Close lightning strike effects

[Paul E. Schoen]

Monday night, while working at my computer, a strong thunderstorm moved
through this area, which is a very damp valley leading to the Loch Raven
Watershed area in MD. Hearing several thunderclaps seconds after flashes, I
considered shutting down my computer and disconnecting the power cord and
phone line. A few seconds later, I saw a bright flash and an immediate loud
"boom", and all power went out. I smelled something that could have been
ozone or burnt phenolic. I set up emergency lighting, looked for any signs
of fire, and took a brief look outside. Electrical power along the road up
to the junction with a main three phase feeder was out, and both my phone
lines were dead. Luckily my pets and I were not.

BGE arrived about 5 AM the next morning, determined that a fuse had blown,
and power was soon restored. When it was light enough to see, I looked for
other signs of damage outside. I have two houses separated by about 80
feet, and at the corner of the second house (used for storage) stands a
huge Sycamore tree, probably 150 feet high. I found some wet, broken
branches, and some pieces of bark, but no signs of major damage. However, I
noticed that several panes of glass in a window just about two feet from
the tree were broken, and two of them appeared to have blown outward. It
looked like a raccoon may have jumped through the glass (which is possible,
as I have found them in that house). Also near the tree is a 240 VAC
twisted utility line, actually touching the tree at one point, and a drop
cable to a meter box which is disconnected. I do have power to the house
through a UF cable for convenience, fed from my residence on two 20 amp
breakers. Also just below the power line is my active phone line, which
connects to an interface box and then through a four wire line to my
residence.

I discovered that one of the breakers had tripped, and I reset it with no
problem. There was a second storm in the afternoon that caused loss of
power again, but it was soon restored. The telephone technician found 48
VDC and a dial tone on one of the pairs, but not the other, and replaced a
blown protector device which restored one line, but the other seemed to be
an open circuit to the pole. An access box on the pole was open, possibly
from the lightning strike or perhaps it was being repaired by another
technician.

The damage to my equipment included a blown modem in my computer, damage to
my computer speaker internal amplifier, and a damaged phone answering
machine. I feel lucky.

I don't know the exact path of the lightning, but I think it may have hit
the 15 kV (probably) main line and arced over to the transformer secondary
and over to the tree, where it traveled down the ground paths. I think a
direct hit to the tree would have caused more damage. I am curious about
the pattern of the broken glass in the window, however. At first thought, I
would expect lightning to ionize the air and create steam pressure from
rain, so it would be an explosion with outward force. I think this caused
some of the initial damage to the window, as evidenced by glass shards
inside the house. But I think this may have been followed by a partial
vaccuum that caused the sudden expulsion of higher pressure air in the
house through the cracked glass. I will take pictures of it before I repair
it.

It was almost prophetic that I was just reading some posts in SED
referencing high voltage arcs and lightning, and also now reading the other
post about conductivity of trees.

Now it's raining again, and I think I hear thunder.. AIEEE!

Paul

 

[John Popelish]

Monday night, while working at my computer, a strong thunderstorm moved
through this area, ...

Are you sure the thunderstorm was working at your computer, or was it
just looking at porn? ;-)

 

[[email protected]]

The damage to my equipment included a blown modem in my computer, damage to
my computer speaker internal amplifier, and a damaged phone answering
machine. I feel lucky.

Replace all of your surge protectors. They were wounded, saving the
rest of your stuff.
With good protection you should be able to survive a nasty strike but
the protector is probably toast..

 

[Abstract Dissonance]

Monday night, while working at my computer, a strong thunderstorm moved
through this area, which is a very damp valley leading to the Loch Raven
Watershed area in MD. Hearing several thunderclaps seconds after flashes,
I considered shutting down my computer and disconnecting the power cord
and phone line. A few seconds later, I saw a bright flash and an immediate
loud "boom", and all power went out. I smelled something that could have
been ozone or burnt phenolic. I set up emergency lighting, looked for any
signs of fire, and took a brief look outside. Electrical power along the
road up to the junction with a main three phase feeder was out, and both
my phone lines were dead. Luckily my pets and I were not.

BGE arrived about 5 AM the next morning, determined that a fuse had blown,
and power was soon restored. When it was light enough to see, I looked for
other signs of damage outside. I have two houses separated by about 80
feet, and at the corner of the second house (used for storage) stands a
huge Sycamore tree, probably 150 feet high. I found some wet, broken
branches, and some pieces of bark, but no signs of major damage. However,
I noticed that several panes of glass in a window just about two feet from
the tree were broken, and two of them appeared to have blown outward. It
looked like a raccoon may have jumped through the glass (which is
possible, as I have found them in that house). Also near the tree is a 240
VAC twisted utility line, actually touching the tree at one point, and a
drop cable to a meter box which is disconnected. I do have power to the
house through a UF cable for convenience, fed from my residence on two 20
amp breakers. Also just below the power line is my active phone line,
which connects to an interface box and then through a four wire line to my
residence.

