I need to get a couple of mains blocks. I can get 4-way Belkin ones with
surge protection (F9H400uk1M) for about £5.50 which is about a quid more
than a normal block costs down the local B&Q.

I'm no electrician, part of me looks at the wave of £30+ surge protectors
out there and thinks they're designed to look pretty and scare people out
of their money, on the other hand I've had enough people bring their home
PCs to me at work because their PCI modem's stopped working after a recent
thunderstorm to think for the sake of a quid more on a mains block I might
as well.

Anyway, looking around the belkin site there's all kinds of joule and
amperage and db ratings and I'm curious what it all means?

I won't be connecting anything out of the ordinary, PC and bits to one, AV
amp/sky/TV/DVD to the other.

It's be nice if any explanations could be "plain english", and not turn
into a "whole house protection" argument as seems to happen on every thread
I've seen on google!

regards
Paul
--
paul at spamcop.net

I'm no electrician, part of me looks at the wave of £30+ surge protectors
out there and thinks they're designed to look pretty and scare people out
of their money, on the other hand I've had enough people bring their home
PCs to me at work because their PCI modem's stopped working after a recent
thunderstorm to think for the sake of a quid more on a mains block I might
as well.

Paul

And how is a mains surge arrestor going to stop a large pulse coming down
the phone line. I, personally think they are all a waste of money, but you
pays your money etc....

Dave

--

Some people use windows, others have a life.

In article , Paul
Hutchings writes

It's be nice if any explanations could be "plain english", and not turn
into a "whole house protection" argument as seems to happen on every thread
I've seen on google!

That's very easy. Just killfile w_tom, since his "advice" almost always
pertains to Northern America and is completely incorrect for UK/Europe,
despite his having been shown to be wrong on more than one occasion.
Treat his advice as you would that from a double-glazing salesman
sitting on your sofa - ask him which surge protector manufacturer he
works for and watch him go quiet; his advice is clearly not at all
impartial.

The "whole house" surge protection devices he constantly advocates for
the Northern American market are totally irrelevant to our (UK) domestic
installations, a point he seems unwilling or unable to grasp.

--
..sigmonster on vacation

And how is a mains surge arrestor going to stop a large pulse coming down
the phone line. I, personally think they are all a waste of money, but you
pays your money etc....

And there's plenty who'll take the money off them as wants to pay it.
But especially here in the UK, neither grotty mains nor lightning
strikes are common, and when they are the kind of penny-priced VDRs
which "provide" the "surge protection" are b'all use...

Stefek

Paul Hutchings wrote:

I need to get a couple of mains blocks. I can get 4-way Belkin ones with
surge protection (F9H400uk1M) for about ï½£5.50 which is about a quid more
than a normal block costs down the local B&Q.

Chepest option is to DIY:

e.g. a 69p Spike suppressor from Maplin is all you need to match most
"spike suppressor" mains blocks.

http://www.maplin.co.uk/Module.aspx?...ID =&doy=3m10

or http://tinyurl.com/6djg6

I'm no electrician, part of me looks at the wave of ï½£30+ surge protectors
out there and thinks they're designed to look pretty and scare people out
of their money, on the other hand I've had enough people bring their home
PCs to me at work because their PCI modem's stopped working after a recent
thunderstorm to think for the sake of a quid more on a mains block I might
as well.

Modems tend to get killed by spikes on the phone wire rather than the
mains. You could try a couple of the above suppressors between each
exchange wire and a ground point on your incoming telephone line.

Anyway, looking around the belkin site there's all kinds of joule and
amperage and db ratings and I'm curious what it all means?

Just an indication of the amount of energy that the suppressor can shunt
before turning its toes up. In theory the bigger the better.

It's be nice if any explanations could be "plain english", and not turn
into a "whole house protection" argument as seems to happen on every thread
I've seen on google!

In plain english: spike supression for the computers is not going to do
that much for you, although at 69p a pop you may as well do it. If you
want any real protection then get a UPS. Never tried proctecting a
phone line, so not sure how effective it will be.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

A surge protector will 'stop' what kilometers of sky could
not? Victims of ineffective protector myths (such as Mike
Tomlinson) who promote these half truths. (Mike will reply
with insults to prove his technical superiority).

It is routine to suffer direct strikes without damage even
in regions that have more serious lightning storms. But the
basic concepts must be understood. Plug-in protectors avoid
all discussion about the most critical function in protection
to sell their ineffective but so profitable products.

Scientists measure direct lightning strikes to a
communication tower atop Hoher Peissenberg in Southern
Germany. Why are those CMOS devices, rated only for tens of
volts, not damaged by million volt lightning strikes? Simple
They use the same concepts demonstrated by Franklin in 1752.

How effective protectors work is summarized in a previous
discussion:
"Pull the wall plug or not?" in nz.comp on 7 Sept 2004 at
http://tinyurl.com/5ttwl

Do not confuse the protector with protection. They are
separate devices of a protection system. A protector is only
effective when connected short to protection. That protection
is earth ground. An effective protector never stops, blocks,
or absorbs surges. Concepts detailed in that previous
discussion.

