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Post by leonski on Feb 2, 2020 21:38:49 GMT -5
That many potential lightning events over a 6 year period of 6 per year is 36 events. IMO? You might want to replace the MOVs IN the Panamax at this point. Read (quote) specification numbers for that Panamax. What is painfully obvious? Six surges per year means a dishwasher, clock radios, refrigerator, many GFCIs, furnace, LED & CFL bulbs, garage door openers, dimmer switches, central air, and smoke detectors have been replaced often. Why do six surges per year damage a near zero joule Panamax? And not unprotected appliances? The answer is defined by a number in that sentence. Yes, protectors have a life expectancy. Then include numbers. A 'whole house' protector remains functional for many decades after many direct lightning strikes. Yes, it does eventually degrade (and must not trigger that protection light). That "years" number is so large that nobody cares. Panamax, with a massive profit margin, fails on a surge too tiny to overwhelm what is superior protection already inside appliances. How many joules does that Panamax claim to 'absorb'? Honest recommendations always include that number. Any recommendation that does not cite relevant spec numbers is best ignored. Honest recommendations state what is relevant. Where do hundreds of thousands of joules harmlessly dissipate? Effective protection means that current is not anywhere inside the house. If connected low impedance (ie less than 10 feet) to an earth ground electrode, then even that tiny joule (high profit) Panamax is protected. Informed consumers always properly earth a 'whole house' protector on AC mains. That and protection (installed for free) on all other incoming wires means effective protection. Best protection must already be installed on an incoming TV cable, telephone, satellite dish, and OTA antenna. Even code required that, long before any of us existed. But AC electric (the most common incoming path for surges) is not required to have that proven protection. I opted for 'whole house' protection, but this protection is provided by my power company for a small monthly fee. This 'surge shield' is installed at the power meter and is not my responsibility. If there is a fault light illuminated, I call the power company to correct it. Like others have said, there are age/life cycle limitations on surge protectors. Steveh - that protector light can only report a failure that must never happen. That light can only report a protector was so grossly undersized that only a fuse prevented a fire. That failure light can only report that the replacement protector must be sized larger. Again, informed replies also include numbers. Lightning is typically 20,000 amps. So a minimally sized 'whole house' protector is 50,000 amps. If that failure light indicates a failure, then a new protector probably should be 100,000 amps. Only answers that also say why with numbers are relevant. That failure light says nothing about the acceptable failure mode - degradation. It only reports catastrophic type failure. No protector does protection. Not one. Best protection on a TV cable is a direct connection to the earth ground electrodes. No protector needed. But AC electric cannot connect direct to what does all protection - earth ground. So that 'whole house' protector must make - and this number is critical - a low impedance (ie less than 10 foot) connect to an earthing electrode. Protection is defined by this question. Where do hundreds of thousands of joules harmlessly dissipate? Clearly not in an obscenely overpriced Panamax with near zero joules and a high failure rate. Protection means hundreds of thousands of joules are harmlessly 'absorbed' outside in earth ground. What is THE most critical item in that protection 'system'? A low impedance (ie hardwire has no sharp bends) connection to single point earth ground. As Ben Franklin demonstrated over 250 years ago, protection is always about a connection to and quality of the item that defines protection - earth ground electrodes. Why is a 'whole house' protector so effective. It has that low impedance connection to earth. Panamax (a profit center) clearly does not. Numbers on that near zero Panamax explain why transients, that are only noise, easily destroy a Panamax. Always learn (demand) the numbers. I noted 36 events. And all are of unknown severity. From 'what was that?' to perhaps a blinding next door tree-strike. Not that it matters, but here in SoCal we have Few such events. My Panamax is still good. And DOES have protection which Keith is unaware of. It'll shut off power to all outlets if voltage is outside the range of 96->134 VAC. It has done that 3, maybe 4 times in decade + of ownership. The lightning storm I was in out in Palm Springs (Cathedral City, really) was awful, lasting maybe 2 hours tops with 3 huge lightning strikes within flash-vision range. Owners of home noted some problems with stuff when they got home. One computer I remember got a fried modem card. Maybe the zap came in thru the phone line? While the ground is OF COURSE of vital importance, the MOVs are connected in a 'Y' scheme. Hot-2-Ground / Hot-2-Neutral / Neutral-2-Ground Aren't neutral and ground connected at the box? I'm no electrician. We've been thru the before and I'm out of here. Keith's idea of Series Mode suppression makes perfect sense and is not sacrificial, unlike a MOV. And YES, absolutely. GOOD ground is absolutely vital. That's why I like the whole-house approach since the active device is at the box, right next to the ground rod. Seems reasonable. |
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Post by leonski on Feb 3, 2020 18:14:04 GMT -5
I just looked up a long-ago review of my Panamax. Model? Max 5510 pro, I think. Pictures match, anyway. And the specs are familiar.
More on point? The claim is for 2100 Joules of surge protection. It also has a 400va isolation transfomer and various switching options
for delay on / off and such. Included are ground options for the transformer.
