Life expectancy

Are you selling lightening protection? You have so much faith. Tell us
about ground loops.
"w_tom" wrote in message
...
Effective protection costs so little. For example, go to
Home Depot or Radio Shack from something called a grounding
block for incoming cable TV line. It costs less than $2
retail. Connect this grounding block less than 10 feet using
12 AWG or heavier wire. Now the CATV line is fully surge
protected. Yes, the cable line requires no surge protector.
A surge protector is nothing more than a temporary connection
to earth ground. BUT the ground block has already made that
protection connection using a 12 AWG wire. Where is the big
cost?

Unfortunately we still don't build new homes for transistor
safety. So effective protection often must be installed as an
after thought. Sometimes, this means the incoming cable -
improperly installed - must be moved. Now we are talking big
bucks; and only because humans were the reasons for failure.
I recently had this discussion with some cable installer who
keep saying, "Is that what they were saying", or "That's
right. They said something about that". Every incoming
wire must connect to single point earth ground. That
connection is either via a protector or hard wire. The
telephone company even installs a 'whole house' protector ....
for free. But again, it is only as effective as the earth
ground provided by the home builder.

I don't see where all this expense is. Many waste big bucks
on plug in protectors that (quietly) don't even claim to
provide effective protection. The missing information is that
damning. IOW those expensive protectors also are ineffective
solutions. The less expensive 'whole house' protector
connected 'less than 10 feet' to protection is the less
expensive and more effective solution.

Which wire is most often struck? Wire highest on telephone
pole. AC electric. This is a direct strike to the computer
inside the house IF effective 'whole house' protectors do not
connect to that all so essential single point earth ground.

"It depends" is a discussion about the human who did or did
not install effective protection - and what it takes to
correct that mistake. There is no reason for any electronics
to be damaged by surges. And some locations make protection
far more essential. The need for earthed protection varies
even with geology AND can vary significantly even within the
same town.

notritenoteri wrote:
You're right 5 years with no damage doesn't prove anything but it
does point to the fact that the cost to take extraordinary
precautions to protect against rare events is probably not worth it.
On the other hand spending money on the best possible lightening
protection for a radio antenna tower may be worthwhile.
Your claim that protection is easily installed is somewhat
misleading. The facts are "it depends"

Ground loops is why surge protection must be the single
point ground. Problems created by ground loop (the damaged
fax machine) is demonstrated by the NIST figure and previously
cited discussion in:
http://www.epri-peac.com/tutorials/sol01tut.html

Which would you believe? Lies promoted by half truths on
retail store shelves? Or fact demonstrated by telephone and
911 emergency operators who never need remove headsets during
every lightning storm. Effective protection is demonstrated by
telephone switching computers that connect to overhead wires
everywhere in town. Its not called faith. Its called facts.
1) Demonstrated by theory and 2) proven by example virtually
everywhere in the civilized world.

Posted was well understood and repeatedly proven even before
WWII. One classic myths is that surge protectors operate too
slow. Even the GDTs that routinely provided surge protection
before WWII and that were much slower were also fast enough
for surge protection. These are facts know to those who
understood how surge protectors work. 'Surge protector works
too slow' is but another myth. Obviously a myth because it is
routinely promoted without numbers. One must believe such
myths only on faith.

notritenoteri wrote:
Are you selling lightening protection? You have so much faith. Tell
us about ground loops.

w_tom wrote:

Effective protection costs so little. For example, go to
Home Depot or Radio Shack from something called a grounding
block for incoming cable TV line. It costs less than $2
retail. Connect this grounding block less than 10 feet using
12 AWG or heavier wire. Now the CATV line is fully surge
protected. Yes, the cable line requires no surge protector.
A surge protector is nothing more than a temporary connection
to earth ground. BUT the ground block has already made that
protection connection using a 12 AWG wire. Where is the big
cost?

I think you'll find - if you check really carefully - that the
grounding block merely ensures that the incoming cable ground
connection is, in fact, connected to a good ground close to it's final
destination.

Surge protectors otoh make sure that the *signal* (or hot wire in the
case of AC cables) can short rapidly to ground in the event of an
over-voltage. It's done by connecting a MOV (metal oxide varistor)
from signal/hot to ground. At normal operating voltages, this device
is an open-circuit but in the case of a voltage surge rapidly
transforms to a short-circuit shunting the surge to ground.

Having a decent ground alone helps but if you think the grounding
block you refer to means your CATV is "fully" surge protected, you are
sadly mislead.

