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.