A surge protector is only as effective as its earth ground.
Same concept that makes Franklin lightning rods effective.
Effective 'whole house' protector typically costs about £1 per
protected appliance. Ineffective protectors cost more -
trying to stop or absorb surges.

Dave Stanton wrote:
And how is a mains surge arrestor going to stop a large pulse
coming down the phone line. I, personally think they are all
a waste of money, but you pays your money etc....

Dave

"w_tom" wrote in message
...
A surge protector will 'stop' what kilometers of sky could
not?
Indeed it can. The cloud/lightning/cable/earth system forms a voltage
divider: so long as the impedence from cable to ground is significantly
lower than that of the lighning strike, then the voltage will be
(relatively) low.

The main components of the impedence in the divider a
- the resistance of the air to the strike. This is quite low once the arc
is extablished.
- the resistance of any spark gaps to ground. Again, quite low once the arc
is struck.

Power lines are equipped with arcing horns to encourage the ground arc to
strike, so the peak spike voltage once the ground arc has struck is probably
about twice the peak mains supply voltage.

There is a short period between the lightning strike and the ground arc
striking when the voltage on the line can rise to many times the supply
voltage.

Telephone lines don't have this protection, but they do have little green
boxes with very small gaps between the connections inside, which also
encourage arcs, and will certainly have surge suppressors somewhere,
probably at the exchange.

From the strike point to the equipment to be zapped, the main impedence
components a
- The inductance of the cables
- The capacitiance of the cables to ground.
These form a low-pass filter that will tend to spread out the energy pulse,
reducing amplitude and rise/fall time and increasing duration.

Hence, fitting a surge suppressor (only) in a domestic situation will help
if the strike is some distance away - the further the better. It won't help
much is the strike is on the phone wires leading from your local pole to
your house!

If you think that you're at real risk, you can buy commercial units (for
rather more than 69p) which contain a spark gap, a series inductor and a
parallel surge protector. These, if connected to a GOOD earth, will filter
out all but the biggest surges. They are available for power, phone, TV
aerial and data lines.

insult snipped

It is routine to suffer direct strikes without damage even
in regions that have more serious lightning storms.

True, but these systems are designed with lightning strikes in mind.

But the
basic concepts must be understood. Plug-in protectors avoid
all discussion about the most critical function in protection
to sell their ineffective but so profitable products.

These devices are NOT inneffective. The worst you can say is that their
effectiveness is limited. There are limits to all forms of lightning
protection. If lightning actually strikes your TV aerial or phone/mains
incomer, then it is almost impossible to avoid some damage - even if it's
only a zapped surge filter!

Scientists measure direct lightning strikes to a
communication tower atop Hoher Peissenberg in Southern
Germany.

And? What is your point here? Engineers regularly monitor lightning strikes
(and induced surges) on a wide range of systems, including mains supplies,
transmitting & receiving masts, phone systems, water and gas distribution
pipes

Why are those CMOS devices, rated only for tens of
volts, not damaged by million volt lightning strikes?
Most devices in transmitter output stages (and receiver input stages) are,
in fact, rated at hundreds of volts, not tens, but I see the point! They
are not damaged because the designers put in a LOT of effort to fit surge
filtering and suppression between the semiconductors and the exposed bits of
metal.

snipped

Do not confuse the protector with protection. They are
separate devices of a protection system. A protector is only
effective when connected short to protection. That protection
is earth ground.

Active surge protectors are normally connected as shunts (i.e. between the
cable to be protected and ground) and normally present a high resistance as
long as the voltage across them does not exceed a particular threashold,
after which they present a virtual short until the voltage drops back to
almost zero. Hence, they need a series impedence (such as an inductor) to
work repeatedly - if they are connected straight across the mains, they will
short the incoming power to ground as well (for the current half-cycle, at
least) and the current may well overheat them. As they are designed
(usually) to fail short, this will probably blow the incoming supply fuse.
Special devices are needed for telephone systems that have a switch-off
voltage higher than the applied DC, otherwise they stay on for ever once
triggered.

A surge protector is only as effective as its earth ground.

Very true. Earth connections must present not only a low DC resistance to
ground but be capable of carrying more current than the protected cable and
also present a low dynamic impedence. The latter requirement means that the
earth connection should be as short and direct as possible. This tends to
reduce the effectiveness of distribution-board protection where the
protected appliances have an alternative path to ground, due to the
relatively high dynamic impedence of most domestic earth wires. Hence
'protected' TVs, for instance, will often be damaged during a strike on the
aerial by arcs developing between the chassis of the TV and any nearby
earthed metal, such as central heating pipes.

snip

snip I, personally think they are all
a waste of money, but you pays your money etc....

As I said earlier, there is very little that you can do to protect against
direct lightning strikes, but most surges are either induced spikes, where a
strike on a pole causes a large voltage gradient down the pole and across
the nearby earth, and this capacitively couples into the affected cabel, or
mains switching transients. Despite the careful design of substation
switches, you still get arcs when circuits are broken and the surges these
produce can never be completely suppressed at source. These surges have a
much higher source impedence and so can more easily be filtered and
suppressed.

