In fact, everybody using any sort of electronic equipment
in any region of this Map is also subjected to
MAN MADE NOISE.
And the modern technology has given us some technical devices to take care of such type of problem.
Problems arise from two major sources.
* Overvoltages induced by lightning strokes striking
directly on the energy (or transmission) lines.
* Overvoltages conduced by your local energy (transmission)
network from a direct stroke on the building.
In that case, everything could occur from 'nothing' to complete destruction of any 'Silicon Inside' device within a short area.
In both case, surges arresters may help you to preserve integrity of human/silicon relationship.
And in many case, putting some sort of surge arrester anywhere in your energy/transmission network is not the worst thing you can do.
But a little comprehension of the how and why of such
surge arrester could greatly improve their effectiveness
by chosing a strategic placement for this device.
SURGE ARRESTERS
WHY
HOW
Considering the first case of induced lightning which
is far from utopic in our european countries.
The main purpose of a surge arrester is to act as a
diverter (some sort of escape door) for the high energy
pulse induced by lightning stroke.
And as every inch of the perturbed line may conduct
this energy, you must place the surge diverter at a
point where it can conduct energy directly to a ground/earth
reference without interfering with your precious equipment.
In fact you must place a primary surge arrester directly
on the entrance point of your energy line (location
called C - Outside and service entrance - in some ANSI
and IEC standards).
HOW AGAIN
And after, and only after , you could install some sort
of direct Plug-In secondary surge arrester in your
wall outlet to protect particular equipment (or small
network).
Avoiding the use of primary arrester while using secondary
arrester is a good way to give a path for the surge
energy with the secondary effect that every equipment
connected is subjected to the overvoltage coming from
the outside lines, going through the secondary surge
arrester and back again to the ground wire and finally
short-circuited by a solid grounded connection.
After choosing a strategic place for the main surge
arrester, you have to connect it to the line to be
protected.
Again, you must know some facts about surge arresters.
* Firstly, they acts only when the voltage on the line
increase to a fixed level called 'Clamping voltage'.
* Secondly, they conduct energy (that is current flow
generated by a voltage level in a given time interval)
contained in the incoming pulse to a ground connection.
But the grounding wire used show what is called a line
inductance proportional to his length. And the speed
variation of current (dI) in a short time interval
(dt) generate a transient voltage proportional to the
self inductance (L) of the grounding wire.
As the transient currents induced by lightning shows
typically a rate of rise of 100 A to 1000 A by microsecond,
and the inductance of a single 3 feet wire AWG 16 is
about 1,5 microHenry we could measure a peak transient
overvoltage of 150 to 1500 V developed between each
extremity of the grounding wire (which is highly destructive
for interface devices working with voltages of only
few volts).
So, the ground wire distributed to any of the domestic
wall sockets must come from the arrester ground plug
and not from the physical grounding/earthing connection.
Protection scheme and grounding
FILTERS
This phenomenon has other effects when using surge arresters/filters
with series inductances to filter voltage transients.
You must be careful that every equipment of a computer
workstation (ie:UC,monitor,printer, HD or CD ROM drives,
etc) which are all connected through low voltage data
transmission lines (ie:RS232/422 or SCSI) must be plugged
on the same side of the surge arrester/filter (preferably
the output :).
I must mention that AppleTalk networks used by Apple
Macintosh computers are less sensitive to current
loops due to the decoupling of AppleTalk boxes (as
is Optical coupling like Midi interfacing of musical
instruments )
Tests I've made on PhoneNet and Appletalk boxes shows
good handling of most medium level surges but this
may not be the case with third party low cost devices.
All this because transients voltages caused by transients
currents across the series inductance of the filter
generate transient loop currents in the other wires
used to interconnect the computer and his peripherals.
As a side effect, it is a good thing to choose a filter
with a line current greater than necessary , allowing
easy add of new peripherals.
UPS's
Sometimes, pleople ask me for a good UPS (Uninterruptible
Power Supply) to prevents disasters caused by surges
current.
In all case, an UPS is not a surge arrester. Furthermore,
while some UPS claims to incorporate some sort of surges
arresters,there is two reasons to avoid this solution:
1 - Arresters fitted inside UPS consist of one or two
low energy components used principally for the commercial
appeal they present
2 - it is always a bad thing to give a way for current
surges inside an electronic equipment.
So , keep surges outside with a stand alone arrester,
and use UPS only for problems with continuity of power
supply furniture.
There are many other fact to take care in designing
a good protection scheme but her are the most importants
and easy to apply.
Allways remember that surge destruction by lightning
are not a fatality and that there are technicals solutions
for about 99% of the problems.
I hope that your are in the 99.
And may be, one stormy day, after a big shot on your installation, you could upgrade your Definitely Out of Service computer to a more friendly MAChine .
PS :I must mention that Apple Macintosh computer networks
are less sensitive to current loops due to the decoupling
of AppleTalk boxes.
Tests I've made on PhoneNet and Appletalk boxes shows
good handling of medium level surges but this may not
be the case with third party low cost devices.
Original file name: Surges