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Big surge protector needed

Discussion in 'Electrical Engineering' started by [email protected], Apr 24, 2008.

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  1. Guest

  2. Palindrome

    Palindrome Guest

    You could have added that it is worth seeing what happens at around the
    17 minutes mark.

    Presumably it shows what happens when the HV primary voltage of a
    distribution system ends up on the the LV supply lines going to a house.

    I'm amazed that the house wasn't actually on fire. Don't people bond
    metal roofs to a ground rod in the US?
     
  3. Guest

    | wrote:
    |> Try this on your surge protector:
    |> http://phil.ipal.org/usenet/aee/2008-04-24/bigsurge.mp4
    |>
    | You could have added that it is worth seeing what happens at around the
    | 17 minutes mark.
    |
    | Presumably it shows what happens when the HV primary voltage of a
    | distribution system ends up on the the LV supply lines going to a house.

    It could be just MV.


    | I'm amazed that the house wasn't actually on fire. Don't people bond
    | metal roofs to a ground rod in the US?

    I don't that it would help in this situation. There's too much available
    current.
     
  4. ehsjr

    ehsjr Guest

    Awesome.
    It looks like a cherry picker shorted against the utility wires.
    Not a surge - the duration is _way_ too long. Kiss your surge
    protector goodbye. In the video, they almost have to kiss the
    house goodbye!

    Ed
     
  5. Guest

    | wrote:
    |> Try this on your surge protector:
    |> http://phil.ipal.org/usenet/aee/2008-04-24/bigsurge.mp4
    |>
    |
    | Awesome.
    | It looks like a cherry picker shorted against the utility wires.
    | Not a surge - the duration is _way_ too long. Kiss your surge
    | protector goodbye. In the video, they almost have to kiss the
    | house goodbye!

    At least three houses I could see were affected. A barely audible comment
    suggested all the houses in "the main street" were affected (presumably
    within the range of commonly connected LV circuits). I wonder if any
    telephone or cable wires were affected.

    I could see in some parts of the video some pulled down wires in places
    apart from where the cherry picker was. Maybe the linemen were there to
    do repairs and the line was re-energized somehow (recloser closing back
    again and getting stuck).

    How many people here think that the houses affected, assuming there was
    minimal fire damage, at least have to have all the wiring replaced (at
    the cost of the power company if it was their fault, or by insurance)?


    Now for theory:

    Sure, surge protectors you buy in Wal-mart would be destroyed by something
    like this. But, what would it take to at least protect a device like a
    computer?

    One thing the plug-in surge protectors are touted to do is maintain the
    same voltage level on all wires once the voltage reaches the level where
    the MOVs would conduct. Now in this case, the available current and the
    long duration would just make those MOVs join the air pollution. So it
    would take something a LOT bigger. If there was something that could
    survive it, then in theory the computer would see the voltage rise (and
    drop and rise the other way and drop, 60 times a second). But as long
    as all connections to the computer rise and drop together, there is no
    voltage _difference_ and only charging current would flow. Lightning
    surges can be a lot higher voltage than MV distribution lines. So it
    should be a matter of making something that can hold up to the distribution
    voltage and the crossover current long enough for some really large fuses
    rated for such voltages to burn out. I'm thinking along the lines of a
    "whole house" type of protector. It might not be practical or worth the
    rare risk like this, but it is a challenging thought project.
     
  6. ehsjr

    ehsjr Guest

    :) Nice turn of phrase!
    Don't know. The assumption we are making is that massive
    energy reaches the point of use protector undiminished.
    But the only thing that counts is the energy that actually
    does reach the point of use protector, not the huge energy we
    see outdoors. I would also assume that massive energy
    reaches the protector so we agree on that - but it's still an
    assumption.

    Well, at the homeowner level it would be treating the symptom,
    not the failure. The fix would have to involve the distribution
    system. The answer to the "cherry picker event" is underground
    distribution - which would bring a different set of possible
    failure scenarios that might somehow short the cables.