The worst design scenario is the nuclear emp, where you have to protect
against pulses with a risetime of 50kV per millisecond - this edge is so
fast that it often manages to couple itself round standard protection and
fry sensitive electronics, even inside sealed metal boxes...

K

Paul Hutchings wrote:

I need to get a couple of mains blocks. I can get 4-way Belkin ones with
surge protection (F9H400uk1M) for about £5.50 which is about a quid more
than a normal block costs down the local B&Q.

I'm no electrician, part of me looks at the wave of £30+ surge protectors
out there and thinks they're designed to look pretty and scare people out
of their money, on the other hand I've had enough people bring their home
PCs to me at work because their PCI modem's stopped working after a recent
thunderstorm to think for the sake of a quid more on a mains block I might
as well.

Surge protectors won't protect modems.

The surge that kills the modem is on the phone line, not the mains.

Almost all low voltage PSU's use rectified mains chopped: The capacitors
and RFI chokes in that constitute enough surge protection: In the limit
the PSU goes and that's it.


Anyway, looking around the belkin site there's all kinds of joule and
amperage and db ratings and I'm curious what it all means?

Nothing. They are as useless as electronic water softeners.


I won't be connecting anything out of the ordinary, PC and bits to one, AV
amp/sky/TV/DVD to the other.

It's be nice if any explanations could be "plain english", and not turn
into a "whole house protection" argument as seems to happen on every thread
I've seen on google!

All right then. Surge protectors don't protect against the sorts of
surges that cause real problems . In short they are a ****ing waste of
money.

Plain enough?

:-)

regards
Paul

w_tom wrote:

A surge protector will 'stop' what kilometers of sky could
not? Victims of ineffective protector myths (such as Mike
Tomlinson) who promote these half truths. (Mike will reply
with insults to prove his technical superiority).


Blimey...what a load of waffle.

Look, I've worked in Africa, where storms are frequent and severe, and
believe me, nothing stops even a near miss from buggering up anything
connected to a long piece of wire in the vicinity of a ground strike.

In the end, opto isolators and line transformers for audio seemed to
reduce but not eliminate returns, and replacing the opto panel was
cheaper...

When I returned to the UK, I DID get struck by lightning. Took out the
overhead phone line and reduced it to a smear of carbon across the road.

What went?

Well, the modem was toast, and the serial/parallel card it was plugged
into. And the input side of the laser printer plugged into THAT. The
lightning then jumped into the mains wiring and raced round the house. I
lost the PSU on a laser printer, I lost a CMOS chip on a digital hi-fi
turntable, and I lost the digital stuff on a TV - but it was old and
went in the skip.

The high stuff survived, as did most of the computer.

The carpet got a bit burnt where some mains cables ran underneath and
over it.

An unused aerial socket connected to nothing was blown to pieces and out
of the wall, as was an unearthed mains socket some cowboy had wired in
on two core cable.

In all it cots me about 300 quid to get everything fixed, including new
second-hand TV.

The landlord got the cottage rewired on the insurance since he felt it
was a good idea and argued that after a strike like that he wouldn't
want to be responsible for its condition.

Surge arrestors are a complete waste of time. Every BT phone socket has
one. They don't work against a direct strike, or even a near miss. They
sort of work a bit when its vaguely in the area.

In general a near miss on my overhead power lines here, causes the RCD
to trip.

The greatest danger to computers is a momentary loss of power as the
mains goes off, followed by auto reconnect, followed by a second loss of
power when the grid discovers the branch is still on the line etc.. If
the computer is set to auto boot, that generally crashes the disk head
JUST in the middle of the boot sector or close to it.

Lost two computers operating systems that way, one past all recovery.

Ken wrote:

"w_tom" wrote in message

Hence, fitting a surge suppressor (only) in a domestic situation will help
if the strike is some distance away - the further the better. It won't help
much is the strike is on the phone wires leading from your local pole to
your house!

First sensible statement.

If you think that you're at real risk, you can buy commercial units (for
rather more than 69p) which contain a spark gap, a series inductor and a
parallel surge protector. These, if connected to a GOOD earth, will filter
out all but the biggest surges. They are available for power, phone, TV
aerial and data lines.


Yes.. And what is on the mains side of most equipment?

Eitherer a whacking great transformer with plenty of (leakage)
inductance and coupled into at least an RFI cap and usually a bloody big
electrolytic....or a RFI circuit comprising er - would you believe
series inductors and capacitors across, and to ground?

Presumably you wouldn't.

The spark gaoop and or varistors are teh only thing missing, BUT
remember that youi DON'T jget kilovolt surges on teh mains as its is
down convreted by a thwacking big transformer somewhere up your street.
THAT is what has the surge proection in it, aand its built like a brick
(or iron) ****house.

You get a smaller surge. Easly enough to be taken care of by a bit of
RFO filtering and/or teh regulation in teh PSU itself.





insult snipped


It is routine to suffer direct strikes without damage even
in regions that have more serious lightning storms.


True, but these systems are designed with lightning strikes in mind.


It isn't routne for anything to survive direct strikes except stuff
specifically designed for it, which a 69p surge arrestor is not.