Power loss will not damage hardware. 'Power loss causes
damage' is often suggested without underlying technical fact.
Why? Underlying facts were never learned.

Sometimes, a power loss is preceded by a surge. Then a
human may blame power loss rather than the undetected surge.
The surge caused both hardware damage and power loss. Human
instead blamed power loss.

Computers using obsolete technology such as FAT file systems
can (in rare cases) erase data previously saved on disk
drive. But power loss does not cause the damage. Damage is
caused by a well known and long since eliminated problem that
still exists in FAT file systems. Systems with critical data
on FAT filesystems should use a UPS - to protect that data.

If 'power loss' causes hardware damage, then 'power off'
also causes hardware damage. Most parts in a computer (ie
hard drive) don't know the difference between 'power loss' and
'power shutdown'. They power down normally no matter how
power is removed.

BTW, how does a UPS protect from power outages? First power
is completely lost for a short time. Then the UPS switches
over to battery. IOW one spec essential for a computer power
supply is its Hold Up Time. Computer power supply must keep
outputting voltage while no power is incoming - while UPS is
trying to decide that power is lost. No problem IF a power
supply contains functions that were defacto 30 years ago AND
that are required in Intel specs. But again, just another
reason why intermittent power loss should not cause damage.

UPS claims no protection from the typically destructive
surges. If it did, then numbers could be provided for that
specification. Anything that provides protection at a
computer is already inside that computer. The plug-in UPS can
even give lightning other destructive paths through the
computer. Yes, an adjacent UPS could even contribute to
hardware damage of adjacent electronics. Instead, the plug-in
UPS manufacturer provided no numerical specs for each type of
transient AND avoids all discussion about earthing. Plug-in
UPS provides no effective hardware protection when the
manufacturer does not even provide numerical specs for that
ability.

Another function that is already in a minimally acceptable
power supply. When line voltage dips so low that incandescent
bulbs are less than 40% intensity: even Intel specs state the
power supply under full load must startup and run as if line
voltage was normal. IOW a UPS for moderate voltage sags is
sometimes a cure for a defective power supply. That is but
another reason why a minimally acceptable power supply retails
for $65. Also why those who buy $25 power supply suddenly
discover they need the plug-in UPS.

Bottom line - the plug-in UPS is only for data protection.
Hardware protection is located elsewhere such as inside a
minimally acceptable power supply, and in the 'whole house'
protection system.

How resilient are computers? Well this plug-in 120 volt UPS
in battery backup mode outputs two 200 volt square waves with
a 270 volt spike while under minimum load. Is that 270 volt
spike, et al destructive? Yes, it can be destructive to some
small electric motors. But this UPS is 'computer grade'.
That means UPS is for devices that are more resilient - such
as computers. Where is the transient protection? Inside the
power supply so that even a UPS in battery backup mode will
not damage the computer.

Leythos wrote:
I agree and have to point out one thing here in case people become
confused: In most homes the typical problem is cause by loss of power
for any length of time - this causes the computer to reset in the middle
of anything it was/is doing. This is more likely to happen than a spike
or sag in line power. A UPS, even a cheap 750VA unit, will protect your
computer from power outages, sags and some increases in line voltage
that happen within the amount of time that the unit can respond.

If you want lightning protection you're looking at something other than
a home user UPS. If you combine lightning protection at the breaker
panel (where this is a good earth ground - at least there's suppose to
be one) with a home user UPS, then you've got the protection you need
for about 99% of anything you will run into.

I have a lot of APC Smart-UPS 2200VA units around the country and love
them, but at $800 they are not something that most home users are going
to buy.

The short of this discussion is that the small UPS units people purchase
for their home computers are not likely to protect them or survive a
lightning surge, but, since those are rare for most of us, the UPS will
save you when the power sags, surges, or goes out completely - which is
much more likely to happen.

Consult industry professionals: if a center conductor
connects to coax shield using an MOV, well, MOVs have too much
capacitance. They would short out (attenuate) high frequency
signals. Even the telco protector does not use MOVs due to
too much capacitance on lower frequency phone lines.

First, MOV shorting center conductor to coax shield is
enough to suspect insufficient technical knowledge. MOV
capacitance and impedance problems created by that capacitance
are well understood - which is why MOVs are not acceptable for
CATV, DSL, ISDN, satellite receivers, etc.

Second, leakages from the center conductor to shield means
that the destructive surge - if surge even gets to the center
conductor - is leaked to shield and earthed by the ground
block.

