Excuse the lengthy OT message, but I noticed that folks in this group
have built metal buildings for their workshops and though you might be
able to help me.

I am considering building a large garage/pole barn using metal.

I am very concerned with lightening strikes due to where I live.

My house is nearly the highest thing in town. When we get lightening
it's always dancing around us. There had been a tree next to the
house about 30 years ago, it would get hit by lightening and they
finally put a lightening rod in it. Eventually got taken out anyway
(big tree they cemented back together at one point). It was gone when
I got here, but I had to deal with the stump which is when I found the
braided wire from the lightening rod.

The roofs of the additions that were put on in the 20's were all metal
covered with tar. It's clear they were not maintained, as many
interior walls had damage, so they were probably exposed as I found
them for some time. The chimneys on either end of the house had
lightening rods, each fastened to their own ground, not in the middle
which I think would have been the right thing to do.
The ligtening rods were disconnected for at least the last 13 years
(since we've been here), but I just had to spend 3 grand having the
tops of both rebuilt as they were loose from being hit by lightening,
and bricks had started falling down.

We have an old three holer outhouse that is now a garden shed. It had
the same sheet metal roof in hip form, and I liked the look so left it
alone (unlike the house where I had the metal torn off and replaced
with a membrane roof). One day I was mowing the lawn and found a
piece of rusty metal, I looked over at the back of the outhouse and
there was a big burn mark and at least 3 feet of the roof had been
blown off.

When I was making some changes to a small old hay barn so my wife
could use the second floor, I noticed what looked like some singed
paper on the roof. Further inspection showed that it had also had a
metal roof, and had clearly been hit and burned by lightening.

If I look off into the woods on the hill to the left of our house, I
can see trees that used to be green that got whacked by lightening and
died from the hits (we think we know when it happened, helluva a
storm, but of course it took years for everything to go bare).

When we walk in the woods behind our house, every now and then we find
a tree top and occassionaly a whole tree that was clearly struck by
lightening.

I've searched around the net and can't seem to find any real input on
this. Someone told me that if I properly bond the building, I'll be
all set. Well this makes sense except it makes me wonder if a 30x60
chunk of metal is going to be so attractive that it will invite the
lightening and I'll end up with strikes on my wooden buildings?

Any real world experience would be greatly appreciated, since
everything I have found on lightening seems inconclusive.

Sorry for the lengthy post, and thanks for any feedback. If emailing,
remove nospam.

On Thu, 31 Mar 2005 21:06:17 -0500, nospamgoingjag wrote:

I am considering building a large garage/pole barn using metal.
I am very concerned with lightening strikes due to where I live.

A metal building is probably the best thing to be in, actually. It
forms what is known as a "faraday cage", and allows the lightning to
find a clear path to ground that doesn't involve going through you.
Ground it well, and you should be fine.

I've searched around the net and can't seem to find any real input on
this. Someone told me that if I properly bond the building, I'll be
all set. Well this makes sense except it makes me wonder if a 30x60
chunk of metal is going to be so attractive that it will invite the
lightening and I'll end up with strikes on my wooden buildings?

No, it'll attract the lightning to itself. You want it to be the most
attractive to the lightning, so ground it well and give the lightning
some nice exciting pointy spikes to go for (serious).

Snodgrass lighning rods used to have a very informative site,
maybe they're a place you could look.

Dave Hinz

Point lightning rods are no longer recommended for lightning rods. The
lightning research center in Socorro NM discovered that a flat, stubby
rod installed in arrays around the perimeter of the roof actually repel
the buildup of the ground charge that precedes a strike. I imagine they
have a web site.
Visiting their research center can get real exciting, so to speak,
during a storm. It is located on top of a mountain and has a large
glass dome for observation. They send up balloons on steel cables to
attract strikes and record their characteristics. I can't recall the
name of the laboratory at the moment.
Bugs

On 1 Apr 2005 04:59:54 -0800, Bugs wrote:
Point lightning rods are no longer recommended for lightning rods. The
lightning research center in Socorro NM discovered that a flat, stubby
rod installed in arrays around the perimeter of the roof actually repel
the buildup of the ground charge that precedes a strike. I imagine they
have a web site.

Interesting. I'll check that out, thanks.