Iso transformer alone is a gem. The first TV I plugged into the Panamax was a big (very heavy) 36" direct view TV. Maybe the last of the
round-front sets. Virtually ALL of the 'snow' disappeared. Help to the picture was drastic and even guests would ask what I had done to
the set.
Panamax willl NOT disclose any information about the MOVs, wanting some fee to replace them. Maybe 5$ in parts and 20 minutes labor.
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Post by westom on Feb 4, 2020 21:50:18 GMT -5
While the ground is OF COURSE of vital importance, the MOVs are connected in a 'Y' scheme. Hot-2-Ground / Hot-2-Neutral / Neutral-2-Ground Aren't neutral and ground connected at the box? I'm no electrician. If that Panamax did anything useful, then listed are so many other unprotected and damage appliances. It is called cherry picking. Simply ignore anything that obviously contradicts a conclusion. What protected central air, GFCIs, LED & CFL bulbs, refrigerator, garage door opener, dimmer switches, dishwasher, and smoke detectors? If a Panamax did anything useful, then all those other appliance must be on invisible protectors. Especially since many are less robust - ie are more easily damaged. They are not damaged? Then Panamax did nothing useful. Second, protectors do nothing until 120 volts well exceeds a let-through voltage - 330 volts. A voltage approaching 1000 volts on protector parts means a same voltage is incoming to appliances. Why does a protector fail and attached appliance does not? Electronics must withstand up to 600 volts without damage. Some computers even define that protection as high as 1800 volts. A surge that can damage a tiny joule Panamax may be too tiny to damage other appliances. That surge is incoming to everything. Why is everything undamaged? 36 surges were only noise. Third, it is called impedance. That wall receptacle safety ground may be 0.2 ohms resistance (to the breaker box). And 120 ohms impedance. A tiny surge (ie 100 amps) through that Panamax would be 100 amps times 120 ohms; less than 12,000 volts. Why less than? An IEEE brochure demonstrates why. A plug-in protector in one room used its MOVs to connect a surge destructively through a TV in the adjacent room. IEEE even put a number to it. 8000 volts destructively. They sell a Panamax to many who, for example, only use speculation to assume that wall receptacle safety ground is an earth ground. It clearly is not. Just another reason why a receptacle's safety (equipment) ground is not called earth ground. Panamax is not one of those companies on a list of integrity. Others (that provide effective protectors) are well known for their many products known for integrity. Their protectors make the low impedance (ie less than 10 foot) connection to earth. Then hundreds of thousands of joules cause no damage. Meanwhile series mode protectors can saturate - stop blocking any surge - after maybe 600 joules. Did you read that number? Destructive surges are routinely well above 600 joules. Even 1000 joules is typically too tiny to damage electronics. Even series mode filters already in electronics are superior. Effective protection is about hundreds of thousands of joules. Never ignore numbers. Scams work when these numbers are ignored. Effective protection always answers this question. Where do hundreds of thousands of joules harmlessly dissipate? Series mode filter numbers are near zero. Four, any facility that cannot have damage ALWAYS earths that transient BEFORE it enters a building. Always. Then best protection means everything is protected. And finally, those MOVs in a Y are for a type of electric current that typically causes no damage. Effective protection is always about longitudinal mode currents. That transient is only averted when that current connects low impedance (ie less than 3 meters) to earth before entering. Then that current is not anywhere inside hunting for earth ground destructively via appliances. Then a Panamax is not simply giving that current even more paths to compromise effective protection already inside all appliances. Then effective protection even protects a Panamax's tiny joules. Then a homeowner spends maybe 100 times less money per protected appliance compared to that expensive and tiny joule series mode filter. Series mode filter only makes sense when one completely ignores all specification numbers. An informed consumer always demands an answer to this question. Where do hundreds of thousands of joules harmlessly dissipate? Only then does effective protection exist - to even protect tiny joules inside a Panamax. And so that tiny protection in a series mode filter does not saturate. |
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Post by leonski on Feb 4, 2020 22:47:01 GMT -5
I can't say for certain that we've even HAD a lightnig or other fault induced 'event' here in my memory. We have had a few low voltage or high voltage events which the Panamax caught as well as cleaning up the AC to the point where both the TV and stereo were better. I had to reset the speakers when first installed....And the TV completely lost all 'snow' giving a better black and the appearance of better color / saturation.
Energy is SUPPOSED to shunt to ground. That's why the MOVs are in a 'Y' with both hot and neutral to ground thru MOVs and hot to neutral also thru MOVs. And that's why I'd agree that the best place is at the box. Which is right next to the ground rod, which is by code driven
some distance into the ground and has a low-ohmic contact to the rest of the circuit. I've seen 'em use a MEGGER to check this connection.
MOV's are typically specs @20% above high spec of the line. So, a 120vac +24 is 144vac. I don't know what max allowed on a 120v line is. My panamax cuts out at 135v. Not 330, which is indeed a common MOV voltage rating.
MOVs are shunt mo\de, not series mode. Whew!