    Ed
     


  7. You know, you can create a news account using a ficticious e-mail address,
    then include your real e-mail address on a case-by-cace basis by entering it
    as <yourname> at <yourISP> dot com. This will allow anybody that wants to
    reply to you to do so, while keeping the spambots at bay. Then you can see
    news messages from the unwashed fools on Google Groups. Even an unwashed
    fool has a valuable thing to say from time to time.

    Spambots know how to ignore "nospam" buried inside an email address,
    especially when you set it off with punctuation. You could filter spam
    better with philnewsnospam at ipal dot net.
     
  8. Guest

    |
    | |> Try this on your surge protector:
    |> http://phil.ipal.org/usenet/aee/2008-04-24/bigsurge.mp4
    |>
    |> --
    |> |WARNING: Due to extreme spam, I no longer see any articles originating
    |> from |
    |> | Google Groups. If you want your postings to be seen by more
    |> readers |
    |> | you will need to find a different place to post on Usenet.
    |> |
    |> | Phil Howard KA9WGN (email for humans: first name in lower case at
    |> ipal.net) |
    |
    |
    |
    | You know, you can create a news account using a ficticious e-mail address,
    | then include your real e-mail address on a case-by-cace basis by entering it
    | as <yourname> at <yourISP> dot com. This will allow anybody that wants to
    | reply to you to do so, while keeping the spambots at bay. Then you can see
    | news messages from the unwashed fools on Google Groups. Even an unwashed
    | fool has a valuable thing to say from time to time.

    The spam issue isn't email spam in this case ... it's usenet spam. Google
    readers can see my posts just fine. Spammers scraping Google Groups can get
    my email address.

    The issue is spam in the usenet postings. Google's CAPTCHA got cracked and
    Google seems to not be taking steps to counter that. The spam volume rose
    dramatically every week until I decided to block it. I see it as Google
    putting the posts by legitimate users of their service at risk, not me.


    | Spambots know how to ignore "nospam" buried inside an email address,
    | especially when you set it off with punctuation. You could filter spam
    | better with philnewsnospam at ipal dot net.

    Actually, the modified email address is a real mailbox. It gets about as
    much spam as my main mailbox, which is seen in a lot more places. I used
    to generate dyanmically random email addresses (within my domain) in the
    signature here. Back when I first started doing that, one of those got
    spammed within 7 minutes of the posting it appeared on.
     
  9. Don Kelly

    Don Kelly Guest

    ----------------------------
    ------------------
    Surge protectors aren't designed for long term situations like this. They
    are intended to handle switching or other surges which are in the order of
    less than a millisecond- but not line frequency currents. To be able to
    conduct for 17 minutes would likely result in a prohibitive cost (more than
    the house). Since it is apparent that circuit breakers on the MV(?) supply
    didn't operate, the current must have been relatively low (or something was
    horribly wrong with the fusing/ protection of the primaries. Assuming 5A at
    7200V, there is only 36KVA involved but in 17 minutes the energy is about 37
    megajoules. I'm not sure that even the surge arrestors used on EHV lines
    could handle that energy. I do know that their 60Hz withstand at anything
    over about 120% of rated voltage is in the order of seconds- not minutes.
     
  10. Guest

    | Surge protectors aren't designed for long term situations like this. They
    | are intended to handle switching or other surges which are in the order of
    | less than a millisecond- but not line frequency currents. To be able to
    | conduct for 17 minutes would likely result in a prohibitive cost (more than
    | the house). Since it is apparent that circuit breakers on the MV(?) supply
    | didn't operate, the current must have been relatively low (or something was
    | horribly wrong with the fusing/ protection of the primaries. Assuming 5A at
    | 7200V, there is only 36KVA involved but in 17 minutes the energy is about 37
    | megajoules. I'm not sure that even the surge arrestors used on EHV lines
    | could handle that energy. I do know that their 60Hz withstand at anything
    | over about 120% of rated voltage is in the order of seconds- not minutes.