Howevr, unlike you guys, I have actually worked servicing kit in the
worst storm area on earth. Southern Africa.




But the
basic concepts must be understood. Plug-in protectors avoid
all discussion about the most critical function in protection
to sell their ineffective but so profitable products.


These devices are NOT inneffective. The worst you can say is that their
effectiveness is limited.

Yah well no fine. Limited to exploding just before teh rest of what they
are conected to explodes.

No pluse that is tamed by a tuppeny ha'penny surge arerestor will even
cause a modern PSU to blink. If the strike is near and big enough to
trouble it, the surge arressor will be long gone.



There are limits to all forms of lightning
protection. If lightning actually strikes your TV aerial or phone/mains
incomer, then it is almost impossible to avoid some damage - even if it's
only a zapped surge filter!


Indeed. But they tedn to blow open and pass te crap straight through.



Why are those CMOS devices, rated only for tens of
volts, not damaged by million volt lightning strikes?

Most devices in transmitter output stages (and receiver input stages) are,
in fact, rated at hundreds of volts, not tens, but I see the point! They
are not damaged because the designers put in a LOT of effort to fit surge
filtering and suppression between the semiconductors and the exposed bits of
metal.

Actuyally you use opto isolators. CMOS is totally and utterly vulnerable
to even a few tens of volts pickup on lines in or near storms. Soldered
in the chips enough times to tell you that fora fact.

If you want to use CMOS, so it in a metal grounded box with opto
isolators on ALL inputs and outputs.

Transmitters may well be valves still. Valves take lightning strikes
well,. being a sort of controlled lightning strike themselves

With a lot of complec protection even a strke on an antenna can be
reduced to something the power stages can handle, but its damned
expenisve, and only worth it if the call out fee to replace yet another
blown head amp up a mast is too high.,..

..
The worst design scenario is the nuclear emp, where you have to protect
against pulses with a risetime of 50kV per millisecond - this edge is so
fast that it often manages to couple itself round standard protection and
fry sensitive electronics, even inside sealed metal boxes...


Quite right too.

K

A surge that damages modems must have both an incoming and
outgoing path. Without both, then no damage occurs. The same
surge is incoming on every moatherboard IC. Why is every
motherboard integrated circuit not damaged? Clearly the
incoming path exists. But no outgoing path means no IC
damage. To have damage, the transient must first have both
incoming and outgoing electrical path.

Modem has both an incoming path and an outgoing path - phone
line and AC electric. Without both, then modem damage would
not occur. A surge enters on phone line, damages modem, then
stops? Nonsense as taught to primary school science
students. First a complete electrical path must be formed.
Only then does something in that electrical path become
damaged.

It is normal and routine to protect modems from damage. But
protectors adjacent to an appliance do not even claim to
protect from the typically destructive surge. Then some will
loudly proclaim nothing can protect modems? Learn how modems
fail by repairing them AND by learning from manufacturer data
sheets why that component failed. Effective modem protection
- done routinely - is to earth a destructive transient before
it can enter the building. That means 'whole house'
protector, properly earthed, on both phone and AC electric
wires.

The Belkin protector is how one wastes good money on urban
myth recommendations. A surge protector is only as effective
as its earth ground. To make the sale, Belkin avoids the
entire discussion.

The Natural Philosopher wrote:
Paul Hutchings wrote:
I need to get a couple of mains blocks. I can get 4-way Belkin ones with
surge protection (F9H400uk1M) for about £5.50 which is about a quid more
than a normal block costs down the local B&Q.

I'm no electrician, part of me looks at the wave of £30+ surge protectors
out there and thinks they're designed to look pretty and scare people out
of their money, on the other hand I've had enough people bring their home
PCs to me at work because their PCI modem's stopped working after a recent
thunderstorm to think for the sake of a quid more on a mains block I might
as well.

Surge protectors won't protect modems.

The surge that kills the modem is on the phone line, not the mains.

Almost all low voltage PSU's use rectified mains chopped: The capacitors
and RFI chokes in that constitute enough surge protection: In the limit
the PSU goes and that's it.


Anyway, looking around the belkin site there's all kinds of joule and
amperage and db ratings and I'm curious what it all means?

Nothing. They are as useless as electronic water softeners.

I won't be connecting anything out of the ordinary, PC and bits to one, AV
amp/sky/TV/DVD to the other.

It's be nice if any explanations could be "plain english", and not turn
into a "whole house protection" argument as seems to happen on every thread
I've seen on google!

All right then. Surge protectors don't protect against the sorts of
surges that cause real problems . In short they are a ****ing waste of
money.

Plain enough?

:-)

regards
Paul

Primary protection is not inside a building. 'Arcing horns'
and other earthing devices outside building on utility lines
are 'primary' protection for that building. 'Secondary'
protection is an earthing device where utilities enter that
building. Secondary protection demands that all utilities
enter at a common location so as to be earthed by the single
point earth ground (SPG).

A connection to earth ground must be short because wire
impedance is high - when discussing transients. Earthing wire
(from each utility wire to earth ground - sometimes via a
surge protector) must be 3 meters or shorter so that wire
impedance is minimized. That also means no sharp wire bends,
etc because what is low resistance may also be high impedance
to destructive transients. Wire impedance to earth ground
must be minimized for effective protection - a concept that
cannot be over emphasized.