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Post by Ex_Vintage on Feb 4, 2020 23:16:38 GMT -5
Just for the record. Assume the clamping voltage for an MOV applied to a 120VAC source has its rated clamping voltage at 330V peak. The aforementioned "100's of thousands of joules" would require a current spike of 252.5 million amps. I really doubt a 120v home circuit is capable of 250 million amps. The IEEE C62.41 standard for a testing lightning strike for a residential circuit is a 6000V 1.2x 50 micro second waveform with a source current capacity of 3000A. That would produce a 50 joule event.
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Post by leonski on Feb 5, 2020 1:59:01 GMT -5
Just for the record. Assume the clamping voltage for an MOV applied to a 120VAC source has its rated clamping voltage at 330V peak. The aforementioned "100's of thousands of joules" would require a current spike of 252.5 million amps. I really doubt a 120v home circuit is capable of 250 million amps. The IEEE C62.41 standard for a testing lightning strike for a residential circuit is a 6000V 1.2x 50 micro second waveform with a source current capacity of 3000A. That would produce a 50 joule event. Thank you for the clarification and the math. That means my Panamax will be good for around 40 of the 'standard' events. Here in SoCal? That's gonna take a Long Time. I have one other question? If I may? Westom mentioned the ground IMPEDANCE as IIRC, 120 ohms. And resistance of 0.2ohms, I think at the outlet. Now? Isn't lightning DC? Or is it a high frequency event? Just asking since impedance is usually referenced to a frequency. |
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Post by mgbpuff on Feb 5, 2020 9:37:27 GMT -5
Just for the record. Assume the clamping voltage for an MOV applied to a 120VAC source has its rated clamping voltage at 330V peak. The aforementioned "100's of thousands of joules" would require a current spike of 252.5 million amps. I really doubt a 120v home circuit is capable of 250 million amps. The IEEE C62.41 standard for a testing lightning strike for a residential circuit is a 6000V 1.2x 50 micro second waveform with a source current capacity of 3000A. That would produce a 50 joule event. Thank you for the clarification and the math. That means my Panamax will be good for around 40 of the 'standard' events. Here in SoCal? That's gonna take a Long Time. I have one other question? If I may? Westom mentioned the ground IMPEDANCE as IIRC, 120 ohms. And resistance of 0.2ohms, I think at the outlet. Now? Isn't lightning DC? Or is it a high frequency event? Just asking since impedance is usually referenced to a frequency. Impedance comes into play on rate of change incidence. If a lightning strike isn't a high rate of change then nothing is!  |
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Post by westom on Feb 5, 2020 10:40:25 GMT -5
Isn't lightning DC? Or is it a high frequency event? Just asking since impedance is usually referenced to a frequency. Lightning obviously is a high frequency event. Hear it on radios. How does the international lightning detection network report lightning strikes in seconds? Radio stations monitor radio frequencies generated by lightning. Switching DC currents is how early 1900 radios worked. How do we create over 15,000 volts to fire spark plugs - from 12 volt DC? Switch the electricity off and on once (called points). That creates high frequency electricity that creates ignition sparks. High frequencies are created when a DC current turns on or off. Even Fourier Transforms (from high school math) demonstrate same. View datasheets for MOVs. Performance is rated in 8/20 microsecond spikes. A typically destructive surge is a high frequency spike. With massive power and actually small energy - only hundreds of thousands of joules or less. And it explains why plug-in protectors fail. How many joules does that Panamax claim to absorb? A thousand joules surge is routinely converted by electronics to safely power its semiconductors. That same energy means a Panamax (or other tiny joule protector) is toast after only one or two such transients. In SoCal, one may not seen even in 20 years. Surges are that rare in some venues. This is a common problem with tiny joule protectors: imgur.com/hwCWHMWAPC recently admitted some 15 million protectors must be removed immediately due to at least 700 house fires. Or this created by a Belkin: www.click2houston.com/consumer/surge-protector-sparks-fires-instead-of-preventing-them-homeowners-say> Lizzie Steinmetz, 5, was getting ready for bed with her little brother when she heard a strange noise. "It was like a buzzing noise sound," Lizzie said. She said she saw flames shooting up from a surge protector sitting on top of her dresser. If a surge is inside, then all appliances are at risk. Protection only exists when charges in a cloud connect to charges in earth (and maybe four miles away) on a path that is not anywhere inside the house. Facilities that cannot have damage properly earth a 'whole house' protector. With specification numbers that say that direct lightning strike does not even damage a 'whole house' protector. Effective protection only exists when a surge current is not and need not be anywhere inside the structure. A protector is only as effective as its connection to and quality of earth ground electrodes. So that even tiny joule plug-in protectors are protected. View any telco CO. Notice wires do not connect to the building. Wires first go underground into vaults. Then each and every wire connects low impedance to the single point earth ground. Then a surge is not anywhere inside the building. Telco COs suffer about 100 surges with each storm. And never fail. Because that protector connects low impedance to earth ground. Separation between protector and electronics also increases protection. Why should be obvious. That less than 50 meter separation means higher impedance. Just another reason why that surge is not hunting for earth ground via electronics. Separation (higher impedance) increases protection. 330 volts is when a protector starts conducting a surge. If a surge is significant, then MOV voltages (and voltages into nearby appliances) can be 900 volts. Protector does absolutely nothing useful until 120 volts is above 330 volts. Tiny joule protector means tiny surges can create 600 or more volts. Reason why is explained by an electrical concept called current source. |
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Post by westom on Feb 5, 2020 11:26:28 GMT -5
Just for the record. Assume the clamping voltage for an MOV applied to a 120VAC source has its rated clamping voltage at 330V peak. The aforementioned "100's of thousands of joules" would require a current spike of 252.5 million amps. A high voltage transmission wire dissipates hundreds of joules. While delivering 100 million joules to consumers. So 100 million joules dissipate in that wire? Of course not. Same mistake made. If that transient current (ie 20,000 amps) is safely conducted to earth, then a 'whole house' protector or ground hardwire does not even absorb 1000 joules (just like the transmission line). And hundreds of thousands of joules dissipate in earth (just like consumers). If that connection from cloud to earthborne charges is not low impedance, then more of that hundreds of thousands of joules does damage inside a structure. So that hundreds of thousands of joules dissipate harmlessly in earth, then a connection from a cloud to earthborne charges (maybe four miles away) must remain outside. Plug-in protector can only 'block' or 'absorb' energy. Protection is always about where energy is absorbed. Hundreds of thousands of joules are harmlessly absorbed in earth (and in the sky) when that connection remains outside AND is low impedance. |
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Post by KeithL on Feb 5, 2020 11:30:47 GMT -5
All basically true.....
