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Post by leonski on Mar 4, 2016 12:44:07 GMT -5
MOV devices DO WEAR OUT. That is why they are called 'sacrificial'. And they are commodity cheap. I'd replace my whole-house unit or get the MOVs replaced after a BIG strike. Or maybe 8 to 10 years Anyway. I do not know, off hand, about a way to TEST them? At least non-destructively. If they conduct, they are SHOT, that's for sure, however. As for where the energy goes? The Idea is to shunt the energy to ground BEFPORE reaching a 'protected' device. MOVs 'turn on' very quickly and are conduits, not 'absorbers' of energy. And yes, even Telephone and Telco can be protected this way. AS LONG as their is an Earth Reference ground to shunt to. Just for example? My small dish cable comes to a distribution block outside. THAT BLOCK is grounded. The signal proceeds into the house and thru another surge protector before getting to the receiver which is ALSO plugged into a point of use surge protector. As well as the Telephone line to/from the receiver. And please note that such whole-house protection (and all point of use, too, for that matter) have 3 MOVs for a 120 line. Line / Neutral :: Line / Ground :: Neutral / Ground In this way, ALL roads lead to ground. Ground can be TESTED (not a bad idea) by a device called a MEGGER. The point WESTOM makes is valid. LOW RESISTANCE GROUND is key. www.megger.com/eu/products/ProductDetailsBySubGroup.php?PSGC=T104&BS=
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Post by westom on Mar 5, 2016 1:29:06 GMT -5
MOV devices DO WEAR OUT. That is why they are called 'sacrificial'. Yes, MOVs do wear out. MOV manufacturer test for "wear out". Yes it does wear out - after 10,000 surges. Nobody cares once we add numbers. That "wear out" is degradation. Its threshold voltage (Vb) changes by 10%. Tested MOVs must not fail catastrophically. Only near zero protectors are sacrificial - fail catastrophically (even create fire). A serious threat created when consumers ignore specification numbers. Sacrificial protectors only exist when designed in violation of what MOV manufacturers define and demand. If 'sacrificing' does protection, then fuses (that cost tens of times less money) do protection better and faster. Why waste so much money on expensive plug-in protectors if a sacrificial fuse is better? A damning question. Reality - sacrifice does not provide effective protection. A direct lighting strike can be 20,000 amps. A properly sized Leviton conducts up to 50,000 amps without damage - no catastrophic failure. Spec numbers say MOVs connect a direct lightning strike harmlessly to earth - if that protector is properly earthed. This superior solution costs tens of times less money per protected appliance. What happens once a surge current is all but invited inside? It hunts for earth ground destructively via appliances. An adjacent protector simply gives that current even more paths to find earth ground destructively via appliances. Damage because it was not earthed BEFORE entering. Damage made easier because a 'whole house' solution was not implemented. Protection is always about a surge current NOT inside. More numbers. IEEE Standard says proper earthing does 99.5% to 99.9% of the protection. Previous post also discussed layering - the item that defines each protection layer. Plug-in (sacrificial) protectors have no earth ground and will not discuss it. MOVs that fail catastrophically are grossly undersized; violates Absolute Maximum Parameters in MOV datasheets. Somehow its near zero joules will magically make hundreds of thousands of joules disappear? An effective protector connect low impedance (ie less than 10 feet) to earth ground (not a receptacle's safety ground). Impedance (not resistance) is critical for effective protection. Protection is always about where hundreds of thousands of joules (another ignored number) are harmlessly absorbed. Then all 120 and 240 volt wires have best (ie 99.5% to 99.9%) protection. A protector is only as effective as its earth ground - as understood and repeatedly demonstrated even 100 years ago when spark gaps once did what MOVs do better today. Then best protection exists for a 240 volt circuit.
