% or more as needed.

| What happens when AC mains goes to a completely normal 125 volts? | All part of a protector design.

Of course. So the real level where the protector acts would be higher than

170V, such as the 330V figure I have read in a number of places.

That 330 volt number is not a threshold voltage for MOVs. But again, MOVs do not have this knee voltage as so many want to believe. Too many think an MOV works like a zener diode. Same MOV rated for

170 volts is also rated by another standard at 330 volts and rated by another standard at 800 volts.

A varistor that does not conduct much at 185 volts and that conducts at 250 volts is the same varistor used in protectors with a "let- through voltage" of 330 volts. A 330 is a UL number which measures the same MOV differently than numbers in manufacturer datasheet. But again, get V-I charts from MOV manufacturers to appreciate why all these numbers are ballpark or arbitrary. Experience will make them more understandable.

Is the standard is too tough?

At the risk of asking a dumb question, would the suppressors likely pass the US-UL tests?

Are you the entity formerly known as snipped-for-privacy@abc.net? (His posts were real interesting.) Still at TUV?

In exile?