And the latter part also hints at the reason why series-mode surge suppressors are so effective...
The events that occur when "a typical surge occurs" are a bit more complex than many people think.
A "simple surge" can occur when the load on the entire electric grid changes suddenly - and the generators and regulating equipment "fail to keep up". This is the sort of surge that sometimes happens when power returns after a blackout. The voltage "jumps up" for a few minutes - then returns to normal.
This sort of surge is mostly harmless to most modern electronic equipment. Motors and incandescent light bulbs are quite voltage sensitive... but the power supplies in most modern gear are not.
(You may hear a pop or crackle... but it's unlikely to cause any real damage.)
The sort of surge caused by a lightning strike is quite different. A lightning strike contains an incredibly large voltage potential - which causes an incredibly large amount of current to flow to ground. Because the impedance of the electrical grid itself is not infinitely low - this current surge causes a voltage spike in the electrical grid. (The effect is analogous to what would happen if you dumped a fifty-gallon drum of water into your bathtub.)
It is this voltage spike that reaches your home and equipment as "a surge". (Note that the electrical grid does have heavy duty protection - which usually does absorb most of the "hit" - what reaches your home is "the leftovers".) What a normal "home" or "whole home" surge suppressor really hopes to do is to provide a LOCAL very low impedance path to ground. This "clamps" the voltage at that point to a safe level - which causes any remaining energy to be dissipated in the wiring and transformer between your home and the grid. (Your little surge suppressor is not carrying the current from that lightning strike to ground.... it is merely "catching the little bit that sloshes over and reaches your house".)
ALL MOV-based surge suppressors work by diverting the current causing the voltage surge to ground.
Under normal conditions they do nothing. However, once the voltage rises too high, they become a short circuit to ground. They then short circuit the current that is causing the local part of the surge to ground... which causes the voltage of the surge to drop and be limited.
However, there are two major "catches" to doing it this way..... 1)
They must be configured so as to NOT act until the voltage is well above some preset "clamping voltage".
In most cases, for a 120 VAC line, this is around 270 - 300 V (remember that, on a 120 VAC RMS line, the voltage waveform actually varies between about -170V to +170V). Note that this is NOT a problem - since most appliances are designed to tolerate voltages above the normal level for short periods of time.
2a) The surge suppressor must be CAPABLE of shunting enough CURRENT to ground to limit the VOLTAGE of the surge. With a close lightning strike, this could involve providing a low impedance path for many thousands of amperes of current to shunt to ground. This means that the surge suppressor must be able to handle that amount of current. This means that it must be able to offer a low enough impedance path to ground to do so and only generate a small voltage drop. This means that the ground circuitry the surge suppressor is connected to must have sufficient capacity to carry that current to ground.
(As it turns out those little tiny MOVs can in fact shunt a really huge amount of current - for an extremely short period of time.) 2b) In the case of MOVs, the ability to shunt that much current, in such a small low cost package, has a catch... An MOV can only shunt that much current a few times before suffering performance deterioration and eventually failing entirely. (The term is "sacrificial" - which is a technical way of saying "they eventually wear out and need to be replaced".)
Of course, MOV-type surge suppressors also have several benefits.... The main benefits being that they're relatively small, relatively cheap, and work reasonably well for a limited number of relatively small surges.
SERIES MODE surge suppressors operate in a very different way... Rather than shunt the surge current to ground, they simply BLOCK the voltage rise resulting from the current surge from entering your equipment (or your entire house). So, much like your water faucet can "block all the water in the reservoir from running down your drain", they have an unlimited "surge current capacity" because the current doesn't have to go through them.