"nospamgoingjag" wrote in message
...
Excuse the lengthy OT message, but I noticed that folks in this group
have built metal buildings for their workshops and though you might be
able to help me.

I am considering building a large garage/pole barn using metal.

I am very concerned with lightening strikes due to where I live.

snip
We have an old three holer outhouse that is now a garden shed. It had
the same sheet metal roof in hip form, and I liked the look so left it
alone (unlike the house where I had the metal torn off and replaced
with a membrane roof). One day I was mowing the lawn and found a
piece of rusty metal, I looked over at the back of the outhouse and
there was a big burn mark and at least 3 feet of the roof had been
blown off.

Good thing it's no longer in active use!

"ATP*" wrote in message
...

"nospamgoingjag" wrote in message
...

snip
We have an old three holer outhouse that is now a garden shed. It had
the same sheet metal roof in hip form, and I liked the look so left it
alone (unlike the house where I had the metal torn off and replaced
with a membrane roof). One day I was mowing the lawn and found a
piece of rusty metal, I looked over at the back of the outhouse and
there was a big burn mark and at least 3 feet of the roof had been
blown off.

Good thing it's no longer in active use!


Perhaps not. Might just be the perfect cure for constipation!

On Thu, 31 Mar 2005 22:38:57 -0500, "ATP*" wrote
something
.......and in reply I say!:


We have an old three holer outhouse that is now a garden shed. It had
the same sheet metal roof in hip form, and I liked the look so left it
alone (unlike the house where I had the metal torn off and replaced
with a membrane roof). One day I was mowing the lawn and found a
piece of rusty metal, I looked over at the back of the outhouse and
there was a big burn mark and at least 3 feet of the roof had been
blown off.

Good thing it's no longer in active use!

Glad I didn't let _that_ one fly in the living room!
************************************************** ****************************************
Whenever you have to prove to yourself that you are
not something, you probably are.

Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

Halloween night, 1956. We decide to steal an outhouse and put it on
the front lawn of the high-school. Sneak into the farmers back yard,
about 10 of us, and three guys go around to the back. Farmer must
have decided to move it within the last few days, and had not covered
over the old hole yet. Two guys fell in. They walked about 3 miles
back to town. We wouldn't even let them in the back of one of the
pickup trucks!

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXX

On Sat, 02 Apr 2005 07:12:25 GMT, (Old Nick)
wrote:

On Thu, 31 Mar 2005 22:38:57 -0500, "ATP*" wrote
something
......and in reply I say!:


We have an old three holer outhouse that is now a garden shed. It had
the same sheet metal roof in hip form, and I liked the look so left it
alone (unlike the house where I had the metal torn off and replaced
with a membrane roof). One day I was mowing the lawn and found a
piece of rusty metal, I looked over at the back of the outhouse and
there was a big burn mark and at least 3 feet of the roof had been
blown off.

Good thing it's no longer in active use!

Glad I didn't let _that_ one fly in the living room!
************************************************* *****************************************
Whenever you have to prove to yourself that you are
not something, you probably are.

Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

Moving an outhouse a "few feet back" was standard practice during
Halloween to one up the tricksters. ;)

Also since many outhouses were used in the dead of night in almost zero
light conditions (many users could and did walk there with their eyes
closed), some outhouses of troublesome neighbors were regularly
relocated by the neighborhood's kids at dusk. ;))

One must remember that this was before kids had other distractions like
television, video games and Internet to keep their attention.

So much for good clean fun....

TMT

On 2 Apr 2005 07:30:59 -0800, "Too_Many_Tools"
wrote:

Moving an outhouse a "few feet back" was standard practice during
Halloween to one up the tricksters. ;)

Also since many outhouses were used in the dead of night in almost zero
light conditions (many users could and did walk there with their eyes
closed), some outhouses of troublesome neighbors were regularly
relocated by the neighborhood's kids at dusk. ;))

One must remember that this was before kids had other distractions like
television, video games and Internet to keep their attention.

So much for good clean fun....

TMT

To set the time frame for this tale; remember when motor oil came in
real cans? (metal content)

A bunch of high school girls were having a Halloween slumber party
about a half mile south of here up a gravel road. A bunch of girls
attracts a bunch of boys; at my house since I lived closest to the
slumber party.

