Re: Close lightning strike effects
- From: "Paul" <pstech@xxxxxxxxx>
- Date: 7 Jul 2006 03:20:39 -0700
Abstract Dissonance wrote:
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)
.
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