Series Mode surge suppressors have a surge voltage rating, and a current rating for the equipment you can connect to them, but a literally unlimited "surge current capacity". (The "joule rating" on a typical series mode surge suppressor is "infinite".)
Also, since they don't rely on having a low impedance path to shunt current to ground, they don't rely on extremely heavy duty ground connections to do their job.
(So they still perform well - even if your ground wiring is less than perfect - and they don't stress your ground wiring.)
And, since they aren't required to pass huge amounts of current, the circuitry involved doesn't heat up or wear out. (If you do manage to exceed their maximum voltage rating, they can fail.... although, for most, that would take more voltage than your wiring could withstand.) (However, and most important, they never "wear out" from repeated or excessive use.)
Isn't lightning DC? Or is it a high frequency event? Just asking since impedance is usually referenced to a frequency. Lightning obviously is a high frequency event. Hear it on radios. How does the international lightning detection network report lightning strikes in seconds? Radio stations monitor radio frequencies generated by lightning. Switching DC currents is how early 1900 radios worked. How do we create over 15,000 volts to fire spark plugs - from 12 volt DC? Switch the electricity off and on once (called points). That creates high frequency electricity that creates ignition sparks. High frequencies are created when a DC current turns on or off. Even Fourier Transforms (from high school math) demonstrate same. View datasheets for MOVs. Performance is rated in 8/20 microsecond spikes. A typically destructive surge is a high frequency spike. With massive power and actually small energy - only hundreds of thousands of joules or less. And it explains why plug-in protectors fail. How many joules does that Panamax claim to absorb? A thousand joules surge is routinely converted by electronics to safely power its semiconductors. That same energy means a Panamax (or other tiny joule protector) is toast after only one or two such transients. In SoCal, one may not seen even in 20 years. Surges are that rare in some venues. This is a common problem with tiny joule protectors: imgur.com/hwCWHMWAPC recently admitted some 15 million protectors must be removed immediately due to at least 700 house fires. Or this created by a Belkin: www.click2houston.com/consumer/surge-protector-sparks-fires-instead-of-preventing-them-homeowners-say> Lizzie Steinmetz, 5, was getting ready for bed with her little brother when she heard a strange noise. "It was like a buzzing noise sound," Lizzie said. She said she saw flames shooting up from a surge protector sitting on top of her dresser. If a surge is inside, then all appliances are at risk. Protection only exists when charges in a cloud connect to charges in earth (and maybe four miles away) on a path that is not anywhere inside the house. Facilities that cannot have damage properly earth a 'whole house' protector. With specification numbers that say that direct lightning strike does not even damage a 'whole house' protector. Effective protection only exists when a surge current is not and need not be anywhere inside the structure. A protector is only as effective as its connection to and quality of earth ground electrodes. So that even tiny joule plug-in protectors are protected. View any telco CO. Notice wires do not connect to the building. Wires first go underground into vaults. Then each and every wire connects low impedance to the single point earth ground. Then a surge is not anywhere inside the building. Telco COs suffer about 100 surges with each storm. And never fail. Because that protector connects low impedance to earth ground. Separation between protector and electronics also increases protection. Why should be obvious. That less than 50 meter separation means higher impedance. Just another reason why that surge is not hunting for earth ground via electronics. Separation (higher impedance) increases protection. 330 volts is when a protector starts conducting a surge. If a surge is significant, then MOV voltages (and voltages into nearby appliances) can be 900 volts. Protector does absolutely nothing useful until 120 volts is above 330 volts. Tiny joule protector means tiny surges can create 600 or more volts. Reason why is explained by an electrical concept called current source. |
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Post by leonski on Feb 5, 2020 14:04:33 GMT -5
I don't understand the 'magic' of 330 volts. MOVs come rated from pretty high to very low voltages. If I believe the design guide, you want 20% above the highest anticipated voltage. If you are dealing with 120, you might expect the highest to be maybe 135 on RARE instances. So you might want to start with a MOV rated about 150vac, depending on what actually is available. Working in the Semiconductor industry for decades, I saw some awful power related events. Once a buried transformer across the street (big 4 lane) and down half a block simply exploded. Heavy steel lid flew across all 4 lanes......Lights OUT. And another time, some drunk hit a light pole a couple blocks away, up on the freeway entrance and Again? Created quite a mess. Again, lights OUT. The only lightning I've ever been near was when I was house-sitting out in Cathedral City, next to Palm Springs. Very Intense summer storm blew threw. We had 3 lightning strikes in the area that I could SEE. One was fairly close (block or so?) and produced a blinding flash of light. Owner later reported a computer modem was Zapped. I think the surge came IN thru a phone line. OH! We've had a few surge events. One took out my amplifier but the Power Company paid for it. And I lived next to some kind of pumpiing station in Anaheim which produced BROWN outs when it started and a higher than normal voltage surge when shutting OFF. I mean a real bright light buld for an instant. It happened regularly. www.littelfuse.com/~/media/electronics/trainings/littelfuse_mov_general_electrical.pdf.pdfLittlefuse guide and application to power supply noted. |
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Post by Ex_Vintage on Feb 5, 2020 14:09:31 GMT -5
120 VAC RMS has a peak value of 170V. A reasonable safety factor would be 150% so 120 * 1.414 * 1.5 would give you 254 volts. This is why a value of 280-330 Volts would be the rating for a 120v circuit.
