Surge / Ground / Lightning
in [Home Built PC]
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From: spamfree on 5 May 2008 21:28 On Mon, 5 May 2008 19:19:16 +0100, Mike Tomlinson <mike(a)jasper.org.uk> wrote: >but their >effectiveness when used on ungrounded outlets is reduced, since the path >to ground doesn't exist. I was going to ask whether this would help protect delicate components in any way, but of course, the neutral is earthed nearby anyways, and the third earth wire is just a backstop? jack
From: nicksanspam on 6 May 2008 18:31 Mike Tomlinson <mike(a)jasper.org.uk> wrote: >... This is an important principle of the UK wiring code. It's >referred to as "equipotential bonding." I wonder if "ring mains" (an extra wire from the last outlet to make a loop back to the fusebox) are legal in the US. Seems like a nice way to improve voltage regulation with a little extra wire, and if the ring wire only breaks in one place, all the outlets keep working. Nick
From: VWWall on 6 May 2008 17:43 trader4(a)optonline.net wrote: > W_ denies MOVs are commonly used in typical electonics or modern > appliances too. He had to, because he can't answer the obvious > question of how MOVs can be used effectively in these applications, > yet they can't work in plug-in protectors and the only way to get any > protection is to have a nearby direct earth ground. Faced with the > problem of MOVs providing protection in electronics/appliance without > an earthground, he simply denies MOVs are used in electronics and > appliances. Here's the references that I provvided him on that one: > > Here, from Appliance Magazine and Appliance Design websites: > > http://www.appliancedesign.com/CDA/Articles/Electronics/BNP_GUID_9-5-... > > > "New thermally enhanced MOVs help protect a wide variety of low-power > systems against damage caused by over-current, over-temperature and > over-voltage faults, including lightning strikes, electrostatic > discharge (ESD) surges, loss of neutral, incorrect input voltage and > power induction. I had a microwave oven that had a MOV across the 120V line ahead of the power switch. The other side of the 120/240 20A circuit supplied a refrigerator. The loss of the neutral applied a good part of the 240V across the MOV when the refrigerator attempted to start. The MOV didn't last long! It would probably have been OK on the load side of the switch. I know that refrigerators should be alone on a "home run" circuit, and neutrals shouldn't be connected with wire nuts, but that wasn't how it was! My only complaint with some plug-in protectors is that the MOVs are often much too small. I've also seen some with only a line-line MOV. -- Virg Wall, P.E.
From: Don Kelly on 6 May 2008 02:38 ---------------------------- "bud--" <remove.budnews(a)isp.com> wrote in message news:e234c$481f53e8$4213eabe$21042(a)DIALUPUSA.NET... > Don Kelly wrote: >> ---------------------------- >> "Tony Hwang" <dragon40(a)shaw.ca> wrote in message >> news:dncTj.112858$rd2.31639(a)pd7urf3no... >>> phil-news-nospam(a)ipal.net wrote: >>>> In alt.tv.tech.hdtv Michael A. Terrell <mike.terrell(a)earthlink.net> >>>> wrote: >>>> >>>> | Bullshit. Like ALL charges, it simply seeks a complete circuit to >>>> | flow. You have absolutely no grasp of the basic concepts, yet you >>>> | continue to spout your ignorance and lies. >>>> >>>> Not true. >>>> >>>> When you close a switch between a power source and a pair of wires that >>>> go >>>> out yonder, the electrical energy does not "know" whether the circuit >>>> is >>>> complete or not. If it refused to flow, it would not be able to find >>>> out. >>>> It will flow, whether the circuit is complete or not. What happens >>>> after >>>> that depends on what is at the other end, which could be an open >>>> condition, >>>> a short circuit, or some kind of resistive or reactive load. >>>> >>>> You've claimed to have worked in broadcasting in an engineering role. >>>> So >>>> you should understand what happens at the end of an open transmission >>>> line. >>>> The electricity flows to get to the open end. Yet it is not a >>>> "complete >>>> circuit". >>>> >>> Hmmm, >>> You seem to be confused between current flow(energy) and >>> voltage(poential) Nothing flows in an open circuit. If not we have to >>> rewrite Ohm's law. Show your credential to make a stamement like that. >>> Shameful. >> ------------------------ >> Actually, you are showing some confusion. Phil is right in that he is >> bringing out a point that normal lumped RLC circuit theory doesn't handle >> because it essentially treats the speed of propagation of electrical >> signals as if it were infinite- which isn't true. >> . >> 2)Also, on energizing a line whether it is