I'm on NTL cable and I assumed that as most of their network is fibre optic
it will be relatively safe from lightning - however the most likely risk
will be from spikes in the power supply. i.e. I disconnect the plugs from
the mains but not the cable inputs.

I'm now wondering if this is a valid assumption?

Chris Gadsby


"Tony Humphreys" wrote in message
...
Something I have only just thought about. Does anyone know if there is a
risk (as with regular modems) of damage during a thunderstorm to ADSL
equipment. I assume that there is but does anyone know differently (like
the microfilter will block this).

Something I have only just thought about. Does anyone know if there is a
risk (as with regular modems) of damage during a thunderstorm to ADSL
equipment. I assume that there is but does anyone know differently (like
the microfilter will block this).

A few weeks ago during a particularly violent thundertorm, my microfilter
went pop and all the phones as a result were dead. Replacing the microfilter
did solve the problem and it appears both my PCs (the one connected directly
to the ADSL via a PCI modem and the one connected via Ethernet to that PC)
survived unscathed. As always tho, it's wise to disconnect your
ADSL/telephone modem from the phone line as soon as you see the 1st signs of
a storm.

Regards,
Far

"Tony Humphreys" wrote in message
...
Something I have only just thought about. Does anyone know if there is a
risk (as with regular modems) of damage during a thunderstorm to ADSL
equipment. I assume that there is but does anyone know differently (like
the microfilter will block this).

Good question - for the record my line is overhead for about 30 metres from
a telegraph pole at the back of our house and the rest of it is underground.
I believe it's a question of luck tho and since most "lightning damage" is
supposedly caused by static from the strike rather than a direct overhead
strike then it may well be a question of how deep the line is buried and
other factors - I am sure someone can answer this properly.

Regards,
Far

"Victor West" wrote in message
...

"Far" *co*uk wrote in message
...
A few weeks ago during a particularly violent thundertorm, my
microfilter
went pop and all the phones as a result were dead. Replacing the
microfilter
did solve the problem and it appears both my PCs (the one connected
directly
to the ADSL via a PCI modem and the one connected via Ethernet to that
PC)
survived unscathed. As always tho, it's wise to disconnect your
ADSL/telephone modem from the phone line as soon as you see the 1st
signs
of
a storm.


Whilst I always unplug, is there any less (or more?) risk when your line
is
underground?

Victor

When there is a lightning flash close to any wire, buried or above ground,
there will be the risk of large induced currents, as a result of the huge
swings in the electro-magnetic field. To protect your equipment and your own
safety, you should disconnect your phone line as close to the MODEM as
possible. you should also disconnect the line at the socket where it comes
into the house. This will protect your phone equipment and filters. You
should also isolate your PC by unplugging at the mains socket. Ditto for TV
and Hi-FI equip. If you get a lightning strike on your house, the mains
wiring will probably all need replacing, plus anything connected to the
mains at the time (cooker, central heating ), but there is nothing
practicable that can be done to protect against that. Also, if you have roof
aerials, dishes etc, the down leads should be removed from their equipment.

--
Bernard Burton
Wokingham, Berkshire, UK.


Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
"Tony Humphreys" wrote in message
...
Something I have only just thought about. Does anyone know if there is a
risk (as with regular modems) of damage during a thunderstorm to ADSL
equipment. I assume that there is but does anyone know differently (like
the microfilter will block this).

Also, its worth remembering that it doesn't need to be a "direct hit" onto
the telephone network...

Just as EMF causes a surge, or lack, of electricity on a high voltage
powerline (causing temporary b/outs) that same EMF power can seriously
damage the more lower voltage telephone exchange or home equipment.

A good ADSL modem should have some kind of Telco line fuse, but usually
inside on the PCB. This still will not protect you from a direct hit
however - the lightning has jumped the gap from the cloud to the ground, so
the distance to jump from one side of a fuse to another should be no
problem... and quite usually, if you are like me and you have the PC tucked
beneath you under a desk... lightning can take the scenic route to earth-
through the PC case, jump across to your knee and down the leg of the chair!
Fancy a picnic?


Barry Kirley
Dursley, Gloucestershire
01.15 BST
20.2c





"Far" *co*uk wrote in message
...
Good question - for the record my line is overhead for about 30 metres
from
a telegraph pole at the back of our house and the rest of it is
underground.
I believe it's a question of luck tho and since most "lightning damage" is
supposedly caused by static from the strike rather than a direct overhead
strike then it may well be a question of how deep the line is buried and
other factors - I am sure someone can answer this properly.

Regards,
Far

"Victor West" wrote in message
...

"Far" *co*uk wrote in message
...
A few weeks ago during a particularly violent thundertorm, my
microfilter
went pop and all the phones as a result were dead. Replacing the
microfilter
did solve the problem and it appears both my PCs (the one connected
directly
to the ADSL via a PCI modem and the one connected via Ethernet to that
PC)
survived unscathed. As always tho, it's wise to disconnect your
ADSL/telephone modem from the phone line as soon as you see the 1st
signs
of
a storm.


Whilst I always unplug, is there any less (or more?) risk when your line
is
underground?

Victor

On Sun, 13 Jul 2003 22:44:21 +0100, "Bernard Burton"
wrote:

When there is a lightning flash close to any wire, buried or above ground,
there will be the risk of large induced currents, as a result of the huge
swings in the electro-magnetic field.

As an electrical engineer and a former meteorologist, I would say that
there is a danger of lightning induced high voltages (as distinct from
direct hits) in any wiring (indeed in anything conductive, such as a
wet washing line or wire fence), although it will obviously be
dependent on a number of factors.

I don't know for sure but any electronic equipment should, if normal
engineering practice has been followed, be protected at all inputs by
protective devices such as zener diodes, voltage dependent resistors
(VDRs or varistors) or spark gaps. These devices will handle voltage
surges but lightning induced spikes may overwhelm them.

The voltage induced does not have to be that high for damage to occur
and the charge can be very small indeed, microcoulombs or less.

Obviously overhead lines are the most prone, and even relatively
distant lightning may cause problems. Underground lines are not
immune, but the effect I would think must be less, as the lines are
"screened" for most of their length by moist soil at earth potential,
acting like a shield. The amount of line above ground at the property
is also a factor.

JPG