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Lightning Damage



 
 
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  #1  
Old August 20th 06, 10:18 AM posted to uk.telecom.broadband
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Default Lightning Damage

There was a major thunderstorm her on Friday. There were several power
surges as the local electricity substation was hit and then the power went
off for a while.

I have a small UPS/Power Surge device and my router and a small server run
through this. The UPS also has protection for the telephone line and the
ADSL lead goes through this.

All the other PCs were off in the house.

When the power came back on the Router had suffered damage in that the ADSL
part and the WiFi part still worked but the 4 wired ports did not.

Three of these ports were connected at the time of the storm. One was an
uplink to an 8 port switch - this still works fine.

The other two were connected to PCs. The network ports on these two PCs no
longer work - they are both on the mother board. The rest of the PCs are
fine as far as I can tell. They boot up fine and all system checks seem Ok.
I have disabled the networks ports in the bios and added in two network
cards, bought a new router and I am up and running again.

What else should I look out for on the damaged PCs? Are they likely to be Ok
long term.

How was the hit so selective?


  #2  
Old August 20th 06, 11:04 AM posted to uk.telecom.broadband
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Default Lightning Damage

In article ,
"R.Daneel Olivaw" [email protected] writes:
There was a major thunderstorm her on Friday. There were several power
surges as the local electricity substation was hit and then the power went
off for a while.

I have a small UPS/Power Surge device and my router and a small server run
through this. The UPS also has protection for the telephone line and the
ADSL lead goes through this.

All the other PCs were off in the house.

When the power came back on the Router had suffered damage in that the ADSL
part and the WiFi part still worked but the 4 wired ports did not.

Three of these ports were connected at the time of the storm. One was an
uplink to an 8 port switch - this still works fine.

The other two were connected to PCs. The network ports on these two PCs no
longer work - they are both on the mother board. The rest of the PCs are
fine as far as I can tell. They boot up fine and all system checks seem Ok.
I have disabled the networks ports in the bios and added in two network
cards, bought a new router and I am up and running again.


Sounds like there was a large differential voltage pulse between
the mains and ground, large enough to arc across the ethernet
isolation transformers built in to the NICs and router ports.
(IIRC, they are rated 4kV, so you're probably looking at a pulse
greater than 10kV.)

What else should I look out for on the damaged PCs? Are they likely to be Ok
long term.


The effect is like that of incorrectly handling static sensitive
components. It rarely completely destroys them, but it damages
the semi-conductor gates and this can create on-going problems.
You get a much higher chance of failures in the next 100 hours
or so of use (just like early failures of new components), but
you also get a much reduced lifetime of the gates (e.g. a gate
which might have lasted 50 years drops to 5 years). The other
effect is that the electrical characteristics of the semiconductors
may have gone out of spec, resulting in marginal behaviour in some
circumstances and correct operation in others.

So to sum up, there's a small chance some more bits might die
in the next few days which you can directly attribute to the
incident, and some parts will have had their lifetime reduced,
which might cause them to die before you would have naturally
scrapped them anyway (harder to directly attribute to the
incident). You might find some things don't work in certain
circumstances (e.g. if systems run hot in warm weather).
As I said, this is the standard characteristic of anti-static
mishandling (and not just instantly destroying things, as is
commonly thought).

How was the hit so selective?


It wasn't. I don't have quite enough information about your
system's interconnections, but from what you say, it sounds
like a pulse between mains and ground. There will also have
been a pulse between phone and ground or mains, but the UPS
protection handled that. The fault path was the connections
between the protected things and the unprotected things, i.e.
your ethernet cables.

--
Andrew Gabriel
  #3  
Old August 20th 06, 11:37 AM posted to uk.telecom.broadband
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Default Lightning Damage


"Andrew Gabriel" wrote in message
...
In article ,
"R.Daneel Olivaw" [email protected] writes:
There was a major thunderstorm her on Friday. There were several power
surges as the local electricity substation was hit and then the power
went
off for a while.

SNIP

How was the hit so selective?


It wasn't. I don't have quite enough information about your
system's interconnections, but from what you say, it sounds
like a pulse between mains and ground. There will also have
been a pulse between phone and ground or mains, but the UPS
protection handled that. The fault path was the connections
between the protected things and the unprotected things, i.e.
your ethernet cables.

--
Andrew Gabriel


Might be worth checking what your earth / ground connection is like, perhaps
it is floating?


  #4  
Old August 20th 06, 11:37 AM posted to uk.telecom.broadband
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Default Lightning Damage

"R. Mark Clayton" wrote in message
...

"Andrew Gabriel" wrote in message
...
In article ,
"R.Daneel Olivaw" [email protected] writes:
There was a major thunderstorm her on Friday. There were several power
surges as the local electricity substation was hit and then the power
went
off for a while.

SNIP

How was the hit so selective?


It wasn't. I don't have quite enough information about your
system's interconnections, but from what you say, it sounds
like a pulse between mains and ground. There will also have
been a pulse between phone and ground or mains, but the UPS
protection handled that. The fault path was the connections
between the protected things and the unprotected things, i.e.
your ethernet cables.

--
Andrew Gabriel


Might be worth checking what your earth / ground connection is like,
perhaps it is floating?


Sorry to be so think - what do I check and where?

Thanx


  #5  
Old August 20th 06, 11:44 AM posted to uk.telecom.broadband
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Default Lightning Damage


Might be worth checking what your earth / ground connection is like,
perhaps it is floating?


Sorry to be so think - what do I check and where?