Again, earth ground - not a surge protector - defines the
quality and effectiveness of protection. Problem with being
'sadly mislead' is that I know why that MOV cannot be located
as was posted.

WoofWoof wrote:
I think you'll find - if you check really carefully - that the
grounding block merely ensures that the incoming cable ground
connection is, in fact, connected to a good ground close to it's final
destination.

Surge protectors otoh make sure that the *signal* (or hot wire in the
case of AC cables) can short rapidly to ground in the event of an
over-voltage. It's done by connecting a MOV (metal oxide varistor)
from signal/hot to ground. At normal operating voltages, this device
is an open-circuit but in the case of a voltage surge rapidly
transforms to a short-circuit shunting the surge to ground.

Having a decent ground alone helps but if you think the grounding
block you refer to means your CATV is "fully" surge protected, you are
sadly mislead.

My house was built this year, so its earthing should be up to 1990
national building codes. But how can I be sure the builder did it
correctly? I don't think this is anything that the local building
inspector can test. I doubt he could tell the difference between a
10-inch grounding rod and one that was driven 20 feet into the ground,
if he even inspects this feature at all. How can I tell if my house
is earthed correctly?

On Fri, 14 Jan 2005 14:28:21 -0500, w_tom wrote:

Plug in protectors claim to protect from one type of surge.
Do some punching. As one arm swings out, the other
withdrawals. That 1-2 punching is an example of a surge that
typically does not do damage. Now instead punch with both
left and right arms simultaneously. That is the common mode
surge that typically damages electronics.

Lightning seeks earth ground. It comes down any and all
'arms', passes through punching bag, and exits out other side
of punching bag. The plug-in protector does not stop, block,
or absorb such destructive surges. IOW it does not sit
between surge and the electronics - even though they hope you
will assume that. And effective protector connects earlier
where wires enter the building so that the 'surge down all
wires simultaneously' all find the same earth ground.

Lightning in 1752 found earth ground destructively via a
church steeple. Franklin simply gave lightning a better path
to earth. Lightning is the 'all arms moving forward at the
same time" type of surge. You don't stop, block, or filter
what miles of sky could not even stop. You 'shunt' lightning
to earth ground. That is also what the 'whole house'
protector does. It provides lightning with a short path to
earth ground.

You are surprised how small the Cutler Hammer unit is. It
need not be large because it does not stop, block, or absorb
the energy. Wire is also not massive because it too carry
massive electrical energy and does not try to stop or block
it. A surge protector is nothing more than a wire. A wire
that conducts only during the rare and short transient. It
can be small because the transient is only in microseconds.

In a parallel example, try to push a common nail into wood.
You cannot. It takes the force of a backhoe to drive that
nail. However, we hit that nail with only a 20 oz hammer.
Does the human arm have same energy as the backhoe? Of course
not. People often confuse energy with power. The hammer has
low energy but high power. Lightning has low energy but high
power. The protector need not be monstrous because 1) it does
not stop or absorb the energy, and 2) the energy is not as
massive as urban myths portray. Too many only 'feel' that a
lightning strike is high energy.

The electrical circuit is best demonstrated by an NIST
figure used in an example from:
http://www.epri-peac.com/tutorials/sol01tut.html
They demonstrate why a fax machine was damaged. Notice that
the phone line was not 'earthed' less than 10 feet to the same
single point ground as AC electric. Telephone line protector
is inside the box labeled NID.

The 'whole house' protector is located where 'Arrestor' is
labeled. Notice that the destructive surge goes through
Arrestor, then to earth ground. Since it need not pass
through fax machine to get earth ground, then an AC electric
surge does not damage fax machine.

All electronic appliances contain effective protection.
Anything that is going to work on the end of a power cord
(those grossly overpriced plug-in protectors) is already
inside electronics - as even required by industry standards.
But we worry that internal electronics protection might be
overwhelmed. So we install a 'whole house' protector on every
incoming utility wire - to same earth ground.

Demonstrated in various posts is the AC electric 'whole
house' protector (such as the Cutler Hammer), the telco
provided protector, and a ground block for cable wire (no
protector required). All are only as effective as that earth
ground.

Now about earthing. Engineered discussed this in two
discussions in the newsgroup misc.rural entitled:
Storm and Lightning damage in the country 28 Jul 2002
Lightning Nightmares!! 10 Aug 2002
http://tinyurl.com/ghgv and http://tinyurl.com/ghgm

Depending on the problem with transients, the earth ground
may need be enhanced. Important is the neighborhood history.
Also important is the geology. Does the ground tend to
attract more CG lightning? For example, mid-west storms may
be spectacular, but most of the lightning remains sky to sky.
WV is a region with high numbers of CG (cloud to ground)
strikes per thunderstorm.