    What would you call (a term to use to identify) protection for a situation
    like this?

    We really don't know why the MV breakers/reclosers did not operate, or came
    back on (there were apparently time intervals where power was off).

    Protection against this I think can be done. But it most certainly would not
    be in the form of long term fault current conduction if the currents are high.

    If the current is LOW, such as the 5A you suggest, then the system impedance
    must be rather high. Maybe too high. How much voltage drop would a street
    of homes see at their 240V service when each draws 100A at each of 5 homes?
    That's 120kW total, 16.66A at 7200V. So the MV system impedance needs to be
    about to deliver that 16.66A without an intolerable voltage drop. Since some
    of that drop would happen in the transformer, the distribution can only be a
    portion of it. But even if we assume a 5% drop in voltage, the impedance has
    to be no more than 21.6 ohms, which would result in 333A in a distribution
    fault. That's a severe voltage drop. I suspect the system impedance would
    be lower.

    So I think we cannot rule out some kind of failure upstream. It happens.

    I believe the arcs in the video are much more than 5A. Remember, the power
    is a function of the amps times the voltage _drop_ of the arc itself, not the
    system voltage. If the system is so high an impedance that a fault would be
    only 5A, then more power is dissipated in the system than at the fault.

    A protection device for this would first need to be able to handle the full
    distribution voltage. It would then have 200A fuses (whatever the amperage
    of the service drop is). These would have to be MV rated fuses. So this is
    not cheap. But it's not the price of a house, either. Then after the fuses
    is a device that would conduct well at medium voltage and do so long enough
    for the fuses to blow. It would have to conduct between the wires.

    The risk here is that the MV phase was contacting the LV wires in common.
    That is, all 3 wires were at the same potential, and the voltage at the house
    was only relative to ground. It would take a very good earthing system to be
    able to get the current high enough to burn the fuses. So there are cases
    where this still won't work.

    Homes in rural areas that are more spread out would typically be served by a
    single transformer. So then there would be no pole to pole LV wires exposed
    to potential MV droppings. By setting in a separate pole away from the MV
    lines, and bringing one MV branch over to one side of it, and run the LV
    drop from the other side of that pole, it would at least minimize the chance
    of such a mess as this video shows, in these rural situations.

    The better solution is to go underground, even if the MV lines stay above
    ground. Using pad transformers (protected against vehicle impacts) would
    be safer, IMHO.

    As for a failure upstream, that can depend on what failed, and how the various
    devices like a recloser are actually designed. I don't know how they really
    work inside. So I'm guessing maybe a recloser would have three current sensor
    transformers. Now what if one shorted out on one phase and that happened to
    be the phase that fell? If it faults to neutral, it would not be detected.
    If it happens to hit another phase, then the fault current on the other phase
    would be detected and the recloser opens. After a while it closes again and
    the whole thing starts over. Can the recloser completely reset altogether if
    current flows normally (from its point of view, being blind to one bad phase)?
     
  11. Don Kelly

    Don Kelly Guest

    ----------------------------
    I pulled out the 5A figure just to show the power and energy levels at a low
    current level. Now consider a current as you indicate (arc impedance
    ignored) and multiply my numbers accordingly.

    However: Your calculation assumes that the transformer and line impedance is
    purely resistive but this is not true. The HV/MV transformer would have an
    X/R ratio of possibly 5 to 8 so that for a 5% drop the resistance would be
    of the order of 15 ohms and reactance 75 ohms for a total impedance of 76.5
    ohms. Using these figures with a current of 16.7A 1.0 pf, at 7200V results
    in a drop of 4.9%. Now consider short circuit conditions- the current will
    be nearly completely reactive (generally resistance is ignored in fault
    studies) and will have a magnitude of 99A. Actually it would be less because
    ground impedance is a factor.
    Note that the fusing would have to be set to trip quickly (at most a second
    or so at, say, 60A (would have to be co-ordinated with the MV system fault
    level at the point under consideration, which presents problems on a 100 or
    200A service as well as logistical problems so, in my opinion in house
    protection is impractical.