In N America, customer premise telephone lines are routinely
installed with secondary ('whole house') protection. Arc type
protectors have been replaced by superior semiconductor based
protectors. And again, this protector must make a less than 3
meter connection to SPG. A typical N American protector is
shown (it is equivalent to a master socket but includes a
protector):
http://www.alarmsuperstore.com/bw/bw%20connectors.htm

Equivalent products that may be installed on UK premise
interfaces:
http://www.keison.co.uk/furse/furse11.htm

http://www.one.co.uk/catalogue/teleb...otect/22PX.HTM

It is completely wrong to cite 'surge filters'. Nothing
filters a transient that travels kilometers through
non-conductive air (and converts that air to plasma, for those
who need be anal accurate). Protection has always been about
making the lowest impedance connection to earth. Shunt so
that the transient does not find a destructive connection to
earth via household electronics. This is well proven,
pre-WWII technology. This is protection from direct strikes
to nearby wires - as has been demonstrated even in my own
abode. Direct strike with no damage is routine if a human has
learned well proven earthing concepts.

No reason for a direct strike to cause appliance damage if
the incoming wire is properly earthed - either by direct
earthing connection or via a properly sized protector. In the
States, where lightning is a greater problem, such protection
is quite effective. Protection is installed for direct
lightning strikes since lightning is the typically destructive
transient.

Series inductors to prolong the life expectancy of a surge
protector - if the protector was undersized. But that filter
is rarely installed in serious protection because, instead, we
install larger and properly sized protectors. For example, a
minimally acceptable 'whole house' protector selling for about
£22 is rated for 50,000 amps. Since a direct strike would be
seeking many paths to earth ground, including via the utility
'primary' protector, then 50,000 amps is more than sufficient
- especially for the typical 18,000 amp direct strike. IOW we
install effective protection by properly sizing the protector;
not wasting good money on grossly undersized protectors such
as in plug-in power strip and UPS protectors.

Shunt mode protectors do not blow line fuses or circuit
breakers. The transient is for microseconds. It takes more
than milliseconds to blow fuses or trip circuit breakers.
When fuses / circuit breakers do trip, it is often due to
follow-on currents created by a damaged appliance. Again, if
the direct lightning strike causes surge protector failure,
then a human has installed a grossly undersized protector.
Protectors are installed for protection from direct lightning
strikes (without protector damage) which is why protection
from other transients is irrelevant.

Since plug-in protectors are not installed for the typically
destructive transient, then the plug-in product is often
undersized as well as overpriced. The manufacturer provides
no dedicated connection to earth ground and avoids discussion
of earthing. Why discuss the most critical component of a
surge protection system if the product does not even provide
that necessary connection? Plug-in protectors are grossly
over priced (on the order of tens of times more per protected
appliance) and do not even claim to provide protection from
the typically destructive type of surge. Protection is about
shunting to earth - which plug-in protectors do not even claim
to accomplish.

A single point earth ground is THE most critical component
in a protection system. Surge filters are not effective.
Protection is by shunting. Any product that does not provide
that earthing connection and avoids all discussion about
earthing is, by definition, ineffective.

Surge protector is only as effective as its earth ground.
No way around that fundamental concept. No earth ground means
no effective protection. Plug-in protectors hope we don't
learn about earthing and about that less than 3 meter
connection to earthing. Concepts discussed previously in
nz.comp at
http://tinyurl.com/5ttwl

Ken wrote:
"w_tom" wrote in message
...
A surge protector will 'stop' what kilometers of sky could
not?
Indeed it can. The cloud/lightning/cable/earth system forms a voltage
divider: so long as the impedence from cable to ground is significantly
lower than that of the lighning strike, then the voltage will be
(relatively) low.

The main components of the impedence in the divider a
- the resistance of the air to the strike. This is quite low once the arc
is extablished.
- the resistance of any spark gaps to ground. Again, quite low once the arc
is struck.

Power lines are equipped with arcing horns to encourage the ground arc to
strike, so the peak spike voltage once the ground arc has struck is probably
about twice the peak mains supply voltage.

There is a short period between the lightning strike and the ground arc
striking when the voltage on the line can rise to many times the supply
voltage.

Telephone lines don't have this protection, but they do have little green
boxes with very small gaps between the connections inside, which also
encourage arcs, and will certainly have surge suppressors somewhere,
probably at the exchange.

From the strike point to the equipment to be zapped, the main impedence
components a
- The inductance of the cables
- The capacitiance of the cables to ground.
These form a low-pass filter that will tend to spread out the energy pulse,
reducing amplitude and rise/fall time and increasing duration.

Hence, fitting a surge suppressor (only) in a domestic situation will help
if the strike is some distance away - the further the better. It won't help
much is the strike is on the phone wires leading from your local pole to
your house!

If you think that you're at real risk, you can buy commercial units (for
rather more than 69p) which contain a spark gap, a series inductor and a
parallel surge protector. These, if connected to a GOOD earth, will filter
out all but the biggest surges. They are available for power, phone, TV
aerial and data lines.

insult snipped

It is routine to suffer direct strikes without damage even
in regions that have more serious lightning storms.