I discovered that one of the breakers had tripped, and I reset it with no
problem. There was a second storm in the afternoon that caused loss of
power again, but it was soon restored. The telephone technician found 48
VDC and a dial tone on one of the pairs, but not the other, and replaced a
blown protector device which restored one line, but the other seemed to be
an open circuit to the pole. An access box on the pole was open, possibly
from the lightning strike or perhaps it was being repaired by another
technician.

The damage to my equipment included a blown modem in my computer, damage
to my computer speaker internal amplifier, and a damaged phone answering
machine. I feel lucky.

I don't know the exact path of the lightning, but I think it may have hit
the 15 kV (probably) main line and arced over to the transformer secondary
and over to the tree, where it traveled down the ground paths. I think a
direct hit to the tree would have caused more damage. I am curious about
the pattern of the broken glass in the window, however. At first thought,
I would expect lightning to ionize the air and create steam pressure from
rain, so it would be an explosion with outward force. I think this caused
some of the initial damage to the window, as evidenced by glass shards
inside the house. But I think this may have been followed by a partial
vaccuum that caused the sudden expulsion of higher pressure air in the
house through the cracked glass. I will take pictures of it before I
repair it.

It was almost prophetic that I was just reading some posts in SED
referencing high voltage arcs and lightning, and also now reading the
other post about conductivity of trees.

Now it's raining again, and I think I hear thunder.. AIEEE!

Paul

One thing you can do is to make sure you ground is actually grounded and not
floating. I have grounded my wall outlet's ground to a 3 foot rebar outside
the outlet because of a similar incident. You could probably also
mechanically hook up a varistor between the ground and hot and another
between the ground and neutral just incase. These things don't require much
expertise although you would need to be careful when handling the mains(try
and turn off the power if you don't know what your doing . It might not be
the easiest method but it would probably be just as good as as a surge
protector(as most are crap). You could even hook up a fuse and make a little
custom box outside that houses these components incase you need to change
them). Its probably cheaper then buying a decent surge protector and would
work well. Ofcourse you could take it farther and add more protection if you
have expensive equipement. Ofcourse this won't stop ESD from getting at your
equipment but will stop voltage spikes from doing any damage(at the cost of
a very cheap varistor). I'm sure someone else more experienced in this area
and make a better suggestion though. Its really up to you... but if you can
drill a hole, splice wires, drive a rod in the ground, and solder then you
could set up a decent amount of protection for your wall outlet in less than
an hr for just a few bucks. (although you could make it more elaborate too
by adding more sophisticated circuits)

 

[Paul]

One thing you can do is to make sure you ground is actually grounded and
not floating. I have grounded my wall outlet's ground to a 3 foot rebar
outside the outlet because of a similar incident. You could probably
also mechanically hook up a varistor between the ground and hot and
another between the ground and neutral just incase. These things don't
require much expertise although you would need to be careful when
handling the mains(try and turn off the power if you don't know what your
doing . It might not be the easiest method but it would probably be
just as good as as a surge protector(as most are crap). You could even
hook up a fuse and make a little custom box outside that houses these
components incase you need to change them). Its probably cheaper then
buying a decent surge protector and would work well. Ofcourse you could
take it farther and add more protection if you have expensive equipement.
Ofcourse this won't stop ESD from getting at your equipment but will stop
voltage spikes from doing any damage(at the cost of a very cheap
varistor). I'm sure someone else more experienced in this area and make a
better suggestion though. Its really up to you... but if you can drill a
hole, splice wires, drive a rod in the ground, and solder then you could
set up a decent amount of protection for your wall outlet in less than an
hr for just a few bucks. (although you could make it more elaborate too
by adding more sophisticated circuits)

The grounds in the electrical system are probably pretty good, as all
of the wiring has been redone, but much of it is still temporary as I
do major work on this house. There are actually two solid grounds on
the incoming power, one to a water pipe and the other to a well-driven
ground rod in moist earth. However, that one was disconnected when I
was putting new siding on and it may not have been tightened up. The
advice to replace the surge protectors is good. Now I have the computer
on a UPS which is in turn connected to a surge protector. However, the
best protection is physically unplugging the computer when storms are
active.

I think the main surge came through the phone lines, as both of them
were damaged. The one is not yet fixed, but the other (the one I use
for the computer) had a blown protector, which essentially shorted to
ground and opened the connection from the external line to the premises
wiring. However, it was not enough to protect the internal modem, so I
am using an old external unit.