    If, however, you assume that the main transformer has 5% impedance based on
    7200V 150MVA (phase) then the fault current would be in the range you give
    (but a lot lower voltage drop under normal load- something less than 1%).
    THen 3 MVA fast blow fuses as you suggest might work as long as clearances
    between the incoming line was such that there was no danger of flashover.

    So- we are considering an unknow scenario because we don't have the facts to
    do a proper analysis-

    Your suggestions regarding arrangements of MV and LV lines are likely more
    practical and could be cheap or expensive depending on the load density.

    We really don't know whether there was a 3 phase MV line in this region--
    one phase and neutral may have been used- this is not uncommon. The
    reclosers are likely single phase- 3 shots and it stays open. If 3 phase, I
    would expect interlocking. You are absolutely correct in that something
    upstream went wrong and it took an unconscionable time to do something about
    it.
     
  12. Guest

    | I pulled out the 5A figure just to show the power and energy levels at a low
    | current level. Now consider a current as you indicate (arc impedance
    | ignored) and multiply my numbers accordingly.

    Multiply what numbers? The arc impedance will dictate the current given a
    voltage. If you have 5 amps, you have far more impedance on a 7200 volt
    system than an arc will give you.


    | However: Your calculation assumes that the transformer and line impedance is
    | purely resistive but this is not true. The HV/MV transformer would have an
    | X/R ratio of possibly 5 to 8 so that for a 5% drop the resistance would be
    | of the order of 15 ohms and reactance 75 ohms for a total impedance of 76.5
    | ohms. Using these figures with a current of 16.7A 1.0 pf, at 7200V results
    | in a drop of 4.9%. Now consider short circuit conditions- the current will
    | be nearly completely reactive (generally resistance is ignored in fault
    | studies) and will have a magnitude of 99A. Actually it would be less because
    | ground impedance is a factor.
    | Note that the fusing would have to be set to trip quickly (at most a second
    | or so at, say, 60A (would have to be co-ordinated with the MV system fault
    | level at the point under consideration, which presents problems on a 100 or
    | 200A service as well as logistical problems so, in my opinion in house
    | protection is impractical.
    |
    | If, however, you assume that the main transformer has 5% impedance based on
    | 7200V 150MVA (phase) then the fault current would be in the range you give
    | (but a lot lower voltage drop under normal load- something less than 1%).
    | THen 3 MVA fast blow fuses as you suggest might work as long as clearances
    | between the incoming line was such that there was no danger of flashover.

    There could be flashover on the service drop triplex. But if the protection
    is somehow installed between it and the house, it could protect the house.


    | So- we are considering an unknow scenario because we don't have the facts to
    | do a proper analysis-

    Probably.

    I'm quite convinced these arcs were a LOT more than 5 amps. I've seen
    real faults that get cleared fairly fast, but they had enough time to do
    things on the scale of what happened in the video. These I saw would not
    be 5 amps since that's only 36 kW max. If the system could not deliver
    more than 5 amps, it can't provide much service to a neighborhood of many
    homes.

    I once did see a downed MV line that was just sizzling and smoking in the
    grass. I could easily believe that one was 5 amps or less, and earth
    impedance was high. At the time I came upon it, a policeman was there
    telling people to stay back. But he was about 10 feet from it himself.
    I had to talk HIM into getting further away. If he were to see this
    video, he might realize the danger he exposed himself to. I'd already
    seen half a dozen such events myself by then, so I already knew. Since
    then I've even seen (online) the gory results of just the arc blast.
    These are things you and I and linemen know to stay well away from.


    | Your suggestions regarding arrangements of MV and LV lines are likely more
    | practical and could be cheap or expensive depending on the load density.

    It would certainly be an issue in a compact residential area. There, the
    way to go (and new installations do this for other reasons) is underground
    and using pad transformers.