Those discussions also mention equipotential which is why
Ufer grounds and halo grounds make the protector even more
effective.

Also is earth conductive or is it sand. I believe that
previous discussion also tells a story of a house struck
multiple times - and lightning rods did not work. Why?
Lightning rods were earthed poorly in non-conductive sand.
Bottom line - a surge protector is only as effective as its
earth ground. In most locations, a single ground rod may
provide massive increase in protection. A house that does not
at least meet post 1990 National Electrical Code earthing
requirements does not have the necessary earth ground.

Also in that misc.rural discussion would be how wire must be
routed. For example, no sharp bends and no splices. A ground
wire bundled with other wires may only induce more surges on
that other wire (which is but another reason why plug-in
protectors have no effective earth ground).

There is much to read. Come back with questions. The
simple earthing of surges is surprisingly not intuitively
obvious. In discussing this, I was amazed how many don't even
know what a Ben Franklin air terminal (lightning rod) does -
AND yet would recommend surge protectors. Many even argue
pointed verse blunt lighting rods - when earth ground defines
the effectiveness of that rod. A surge protector is only as
effective as its earth ground.
snip
Ron

In article ,
wrote:

My house was built this year, so its earthing should be up to 1990
national building codes. But how can I be sure the builder did it
correctly? I don't think this is anything that the local building
inspector can test. I doubt he could tell the difference between a
10-inch grounding rod and one that was driven 20 feet into the ground,
if he even inspects this feature at all. How can I tell if my house
is earthed correctly?

Try searching on "National Electrical Code", grounding, lightning
as search terms. I found an article he

http://bg.ecmweb.com/ar/electric_com...tning_florida/

"He measured the ground resistance of the system using a
fall-of-potential meter, gathering a reading of 105 ohms.
Though it was high, it wasn't unusual in that part of Florida,
despite the area's high water table."

"The NEC allows for a maximum resistance of 25 ohms at the
grounding electrode (250.56)."

Just what I found in a five minute search. As that article
notes, ground depends on local geology, so practice could be
different between regions of the country. (More rods, different
depth, etc.)

When I searched on "fall-of-potential meter", it turned out
someone made the term up, as there were few hits on that
exact phrase. This article describes the method used:

http://ceenews.com/mag/electric_quick_primer_grounding/

"The most reliable post-installation testing procedure involves
the Fall-of-Potential (three point) method. Utilizing a digital
ground resistance meter, two auxiliary electrodes are driven into
the soil at predetermined distances as per testing specifications
in a straight line from the ground rod under test. The meter
supplies a constant current between the ground rod under test
and the most remote electrode."

Sounds pretty hokey to me. That article at least contains terms
that you could use to query a contractor.

Paul

A ten foot rod with a less than ten foot connection to each
utility provides a major protection improvement. To get
additional but lesser improvements, the grounding system gets
exponentially larger and expensive. High reliability systems
can spend $thousands just to get a minor increase in earthing.

The ten foot rod is often more than sufficient. However
earth geology itself can be a major determining factor. For
example, clay can be an excellent earthing material. Sand can
be horrendous. And as the 'house with lightning rods' failure
story demonstrated, if something else in the house makes a
connection to more conductive (deeper) geology, then the
single point earthing can be compromised. To understand
earthing, understand your geology.

If the house has a water well, this can make a complication
that is firstmost solved by routing the water and power lines
in at the same single point service entrance. Will the surge
use your single point ground or will it cross the house to get
to water well? Later could result in household appliance
damage AND a damaged well pump.

Other factors may make surges problematic such as being at
the end of a street and therefore at the end of an AC electric
distribution line. Is that a vein of copper, graphite, or
iron nearby? Those too could compromise an earthing system
that is on the wrong side of the house - farthest from that
most conductive earth.

As noted, if we built new homes as if the transistor
existed, then rebar to reinforce footings are connected to
become the earthing system. An Ufer ground that surrounds the
building both makes a most superior ground AND makes earth
beneath that building equipotential. We would do this to
every building if we really were serious about surge
protection. Costs so little. Does so much.