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Post by leonski on Mar 5, 2016 3:25:51 GMT -5
What's your point? The take away for most users is that the MOV based surge protection is a good thing in a good electrical system. If you doubt your ground scheme, get an electrician with a MEGGER to test it. Install a good first layer of protection in the service panel. Protect ALL 3 wires or 4 if 220 (2x hot @120, a neutral and a ground) A lightning strike can have as much as 5 BILLION Joules of energy, many orders of magnitude greater than the average surge protection device, not that YOU'D get the whole 'blast'. It'll be distributed thruout the effected grid. A single MOV might take 70,000 amps single event OR 1000 zaps @100 amps. Some specified duration of each pulse, too. The test for Vb you refer to is WAY under capacity for the device. It is apparently designed as a form of 'lifetime' test. A sufficiently large (and unlikely) SINGLE zap could still take it out. NOTE the use of 'unlikely'. The idea is that SURE, you NEED proper earthing. A good Copper Rod driven down 8 or 10 feet is a FINE idea. Link is to the FIRST one I found. But if the surge comes in thru the HOT wire, it must get to ground SOMEHOW. The intercept done by a MOV seems to work. And done best at the service panel. www.gmesupply.com/gr-5080-copper-clad-ground-rod-5-8-x-8?gclid=CPXhlIuKqcsCFU6BfgodHlQACAMany other faults can mess up your gear. My power conditioner shuts off CONTINUOUS voltages <95vac and >135vac. It has done so 2x or 3x in well over a decade. BTW, this is a fairly hi-end unit which includes an isolation transformer, yet is advertised at only 4500 joules of energy absorption. Where I live, I'm NOT worried about lightning at all. When I worked (Semiconductor process technician in a manufacturing environment) we had a few power problems, including one late evening the transformer in the street a couple hundred yards down, BLEW UP. Or the Idiot that knocked down a Power Pole and took out the power for a couple block radius. OUCH! This is a reasonable point and a good reason to locate such surge devices AT THE SERVICE PANEL right next to the GROUND ROD. An effective protector connect low impedance (ie less than 10 feet) to earth ground (not a receptacle's safety ground). Impedance (not resistance) is critical for effective protection. Protection is always about where hundreds of thousands of joules (another ignored number) are harmlessly absorbed. Then all 120 and 240 volt wires have best (ie 99.5% to 99.9%) protection. The noted '10,000 surges' test is at sub-critical energy values. ONE good strike close enough to your service can induce enough current / energy to seriously degrade further protection. I was house sitting in Palm Springs one SUMMER. Supposed to be dry, right? One day 110f, the next, a STORM blew in dumping maybe an INCH of rain in 3 hours AND we had 3 lighning strikes within a couple blocks of the house. Took out my niece's computer MODEM on the PHONE side of things. Rest of confuser was fine. When the owners returned, I think they replaced another phone and I came back and installed a new modem. You could SMELL the Ozone from the strike nearest. And yes, surge protectors DO have reference to ground. They have 3 lines coming in. Hot, Neutral and Ground. EACH PAIR of lines has a MOV between them. So a blast entering on the HOT wire, if exceeding the voltage rating of the MOV, which is essentially (looks like, anyway) 2 back-to-back Zeners, conducts to ground. And neutral. BEFORE the Zap gets to the 'protected' device. I'll be the FIRST to admit such protection is well-short (no pun intended) of perfect, but in lightning prone areas, a 2 layer approach does substantially HELP. When I lived in Florida, summer was one lightning storm after another. Awful.
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Post by westom on Mar 6, 2016 2:41:11 GMT -5
If you doubt your ground scheme, get an electrician with a MEGGER to test it. Install a good first layer of protection in the service panel. Protect ALL 3 wires or 4 if 220 (2x hot @120, a neutral and a ground) A MEGGER is a resistance test. A protector is as effective as its earth ground. That is about impedance - not resistance. A wire that can be less than 0.2 ohms resistance can also be 120 ohms impedance. An effective protector connects low impedance (ie less than 10 feet, ie wire has no sharp bends) to single point earth ground. All four words have electrical significance. That earth ground (not protectors) is THE most critical component in every protection 'system'. Effective protectors are not sacrificial. Sacrificial protectors do not even claim to protect from destructive surges. Hyping fictional numbers such as 5 billion joules is plain nonsense. Experience and protection from direct lightning strikes is well understood with numbers. Effective protection is about where hundreds of thousands of joules dissipate. That means a properly earthed 'whole house' protector is at least 50,000 amps. And again, it makes a low impedance (ie wire is not inside metallic conduit) connection to single point earth ground. Direct strikes without damage was so routine that damage is considered a human mistake. Should damage occur, an investigation begins at earth ground to locate a human mistake. A 'whole house' protector is only secondary protection. 'Primary' protection layer was defined and should be inspected. Pictures (not text) after "open vertical grounds" label demonstrate what in a 'primary' layer to inspect: www.fpl-fraud.com/Protectors connected to receptacles have all but no earth ground connection. Numbers such as 120 ohms impedance demonstrate why safety ground is not earth ground. Protectors without a good earth ground are only for one type of surge - typically made irrelevant by protection already inside appliances. Near zero joule (ie sacrificial) protectors are ineffective during potentially destructive surges (ie hundreds of thousands of joules). And must be protected by a properly earthed 'whole house' solution. More relevant numbers. A properly earthed 'whole house' solution does 99.5% to 99.9% of the protection. Like every effective protector, it is not sacrificial. Plug-in protectors (without that critically necessary and low impedance connection to earth) might provide an additional 0.2% protection. Necessary to protect all 120 and 240 volt circuits is one properly earthed 'whole house' solution. It is also a least expensive solution at about $1 per protected appliance. Of course, sacrificial protectors create another rare problem - fire. Low voltage (ie 95 VAC) cause no electronics damage. Low voltage is a threat to motorized appliances. Good voltage for electronics exists even when incandescent bulbs dim to 50% intensity. If voltage drops lower, electronics simply power off - without damage. Examples of robust protection already inside appliances. Concern is a rare transient that might overwhelm that protection. Only a properly earthed 'whole house' solution claims to protect from that type of transient. No plug-in protector does. BTW, any semiconductor fab that can be interrupted by loss of AC utility power is seriously deficient. We designed equipment for fabs. Voltage below 95 and above 135 would never cause damage or interruptions. Emergency backup power is routine. Such anomalies cost too much and must never happen.