    I'm looking at building a house in a rural location, so I would have room.
    The question I want to figure a good answer for is just how far from the
    house I want to have the step from MV to LV. Too close and I have MV over
    or under more of my land. Too far and I get more voltage drop on the LV
    service. If I could get 480 volts (remote possibility in a rural area),
    that might work out better.


    | We really don't know whether there was a 3 phase MV line in this region--
    | one phase and neutral may have been used- this is not uncommon. The
    | reclosers are likely single phase- 3 shots and it stays open. If 3 phase, I
    | would expect interlocking. You are absolutely correct in that something
    | upstream went wrong and it took an unconscionable time to do something about
    | it.

    My hypothesis is the recloser was acting sometimes. That's based on the way
    the tape was edited. If I had 20 minutes of tape with about 4 minutes worth
    of "fun arcs" to show on YouTube, I'd edit it down and indicated the times.
    That seems to be what was done (this did come from YouTube). So I believe it
    quite likely that the missing times on the tape are times without faults.
    That may be because the wires were not touching (it was windy at times as
    seen in the trees, so that can change). But maybe the lines were dead at
    the times of no arcs. Why would a lineman go up in a bucket if he believed
    a damaged line was still energized? It may have been a combination of
    recloser activity and lines not always contacting.

    OTOH, the linemen should have made sure the circuit was shut off _and_
    grounded on the downstream side before working on it. During a big storm
    that knocked out a lot of power in my area, I could tell when driving back
    home from a trip into town to eat at a restaurant, that the linemen were
    finally in my area working on it when I noticed grounding cables had been
    attached just beyond the last point where fuse cutoffs were on the line
    leading to where I lived. Power was back on 45 minutes after that.

    In any case, I'm trying to guess a hypothesis of why a recloser might work
    sometimes, and just leave fault current flowing at other times. If I knew
    more about how they were designed, I could probably guess better. But even
    then it is a guess, as we don't know what really happened in this event.

    Still, my guess seems to fit. That is, these are three phase lines (they
    look like it) and the CT used by the recloser was defective (or shorted)
    on the one phase that was the primary culprit. When that phase arced to
    ground, the recloser didn't see it. When it crossed over to another phase
    (infrequent event) then it saw it.

    What does a recloser, that is supposed to lockout after 3 tries, do if it
    only had to open 1 or 2 times, and the fault was cleared? Does it reset
    the count after some time? Or is the next event in a few months going to
    lock out immediately? If there is a timer that resets the count after some
    amount of time with no observable faults, then maybe it was resetting for
    the times between phase crossover faults in this video? Again, just a guess.

    BTW, in the video, a couple shots of the lines give the appearance that at
    least one pole has been pulled partly down sideways in a way that would have
    pull on the lines downstream and snapped one or more. I definitely saw at
    least one broken wire.

    Another thing I notice is that the point of arcing were moving along the
    line. It's hard to see as the guy operating the camera was moving toward
    the arcs as they moved back away from him. In one scene a row of small
    bushes were well ahead. In another he had come just past them.
     