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Post by KeithL on Feb 5, 2020 14:45:16 GMT -5
When we talk about "120 VAC" we're talking about the RMS voltage... When you choose an MOV you must select a voltage that is safely above the PEAK voltage... which works out to about 170 V. Then, since the line voltage in many areas listed as "120 VAC" may run as high as 127 V or 128 V, you need to go up another ten volts or so.
You also want to allow for some safety margin above that (since an MOV that attempts to "clamp the line voltage" is going to self-destruct). Then you add a little more safety margin for individual component variations. And a little more safety margin for the fact that the breakdown voltage may change significantly as the MOV wears out.
You also need to consider that there is a difference between "clamping voltage" and "actuation voltage".
When the MOV starts working, it shunts current to ground, and in doing so reduces the overall voltage.
However, it still has a finite internal impedance, which is not zero. Therefore it cannot literally "clamp the maximum to an absolutely specific voltage regardless of the current involved". Once that MOV's "clamping voltage" has been exceeded... it offers the equivalent of a low impedance path to ground for voltages above that. (Once you exceed that voltage, the MOV switches on, and starts shunting progressively more current...) (The result is that "it becomes progressively more difficult for the voltage to rise above that".)
That "330 V" number isn't so much "magic" as it is arbitrary.... although it seems to be the currently accepted "standard" for such devices.
What they're saying is that: "In a typical surge you're likely to encounter, on a typical circuit, this device will limit the maximum voltage to around 330 V".
(They've chosen the amount of voltage that they expect most equipment they're protecting to survive for a short period without being damaged.)
Wikipedia has an excellent, and quite detailed, entry on the subject...
They also describe several less common types....
In practical terms almost all low cost consumer "surge suppressors" are of the MOV type...
With only a few companies offering Series Mode types (the only ones I know of offhand are BrickWall and SurgeX)... The others are more or less either no longer in common use or are limited to commercial or power-grid use...
I don't understand the 'magic' of 330 volts. MOVs come rated from pretty high to very low voltages. If I believe the design guide, you want 20% above the highest anticipated voltage. If you are dealing with 120, you might expect the highest to be maybe 135 on RARE instances. So you might want to start with a MOV rated about 150vac, depending on what actually is available. Working in the Semiconductor industry for decades, I saw some awful power related events. Once a buried transformer across the street (big 4 lane) and down half a block simply exploded. Heavy steel lid flew across all 4 lanes......Lights OUT. And another time, some drunk hit a light pole a couple blocks away, up on the freeway entrance and Again? Created quite a mess. Again, lights OUT. The only lightning I've ever been near was when I was house-sitting out in Cathedral City, next to Palm Springs. Very Intense summer storm blew threw. We had 3 lightning strikes in the area that I could SEE. One was fairly close (block or so?) and produced a blinding flash of light. Owner later reported a computer modem was Zapped. I think the surge came IN thru a phone line. OH! We've had a few surge events. One took out my amplifier but the Power Company paid for it. And I lived next to some kind of pumpiing station in Anaheim which produced BROWN outs when it started and a higher than normal voltage surge when shutting OFF. I mean a real bright light buld for an instant. It happened regularly. www.littelfuse.com/~/media/electronics/trainings/littelfuse_mov_general_electrical.pdf.pdfLittlefuse guide and application to power supply noted. |
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Post by leonski on Feb 5, 2020 17:13:56 GMT -5
NTE semicondutor MOV ratings: And how to size. www.nteinc.com/Web_pgs/MOV.htmlBut I DO have a question. For as complete a protection as a MOV can provide, you need 3 of 'em......Hot-Ground / Hot-Neutral / Ground-Neutral. So, If I chose an 80 joule part, would I rate the protection as 80 joules OR 240 joules? Also, much stereo equipment is provided ONLY with a 2-prong plug. Hot and Neutral with the ground omitted. Since the idea is to shunt the surge to ground, you are left with neutral..... This kind of points me to a Whole House Solution.......for that and a couple other reasons...... |
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Post by KeithL on Feb 5, 2020 17:24:44 GMT -5
The most impressive fault I've ever seen close up was when I lived in California. A pole-top transformer about a block from where I lived decided to explode for no obvious reason. It made a serious noise (like an exploding garbage can).
I don't know where the transformer ended up, but the top ten feet of the wooden pole where it was mounted disappeared, and the edge of a roof nearby caught fire.
It also turned the entire near side of a palm tree slightly above it into ash.
I also watched one short circuit quite badly and not explode.
It simply sat there, lighting up the neighborhood with a garish green arc-glow, dribbling bits of burning copper wire, until it was shut down. (It arced continuously off the secondary for at least ten minutes... long enough for me to go home and fetch my camera... before someone showed up.)
I've experienced plenty of brown-outs and outages...
And one or two surges heavy enough to make the lights noticeably brighter for a second or two... But I've honestly never had a significant surge (where equipment was actually damaged).