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Post by leonski on Mar 6, 2016 3:17:47 GMT -5
No time now, but virtually EVERY fab I ever worked in was subject to power interruption at one time or another. Weather? Man-Caused? Even once when we had the building REWIRED, they couldn't get the Gigantic GFI breaker to stay closed so they had to disconnect the GFI portion of the breaker. Last memory is 45yrs old, so don't hold me to THAT one in detail.
NOBODY had a large enough generator out back to power the place during outages. NO power grid is IMMUNE. Here in SoCal back in 2014 (IIRC)somebody tripped on the Extension Cord to Arizona and most of the state from Santa Barbara SOUTH and into parts of Mexico went dark. Where I live? We were down about 12 hours.
Florida Fabs, if they still exist, were REALLY screwed. FPL (Florida Flicker and Flash, the power company) had to contend with one of THE most active lightning enviroments in the lower 48.
Impedance? Resistance? I KNOW the difference. But, is lightning AC or DC? Once you've got 8 FEET of copper driven into the ground, you are up to CODE. At least if it's near the box and other considerations. I know here in SoCal, the soil is typically VERY dry.
Many years ago I experimented using an Audio Amp to transmit CW thru the ground. 2 wires 40 or 50 feet apart, driven into the ground and a similar receiver 100 feet away. You needed a code key and an oscillator. It worked. sort of.
What is a non-sacrifical protector? What device or technology? I understand even spark gap has 'limits' ALL MOVs have limits.
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Post by afterburner on Mar 6, 2016 9:32:41 GMT -5
The problem with the "Pole" idea... All our wires for over 1000 homes is underground.
Greatly appreciate the information you are both providing!
I am still using the $400 power cleaner/protector for my equipment at the socket they are plugged into. My reason for doing the whole house one is because so many item are using some form of computers. And any little extra help the brown outs and fluctuations I think is a good thing.
In fact, over the last five years I have lost enough "Electronics" that I think it is because of brownouts. Not because the product was weak. One day the are fully function, The next they fail to power up.
Heck, look at how many items connect to the web now! Clearly the more tech they place in our kitchen appliances/light switches and so on. The more sensitive the item is to power issues.