True, but these systems are designed with lightning strikes in mind.

But the
basic concepts must be understood. Plug-in protectors avoid
all discussion about the most critical function in protection
to sell their ineffective but so profitable products.

These devices are NOT inneffective. The worst you can say is that their
effectiveness is limited. There are limits to all forms of lightning
protection. If lightning actually strikes your TV aerial or phone/mains
incomer, then it is almost impossible to avoid some damage - even if it's
only a zapped surge filter!

Scientists measure direct lightning strikes to a
communication tower atop Hoher Peissenberg in Southern
Germany.

And? What is your point here? Engineers regularly monitor lightning strikes
(and induced surges) on a wide range of systems, including mains supplies,
transmitting & receiving masts, phone systems, water and gas distribution
pipes

Why are those CMOS devices, rated only for tens of
volts, not damaged by million volt lightning strikes?
Most devices in transmitter output stages (and receiver input stages) are,
in fact, rated at hundreds of volts, not tens, but I see the point! They
are not damaged because the designers put in a LOT of effort to fit surge
filtering and suppression between the semiconductors and the exposed bits of
metal.

snipped

Do not confuse the protector with protection. They are
separate devices of a protection system. A protector is only
effective when connected short to protection. That protection
is earth ground.

Active surge protectors are normally connected as shunts (i.e. between the
cable to be protected and ground) and normally present a high resistance as
long as the voltage across them does not exceed a particular threashold,
after which they present a virtual short until the voltage drops back to
almost zero. Hence, they need a series impedence (such as an inductor) to
work repeatedly - if they are connected straight across the mains, they will
short the incoming power to ground as well (for the current half-cycle, at
least) and the current may well overheat them. As they are designed
(usually) to fail short, this will probably blow the incoming supply fuse.
Special devices are needed for telephone systems that have a switch-off
voltage higher than the applied DC, otherwise they stay on for ever once
triggered.

A surge protector is only as effective as its earth ground.

Very true. Earth connections must present not only a low DC resistance to
ground but be capable of carrying more current than the protected cable and
also present a low dynamic impedence. The latter requirement means that the
earth connection should be as short and direct as possible. This tends to
reduce the effectiveness of distribution-board protection where the
protected appliances have an alternative path to ground, due to the
relatively high dynamic impedence of most domestic earth wires. Hence
'protected' TVs, for instance, will often be damaged during a strike on the
aerial by arcs developing between the chassis of the TV and any nearby
earthed metal, such as central heating pipes.

snip

snip I, personally think they are all
a waste of money, but you pays your money etc....

As I said earlier, there is very little that you can do to protect against
direct lightning strikes, but most surges are either induced spikes, where a
strike on a pole causes a large voltage gradient down the pole and across
the nearby earth, and this capacitively couples into the affected cabel, or
mains switching transients. Despite the careful design of substation
switches, you still get arcs when circuits are broken and the surges these
produce can never be completely suppressed at source. These surges have a
much higher source impedence and so can more easily be filtered and
suppressed.

The worst design scenario is the nuclear emp, where you have to protect
against pulses with a risetime of 50kV per millisecond - this edge is so
fast that it often manages to couple itself round standard protection and
fry sensitive electronics, even inside sealed metal boxes...

K

All electronic appliances have sufficient protection. Any
protection that would work at the appliance is already inside
that appliance (which again is why plug-in protector are not
effective). Protection that assumes an incoming transient
will be earthed before entering the building. If this was not
true, then every telephone switching center, connected to
overhead wires everywhere in town, must shutdown to protect
the £million machine. BT does not do that. Why? BT earths
every incoming wire. Therefore no damage. Protection is that
routine and that effective when earthing is the protection.

When damage results from thunderstorms, the learned human
then starts at the earthing system. Protection from direct
lightning strikes is routine and well published.
Unfortunately too many fail to learn reality and just keep
repairing the equipment. We who acknowledge that lightning
damage is directly traceable to human failure suffer direct
lightning strikes without damage. Its called learning from
your mistakes - earthing the incoming transient:
http://www.harvardrepeater.org/news/lightning.html
Well I assert, from personal and broadcast experience spanning
30 years, that you can design a system that will handle *direct
lightning strikes* on a routine basis. It takes some planning
and careful layout, but it's not hard, nor is it overly
expensive. At WXIA-TV, my other job, we take direct lightning
strikes nearly every time there's a thunderstorm. Our downtime
from such strikes is almost non-existant. The last time we
went down from a strike, it was due to a strike on the power
company's lines knocking *them* out, ...
...
The keys to effective lightning protection are surprisingly
simple, and surprisingly less than obvious. Of course you
*must* have a single point ground system that eliminates all
ground loops. And you must present a low *impedance* path for
the energy to go. That's most generally a low *inductance*
path rather than just a low ohm DC path.