Thanx


Doh! For think read thick!!!


  #6  
Old August 20th 06, 12:24 PM posted to uk.telecom.broadband
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Default Lightning Damage

In article ,
"R.Daneel Olivaw" [email protected] writes:
"R. Mark Clayton" wrote in message
...

"Andrew Gabriel" wrote in message
...
In article ,
"R.Daneel Olivaw" [email protected] writes:
There was a major thunderstorm her on Friday. There were several power
surges as the local electricity substation was hit and then the power
went
off for a while.

SNIP

How was the hit so selective?

It wasn't. I don't have quite enough information about your
system's interconnections, but from what you say, it sounds
like a pulse between mains and ground. There will also have
been a pulse between phone and ground or mains, but the UPS
protection handled that. The fault path was the connections
between the protected things and the unprotected things, i.e.
your ethernet cables.


Might be worth checking what your earth / ground connection is like,
perhaps it is floating?


Sorry to be so think - what do I check and where?


The scenario I described does not point to any wiring fault.

Your installation is not lightning protected, but neither are
most peoples' installations (although your UPS protection
probably protected you against more damage). To make a house
installation properly protected against the type of incident
you had would cost a good deal more than replacing the damaged
kit, so it's not worth it unless you have a lot of expensive
kit and/or are for some reason much more suscpetable to
lightning strikes than most people.

Note that the lightning protection in the UPS may no longer
be effective, now that it has had a good belt.

--
Andrew Gabriel
  #7  
Old August 20th 06, 06:36 PM posted to uk.telecom.broadband
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Default Lightning Damage

Andrew Gabriel wrote:

Your installation is not lightning protected, but neither are
most peoples' installations (although your UPS protection
probably protected you against more damage). To make a house
installation properly protected against the type of incident
you had would cost a good deal more than replacing the damaged
kit, so it's not worth it unless you have a lot of expensive


Out of interest, with aluminimum-backed plasterboard, and other
possible materials (eg the safety glass with thin wire grid in
it), would something akin to a Faraday cage protect one room,
or is that, too, not really viable for the low cost of kit,
or just wouldn't be sufficient, and merely lull one into a
sense of false security about it ? I only ask, as I rarely
turn kit off, so would be away from home/office (can only be in
one place!) if there was a thunderstorm, so one or other could
be hit. I use remote backup, so important files are away on a
server in Norway or another in the USA, so loss of some PC is
just a minor inconvenience, as I have others (unpowered) as
backups to the ones in day-to-day use. Thanks.
  #8  
Old August 20th 06, 08:05 PM posted to uk.telecom.broadband
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Default Lightning Damage

In article ,
NoNeedToKnow writes:
Out of interest, with aluminimum-backed plasterboard, and other
possible materials (eg the safety glass with thin wire grid in
it), would something akin to a Faraday cage protect one room,
or is that, too, not really viable for the low cost of kit,
or just wouldn't be sufficient, and merely lull one into a
sense of false security about it ?


It depends what you want to protect against. That sort of
thing might be appropriate for avoiding damage in a direct
hit, but they are rare compared with nearby hits which come
in via services (mains, phone, ...) as in the OP's case.
After a direct hit, you are going to need to rewire the
whole house and possibly rebuild parts of it anyway,
although lightning conductors can reduce that sort of
damage.

Protecting against spikes coming in on services is easier.
You basically have to arrange they all enter nearby each
other, and are cross-bonded. In the case of mains and phone
wiring where you can't just earth all the wires, appropriate
lighning filters need fitting and cross-bonding with the
other services. This prevents voltage spikes appearing
between services inside the house. A decent lighning filter
will cost more than a new router and a couple of NIC cards
though ;-)

I only ask, as I rarely
turn kit off, so would be away from home/office (can only be in
one place!) if there was a thunderstorm, so one or other could
be hit.


I don't know that being switched on or off is likely to make
much difference to the damage.

--
Andrew Gabriel
  #9  
Old August 20th 06, 08:06 PM posted to uk.telecom.broadband
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Default Lightning Damage


On 20-Aug-2006, "R.Daneel Olivaw" [email protected] wrote:

How was the hit so selective?


A lot of the risk is from the incoming phone line. A nearby
strike can raise your local ground about 100V relative
to power and exchange grounds.

Voltage is shared so that most voltage occurs across the
smallest capacitance, in most cases the pico-farads of the
front end signal processing semi-conductors. So they
usually suffer most. As in the days of dialup modems.

Opto couplers, and isolated digital power rails, don't help
much because the isolated digital power is usually from
an isolated winding in the PSU, and this winding has a
high self capacitance to ground, so it doesn't do much
to aid protection.

Transformer isolated ferrite cored, small signal pulse
type transformers, help a lot with strike immunity.

Most domestic residences aren't well grounded for
impulse strikes, the long earth conductor acting
as a high frequency choke to steep fronted fast rise
time pulses. Even if it's fine at 50hz and able to trip the
ELCB when your hedge trimmer trims it's cable.

Phones don't have a local ground so are mainly immune
unless they have a mains powered answering machine
or DECT function. Then they become at risk like other
devices with a path to ground for the strike.
  #10  
Old August 20th 06, 08:22 PM posted to uk.telecom.broadband
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Default Lightning Damage


"R.Daneel Olivaw" [email protected] wrote in message
...


Sorry to be so think - what do I check and where?

Thanx


Earth continuity (back to the board) and that there is a good earth. This
can be a copper rod in the ground or [perhaps] if your supply comes in
underground the shield on it.


 




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