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Post by leonski on Mar 6, 2016 15:25:50 GMT -5
I think Westom and I would AGREE that surge protectors, regardless of what you think they do or DON'T do, will have no effect on long term (say greater than 500miliseconds) either increases or decreases in line voltage. My power condidtioner shuts off <95vac and >135vac. And has done so 2x or 3x since purchased, at least 15 years ago. maybe 40 years ago I lived NEAR a large pumping station. We would get large voltage SURGES while incandescent lamps got VERY bright. I think it was when pumps shut OFF. And I don't care for what Westom said about Low Voltage NOT being a problem. If so, WHY did the power company Pay To Fix my amplifier after I told them the EXACT date / Time the amp was damaged by an extensive brownout? If brownouts have 'no effect' they could have EASILY denied the claim, right? Instead, they sent the amount of the bill upon certification of the fix. Easy procedure. I think what you MAY want for computers and such is a UPS which will provide a seamless 120vac to the connected device, regardless of state of the input power. But there ARE time limits, right? Good Article on MOVs www.circuitstoday.com/metal-oxide-varistor-mov
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Post by westom on Mar 7, 2016 0:33:53 GMT -5
In fact, over the last five years I have lost enough "Electronics" that I think it is because of brownouts. Not because the product was weak. One day the are fully function, The next they fail to power up. As leonski notes, protectors (and conditioners) do nothing useful for voltages from 95 to 135. Electronics must be perfectly happy at all those voltages. Normal voltage for electronics is even when incandescent bulbs dim to 50% intensity. How often do your light bulbs dim less? Brownouts do not damage electronics. If electronics fail, nothing further is known until hard facts exist - ie the autopsy. Best evidence is always inside a dead body. Which part failed? International design standards long before PCs existed define no damage from any low voltage. In fact, the chart has this expression, in all capital letters, in the entire low voltage region. No Damage Area. If low voltage can damage electronics, then a part damaged by low voltage can be identified even in its datasheets. Was designing over 40 years ago. Where is this electronic part damaged by a low voltage? Motors can be harmed by low voltage. But not electronics. Poles: does not matter if wires are overhead or underground. Same transient damage can still happen. But if wires are underground, then nothing is exposed to inspect. For example, that earth ground (essential to protect household appliances) would be inside a box that covers the transformer. Cannot be inspected. But the bottom line remains. That earth ground is a 'primary' and necessary protection layer. AC utility voltage must be sufficient. Or an AC utility disconnects power. Because long before AC electric powered semiconductors, motors were at risk. Your voltage must be sufficient for motors; or AC power is disconnected. Just another reason why low voltage does not damage electronics. At what voltage do 120 volt protectors become sacrificial? About 900 volts. If a protector is grossly undersized, then a resulting voltage across that protector (and incoming into adjacent 120 volt appliances) is more than 900 volts. What kind of protection is that? Effective protectors (that do not fail) would never let voltage get that high or near to appliances. Undersized protectors do. Protection inside 120 volt electronics (even before PCs existed) was typically up to 600 volts. Many electronics can withstand up to 1000 or 1800 volts. Again, best protection at an appliance is often inside that appliance. Your concern is a transient that can overwhelm that existing internal protection. Protection must be inside every household appliance - including LED bulbs, GFCIs, refrigerator, smoke detectors, all computers, microwave ovens, the furnace, and clocks.
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Post by leonski on Mar 7, 2016 15:01:43 GMT -5
We are now pretty much on the SAME PAGE. One minor problem is the idea of Sacrificial. By that, the meaning is that the device which does the protection has a FINITE LIFE. Not that when it gets zapped you end up with a couple wire stubs connected by smelly charcoal. The data sheets are clear in this regard. Here is link to LITTLEFUSE MOV datasheet. Please scan down to 'Repetitive Surge Capability for Xmm Parts' www.littelfuse.com/~/media/electronics/datasheets/varistors/littelfuse_varistor_la_datasheet.pdf.pdfTheir are ratings from Infinite (life) to basically 'single use'. I too, am not particularly worried about low voltage. As I stated before, the high/low cutout of my Power Conditioner has operated 2x or 3x in 15 years. The event that damaged my Carver Cube is what induced me to go this route. It was DEFINATELY a Brownout that killed the amp. I sat there and WATCHED it happen. Maybe an artifact of the odd power supply design used by Carver?
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Post by westom on Mar 7, 2016 23:07:53 GMT -5
Littlefuse is discussing degradation on pages 5-9; not catastrophic failure. When an MOV's Vb voltage changed by 10%, then an MOV has degraded. It still works like an MOV - at a degraded voltage. It does not physically look burned; did not get excessively hot. In short, it was properly sized so as to not fail sacrificially. If an MOV gets excessively hot (ie catastrophic failure), then a thermal fuse must disconnect that MOV. That is a potentially sacrificial failure. An indicator light reports only that type of failure. Degradation (as discussed by that datasheet) is not reported by that light. Thermal fuse does not disconnect MOVs due to degradation. Catastrophic failure is when Absolute Maximum Ratings (on page one) are exceeded. Thermal fuse must disconnect MOVs due to catastrophic (sacrificial) failure - to avert a fire. Catastrophic (sacrificial) failure is defined on page one. Degradation is defined on pages 5-9. An indicator light reporting catastrophic failure says the protector was grossly undersized. Degradation failure is not and cannot be reported by a that light. Properly sized protectors (ie 50,000 amps) typically degrade after many decades.
