As promised, the rest of the puzzle:
I found, with my voltmeter, that the other computers damaged were on the
opposite leg of the power system from my G4. The one that was not
damaged was on the same leg. And the Isotel supplying the HD connected
into my computer was on the opposite leg too. That's two plugins that
are only about 7' apart, but have a voltage difference between them of
220 volts.
My theory is that the power surge that came in was riding on only one
leg of the power. And the SCSI card got caught in the middle and that
was how it all got into my computer. Also caught in the middle was the
ethernet lan. My computer lost the transmit side of it's ethernet, the
others lost the receive. It's not clear if the phone line surge was
internal to the house from this difference, or a separate surge that
came in from outside via the phone line. It's only damage was fried suppressers.
For those that are going, what's that? US home power comes in as two 110
volt legs, and the difference between the power side of the two legs is
220 volts, which supplies the power for major appliances. The two legs
get apportioned out various 110 volt circuits in the house so as to keep
the load close to even. The ground line is in common for everything, and
is also attached to one or more ground rods. In my house there are two
12' ground rods, one at each end, plus the ground is also tied to the
475' deep steel well casing. Both the power and phone are using this
ground. What this means is that although any individual wall plug will
be 110 volts, between the hot sides of some wall plugs there can be a
220 volt difference. And they are separate all the way out to the power
transformer 250' away from the house.
What I'm in the process of doing now is making sure all computer
equipment is on only one leg of the house power, no matter where it's
located. And as a farther measure, I'm putting in individual surge
suppressers on each ethernet port at the computer or printer which is
tied to ground. Same with each modem, TV satellite receiver and all the
rest hooked to the phone system. Each will get a individual surge
suppresser at the equipment on the interconnecting line, in addition to
the surge suppression of each main phone feed via the Isotel's. All to
try and stop surges internal to the house. I believe the external
suppressers are pretty much as good as I can do short of really spending
bucks for a whole house isolation ferroresanant transformer. That would
actually cut my electric bill by regulating the power, but it's a very
costly option.
I spent this afternoon in the spiders and dust rewiring the room my
computer is in. It's all coming from just one plug now.
Only thing else I've considered is putting in a separate heavy wire
ground line between all the rooms independent of the power one to tie
all system grounds to. The ethernet system is all run in the crawl space now.
I don't consider unplugging, or turning systems off to be a real viable
option, as it depends on someone being here to do it and it would
involve quite a bit of disconnecting. For Georgia that would happen
frequently. Modern computer power supplies don't provide much additional
protection even if turned off anyway.
This is the third time I've had lightning damage in 15+ years here. The
first time we had a phone line run along the ceiling between two modems
in different rooms, and those two modems died when a bolt passed very
close over the roof of the house to hit a tree in the back. The second
time was through the phone line which took a hit a few hundred feet from
the house, a cheap phone line suppresser did not stop it. It fried a
external modem, ran in the serial line on my 8500, jumped across to the
ethernet on the motherboard, ran out the lan and fried a AAUI adapter at
another 8500 but did not have enough left to get into it. After that one
I put in all the ISOTEL suppressers to replace the cheaper stuff. Two
died, but the modems they protected are fine.
Anyway, this experience revealed a whole new danger if you have a lan.
Walt
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