  13. Don Kelly

    Don Kelly Guest

    ----------------------------
    --------
    Scale up to the levels you are considering. The 5A was just a number drawn
    out of a hat to indicate that even at a low level, for the duration
    involved, the energy is such that a practical MOV isn't going to hack it.
    -----------------
    -----------
    That is possible. However, it likely couldn't be done on a "one size fits
    all" as the fuse rating would depend on the impedance of the upstream
    transformer and the line between, on the basis of the small probability that
    something like this incident would happen. Next would be to design cars to
    survive head on collisions with semi's as the probability of such
    collisions is definitely higher.
    -------------
    -----------
    It appears that you did not read what I wrote after you first questioned the
    5A figure.
    I do agree -see the second part of what I wrote.
    The first part (paragraph starting with However) is based on 5% drop with
    normal loading and pointing out that your calculation , on the basis of a
    unity pf load, doesn't deal with the actual fault conditions. The next
    paragraph (If, however....) considers what is more realistic in considering
    an ideal source behind the HV/LV transformer and assuming 5% impedance
    (actually a bit low considering lines). This will result in a "bolted" fault
    current of 417A and a fuse able to handle 3000KVA (single phase -more if 3
    phase).
    Will such fusing do the job? It depends on other factors such as ground
    potentials that may occur.
    ------------
    --------------
    I have met, after the fact, such a situation- really a longer story
    involving a day starting with a lot of whiskey and a broken guy wire
    flipping over a 7200V single phase line and an attempt to clear the wire
    from ground- it blew out his rubber boots at the ankles, and ended up on the
    guy's back, burning holes in his flesh but not knocking him out and not
    being detected by the recloser. This went on for over 15 minutes- every now
    and then he would try to get up but this - he lived but was essentially a
    basket case.
    -----------
    --------
    Right and the cable drop to the underground system is on a pole at the edge
    of my lot. It could have been across the street where the 3 phase line is
    but then the developer would have to pay for the extra run under the road
    (and patching the road). It is not a problem.
    ----------------
    --------
    A friend of mine dealt with this in another way - one MV span into his
    (wooded) property and the rest underground at 120/240V. He did all the UG
    wiring and dealt with the appropriate wire sizing. No problems and no
    eyesores. More money on copper in this case bt it was worth it.
    -----------
    ----------
    That's possible. As far as a lineman in a bucket- the purpose of the bucket
    is to allow live line work. In addition, a lineman who wants to collect his
    pension should never assume a line is dead. It should be grounded on both
    sides of the work area (particularly where otherlines are physically in
    parallel. There are standard safety procedures to be followed.
     
  14. bud--

    bud-- Guest

    A primary line dropping on secondaries will rapidly destroy MOVs. UL
    (US) requires the MOVs be disconnected when they overheat and fail.

    Plug-in suppressors may connect the protected load across the MOV so it
    is disconnected with the failing MOV, or across the incoming line. If
    connected across the MOV a plug-in suppressor may (or for crossed
    primary wire may not) provide protection. A few plug-in suppressors
    disconnect on overvoltage. A UPS may provide protection.

    Long ago Byte magazine columnist Jerry Pournelle had a 16kV primary wire
    cross. A computer connected to a UPS continued to function through the
    event. Some other equipment was not so fortunate. (This was well before
    UL required thermal disconnects.)
    http://www.jerrypournelle.com/computing/august89.html

    At about 6kV there should be are-over from bus to panel enclosure (US).
    That may provide slight protection, but may also start a fire in the house.
     
  15. Guest

    | Scale up to the levels you are considering. The 5A was just a number drawn
    | out of a hat to indicate that even at a low level, for the duration
    | involved, the energy is such that a practical MOV isn't going to hack it.

    If an MOV cannot conduct 5A for a long sustained time, then sure, it is not
    a good solution. The time frame doesn't need to be as long as the video was
    showing faults taking place. It only needs to be as long as necessary to
    blow the fuses. Of course, if you have fuses intended for a 200A service,
    getting them to blow is a function of getting enough energy dissipated in
    them, over some time frame, to burn out the fuse element. That might be
    400A for a long time or 4000A for a very short time. You need to make the
    conductive element last LONGER than the fuse, obviously. But that is all.
    We can assume a requirement that if the fuses blow and need to be replaced,
    the conductive element also needs to be replaced because it will have taken
    enough damage that it cannot do the job the next time.

    Clearly, a simple MOV like you find inside a plug-in surge protector is not
    going to accomplish that. I don't know if an MOV can be scaled up enough
    for one, or even several in parallel, to do the job. I'm leary of parallel
    because I can envision them not all working at the same time, and the high
    current blowing them up in cascade too quickly.

    I'm thinking more along the lines of a sacrificial arc gap combined with
    current limited MOVs.