(However, a buddy of mine who lives in Texas went through three or four TiVo boxes, before he finally broke down and bought a serious surge suppressor.)
I don't understand the 'magic' of 330 volts. MOVs come rated from pretty high to very low voltages. If I believe the design guide, you want 20% above the highest anticipated voltage. If you are dealing with 120, you might expect the highest to be maybe 135 on RARE instances. So you might want to start with a MOV rated about 150vac, depending on what actually is available. Working in the Semiconductor industry for decades, I saw some awful power related events. Once a buried transformer across the street (big 4 lane) and down half a block simply exploded. Heavy steel lid flew across all 4 lanes......Lights OUT. And another time, some drunk hit a light pole a couple blocks away, up on the freeway entrance and Again? Created quite a mess. Again, lights OUT. The only lightning I've ever been near was when I was house-sitting out in Cathedral City, next to Palm Springs. Very Intense summer storm blew threw. We had 3 lightning strikes in the area that I could SEE. One was fairly close (block or so?) and produced a blinding flash of light. Owner later reported a computer modem was Zapped. I think the surge came IN thru a phone line. OH! We've had a few surge events. One took out my amplifier but the Power Company paid for it. And I lived next to some kind of pumpiing station in Anaheim which produced BROWN outs when it started and a higher than normal voltage surge when shutting OFF. I mean a real bright light buld for an instant. It happened regularly. www.littelfuse.com/~/media/electronics/trainings/littelfuse_mov_general_electrical.pdf.pdfLittlefuse guide and application to power supply noted. |
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KeithL
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Post by KeithL on Feb 5, 2020 17:34:07 GMT -5
You're forgetting that the whole point of a surge suppressor is to keep the surge out of your audio gear.
None of that involves the power cable on your gear - which is plugged into the "safe side" of the surge suppressor. The critical requirement is that the surge suppressor itself have a solid ground connection.
NOTHING is going to protect you from a really close strike... (according to one article a typical lightning strike is estimated to carry about a billion joules... with a B). However, luckily, the power grid is able to absorb all but the worst ones, and your best bet is to try and keep the surge out of your stuff, rather than hope to have enough protection to divert it if and when it gets in. (But, yes, some estimates claim that "a typical surge" can be "stopped" by a suppressor rated at 100 joules or so.)
If you're buying a MOV-based product, forget about trying to calculate what you need, and buy one that includes INSURANCE. Several companies, including APC, promise to replace any equipment that suffers damage while connected to one of their products.
I've heard that it is often difficult to collect on such claims - but at least you have a chance. (You can also assume that, with even the possibility of having to pay off, they will take care of the fussy math for you.)
Most homeowner's insurance also covers that sort of thing - past the deductible.
It's also worth noting that ALL shunt type surge suppressors - which includes MOV types - rely on a solid ground connection. If your skinny little ground wire vaporizes then the MOVs will have no place to shunt that current to.... so they won't do much. (If you connect a shunt type surge suppressor to an outlet then the weak link is probably the ground wire from that outlet to true ground.)
I've got to throw in a plug here (pun intended).... If you want to play with rating numbers for significant protection... then check out these:
(The smaller models only cost a few hundred bucks.)
NTE semicondutor MOV ratings: And how to size. www.nteinc.com/Web_pgs/MOV.htmlBut I DO have a question. For as complete a protection as a MOV can provide, you need 3 of 'em......Hot-Ground / Hot-Neutral / Ground-Neutral. So, If I chose an 80 joule part, would I rate the protection as 80 joules OR 240 joules? Also, much stereo equipment is provided ONLY with a 2-prong plug. Hot and Neutral with the ground omitted. Since the idea is to shunt the surge to ground, you are left with neutral..... This kind of points me to a Whole House Solution.......for that and a couple other reasons...... |
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Post by leonski on Feb 5, 2020 18:11:19 GMT -5
I worked semiconductor manufacturing for decades. You've never lived until you've seen a 6 digit electric bill for ONE MONTH. I came to work late one day. I was in the R+D group and we had limited amounts of our OWN equipment and borrowed the rest from production as need arose. So, I got in late.....And went into fab since my note said a few things were going on which when done would require my carrying on. I looked at one of the processing tubes. They would normally run anywhere from maybe 800c to as hot as 1100c. That's HOT in any system. But one tube looked TOO hot. Wrong color. You got used to being able to tell just by looking so you didn't need to access the tube computer (shared with 3 other tubes) to see where / when in the process. But this was above orange, heading for yellow which I'd NEVER seen. I went to the computer and it was LOCKED UP. sh**! So I went around back and used a broomstick to flip the main breaker to the tube off. Than I waited about 4 or 5 hours for it to cool. Ever seen MELTED quartz? Know how hot that was? And th interior tube (also quartz) was sagged. A total loss. Product and the experiment as well as all the interior fixtures, quartz boats and all. THOUSANDS of $$ down the tubes, so to speak. When the maintenance guy went to turn the breaker back ON, it shorted and made an explosion like a shotgun INDOORS. 12 Ga. Part of the fab went dark and I think the guy soiled himself. www.thermcosystems.com/wp-content/plugins/literature_upload/uploads/pdf/5100-5200-main-V4.pdfModern thermco. Only thing the same is that they've always been '4 hole' from top to bottom and can be configured at purchaser request for any purpose. The old ones I worked on had a 'MUX' for entire stack and you asked for info for specific tube. This is ALL Pre-Windows so all exclusive language. Last fab I was in had a DOZEN such stacks, divided into functional areas. Some were ultra clean, like Gate Oxidation and Field oxidation while others were 'dirty' system, like PoCl3 which is a phosphorous dopant. CVD was included, which puts on a layer of 'glass' as an insulator. |
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Post by dlaunde on Feb 5, 2020 19:43:12 GMT -5
This is has been a very interesting read.