To improve their earthing system, some bury a bare copper
ground wire around the building. This halo ground both makes
earthing more conductive AND again makes earth beneath the
building equipotential:
http://www.cinergy.com/surge/ttip08.htm

Another example of everything that could be done in a cell
phone tower site is the figure on page 14 of:
http://www.leminstruments.com/pdf/LEGP.pdf or
the section entitled "Measuring Ground Resistance at Cellular
Sites,Microwave and Radio Towers" in:

http://leminstruments.com/grounding_...ml/index.shtml

Lem Instruments makes equipment to measure earthing - for
those who are serious. You need not get so extreme because
you don't need the reliability of a power company or a
telephone switching station.

Above are ideas. Implement any of these ideas if easy.
Outside of anomalies such as a vein of buried iron or unusual
number of strikes in your neighborhood, then a single 10 foot
ground rod (or rods) is often more than enough earthing to
eliminate problems from most direct strikes.

Should you feel more is needed, then expand a single point
ground with more 10 foot ground rods. NEC notes how far apart
those rods must be. Best to interconnect those rods with
buried ground wires - again per code requirement for wire size
and depth. Interconnecting wire supplements - makes that
network of ground rods even better. Better to make those
below surface rod connections inside a 4 or 6" plastic pipe
with a cover so that the below ground rod connection can be
uncovered and inspected.

All this is the secondary protection system. You should
also inspect your primary protection system:
http://www.tvtower.com/fpl.html

Yes there is much you can do. But again, what is the
neighborhood history?

Don't remember if those previous posts included application
notes from erico.com. Their figure and application note 002
makes another point. Surges are carried into the building
even on buried cables. Even buried cables must make a
connection to single point earth ground before entering the
building.

One thing I have seen is some electricians cut the ground
rod in half. Too short. That rod must be at least 8 feet
down (because the first couple of feet really is not good
earthing) AND must remain firm in ground. If you can shake a
ground rod, then it is not electrically connected to earth.

Yes it is an art - as to what is good enough. Complicating
is that earthing measurements are only in resistance. Surges
are really more concern with impedance - due to higher
frequencies. So yes, a lower resistance can mean a better
impedance - most of the time. The art. But as I said, most
have more than sufficient earthing with one earth ground rod
in good conductive soil and a very short connection to every
incoming utility.

Inspectors don't verify any of this. Inspector are concerned
with human safety. You also want transistor safety. Both use
many of the same components. But both have slightly different
needs - as that discussion in misc.rural should demonstrate.

Milleron wrote:
My house was built this year, so its earthing should be up to 1990
national building codes. But how can I be sure the builder did it
correctly? I don't think this is anything that the local building
inspector can test. I doubt he could tell the difference between a
10-inch grounding rod and one that was driven 20 feet into the ground,
if he even inspects this feature at all. How can I tell if my house
is earthed correctly?

On Fri, 14 Jan 2005 14:23:43 -0500, w_tom wrote:

What you describe as describe as "all SPSes include at least
as much separate surge protection on the mains supply line as
a decent standalone surge protector would provide;" is really
near zero protection for numerous reasons. Both the plug-in
UPS and power strip protector have the same protector
circuit. And both are typically so grossly undersized to be
ineffective. Always start with the numbers. In this case
joules.

Unless you live in an area with frequent major thunderstorms, your
surge protector will mainly be blocking the much smaller surges and
spikes on the power line caused by local appliances starting and
stopping. If you have a lighting strike near enough to damage
unprotected equipment in your house, you may anyway want to replace
your surge protectors (or surge-protector containing SPSes), for some
of the reasons you imply - you can do that quite frequently for the
cost of one good enough not to need replacing!


In another post and in those previously cited posts are
examples of how joules define protection. Notice that so many
plug-in protectors AND their plug-in UPS counterparts may be
rated at 345 joules. As joules increase, the life expectancy
of that protector increases exponentially. IOW if the plug-in
protector is good for two same size surges, then the 1000
joule 'whole house' protector is good for something on the
order of 300 of those same size surges.

See above.

Then it continues farther. The plug-in protector has no
earth ground. Therefore the manufacturer avoids the entire
topic altogether. This is how one identified ineffective (and
grossly overpriced - yes grossly overpriced) plug-in
protectors. 1) No dedicated wire connection to earth ground
AND 2) manufacturer avoids all discussion about earthing.

I live in England - all power circuits installed in the last 40 or 50
years here are wired with a separate earth ground, and all half-way
decent UK surge protectors will shunt common-mode surges to this
ground. I must admit that I had forgotten that this (wired grounds to
every power point) "aint necessarily so" in the rest of the world.