WE decide to scare the girls. We had a lot of old farm machinery at
our place. Among this collection was the front axle from a horse drawn
wagon. WE decide to tie empty oil cans to the wheel spokes with baling
wire and make a screaming run around the farm house full of girls. WE
decide to put a handful of gravel in each can for effect. WE decide to
hitch ourselves to the tongue with wire around our waists.

We sneak up their drive before tying the cans to the wheels. Someone
gives the signal (there is always a signal) and away we go around the
house a few times, yelling and making teenage boy noises.

The girls all run out on the porch screaming. You would think they
would run inside if they were frightened. Female logic.

We break the circle, head down the drive and hit the gravel road back
to my house. We still making all the noise we can when Vaughn falls
down. With all the noise, no one notices in the dark. He's tied to the
tongue with wire. The wheels run over him a few times and the cans are
banging him pretty good. Anyway, after this half mile run and dragging
Vaughn half that, we're really worn out. We darned near killed him.

We peeled off what was left of his clothes, layed him in the bed of a
pickup and washed him off with a hose. He was cussing quite a bit. Of
course, it was October. WE decided we had better take him home to his
Mama. That would at least stop the cussing. It took two weeks of
healing before he could come back to school.

In article , Brian Lawson says...


Halloween night, 1956. We decide to steal an outhouse and put it on
the front lawn of the high-school. Sneak into the farmers back yard,
about 10 of us, and three guys go around to the back. Farmer must
have decided to move it within the last few days, and had not covered
over the old hole yet. Two guys fell in. They walked about 3 miles
back to town. We wouldn't even let them in the back of one of the
pickup trucks!

Heh. I think *somebody* played a halloween prank there. I bet
that ****ter got put right back over the hole the next day!

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

jim rozen wrote:

In article , Brian Lawson says...


Halloween night, 1956. We decide to steal an outhouse and put it on
the front lawn of the high-school. Sneak into the farmers back yard,
about 10 of us, and three guys go around to the back. Farmer must
have decided to move it within the last few days, and had not covered
over the old hole yet. Two guys fell in. They walked about 3 miles
back to town. We wouldn't even let them in the back of one of the
pickup trucks!

Heh. I think *somebody* played a halloween prank there. I bet
that ****ter got put right back over the hole the next day!

Jim

--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

I have heard more than one report of the intended target of such a
prank having moved his own outhouse a few feet FORWARD of the hole and
causing similar results.
Some of those old farmers were young and bored once, too. :-)

Cheers
Trevor Jones

One Halloween when my Grandfather was a teenager (1901-1905) his brothers
and friends decided to put the wagon on top the barn. So they spent several
hours in the dark hauling the parts up onto the roof and putting it back
together. The next morning when my Great-grandfather got up and walked
outside he saw the wagon up on the roof . He walked back inside and said "I
don't know how the wagon got itself up on the barn roof but it better get
itself down real quick." At which point my Grandfather and his brothers set
a new record getting the wagon back on the ground.
I've always wondered if they woke up my Great-grandfather. It would be
pretty hard haul the wagon parts up onto the roof without making some noise
or setting the dog off barking. I can see him sitting at the window watching
them, laughing to himself, waiting to get them in the morning.
Karl

"Brian Lawson" wrote in message
...

Halloween night, 1956. We decide to steal an outhouse and put it on
the front lawn of the high-school. Sneak into the farmers back yard,
about 10 of us, and three guys go around to the back. Farmer must
have decided to move it within the last few days, and had not covered
over the old hole yet. Two guys fell in. They walked about 3 miles
back to town. We wouldn't even let them in the back of one of the
pickup trucks!

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXX

On Sat, 02 Apr 2005 07:12:25 GMT, (Old Nick)
wrote:

On Thu, 31 Mar 2005 22:38:57 -0500, "ATP*" wrote
something
......and in reply I say!:


We have an old three holer outhouse that is now a garden shed. It had
the same sheet metal roof in hip form, and I liked the look so left it
alone (unlike the house where I had the metal torn off and replaced
with a membrane roof). One day I was mowing the lawn and found a
piece of rusty metal, I looked over at the back of the outhouse and
there was a big burn mark and at least 3 feet of the roof had been
blown off.

Good thing it's no longer in active use!

Glad I didn't let _that_ one fly in the living room!
************************************************ ******************************************
Whenever you have to prove to yourself that you are
not something, you probably are.

Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

Brian Lawson wrote:
Halloween night, 1956. We decide to steal an outhouse and put it on
the front lawn of the high-school. Sneak into the farmers back yard,
about 10 of us, and three guys go around to the back. Farmer must
have decided to move it within the last few days, and had not covered
over the old hole yet. Two guys fell in. They walked about 3 miles
back to town. We wouldn't even let them in the back of one of the
pickup trucks!



I'm glad they got out alive. It could have been much worse, as in:

There once was a man named McBride,
Who fell down the outhouse and died.
His next elder brother,
Fell into another,
So now they're in turd side-by-side.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

Brian Lawson wrote:
Halloween night, 1956. We decide to steal an outhouse and put it on
the front lawn of the high-school. Sneak into the farmers back yard,
about 10 of us, and three guys go around to the back. Farmer must
have decided to move it within the last few days, and had not covered
over the old hole yet. Two guys fell in. They walked about 3 miles
back to town. We wouldn't even let them in the back of one of the
pickup trucks!



I'm glad they got out alive. It could have been much worse, as in:

There once was a man named McBride,
Who fell down the outhouse and died.
His next elder brother,
Fell into another,
So now they're in turd side-by-side.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"
***snortttttt***** Time for *another* shirt change..... Jeeeezzzz
Jeff, you must have a book full of these..,.. :-)
Ken

Brian Lawson wrote:

Halloween night, 1956. We decide to steal an outhouse and put it on
the front lawn of the high-school. Sneak into the farmers back yard,
about 10 of us, and three guys go around to the back. Farmer must
have decided to move it within the last few days, and had not covered
over the old hole yet. Two guys fell in. They walked about 3 miles
back to town. We wouldn't even let them in the back of one of the
pickup trucks!

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXX

On Sat, 02 Apr 2005 07:12:25 GMT, (Old Nick)
wrote:


That outhouse theme and the melting of the last traces of snow here in
Red Sox country reminded me of yet another childish endeavor - Writing
your name in the snow while relieving yourself.

Now you can relive (relieve?) those boyhood urgings right on your monitor:

But first, I couldn't resist writing one more limerick:

The name of the old Earl of Whiting,
Was writ in a hand quite indicting.
Found etched in the snow,
It amused most folks so,
'Cause it was in the housemaid's handwriting.

Do it yourself he

http://home.comcast.net/~jwisnia18/temp/snow_text.html

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

On Sun, 10 Apr 2005 12:43:59 -0400, Jeff Wisnia
wrote:

Brian Lawson wrote:

Halloween night, 1956. We decide to steal an outhouse and put it on
the front lawn of the high-school. Sneak into the farmers back yard,
about 10 of us, and three guys go around to the back. Farmer must
have decided to move it within the last few days, and had not covered
over the old hole yet. Two guys fell in. They walked about 3 miles
back to town. We wouldn't even let them in the back of one of the
pickup trucks!

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXX

On Sat, 02 Apr 2005 07:12:25 GMT, (Old Nick)
wrote:


That outhouse theme and the melting of the last traces of snow here in
Red Sox country reminded me of yet another childish endeavor - Writing
your name in the snow while relieving yourself.

Now you can relive (relieve?) those boyhood urgings right on your monitor:

But first, I couldn't resist writing one more limerick:

The name of the old Earl of Whiting,
Was writ in a hand quite indicting.
Found etched in the snow,
It amused most folks so,
'Cause it was in the housemaid's handwriting.

From some years back:
"F**k Bill written in the snow with Al Gore's urine in Hillary's
handwriting"
Gerry :-)}
London, Canada

Do a google search
One example is http://www.lightningrod.com/manual4_why.html
I lived on the lower part of a hill that was regularly hit by lightning.
The main power line that supplied the community came over that hill and
every few years it got struck. If you have strikes so close it would be
prudent to put up lighting rods.
I have seen a hilltop above me being stuck by lightning while I was still
securing my sailboat. There must have been a four inch spark that jumped
between my fingers and the metal mast. The massive current that had to be
at least half a mile away had induced enough current to feel like a live
spark plug. Induced or stray currents can cause havoc with anything
electronic nearby.
At least put up a rod at the highest point on your property to draw a
strike.
Randy

"nospamgoingjag" wrote in message
...
Excuse the lengthy OT message, but I noticed that folks in this group
have built metal buildings for their workshops and though you might be
able to help me.