    And maybe a transformer after that point.


    |> There could be flashover on the service drop triplex. But if the
    |> protection
    |> is somehow installed between it and the house, it could protect the house.
    | -----------
    | That is possible. However, it likely couldn't be done on a "one size fits
    | all" as the fuse rating would depend on the impedance of the upstream
    | transformer and the line between, on the basis of the small probability that
    | something like this incident would happen. Next would be to design cars to
    | survive head on collisions with semi's as the probability of such
    | collisions is definitely higher.

    The transformer that is stepping the 7200+ volts down to 240 would not be a
    part of that equation, since the issue is voltage bypassing it. But that is
    probably an oversimplification of the range of possible scenarios.



    |> I'm looking at building a house in a rural location, so I would have room.
    |> The question I want to figure a good answer for is just how far from the
    |> house I want to have the step from MV to LV. Too close and I have MV over
    |> or under more of my land. Too far and I get more voltage drop on the LV
    |> service. If I could get 480 volts (remote possibility in a rural area),
    |> that might work out better.
    | --------
    | A friend of mine dealt with this in another way - one MV span into his
    | (wooded) property and the rest underground at 120/240V. He did all the UG
    | wiring and dealt with the appropriate wire sizing. No problems and no
    | eyesores. More money on copper in this case bt it was worth it.

    I want to minimize the amount of MV on my land. If I can't do maintenance
    on it myself, I want as little of it there as possible, preferrably none.
    But I'm not talking about miles of distance. It would just be hundreds
    of feet or meters. My calculations using Gerald's voltage drop calculator
    indicate that for the shorter distances I'm thinking of, 240V all the way
    would be OK. If I can get 480V or 600V, that distance without MV would be
    even more. Then if the distance is any longer, I will have to have MV.
    Then it is a matter of whether the advantage of putting the MV underground
    is worth the extra cost.


    | That's possible. As far as a lineman in a bucket- the purpose of the bucket
    | is to allow live line work. In addition, a lineman who wants to collect his
    | pension should never assume a line is dead. It should be grounded on both
    | sides of the work area (particularly where otherlines are physically in
    | parallel. There are standard safety procedures to be followed.

    And either the line the guy was approach in the bucket was NOT grounded,
    or the grounding came loose. It sure seems to me that more than one or
    two things went wrong at the same time in that event. Possibly, he was
    trying to ground it in that trip up the bucket, or maybe pull fuses too
    close to the fault area?


    | As to what the sequence of "failures" was or why they occurred- is a matter
    | of conjecture.

    Unfortunately, that's about all we can do, here.

    But given that I know about multiple incidents of MV crossing over to LV for
    various reasons, I have an interest in explore all the possible approaches to
    protection and prevention against this, above and beyond what is already done.
    I do know the whole scenario is possible well before any linemen show up to
    even try to work on it. I've seen lightning hit and break a MV line and said
    line drop to ground and arc there briefly before being cut out. It could have
    just as easily come down across LV lines right then and there.

    I once saw multiple events like this during an ice storm. I already had
    _everything_ in my apartment unplugged (that I could unplug) just in case.
     
  16. Guest

    | At about 6kV there should be are-over from bus to panel enclosure (US).
    | That may provide slight protection, but may also start a fire in the house.

    Mount the panel on a large (expensive) copper sheet that is multiply grounded.
    You could run the grounding wires from the panel along this sheet and bolt or
    weld them to the sheet every few inches along the way. Just keep as much that
    is burnable away from the panel as possible.
     
  17. bud--

    bud-- Guest

    Apparently w__ already converted it into a pissing contest.
    w_ can't understand his own hanford link. It is about "some older
    model" power strips and says overheating was fixed with a revision to
    UL1449 that required thermal disconnects. That was 1998. There is no
    reason to believe, from any of the links, that there is a problem with
    suppressors produced under the UL standard that has been in effect since
    1998. None of the links even says a damaged suppressor was UL listed.
    A service panel suppressor, on failure of it’s MOVs, may only open the
    UL required internal thermal disconnects. It may trip the circuit
    breaker for the branch circuits it is connected to. Or it may trip the
    main circuit breaker.
    As my post clearly said, the protected load may be connected across the
    MOVs and be disconnected with the MOVs when they overheat, fail, and are
    disconnected. A good suppressor will be connected that way. There is
    extensive discussion of this at an IEEE guide on surges and surge
    protection:
    http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf
    I made no recommendations.
    I said nothing about whether w_’s event happened. But I would like to
    see an independent news article. Must have made it into the news.