Further details will be provided in response to Milleron.
But the plug-in protectors are on the order of 10 and 50 times
more expensive per protected appliance. So yes, what you are
calling cheap protectors are really overpriced and expensive
protectors that also are not effective.

BTW, UPSes switch in milliseconds. (One must be careful to
buy power supplies with numerical specs that read: Hold up
time, full load: 16ms. typical). Surges do their damage and
are done in microseconds. 300 consecutive surges could pass
through a UPS before the UPS even considered switching to
battery power. Plug-in UPSes have one function - data
protection. They do not provide the hardware protection so
often implied.

I think that it was perfectly clear from my earlier response that I
did not believe that _the_ _SPS_ _component_ of a cheap "UPS" provided
any surge or spike protection.


You want a UPS that also provides hardware protection? That
is typically the building wide UPS that also makes this all so
important 'less than 10 foot' connection to earth ground.
Plug-in UPSes are for data protection; not for hardware
protection.

I stand by my original statement, though with the proviso that plug-in
surge protectors, to be reasonably effective, must have a separate
wired ground connection (which can be, and in the UK usually will be,
a connection to a properly wired ground circuit in the house wiring),
and must shunt common mode spikes to it. If your
system/application/business is so critical that you want a guarantee
of 24/7 operation through any reasonably conceivable electrical storm,
then the sort of approach to power protection that you advocate makes
perfect sense, but most people are not in that position. As I think
you or someone else says elsewhere, hardware can be replaced at finite
(and often quite low) cost - lost data may be irreplaceable, and
can't always be backed up to the minute. Relatively cheap UPSes
provide a very high level of data protection gainst brownouts and
power outages and (by virtue of their separate surge protection
circuitry) a significant, though incomplete, level of hardware
protection from the effects of "normally" dirty power. I would be very
concerned if someone read your posts and concluded that, if (s)he
can't afford to spend $1,000+ on whole-house power protection, (s)he
should not bother with anything less.


"Peter R. Fletcher" wrote:
On Sun, 09 Jan 2005 19:50:06 -0500, (Paul) wrote:
......
wiring exposure to just the power lines. A real ($1K purchase
price) UPS would reduce the risk of an AC power event from
getting you, and would help protect the PSU from getting
damaged. Cheap UPSes offer no protection at all, as they are
actually SPS (standby power supplies) - they are a "straight wire"
to power spikes, and the unit only cuts over to batteries if
the AC power dies for enough milliseconds.

I think that you are being unduly negative about cheap "UPSes". You
are absolutely correct that they are not true UPSes, since:
a) they normally connect the mains power (effectively) straight
through to the controlled devices, thus offering no _intrinsic_
protection from spikes; and
b) they have to switch to inverter mode when the power fails, which
takes finite time.
However:
a) almost all SPSes include at least as much separate surge protection
on the mains supply line as a decent standalone surge protector would
provide; and
b) All except the cheapest, no-name, ones switch fast enough so that a
normal computer system power supply does not "notice" the transient
power loss (though network switches, hubs, and the like may "glitch").
For most home and SOHO users, an SPS will provide cost-effective
protection against most of the data loss problems which might
otherwise be caused by brownouts and/or power outages, while their
built in (but unrelated) surge protection circuitry is a _lot_ better
than nothing as insurance against damage from power line spikes.

Please respond to the Newsgroup, so that others may benefit from the exchange.
Peter R. Fletcher


Please respond to the Newsgroup, so that others may benefit from the exchange.
Peter R. Fletcher

On Fri, 14 Jan 2005 23:54:14 -0500, w_tom wrote:
snip

Other factors may make surges problematic such as being at
the end of a street and therefore at the end of an AC electric
distribution line. Is that a vein of copper, graphite, or
iron nearby? Those too could compromise an earthing system
that is on the wrong side of the house - farthest from that
most conductive earth.

Interesting point about being the last house on the street. Several
years ago, we had a nasty summer electrical storm in central Ohio that
knocked out power to many homes and neighborhoods. We had no
lightning real close to my house, but we lost power. We have
underground wiring with transformers every so often. I'm sure it's
exactly like overhead wires. At any rate the crew that came out
pointed out that our transformer was the LAST one in a long chain.
They thought the strike was distant and surged all the way to that
point. It ruined our transformer (took 30 hours to replace it), but
there was no damage at all in any of the houses that drew power from
that particular transformer. What happened in this scenario? If the
surge went to earth at that point, what killed the transformer without
hurting any of the transformers farther up the line?

snip
Ron