An answering machine on the other line was damaged. The 9 VAC adapter
showed an open circuit input, but the machine does not power up when a
separate source is applied. I have a new one I hadn't yet installed.
Time to do that. This indicates a power line surge, but with voltages
and currents as high as lightning the path of the arc is unpredictable.
I think the main ionizing blast was along the outside of the tree and
to the power lines and phone lines outside the house next to it. Of
course, some pretty hefty transients were likely conducted into other
parts of the telephone lines and power circuits.

I think the computer speakers were damaged by the same power line surge
that damaged the answering machine. They were also on an AC adapter,
and the high voltage spike probably damaged the amplifier inside (it
now runs hot). Possibly a DC output adapter would have limited the
surge due to its internal capacitance. The computer power supply may
have been spared because the input consists of inductors, diode bridge,
and large capacitors, and the surge protector also limited what it saw.

Just tonight I managed to inflict my own damage, but I was a little bit
lucky. I had a Microchip ICD2 (on a USB port) connected to a target
board that was plugged into the AC line. I was measuring voltage on the
board when my probe slipped, and it connected the circuit ground to a
point that went to 120 VAC through an LED and optoisolator. Both of
them instantly opened up, which probably limited the possible damage,
but the ICD was hurt. I thought I may have damaged the USB port on the
computer, but it worked with another device. Luckily the fault occurred
to ground, but apparently the ground of the ICD was not as solid. It
seems like an internal regulator in the ICD is getting hot, so it may
be repairable. Luckily it is only about $150 for a new one, but now I
will need to wait until it is repaired or replaced, and I need it for
working on this new SCR board design. Maybe I'll power it from a
separate 12 VDC source while I am doing the development work.

Thanks for the ideas. Maybe the safest method is to run the computer
off a battery and an inverter, and possibly rig up a fiber optic phone
line for internet access. I can keep the battery charged up with a
generator on an exercise bike, and not be connected to the power grid
at all!

Paul
(reposted via Google - lost by Coretel)

 

[w_tom]

Water pipe ground typically is not sufficient for transient
protection - often too far away. It's not just earthing that is
important. Distance to earthing and how that connection is routed are
also essential. Earthing for household transient protection typically
means a connection should be less than 10 feet. Other factors such as
no sharp bends, not inside metallic conduit, no splices, and separated
from other non-earthing wires also apply.

Typically phone lines are not struck being below AC electric. And
destructive surges don't just enter on one wire, damage, and stop.
First the transient forms a complete electrical path from cloud to
earth. Then electricity flow through everything in that path. Finally
something in that path fails. Most often, telephone appliances that
connect to both AC electric are damaged by transients incoming on AC
electric.

A most typical path is incoming on AC electric, through answering
machine, and then outgoing to earth ground via telephone line. Those
phone line protectors may have failed because a larger AC electric
transient found earth ground via answering machine, computers, or
portable phone base station. Other damaged electronics (speakers) were
also powered from AC; not connected to phone line. Without a well
earthed 'whole house' protector, then virtually everything inside the
building was exposed to incoming surge. Things damaged must also
complete an outgoing circuit to earth - ie telephone line appliances.

Your post implies insufficient earthing (path to earth ground either
too long or maybe not common to all utilities). Also demonstrates how
telephone appliances are so often damaged - incoming on AC electric and
outgoing through the telco's 'whole house' protector.

Earthing means every incoming utility wire in every cable (overhead
or underground) must make a short (low impedance) connection to the
same earth ground before entering a building. Coax cable needs only a
ground block and short hardwire connection to earth. Phones have a
'whole house' protector provided by the telco. AC electric is the most
common incoming path for surges; needs a 'whole house' protector.

Your post is typical of a surge incoming on AC electric, through
telephone appliances, and to earth via telco provided 'whole house'
protectors. A surge so large as to damage those telco protectors also
suggests it was larger - incoming on AC electric.

 

[Jeff L]

Water pipe ground typically is not sufficient for transient
protection - often too far away. It's not just earthing that is
important. Distance to earthing and how that connection is routed are
also essential. Earthing for household transient protection typically
means a connection should be less than 10 feet. Other factors such as
no sharp bends, not inside metallic conduit, no splices, and separated
from other non-earthing wires also apply.

Typically phone lines are not struck being below AC electric. And
destructive surges don't just enter on one wire, damage, and stop.
First the transient forms a complete electrical path from cloud to
earth. Then electricity flow through everything in that path. Finally
something in that path fails. Most often, telephone appliances that
connect to both AC electric are damaged by transients incoming on AC
electric.

