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 on 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 firs level of defense. This layered defense method has proven highly reliable in commercial communications systems where radio towers are subject to severe dire lightning strikes. Even with such severe EMP and direct surge conditions which excede 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 singe junction device similar to an avalanch diode. Its maker is National Semiconduc 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 VDC 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 w 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 recomend 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 avalanch diodes.