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Post by leonski on Mar 7, 2016 23:58:35 GMT -5
I must be Mis-reading the Littlefuse data. the chart labeled 'Repetitive Surge Capability For (part size)' clearly shows Impulse Duration VS Current. At quick enough / low enough current, the part will NEVER fail. The NINE (9) lines on each chart are CLEARLY identified from 1 repetition to 'indefinite' with Longer duration at Higher currents resulting in LESS device lifetime as measured in 'repetitions'. Cross reference of that chart with the the 'maximum clamping voltage' chart will give some idea of the device limits. Multiple parts in parallel will add energy capacity while leaving the breakdown voltage alone.
Is sacrificial too 'final' a word? These devices clearly DO wear out, though in a home situation, the lifetime is much longer than I first imagined. Lots. You are the one who brought up Catastrophic. I've never seen an obliterated MOV. In any event, I doubt that plays into a home unit meant for point of use. The proposed Home Unit, coupled, yes, with a good ground, should knock down a spike to levels where a point of use will not fail in normal use. I suspect that in some circumstances, a direct hit to the transformer outside your Rural home will result in massive surge protection failure. Just Too Much energy to dissipate. Fine with me if you want to call it degradation. The device is FINISHED for its intended use when these limits are met or Exceeded. Period.
Semantics for fun and profit. Catastropic and sacrificial are NOT the same. Catastropic is as you say. the device essentially blows up. ZORCH. Finished. Sacrificial means the device SACRIFICES itself to 'save' something else. If the sacrifice is NOT fatal, (catastrophic, maybe?) it can do so again and again until maximum ratings are exceeded. Lifetime Over.
I'm repeating myself now, since you can't seem to understand the difference between lifetime testing and destructive testing. I worked in a fab F.A. department for a while. 1000 hour burning was a required qualification for ALL new devices. From the failure data and failure MODES, the brain trust could give reasonable numbers for MTBF and if enough failures were for the SAME cause, perhaps ask for process improvements….which needed a requal before release.
I'm still trying to figure out if lightning is AC or DC? Anybody know?
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KeithL
Administrator
Posts: 9,902
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Post by KeithL on Mar 8, 2016 11:14:12 GMT -5
Lightning is DC - rather like a VERY high voltage capacitor discharging (the clouds being one pole and the ground the other). What happens in a "strike" is that a big high-voltage spark jumps to the electrical grid trying to find a path to ground. The lightning arrestors on the power grid itself, and every house connected to it, constitute a whole slew of parallel paths to ground. As the current finds its way to ground, it causes a voltage drop across the entire grid, which forces the voltage up - and this is you power surge. Since the lines leading to your house, and the transformers, all have their own impedance, the current from this voltage spike distributes itself across them. And, in turn, pushes current through each to ground. Which causes voltage drops in each. When you put a "shunt mode surge protector" on your house, your goal is to provide a low enough impedance path to ground that it can carry the small percentage of the overall current that reaches your house to ground without producing enough of a voltage drop to allow anything to get damaged. You should also note that many of the better sacrificial MOV-based surge suppressors do include a warning light to tell you when their MOVs have "sacrificed themselves". (They tell you when to replace the device because it's toasted.) There is in fact a more effective way to do this that isn't sacrificial; rather than conduct the current that enters your house wiring to ground, you simply block the voltage and the excess current. These are known as series-mode surge protectors - and use a large inductor to stop the current from entering rather than dumping it to ground after it has already entered. Series mode suppressors have a "withstand voltage" rating rather than a "joules" rating.... They can block an infinite amount of current (just like your water faucet can "block" the billions of gallons of water in the reservoir from flooding your property rather than drain it away). stormhighway.com/surge_protectors_ups_lightning_protection_myth.phpThese links go to the website of a company who makes series-mode surge suppressors. Several companies make these (this is the brand I use at home). (Check out their repetitive withstand specs ) www.brickwall.com/pages/how-it-workswww.brickwall.com/pages/no-failureswww.brickwall.com/pages/line-conditionersNote that all of our Emotiva equipment can generally tolerate the types of surges you generally see on your home power lines without damage. I must be Mis-reading the Littlefuse data. the chart labeled 'Repetitive Surge Capability For (part size)' clearly shows Impulse Duration VS Current. At quick enough / low enough current, the part will NEVER fail. The NINE (9) lines on each chart are CLEARLY identified from 1 repetition to 'indefinite' with Longer duration at Higher currents resulting in LESS device lifetime as measured in 'repetitions'. Cross reference of that chart with the the 'maximum clamping voltage' chart will give some idea of the device limits. Multiple parts in