Understanding Electromagnetic Pulse
and
How to Prevent Resulting Damage to Electrical Equipment
by Joe Bobier

One  of  the  many  fables of nuclear war that has been worn out in an effort to convince us all of the futility  of  it  all  is  EMP.  When understood, the problem can take on realistic proportions.

When  a  nuclear  explosion occurs, a very broad spectrum of energy is released. It ranges from nearly  DC  (o  KHZ)  to  beyond  1021  hertz (gamma  rays).  The  portion  concerned with here ranges from 0 KHZ to 1000 GHZ (beyond radar uses).

Two  basic  sorts  of  damage can occur as a result of EMP. The first being what we will call " power line " type of damage, and the other  being  what I'll  call  "  radio  "  damage.  Power  line  damage is resultant from the induction of high levels of current into relatively long wires such as home or shelter wiring, electrical generating system wiring such as  the  cables running  to and from PV ( photovoltaic ) panels, generators, windmills, and of course in the already famous auto electronic ignition system. This  type of  damage  can  be  virtually  eliminated  by a multi-level approach, that provides front line defenses, and various levels of backup systems  in  the event  that  EMP  should  overcome the first level of defense. This layered defense method has proven  highly  reliable  in  commercial  communications systems  where radio towers are subject to severe direct lightning strikes. Even with such severe EMP and direct surge  conditions  which  exceed  most predicted  EMP  conditions,  the  communications  systems survive often for years of storm seasons.

The first layer of EMP defense is the THYZORB. This is a solid state single junction device similar  to  an  avalanche  diode.  Its  maker  is  National Semiconductor, and it is distributed by Square D. You should purchase these devices  specifically  matched  to  the  type of system voltage you wish to protect. For instance, if you wish to protect  a  12  VDC  PV  system,  you should  consider  that the open circuit voltage of most PV panels is around 19 VDC so a 25 VD  C  THYZORB  would  provide  excellent  protection.  Also remember  that  as  the  amount of current through the device increases, so does the voltage drop across the device. Generally about 10 VDC  is  to  be expected  at  maximum  rating,  thus we can expect that no more than 35 VDC will develop at the protected area.

I would place a Thyzorb on each panel at the output terminals and then  one more  at the junction of the panels where your main feed line is connected. The THYZORB is available in many power  ratings  from  1.5  KW  to  15  KW.  Generally  you should be safe with the small ones on the panels, and the 15 KW unit at the junction point. At the other end of the feedline add another THYZORB just as the first one at the junction point was.  The  device  only has  two connections on it which are placed directly across the lines to be protected.  Under  normal  conditions,  the  unit  has  no  effect  on  the circuitry.  The  unit  is  reliable  and  re-useable.  After  thousands  of
operations, it will still be as good as new. The reaction  time  for  those who  wonder  about  such things is about 10 nano seconds. In the event your cables are longer than ten feet or so, it wouldn't hurt to  add  a  THYZORB
every  ten  feet.  THYZORBS are available in many voltages and in AC or DC.

This means you should be installing them in any AC lines such  as  inverter outputs  or  generator  outputs.  I  would put one in every wall outlet and light fixture also. Now for the layered effect I mentioned earlier.

In the event the THYZORB fails you need to have another device in place  to soak  up  the  balance of the surge. In low voltage DC systems your choices are somewhat limited. You could use an MOV ( metal oxide varistor ).  These are  devices  made by General Electric. They are widely available at stores like Radio Shack. The only problem with MOV's is that every time they  fire (see  a surge) they drift in value a little. Pretty soon your surge stopper isn't turning on at the right time or worse yet fails  altogether.  In  low voltage systems, you can't really use a gas discharge tube, since they only work  at  150  volts  or higher. By then your low voltage equipment will be fried. Instead, at the risk  of  sounding  redundant,  I  recommend  another THYZORB  but selected at a slightly higher voltage. Five volts higher would be a good choice since the second one would only fire if the first one were
working at 1/2 of its full capacity. This would  cause  a  current  sharing condition  and  increase overall device reliability. You could in theory go several layers in this manner until you felt completely safe,  or  you  ran out  of  EMP  money.  The  actual  connections would be to earth ground the negative (-) side of your DC power system in several  locations.  Use  long bronze, brass, or copper rods with heavy, short cables to the power system. Next  attach  the  negative (-) side of the protection device, ( THYZORB or other ), to the ground system. Finally, attach the  positive  side  of  the protection  device  to  the  positive  side  of  the power system. In an AC system, you can do exactly the same as above with proper device  selection.

You may also use a gas discharge tube here since we are dealing with a high voltage to start with. In this case you will have three wires to deal with; one  for  each  side  of  the  AC,  and  one  for  earth ground. Additional preventive measures include  grounding  the  frame  of  the  PV  panel  and grounding  generator  frames.  A good earth ground is very important if you use gas discharge tubes. If scenes from the " DAY AFTER " have you paranoid about being trapped in an immobile car, then take heart. You can EMP  proof your  auto  electrical  system  the same way as your low voltage DC system.

Just put a couple layers of THYZORBS or MOV's across the DC  input  to  the ignition  system.  A few more sprinkled here and there like the power wires of your CB radio, or your AM/FM receiver will work wonders. An easy way  to reduce the risk of appliance damage in your home or shelter, if it is an AC device  is to use a personal computer style surge protector. They are cheap and very easy to install. Most of these devices use  MOV's  or  better  yet THYZORBS or avalanche diodes.

Original at: http://www.geocities.com/HotSprings/Falls/1984/emp.htm