A most typical path is incoming on AC electric, through answering
machine, and then outgoing to earth ground via telephone line. Those
phone line protectors may have failed because a larger AC electric
transient found earth ground via answering machine, computers, or
portable phone base station. Other damaged electronics (speakers) were
also powered from AC; not connected to phone line. Without a well
earthed 'whole house' protector, then virtually everything inside the
building was exposed to incoming surge. Things damaged must also
complete an outgoing circuit to earth - ie telephone line appliances.

Your post implies insufficient earthing (path to earth ground either
too long or maybe not common to all utilities). Also demonstrates how
telephone appliances are so often damaged - incoming on AC electric and
outgoing through the telco's 'whole house' protector.

Earthing means every incoming utility wire in every cable (overhead
or underground) must make a short (low impedance) connection to the
same earth ground before entering a building. Coax cable needs only a
ground block and short hardwire connection to earth. Phones have a
'whole house' protector provided by the telco. AC electric is the most
common incoming path for surges; needs a 'whole house' protector.

Your post is typical of a surge incoming on AC electric, through
telephone appliances, and to earth via telco provided 'whole house'
protectors. A surge so large as to damage those telco protectors also
suggests it was larger - incoming on AC electric.

On a very near by strike, I lost 2 Ethernet cards, a wireless router (AC
adaptor still works good), a DSL modem, and a wireless USB mouse receiver.
The phones, TV gear, VCR, stereo's (some were on), clock radio's, etc were
all fine. I think what had happened was that the 100 - 150 feet of Ethernet
cable acted as a large antenna / air core transformer.

A similar thing happened about 10 years ago where a large arc came out of
our wood boiler controller, when a close by strike occurred. The boiler has
a ~35 foot length from the floor to the tip of the stainless steel chimney.
The only grounds on the system are from the 120V AC feeding the system, and
the copper water lines, which are only grounded by the pump switch and the
water, which has to go through 50 feet of plastic tube to get to the bottom
of the well.

 

[[email protected]]

I think what had happened was that the 100 - 150 feet of Ethernet
cable acted as a large antenna / air core transformer.

More likely is it was the path that reconciled a ground shift.
We ended up fixing problems like that with a fat bonding wire (PC case
to PC case) between machines that were far apart or on different A/C
circuits and adding ferrite beads to the LAN.

 

[Jeff L]

More likely is it was the path that reconciled a ground shift.

Possible, but the bolt hit the ground (close to the driveway), and there was
no other damage to any other equipment in the house other then listed. The
AV gear (TV's, cable boxes, VCR's, etc) were fine, even though they are on
separate circuits and connected with a common cable, but the cable is
grounded where it enters the house. The computers were otherwise fine, The
Computers are basically right above each other, one on the main floor and
one on the second. Power comes from the panel in the basement, also in that
same corner of the house, but are on separate circuits. The telephones were
fine and most have wall warts for power, like the DSL modem so I doubt that
the telco and power lines had much of a voltage differential during the
strike. The USB wireless mouse receiver was totally enclosed in plastic,
sitting on a wooden desk, and that was completely dead.

We ended up fixing problems like that with a fat bonding wire (PC case
to PC case) between machines that were far apart or on different A/C
circuits and adding ferrite beads to the LAN.

That should add a bit of protection! I once installed a short optical link
(RS 232 IIRC) for eliminating a ground loop in an industrial app, that it
would be ideal for this type of isolation. Someone must make Ethernet
optical isolators, then again maybe not since Ethernet (not PoE) uses
isolation transformers on each end, and fiber could be used in apps that
required more.

 

[Paul E. Schoen]

[snip original text]

I took some pictures of the effects of this lightning strike. I looked
closely at the power line, and saw that the neutral (steel support cable)
around which are wrapped the two 120/240VAC feeders, was vaporized open in
the vicinity of the big sycamore tree. The window near this was broken
along the path of the arc which I think continued along the side of the
tree down to the ground, where it also got into the phone lines. I think
the first strike may have been on the incoming power lines, even though
they are disconnected at the meter. They are actually touching the tree,
and that is where the neutral was damaged. I called BGE and they will be
removing these power lines.

There are four pictures (about 300 kb total) on
www.smart.net/~pstech/Lightning.

My personal phone service (through MCI) is still out, but by business
service was fixed by Verizon within 24 hours. Apparently business customers
get top priority. The estimate on the MCI repair was 1 week. They have two
more days. I wonder if I can prorate my payment for phone service to deduct
for a week without the service?

BTW, I saw on the news that someone was struck by lightning while listening
to an iPod while mowing the lawn in a thunderstorm, and they warned against
use of iPods and cell phones during electrical storms. I really don't think
there is enough metal and electrical field with such devices to attract
lightning. A steel mower with a high voltage spark plug is a more likely
culprit. Any thoughts?

Paul