parallel will add energy capacity while leaving the breakdown voltage alone. Is sacrificial too 'final' a word? These devices clearly DO wear out, though in a home situation, the lifetime is much longer than I first imagined. Lots. You are the one who brought up Catastrophic. I've never seen an obliterated MOV. In any event, I doubt that plays into a home unit meant for point of use. The proposed Home Unit, coupled, yes, with a good ground, should knock down a spike to levels where a point of use will not fail in normal use. I suspect that in some circumstances, a direct hit to the transformer outside your Rural home will result in massive surge protection failure. Just Too Much energy to dissipate. Fine with me if you want to call it degradation. The device is FINISHED for its intended use when these limits are met or Exceeded. Period. Semantics for fun and profit. Catastropic and sacrificial are NOT the same. Catastropic is as you say. the device essentially blows up. ZORCH. Finished. Sacrificial means the device SACRIFICES itself to 'save' something else. If the sacrifice is NOT fatal, (catastrophic, maybe?) it can do so again and again until maximum ratings are exceeded. Lifetime Over. I'm repeating myself now, since you can't seem to understand the difference between lifetime testing and destructive testing. I worked in a fab F.A. department for a while. 1000 hour burning was a required qualification for ALL new devices. From the failure data and failure MODES, the brain trust could give reasonable numbers for MTBF and if enough failures were for the SAME cause, perhaps ask for process improvements….which needed a requal before release. I'm still trying to figure out if lightning is AC or DC? Anybody know?
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Post by westom on Mar 8, 2016 11:18:49 GMT -5
I must be Semantics for fun and profit. Catastropic and sacrificial are NOT the same. Catastropic is as you say. the device essentially blows up. ZORCH. Finished. Sacrificial means the device SACRIFICES itself to 'save' something else. A fuse is a sacrificial device. It does not protect electronics. It sacrifices (fails catastrophically) so that a defect does not create other and further problems - ie a house fire. Parts that fail catastrophically (ie fuse, MOVs) do not operate again. MOVs must not fail catastrophically - sacrificially. Degraded MOVs continue to work; just not in spec. Structure fires have occurred because MOVs failed catastrophically. Because an emergency protection device - a thermal fuse - did not blow fast enough. Pictures demonstrate what happens when a protector is grossly undersized: www.zerosurge.com/technical-info/truth-about-movs/Catastrophic failure is the reason for so many (million?) APC protectors recently removed immediately. A protector's indicator light can only report a potential catastrophic failure. It cannot report the other and acceptable failure mode - degradation. That indicator light reports when a protector was grossly undersized and a potential threat to human life in that venue. Please appreciate as a technician, then you have little knowledge of what we design in equipment that, for example, must not fail catastrophically. That is especially critical in semiconductor fab equipment for silane, phosphene, and other hazardous materials. Then a technician only need understand what does and does not work. You did not even trace damage created by those near zero protectors. We did by literally replacing each damaged IC to trace the damage path. To discover what human mistake created that damage. BTW, it was always the joke - a DC surge. No such thing exists. As made obvious by Fourier analysis. A concept always taught to engineers, introduced in high school math, and often not taught to technicians. Lightning (like all spikes) are AC. DC spike is a popular joke. For all: 'sacrificial' was used subjectively. Subjective reasoning is how junk science exists. Any condition, event, threat, or need must be defined quantitatively - using perspective - ie by numbers. Defined with numbers is sacrificial (also called catastrophic failure) verses what all MOV based products must do (degrade). MOV life expectancy charts discuss degradation. Catastrophic failure (unacceptable MOV failure) occurs when other numbers - Absolute Maximum Ratings - are exceeded. That indicator light can only report a potential catastrophic failure - a safety warning to a homeowner. Light cannot report degradation. A 'whole house' protector, rated at least 50,000 amps, is strongly recommended for homes. Then that protector degrades over many decades. Then protection exists even during direct lightning strikes. Then near zero (plug-in) protectors are protected.
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Post by leonski on Mar 8, 2016 11:20:22 GMT -5
Thanks keith: Most of what I wrote supported, I'll look up series mode protection at first opportunity. But today is a 'travel day' and I'm already a Little Late.
I'd have thought lightning was DC. But another poster 'red-herring'd the issue by brining up the impedance to ground, not resistance. To me, the data sheet makes sense if you read the table I ref'd. Near-infinite lifetime below a certain level, than you start eating into device lifetime. Rather like metal fatigue (not aluminum which HAS no fatigue limit)
I'll check my Panamax for the little red light! It's a good unit, but we simply don't USE it much as a surge device since SoCal gets FEW lightning strikes.
Cheers:
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