    In any case, it is anecdotal science.

    Neither plug-in or service panel suppressors are intended to protect
    against crossed power lines.
     
  18. bud--

    bud-- Guest

    You need to get your meds adjusted.
    It is really hard to understand how someone could be stupid enough to
    confuse a creation date with a revision date.

    From w_'s hanford link:
    "Underwriters Laboratories Standard UL 1449, 2nd Edition, Standard For
    Safety For Transient Voltage Surge Suppressors, now requires thermal
    protection in power strips. This protection is provided by a thermal
    fuse located next to the MOV."

    From w_'s Gaston Co. link:
    "More modern surge suppressors are manufactured with a Thermal Cut Out
    mounted near, or in contact with, the MOV that is intended shut the unit
    down overheating occurs [sic]."

    If w_ had any knowledge of the field he would know UL 1449, 2nd Ed was
    effective in 1998.

    The hanford event was 1999. What is the probability the suppressor was
    manufactured under the new standard?
    Lacking technical arguments w_ resorts to personal attacks. My only
    association with surge protectors is I have some.
    Still missing - a source that says there is a problem with UL listed
    suppressors manufactured under UL1449 2ed (1998).
    bud posts facts from w_’s own sources.
    Service panel suppressors (like plug-in suppressors) are not designed to
    protect against crossed power lines. After the MOVs burn out (in
    seconds), and are disconnected by the required thermal disconnect, you
    have no protection.
     
  19. bud--

    bud-- Guest

    To the contrary - still missing - any source that says there is a
    problem with UL listed suppressors made after 1998. Why no source w_?
    w_ must ignore what the NC fire marshal actually said (repeating):
    "More modern surge suppressors are manufactured with a Thermal Cut Out
    mounted near, or in contact with, the MOV that is intended shut the unit
    down overheating occurs [sic]."
    Neither the thermal fuse in a service panel suppressor or the service
    panel circuit breakers are rated to "stop primary voltages". Yet w__
    continues to claim a service panel suppressor protects against crossed
    primary wire.
    My only "insult" was to state the obvious: "It is really hard to
    understand how someone could be stupid enough to confuse a creation date
    with a revision date." Apparently w_ still doesn’t know the difference.
    Provided many times and ignored by w_.

    Where is the manufacturer spec that any service panel suppressor will
    protect against crossed power lines?
    If you want accurate information on surges (not crossed power wires)
    read an excellent IEEE guide at:
    http://www.mikeholt.com/files/PDF/LightningGuide_FINALpublishedversion_May051.pdf
    Or a simpler NIST guide at:
    http://www.nist.gov/public_affairs/practiceguides/surgesfnl.pdf

    The elephant hiding in the closet is w_'s religious belief (immune from
    challenge) that surge protection must use earthing. Thus in his view
    plug-in suppressors (which are not well earthed) can not possibly work.
    The IEEE guide explains plug-in suppressors work by CLAMPING the voltage
    on all wires (signal and power) to the common ground at the suppressor.
    Plug-in suppressors do not work primarily by earthing (or stopping or
    absorbing). The guide explains earthing occurs elsewhere. (Read the
    guide starting pdf page 40).

    Because w_ is evangelical in his belief in earthing, he uses
    google-groups to search for "surge" to spread his beliefs. That is why
    he is here and said in his first post that favored service panel
    suppressors work and plug-in suppressors do not - for crossed power lines.
    Demonstrated repeatedly - w_ is not in touch with reality. Provide a
    source that says service panel suppressors will protect from crossed
    power lines.
     
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