I am considering building a large garage/pole barn using metal.

I am very concerned with lightening strikes due to where I live.

My house is nearly the highest thing in town. When we get lightening
it's always dancing around us. There had been a tree next to the
house about 30 years ago, it would get hit by lightening and they
finally put a lightening rod in it. Eventually got taken out anyway
(big tree they cemented back together at one point). It was gone when
I got here, but I had to deal with the stump which is when I found the
braided wire from the lightening rod.

The roofs of the additions that were put on in the 20's were all metal
covered with tar. It's clear they were not maintained, as many
interior walls had damage, so they were probably exposed as I found
them for some time. The chimneys on either end of the house had
lightening rods, each fastened to their own ground, not in the middle
which I think would have been the right thing to do.
The ligtening rods were disconnected for at least the last 13 years
(since we've been here), but I just had to spend 3 grand having the
tops of both rebuilt as they were loose from being hit by lightening,
and bricks had started falling down.

We have an old three holer outhouse that is now a garden shed. It had
the same sheet metal roof in hip form, and I liked the look so left it
alone (unlike the house where I had the metal torn off and replaced
with a membrane roof). One day I was mowing the lawn and found a
piece of rusty metal, I looked over at the back of the outhouse and
there was a big burn mark and at least 3 feet of the roof had been
blown off.

When I was making some changes to a small old hay barn so my wife
could use the second floor, I noticed what looked like some singed
paper on the roof. Further inspection showed that it had also had a
metal roof, and had clearly been hit and burned by lightening.

If I look off into the woods on the hill to the left of our house, I
can see trees that used to be green that got whacked by lightening and
died from the hits (we think we know when it happened, helluva a
storm, but of course it took years for everything to go bare).

When we walk in the woods behind our house, every now and then we find
a tree top and occassionaly a whole tree that was clearly struck by
lightening.

I've searched around the net and can't seem to find any real input on
this. Someone told me that if I properly bond the building, I'll be
all set. Well this makes sense except it makes me wonder if a 30x60
chunk of metal is going to be so attractive that it will invite the
lightening and I'll end up with strikes on my wooden buildings?

Any real world experience would be greatly appreciated, since
everything I have found on lightening seems inconclusive.

Sorry for the lengthy post, and thanks for any feedback. If emailing,
remove nospam.

Don't shortcut the grounding system. A good system includes lightning
rods, heavy wire (#6?), and ground rods. One good grounding system is
an underground circle of heavy wire going all around the building,
bonded to the building and the lightning rods. I recall that this is
what they would use in rocky areas where ground rods cannot be driven in
very far. The large industrial building I was associated with had heavy
copper wire surrounding the building, about 20 feet away, as part of the
ground system, with that bonded to ground rods and the building frame.

Be sure to bond everything to everything, bond the metal frame of the
building to the lightning rod and the ground system. Actually, for a
metal building, you could probably forget the lightning rods, and just
ground the frame. However, if you are in a lightning prone area, better
to overdesign it some. I recall some sources recommending heavy wire
running across the ridge of the roof and then down to ground rods at
both ends of the ridge.

The web site below shows a lightning protection system, although I think
they don't put enough emphasis on the grounding.

http://wvlightning.com/protection.html

The state farm site has a good description, but not that good a picture.

http://www.statefarm.com/consumer/electrichazards.htm

You did not say where the water table is on your property. The drier is
is, the harder it is to get a good ground, so the more ground rods and
the longer ground rods you will need. 10 foot ground rods are a good
choice, if the soil will allow them, I noticed a couple of sources
recomending the 10 foot length. In a perfect world, you would measure
the resistance of the grounding system, but that is not that easy to do.
Probably better to just drive more ground rods. One 10 foot ground
rod at each corner of the building, bonded to the metal building frame,
sounds pretty good to me. If the water table is high, maybe two ground
rods would be enough.

You should be able to find something in the national electric code that
would help you come up with a simple but effective lightning protection
system, but when I took a look the advice seemed kind of vague, which is
what you reported.

Lightning is ultimately unpredictable, but if you do the basics right
you should be protected against most lightning strikes.

Given the history of your property, it might be worth it to hire a
lightning consultant to give you specific recommendations. I think that
the work could be done by you if you know what to do.

