Surges and Spikes

IF YOU RESIDE somewhere in a dark blue area of the World Map behind
Keraunic levels
you are subjected to be hassled by

GOD MADE NOISE

but, you can stay in place.

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
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.

WHY
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).
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.

HOW AGAIN
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.


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Original file name: Surges