Electronic power supplies are typically rated to withstand
transients approaching 2000 volts. Optocouplers are also
sufficient only for same voltages. Appliances have sufficient
internal protection that assumes the destructive direct strike
will be earthed before it can enter a building. If not, then
internal appliance protection can be overwhelmed. Effective
protection assumes the secondary or 'whole house' protectors
are properly earthed. In the UK, such protection rarely
exists which is why homeowners uselessly suffer damage. In
other places, people just assume a 'woe is me' attitude and
keep fixing damaged components. Its also called job security
when the boss is also technically ignorant.

The Natural Philosopher wrote:
w_tom wrote:
A surge protector will 'stop' what kilometers of sky could
not? Victims of ineffective protector myths (such as Mike
Tomlinson) who promote these half truths. (Mike will reply
with insults to prove his technical superiority).


Blimey...what a load of waffle.

Look, I've worked in Africa, where storms are frequent and severe, and
believe me, nothing stops even a near miss from buggering up anything
connected to a long piece of wire in the vicinity of a ground strike.

In the end, opto isolators and line transformers for audio seemed to
reduce but not eliminate returns, and replacing the opto panel was
cheaper...

When I returned to the UK, I DID get struck by lightning. Took out the
overhead phone line and reduced it to a smear of carbon across the road.

What went?

Well, the modem was toast, and the serial/parallel card it was plugged
into. And the input side of the laser printer plugged into THAT. The
lightning then jumped into the mains wiring and raced round the house. I
lost the PSU on a laser printer, I lost a CMOS chip on a digital hi-fi
turntable, and I lost the digital stuff on a TV - but it was old and
went in the skip.

The high stuff survived, as did most of the computer.

The carpet got a bit burnt where some mains cables ran underneath and
over it.

An unused aerial socket connected to nothing was blown to pieces and out
of the wall, as was an unearthed mains socket some cowboy had wired in
on two core cable.

In all it cots me about 300 quid to get everything fixed, including new
second-hand TV.

The landlord got the cottage rewired on the insurance since he felt it
was a good idea and argued that after a strike like that he wouldn't
want to be responsible for its condition.

Surge arrestors are a complete waste of time. Every BT phone socket has
one. They don't work against a direct strike, or even a near miss. They
sort of work a bit when its vaguely in the area.

In general a near miss on my overhead power lines here, causes the RCD
to trip.

The greatest danger to computers is a momentary loss of power as the
mains goes off, followed by auto reconnect, followed by a second loss of
power when the grid discovers the branch is still on the line etc.. If
the computer is set to auto boot, that generally crashes the disk head
JUST in the middle of the boot sector or close to it.

Lost two computers operating systems that way, one past all recovery.

Paul, those surge suppressors are rather pointless as
a) computers and electronic power supplies have more effective
protection built into them already,
b) theyre not very useful against direct or indirect lightning
strikes,
c) lightning is a tiny risk that, if it does strike, you can do very
little about, short of spending real money upfront.

They _are_ effective against surges caused by large dirty industrial
loads, or small dirty loads running on small unfiltered private
generators, but very few houses have either of those to deal with.

Youll get more joy spending your 69p on a cup of tea.



OK, why not...

"Ken" wrote in message ...
"w_tom" wrote in message
...
A surge protector will 'stop' what kilometers of sky could
not?
Indeed it can. The cloud/lightning/cable/earth system forms a voltage
divider: so long as the impedence from cable to ground is significantly
lower than that of the lighning strike, then the voltage will be
(relatively) low.

that simply doesnt follow. 1 million volts divided by 10 is still
death to anything it touches. Or divided by 100...


The main components of the impedence in the divider a
- the resistance of the air to the strike. This is quite low once the arc
is extablished.
- the resistance of any spark gaps to ground. Again, quite low once the arc
is struck.

dont forget the wiring inductance to earth, which is the real killer
to your voltage divider idea.


Power lines are equipped with arcing horns to encourage the ground arc to
strike, so the peak spike voltage once the ground arc has struck is probably
about twice the peak mains supply voltage.

There is a short period between the lightning strike and the ground arc
striking when the voltage on the line can rise to many times the supply
voltage.

Telephone lines don't have this protection,

they do since 1930. Before then, people were killed occasionally by
using the phone during a storm.

but they do have little green
boxes with very small gaps between the connections inside, which also
encourage arcs,

nope, white boxes with white gas discharge tubes, GDTs. PCB gaps went
out with the passing of dial phones in the 80s.

and will certainly have surge suppressors somewhere,
probably at the exchange.

From the strike point to the equipment to be zapped, the main impedence
components a
- The inductance of the cables
- The capacitiance of the cables to ground.
These form a low-pass filter that will tend to spread out the energy pulse,
reducing amplitude and rise/fall time and increasing duration.

Hence, fitting a surge suppressor (only) in a domestic situation will help
if the strike is some distance away - the further the better.

this just doesnt logically follow. Run some numbers and see.

It won't help
much is the strike is on the phone wires leading from your local pole to
your house!

If you think that you're at real risk,

youre not, not in UK.

you can buy commercial units (for
rather more than 69p) which contain a spark gap, a series inductor and a
parallel surge protector. These, if connected to a GOOD earth, will filter
out all but the biggest surges.

not really, lightning makes mince meat of everything it touches. It
isnt going to take the slightest notice of the insulation on that
inductor. Lightning makes whole wiring systems light up like christmas
trees.