open or closed, there is a >> current flow as the applied voltage "sees" the characteristic impedance >> of the line (wire or whatever) so a current will flow-even on an open >> circuit- until there is a modifying reflection from the termination. For >> a house the distances are such that this may be of the order of 0.1-0.2 >> microsecond. After all such reflections at terminations have ceased or >> are negligable, conventional circuit theory is applicable. >> In these situations, you are dealing with wave propagation rather than >> conventional circuit theory. >> This is the regime that is of interest in considering "surge protectors" > > The last standards for simulating typical surge waveforms I have seen > (IEEE) were > 1.2 us rise time, 50 us duration > 8 us rise time, 20 us duration > a ring wave with a frequency about 100kHz. > > All are long relative to 0.2 microsecond, so wave propagation should not > be relevant for household circuits. ---------------------------------------- Your point is true- the time interval is so small that for practical purposes it can be ignored. I am not denying that. Obviously I gave that impression- sorry for that. I was simply pointing out that phil had it right in theory and Tony had it wrong. After this time for the wave to travel to the end and be reflected (and other re-reflections die out) then conventional circuit theory is applicable. The fact that the time is extremely small simply means that we can pretend that it doesn't even exist. While Matzloff is right in the time for a round trip is of the order of 200m, it is also dangerous to assume that one can ignore waves for shorter distances. For example, a stroke to a tower of an EHV line (a lot less than 200m) will go down the tower, meet ground resistance and be reflected. Such reflections have been found to be more likely to cause flashover than direct strokes to the line (EPRI). Similarly, the practice in substations is not "whole station" protection (where this is applicable, it must be done considering a number of factors- quite interesting ) and putting specific protection as near as possible to the protected apparatus-definitely within, say, 10m. - It's not just the time to peak that is the critical factor. Do a lattice diagram approach or use Bergeron's method (Hermann Dommel did a lot of work with this at EPRI and has a lot of papers in IEEE- more dealing with switching surges than lightning). It's been a long time since I did any calculations in this area so I would have to brush up. Now - is this all germane to household protection? You say not and I agree with you- because household equipment can ride through - at worst- doubling of the clamped voltage for a very short time even though the clamped voltage is relatively small compared to the peak of the incoming surge. -- Don Kelly dhky(a)shawcross.ca remove the X to answer > > A favorite article from w_ also uses a "8x20 us impulse as a very rough > representative pulse" with most harmonic content from 20kHz to 100kHz. > > Martzloff, using the shorter rise time, has written: "For a 1.2/50 us > impulse, this means that the line must be at least 200 m long before one > can think in terms of classical transmission line behavior." > > What reason is there to believe wave propagation is relevant to house > circuits? > >> >> As to the advantage of "whole house" vs local surge protection, "whole >> house protection depends on distances to all "protected" items being >> small. > > Longer distances make the system more subject to effects like direct > induction from lightning into the wiring. I don't see why, in general, > the distance has to be small. > > > -- > bud--
From: w_tom on 6 May 2008 02:42
On May 5, 1:05 pm, spamf...(a)spam.heaven wrote: > I'm curous to know how surge suppression can work without a ground > (earth) of any sort. Does the "black box" detect overvoltage and > disconnect the power like an earth leakage safety switch? > > This might be fine for a TV, but surely not for a computer. > > I don't recall any computer I've owned that did not have a three wire > connection to the mains. That and a MOV is OK for smallish surges, but > I believe that for a large surge, the sort that will blow a telephone > off the wall, one needs a large, short-path earth for the surge > detector to dump the extra power down. > > I've got a few plug in protectors here and there to sop up a small > spike, but when a storm is within a few km, I pull the phone wire out > of the ADSL router, and the plug out of the mains. If I'm working at > the time, I might just keep a watch on the weather radar and count > lightning fashes to thunder times. It's rare that I get interrupted. I > have underground