Fwiw, I got a brand new SurgeX Defender Series SX-DS-158 surge suppressor for my amps and receiver, the same SurgeX product but in a single plug form for my Funk subwoofer, and a Panamax 360 surge protector for all my smaller/misc devices.
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Post by westom on Feb 5, 2020 22:53:12 GMT -5
The surge suppressor must be CAPABLE of shunting enough CURRENT to ground to limit the VOLTAGE of the surge. With a close lightning strike, this could involve providing a low impedance path for many thousands of amperes of current to shunt to ground. This means that the surge suppressor must be able to handle that amount of current. This means that it must be able to offer a low enough impedance path to ground to do so and only generate a small voltage drop. This means that the ground circuitry the surge suppressor is connected to must have sufficient capacity to carry that current to ground. ... An MOV can only shunt that much current a few times before suffering performance deterioration and eventually failing entirely. (The term is "sacrificial" - which is a technical way of saying "they eventually wear out and need to be replaced". ) A 1970 research paper put numbers to that. A 100,000 amp surge (extremely rare) meant utility protection (the 'primary' protection layer) will shunt 40,000 amps to earth. Another 20,000 amps uses other consumers to make that earth connection. Meaning 40,000 amps can be incoming to a nearby home. That is why a minimal 'whole house' protector is 50,000 amps. To withstand without failure many such surges. And many times more smaller ones. Yes, some current will still splash over (approach) appliances. So small that protection even inside LED and CFL bulbs, clocks, and GFCIs make it irrelevant. With increased separation between protector and appliances, that current is even smaller. A properly sized and earthed 'whole house' protector must remains functional for many decades after many direct lightning strikes. And must not fail catastrophically. It must only degrade. Meaning after many direct lightning strikes, its threshold voltage (Vb) might change 10%. Protector is still working; it only degraded; did not fail catastrophically. Protector must never be sacrificial (fail catastrophically). It must only degrade. An MOV manufacturer defines testing for degradation. To say more requires charts provided by an MOV manufacturer. Lightning is a typical surge. Protectors that protect from lightning also protect from other transients created by wind, transformer failure, tree rodents, utility switching, stray cars, linemen errors, etc. If a 50,000 amp 'whole house' protector fails, then that venue needs a 100,000 amp protector. That number defines protector life expectancy over many surges and decades. Protection during each surge is defined by its connection to and quality of earth ground electrodes. It must be a single point earth ground. That is critical. 330 volts is a ballpark number. A 120 volt protector typically starts conducting current at maybe 170 volts (peak). Obviously a 1 milliamp surge is only noise. At 330 volts, it starts conducting a tiny but larger current - anywhere from maybe 1 to 10 amps. A current typically too tiny to damage any appliance. MOV voltage quickly increases as a surge current increases. Generally, current necessary to make 900 volts will catastrophically destroy a 120 volt protector. Just another reason why protectors must not fail. A failure that exists only because that protector was grossly undersized and a potential fire. Noted previously is inspection of that 'primary' protection layer. For example, a lightning strike to high voltage wires (highest on a pole) is hunting for earth ground. If a transformer earth ground has not been compromised by copper thieves, then it connects harmlessly to earth. However, if that earth ground is missing, then lightning constructs a plasma path from primary to secondary. No problem. Lightning energy is not that massive. Even a home's 'whole house' protector should make that irrelevant. Problem is a 'follow through' current. Now 4000 or 13,000 volts is connected directly into 120/240 volt homes. That energy is significantly larger than lightning. Even sparks may be observed flying from wall receptacles. In once case, a CA radio transmitter and its entire building exploded and burned down. Even the transformer was only found in tiny pieces. Because 33,000 volts was connected directly into that transmitter. A critical earth ground on that transformer was missing. Also inspect your 'primary' protection layer. So that 13,000 volts does not connect directly into the house. |
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Post by leonski on Feb 7, 2020 2:00:05 GMT -5
Mostly off-topic, but a mechanic at work once dropped a wrench across the output of a 480v transformer, which itself was about as large as an end table. Wrench vaporized. Mechanic deafened for a couple days.
And yes, for the charts westom refs? Please see the link I provided to LITTLEFUSE. They examine all aspects of MOV behavior. Take your time with the graphics. That'll help make some points more 'accessible'.
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