Richard




nospamgoingjag wrote:
Excuse the lengthy OT message, but I noticed that folks in this group
have built metal buildings for their workshops and though you might be
able to help me.

I am considering building a large garage/pole barn using metal.

I am very concerned with lightening strikes due to where I live.

My house is nearly the highest thing in town. When we get lightening
it's always dancing around us. There had been a tree next to the
house about 30 years ago, it would get hit by lightening and they
finally put a lightening rod in it. Eventually got taken out anyway
(big tree they cemented back together at one point). It was gone when
I got here, but I had to deal with the stump which is when I found the
braided wire from the lightening rod.

The roofs of the additions that were put on in the 20's were all metal
covered with tar. It's clear they were not maintained, as many
interior walls had damage, so they were probably exposed as I found
them for some time. The chimneys on either end of the house had
lightening rods, each fastened to their own ground, not in the middle
which I think would have been the right thing to do.
The ligtening rods were disconnected for at least the last 13 years
(since we've been here), but I just had to spend 3 grand having the
tops of both rebuilt as they were loose from being hit by lightening,
and bricks had started falling down.

We have an old three holer outhouse that is now a garden shed. It had
the same sheet metal roof in hip form, and I liked the look so left it
alone (unlike the house where I had the metal torn off and replaced
with a membrane roof). One day I was mowing the lawn and found a
piece of rusty metal, I looked over at the back of the outhouse and
there was a big burn mark and at least 3 feet of the roof had been
blown off.

When I was making some changes to a small old hay barn so my wife
could use the second floor, I noticed what looked like some singed
paper on the roof. Further inspection showed that it had also had a
metal roof, and had clearly been hit and burned by lightening.

If I look off into the woods on the hill to the left of our house, I
can see trees that used to be green that got whacked by lightening and
died from the hits (we think we know when it happened, helluva a
storm, but of course it took years for everything to go bare).

When we walk in the woods behind our house, every now and then we find
a tree top and occassionaly a whole tree that was clearly struck by
lightening.

I've searched around the net and can't seem to find any real input on
this. Someone told me that if I properly bond the building, I'll be
all set. Well this makes sense except it makes me wonder if a 30x60
chunk of metal is going to be so attractive that it will invite the
lightening and I'll end up with strikes on my wooden buildings?

Any real world experience would be greatly appreciated, since
everything I have found on lightening seems inconclusive.

Sorry for the lengthy post, and thanks for any feedback. If emailing,
remove nospam.

I looked up the Socorro lightning research center.
Check:http://www.powerquality.com/mag/powe...nal_lightning/
For a good article and some great pictures taken at the Langmuir lab.
Bugs

I believe there is a general misunderstanding about how lightning rods
work. It's not clear whether the original poster understood or not, so
I'll just chime in anyway.

A static charge builds up in the air during a lightning storm. It
originates in the clouds, but induces an electric field through the
atmosphere. When the voltage between two points (two clouds, cloud and
ground, or cloud and building, animal, person, tree, etc.) builds up to
the breakdown voltage of air (on the order of 10,000 volts per inch
distance) then an arc or spark (lighning) jumps between the two.

To prevent such arcing, you want to dissipate the electric field in the
vicinity of your building.

Now, what's not always understood is how an electric field induces an
opposite field in an object. I.e., if the cloud is negatively charged
(sorry - I don't recall which charge the cloud normally will have) then
it will induce a positive charge in the building.

The critical thing is that this positive charge will not be uniform
across the building. It will be greater on the roof, and will have the
greatest charge density at abrupt corners. What a lighting rod is is a
VERY abrupt corner.

When the thunderstorm passes into the area and starts inducing electric
charge on buildings, the charge density at the tip of the lighning rod
becomes so intense as to leak current. This, in turn, dissipates the
field. Exactly what we want to accomplish. (Thank you, Benjamin
Franklin!) At the voltages we're dealing with here, this would be true
whether or not the lighning rod were grounded. But the current to
(from?) the rod must travel through something, and if the reisitance of
what it must travel through is great, its voltage will rise to that of
the air, ending its effectiveness at dissipating the charge. Hence,
the rod must be grounded sufficiently to conduct whatever current it
must, or else it will end up attracting lightning.

Hope this helps.