I have several steel cabinets, including filing cabinets, I keep the electronics in .
I have a question,.
Why would you want to attract an electric charge to the box by grounding it.
In amature radio ,the best transevers are grounded the worst (hand held ) are not .
By grounding ,one is assured that the charge will definately strike the box going through and past it.
Where as , by being ungrounded ,the magnetic pulse has no draw to it what so ever accept that it is metal, and would disapate just as quickly .
With lightening the rule is to create the least attention poassable ,and during an event unhapily being caught in it , the best move is to place your feet as close to gether as possable ,because the ground is a shunt , and the body being mostly water and minerals is a better conductor the charge will leave the ground in it route of travel and pass through the body to the leg closest to the heading it has chosen .
The closer your feet are together the less of a charge will choose the body, and of course the reverse is true. Running is very bad.
Point is, grounding insures a hit, like a lightening rod.
Any thoughts ?
Several key items you've touched on, and they are all very different and should not be confused with each other. While each of the above listed items has components of the other in it, the method of protection is built on different concepts and theory.
1. Lightning. Primarily an electrostatic effect. It's high voltage and current will go everywhere it feels like; with no rhyme or reason. Ground path or not, but you can help dissipate the electrostatic field that becomes the starting point for a lightning attachment by keeping all metal things grounded. Or, better, yet, have lightning rods for lightning, and electrostatic and EMI/EMP grounding for EMP. Never tie them together, or even close together, in any way, even in the ground.
2. EMI. Electromagnetic interference. Key word here is interference. It's the fuzz that finds its way onto your receiver, it's the whine in my car radio when I plug my cell phone charger in. It's a lot of things, but for the most part, it's an annoyance bordering on malfunction. In conjunction with some pretty sophisticated filtering algorithms, it can can also be a source of key information to someone else who wants to monitor your transmissions. Most EMI protection components are designed with specific frequencies and sources in mind, and only have to attenuate just enough to allow continued operation.
3. EMP. Electromagnetic Pulse. A indescribably large electromagnetic pulse whose magnetic fields generate electric currents in conductors where those magnetic lines cross. Those currents again, in turn, create magnetic fields and the process continues until it runs out, which thanks to electric lines running across the country, will go for thousands of miles and touch billions of devices even further than that. The phenomenal power generates very high frequencies and amplitudes, which overpower the EMI protections built into just about every existing electronic device. Long power lines act as antenna, retransmitting the signal even further out, hence the cause of the spread of the signal.
Got a key bit of information to understand here. There's a term used in electrostatics called isolated conductor. In a nutshell, it means a conductive object that can store an electrostatic charge, and has no external path to ground. Now, if there _is_ a path to ground, and it's a tiny wire that routes through your house wiring to the circuit breaker panel, it will drain low frequency voltage and high frequency signals of low power to ground. However, due to inductive issues, a high frequency signal of high power may not even "see" the ground path, so in essense, it acts as an isolated conductor. A ground lead needs to be short relative to its wavelength, preferably less than 1/4 wavelength, and when your wavelength is in the millimeters, you have a problem. The other thing is that high frequencies tend to travel along the outside surface of a conductor, rather than through the center (skin effect) so you want maximum _surface_ area in lieu of maximum wire cross section (such as wire gauge.) If you were to look around the cell phone towers that dot your area, you'll see wide, flat straps of copper for grounding rather than skinny wires normally used for low frequency applications like homes and TV's and such. The coaxial cables actually have hollow conductors, which, due to the skin effect, saves a ton of unnecessary copper. If you need to ground a system for high frequency and high power, you want to maximize the surface area of the conductor and minimize its inductance and imedance, and to do that, you need the widest conductor strip that's practical and have the least number of bends or direction changes in it. The longer the ground lead, the more of an antenna it will be, and the more that lead itself will retransmit electromagnetic signals.
For the record, I'm not an expert in this stuff, nor have I been trained in the field. I do, however, work with this technology for a living (among other cool physics stuff, quite often all at the same time) and have a very strong practical understanding, as well as the ability to translate the concepts into lay terms.
Some useful articles about grounding:
http://www.gacopper.com/Link.html
By the way, if any of your devices has any leads that come out of your faraday cage to go to wall power, the internet, or phone, you've just defeated the entire purpose of the cage. There are ways around that problem, but you need a very specialized education to do a good job.
Unfortunately, there is far more ignorance than understanding on the topic of EMP. Every time I do a little research on some detail or the other, I have to sift through pile of articles written by people who know just enough to be dangerous, or worse, things like folks who sell metalized plastic bags (made for EMI attentuation) as EMP shields, making money off of the ignorance of the masses. Either they're ignorant and selling what they think is a legitimate product, or they're intentionally getting rich off of the gullible masses who fall for the fluff like snake oil, cryonics, global warming, Barack Obama, and so on. Buyer's remorse may come in time, it may come with damages, or it may come too late. With doomsday oriented products, buyer's remorse will really suck, unlike still being able to vote in 2012.
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