power and phone lines so that gives a little extra > protection, I believe. This will address some of your questions only in summary. Details are provided in other posts. First, much of this stuff was learned by earliest 20th century hams. They would disconnect their antenna, put the lead inside a mason jar, and still suffer radio damage. Even mason jars could not stop or block lightning. But then the antenna was earthed, then damage stopped. It's just like Franklin's lightning rod (air terminal). Protection has always been about diverting "it to ground, where it can do no harm". Disconnecting did not provide sufficient protection. That wire had to be earthed. Protection for the TV, computer, and all other appliances is same. Computers contain some of the most robust protection. Computer grade UPSes can output electricity so dirty (when in battery backup mode) as to even harm some small electric motors. But computers are so robust as to make even that 'dirty' electricity irrelevant. Do not assume computers have less internal protection. Intel ATX standards require computers to be more robust than what is standard for other appliances. No protection exists by disconnecting - the black box. Air is a best insulator. Lightning travels through 3 miles of air to contact earth. What magic black box do you own that can stop what three miles of sky could not? Protectors do not stop, block, or disconnect from lightning. Furthermore, a lightning surge does damage too fast. A fastest disconnect relay takes milliseconds. Lightning surges do damage in microseconds. Two of so many reasons why protection is not achieved by disconnecting. Try damming a river to stop a flood. Dam gets swept away. Move that dam off to the side; call it a dike. Open a large channel downriver. Protecting by disconnecting, blocking, or absorbing surges is akin to that dam - useless. Instead, install (and earth) a 'whole house' protector - akin to a large channel downriver. And then install dikes - internal protection inside appliances or other supplementary protection. Even dikes (supplementary protectors) are useless without that large channel downriver - the properly earthed 'whole house' protector. MOVs are routinely installed where direct lightning strikes are earthed - without damage to MOVs. MOVs used in properly sized 'whole house' protectors. But when a plug-in protector is sold to maximize profits (not for protection), then grossly undersized protectors also create another problem - scary pictures: http://www.hanford.gov/rl/?page=556&parent=554 http://www.westwhitelandfire.com/Articles/Surge%20Protectors.pdf http://www.ddxg.net/old/surge_protectors.htm http://www.zerosurge.com/HTML/movs.html http://tinyurl.com/3x73ol or http://www3.cw56.com/news/articles/local/BO63312/ Routine is for direct lightning strikes to be earthed by a 'whole house' protector. Routine is for a properly sized protector to earth surges AND remain functional. A protector damaged by a direct lightning strike - grossly undersized - is designed in direct violation of MOV manufacturer's specs. MOV manufacturers are quite clear about this. MOVs must only fail by degrading; not fail by vaporizing. MOVs also do not work by sopping up surge energy. But grossly undersizing a plug-in protector and a resulting explosive damage gets the naive to recommend an obscenely overpriced protector. Yes, grossly undersizing a protector can get the naive to recommend more ineffective protectors. An effective protector earths direct lightning strikes AND remains functional. An effective protector means nobody knew the surge even existed. But no explosive failure means some here would not recommend that protector. Above described secondary protection. Homeowners should also inspect their primary inspection system: http://www.tvtower.com/fpl.html Buried wires do not provide effective protection. An industry professional provides this application note. Notice even underground wires must be earthed before entering the building. Even underground wires can carry surges, destructively into the building. Any wire that enters the building - overhead or underground - must connect to a single point earth ground either directly (ie cable TV, satellite dish) or via a protector (ie telephone, AC electric). The app note shows two structures. Any wire into either structure first connects to that structure's single point earth ground: http://www.erico.com/public/library/fep/technotes/tncr002.pdf And finally, it is posted multiple times including a reference to an article for EE entitled "Protecting Electrical Devices from Lightning Transients". That safety ground and neutral wire cannot provide earthing for a long list of reasons. |