At 9:06 AM -0400 6/23/05, Peter Saint James wrote:
Several months ago, we discussed using or not using surge
suppressors with Powerbooks, and I found out the hard way that we
came to an erroneous conclusion.
We concluded that the power adapter would protect the Powerbook
from a surge. Turns out this is not true.
I have to admit that the surge to my book was a big one. A bolt
of lightening hit near my house. It knocked out the surge
suppressor then continued on, zapping the printer, other items that
were plugged into it, and my powerbook.
Well, there are surges, and then there are surges. A surge protector
will protect your kit against things like switching transients and
the like - the "typical" kind of thing that happens on a distribution
system, but it would be an inappropriate expectation if you thought
that it could protect you against a close lightning strike.
Just consider for a moment what's going on. You have a bolt of
lightning that has the potential to overcome the insulating value of
a layer of air that's a mile or more thick. If it strikes the
distribution line near your house, it has a path to all of your
appliances (with only the distribution transformer to mitigate the
intensity). If it hits the secondary side of the transformer (your
service drop) then you're really in for a blast.
Even unplugging the appliances isn't a guarantee that they would be
spared. The surge can jump the gap between the plug socket and the
end of the cord on the floor (remember, it just jumped a gap of a
mile, so this gap of a foot is nothing). And it can certainly pass
through and destroy your surge protector, fusing metal on the way.
There is a tremendous amount of energy in a lightning strike, and to
think that some little circuit in a plastic box is going to stop it
is sheer folly.
About two years ago we had an incident here where I live in which
there was a lightning strike near a home (occupants were at work) and
when the owners returned they found most of their appliances - TV,
Fridge, stereo, etc. - totally destroyed. They were lucky that the
house didn't burn down.
What can you do? Well, if you are worried about a close strike, you
should power down all of the computer gear, then unplug the cords and
move them away from the wall outlet as far as you can. If you have a
laptop, either use it on a battery or shut it off too. If you get a
lightning strike just outside of the house the air around you will
have a very high field strength, and it could damage your computer
even if it is unplugged. You'll feel it on your skin. Remember, we're
talking about tens of millions of volts here. And relatively speaking
it doesn't take a lot of voltage to damage silicon. Putting the
PowerBook in a metal box would help.
Mostly lightning doesn't strike close enough to worry about. And it
more often than not strikes a tree as opposed to the distribution
system. And strikes on the secondary would be even more rare. So
statistically you are not likely to become a victim of the lightning
surge, but it can happen, and when it does, if it's close, you'll be
lucky if you don't get some damage.
I know of no commercial product that would protect your computer
gear from lightning if the strike is just outside your house. The
brochure may say it will, but you can take it to the bank that
lightning doesn't know what the brochure says.
- web
P.S. I used to be a utility engineer and for three years I did the
protective device coordination for the provincial power utility.
Trust me, lightning is impressively powerful.
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