It is routine to suffer direct strikes without damage even
in regions that have more serious lightning storms.

True, but these systems are designed with lightning strikes in mind.

certainly not true in UK. If you do get hit, your entire eletrical
system is toast, try and reuse it at your peril.


But the
basic concepts must be understood. Plug-in protectors avoid
all discussion about the most critical function in protection
to sell their ineffective but so profitable products.

These devices are NOT inneffective. The worst you can say is that their
effectiveness is limited.

wrong again, could say much worse.

There are limits to all forms of lightning
protection. If lightning actually strikes your TV aerial or phone/mains
incomer, then it is almost impossible to avoid some damage - even if it's
only a zapped surge filter!

There isnt any hope of it being just a zapped surge filter, we're
talking over a million volts. If it strikes anything on the house, its
toast time. The insulation in domestic wiring and appliances means
very little to lightning.


Scientists measure direct lightning strikes to a
communication tower atop Hoher Peissenberg in Southern
Germany.

And? What is your point here? Engineers regularly monitor lightning strikes
(and induced surges) on a wide range of systems, including mains supplies,
transmitting & receiving masts, phone systems, water and gas distribution
pipes

Why are those CMOS devices, rated only for tens of
volts, not damaged by million volt lightning strikes?
Most devices in transmitter output stages (and receiver input stages) are,
in fact, rated at hundreds of volts, not tens, but I see the point! They
are not damaged because the designers put in a LOT of effort to fit surge
filtering and suppression between the semiconductors and the exposed bits of
metal.

wrong again.


Do not confuse the protector with protection. They are
separate devices of a protection system. A protector is only
effective when connected short to protection. That protection
is earth ground.

Active surge protectors are normally connected as shunts (i.e. between the
cable to be protected and ground) and normally present a high resistance as
long as the voltage across them does not exceed a particular threashold,
after which they present a virtual short until the voltage drops back to
almost zero.

Those are passive surge protectors.


A surge protector is only as effective as its earth ground.

Very true. Earth connections must present not only a low DC resistance to
ground but be capable of carrying more current than the protected cable and
also present a low dynamic impedence. The latter requirement means that the
earth connection should be as short and direct as possible.

ah! correct.

This tends to
reduce the effectiveness of distribution-board protection

Domestic CUs havent been called distribution-boards in a very long
time.


where the
protected appliances have an alternative path to ground, due to the
relatively high dynamic impedence of most domestic earth wires. Hence
'protected' TVs, for instance, will often be damaged during a strike on the
aerial by arcs developing between the chassis of the TV and any nearby
earthed metal, such as central heating pipes.

often?


snip I, personally think they are all
a waste of money, but you pays your money etc....

As I said earlier, there is very little that you can do to protect against
direct lightning strikes,

indeed, it can be done but is not worth the high expense. Such
protection is more suited to commercial broadcasters and power
utilities.

but most surges are either induced spikes, where a
strike on a pole causes a large voltage gradient down the pole and across
the nearby earth, and this capacitively couples into the affected cabel, or
mains switching transients. Despite the careful design of substation
switches, you still get arcs when circuits are broken and the surges these
produce can never be completely suppressed at source. These surges have a
much higher source impedence and so can more easily be filtered and
suppressed.

those arent a problem here, you dont need a little box to deal with
them.

The worst design scenario is the nuclear emp, where you have to protect
against pulses with a risetime of 50kV per millisecond - this edge is so
fast that it often manages to couple itself round standard protection and
fry sensitive electronics, even inside sealed metal boxes...

I suspect thats a non issue for domestic apps.


w_tom, if you put real numbers to your arguments, a few things would
become clearer. And some of what you say simply doesnt line up with
British practice.


NT

The greatest danger to computers is a momentary loss of power as the
mains goes off, followed by auto reconnect, followed by a second loss of
power when the grid discovers the branch is still on the line etc.. If
the computer is set to auto boot, that generally crashes the disk head
JUST in the middle of the boot sector or close to it.

Amen to that. Even better are power supplies fitted with a bizarre
semi-autosensing-powersupply, which works out whether it's on 110V or
240V, and seems to select power transformer taps "appropriately".
Brilliant design when a brownout on the 240V supply makes the thing
decide it's moved across the Atlantic, and then the voltage comes back
up to 240V after a few seconds...

Even yer green-CD-pen wound-by-virgins oriented-crystal
oxygen-free-copper power conditioner won't help with that one!

In article , w_tom
writes

Victims of ineffective protector myths (such as Mike
Tomlinson) who promote these half truths.

I seem to have got under your skin. Good. Anything to counter the
lies, slander, evasions, half-truths and distortion of facts that you
post.

Your unique 'demented rant' posting style on a single subject simply
makes it look like you have an axe to grind and allows you to avoid
direct questions. If you want to appear at all credible, post in-line.
The convention in uk.* is not to top-post: http://www.usenet.org.uk/ukp
ost.html

HTH. HAND. FOAD.

--
..sigmonster on vacation