What is a “Faraday Cage” and How You Can Build Your Own Cheaply and Easily from Common Everyday Items.
This is a bubba-fied explanation of what it is, what it does, and how to build an effective one. If you’re going to cite this as a source in your college research paper, you’re nuts.
Electromagnetic Pulse (aka EMP) or a Coronal Mass Ejection (CME) from our sun produce high powered electromagnetic ‘rays’ that are very damaging to electrical and electronics based equipment.
Rubbing your bare feet across the carpet generates a significant electro static potential that you feel when you then touch something metal like a door handle – that spark is a discharge of roughly 4,000 volts to 35,000 volts. Lightning cracks across the sky are 10,000 volts and more . YES, the voltages created from you rubbing your feet and lightning is roughly the same but there is an ‘umph’ factor behind the voltages that I could explain but do not want to have anyone’s eyes cross.
Ever tried to heat up some Earl Grey with your DW’s gold trim porcelain tea cups in the microwave? Did you notice the fireworks from that boneheaded move? For comparison EMP is both similar and different to the above but much more powerful the closer to ground zero one is, and CME could not only be up to EMP powerful but is also sustained – the Earth could be in the sun’s blast zone for hours or days whilst an EMP burst is miliseconds. EMP from a nuclear detonation can still be higher than 100,000 volts hundreds of miles away.
What this electromagnetic energy does is to create (‘induce’) energy potential (voltage) in equipment even when it is not plugged in. This is bad, as not only is this not controlled (like plugging something in backwards the energy doesn’t go in the correct pathways and it burns up) but also that that energy could very easily exceed tolerances of the components of the equipment – something as low as 30V inducement could irreparably damage electronics. And electronics are everywhere, and are needed for/included in electrical systems like your car, generators, central air conditioners, etc.
If that electronic control goes kaput it is hard if not impossible to get that electrical system it controls/manages to work. Furthermore, susceptibility of electronic memory components needs to be considered: even if the electronic memory component physically survives the inducement there is a strong chance that the critical programming codes it contains may be altered enough to ‘break’ it! Your Kindle or laptop may survive undamaged but the software it needs to power up and run would be corrupted enough to make it useless and its data irretrievable.
To be honest, until there is a detailed study of a modern day nuclear detonation near a population center I do not believe the magnitude of EMP effects are truly understood, anticipated or expected – I can only fantasize about what the results are and believed that most experts just don’t know every cause-and-effect nor the true extent of the damage (the good-stuff data is Classified). Yeah, there was Project Starfish Prime in Hawaii, but that was more of an incidental byproduct and not specifically set up to be monitored – “uugh… Honolulu just called and said their streetlights all went out; did we just do that? Yes, but let’s call it part of a study so Congress will fund it. Ka-ching!” I do recognize EMPs and CME events as being catastrophic no matter what.
So how does one protect his precious ham radio, her dc/ac inverter, or their computer from these high energy discharge events? While some special equipment can be ‘hardened’ by design the chances of you acquiring this military-grade engineering or old-school manufacturing is not expected. Automobiles and airplanes used to be made without electronics; today nearly everything is and today’s products are soundly engineered using the least amount of material necessary in its construction. Great for cost savings, but no wiggle room for extra capacity.
Grandpa’s wire wound antenna I inherited in his vacuum-tube based radio weighs more than my entertainment center – this is the old-school manufacturing that I am referring to. The wiring in those old electrical systems would be considered over-engineered in today’s standards; they were bigger back then and those bigger wires can conduct more power through them before overheating and burning out. Hardening and modern RF shielding is a whole ‘nuther bag of beans topic-wise, and this is just a brief snippet to show contrast to the other option.
…and that other option is to Shield it. There is a reason UFO nutters wear tinfoil hats – it is actually sound physics in shielding from electrical waves; however, unless it is properly Grounded then it is useless. So do you truly know what ‘grounding’ is?
Earth ground is special in that it is ASSUMED to be able to absorb an unlimited amount of Current without changing its potential (Voltage). Another way of saying it is that earth ground is always ASSUMED to have zero volts, no matter how much current/power it is subjected to. Electromagnetic radiation continues to propagate until dissipated through earth ground… err… it travels until stopped by the earth.
Let us assume the equipment is plugged into the wall outlet and is exposed to EMP. This means that is being zapped and induced with ~100,000 volts of energy, more than likely turning whatever was plugged in into a heavy paperweight. Light bulbs will explode, electronics will pop n fizzle, and if it was already running then it may catch fire.
Not to mention that the power lines are already saturated with its own induced energy, causing further mayhem and destruction. “But I had it turned OFF” you say; well, unfortunately most On/Off switches only opens one leg of the circuit loop so that induced power will flow through the ‘neutral’ just like if it was running (and destroying it) or it will flow at the speed of light through the ‘hot’ and then to another piece of equipment you have running and THEN back to earth ground.
It still go ‘poof’. Or it may even arc the distance across the leads of the On/Off switch. Multiply this effect by all of the items you have plugged into the walls of your house, then all of the houses tied in to your electrical grid. Many, many ‘poofs’. Even if the mains breaker on your house trips you’re still left with 100,000v inducement in the house wiring.
“So just leaving it unplugged will protect it, right,” you ask? Not really. Let us say you’ve got a nice 1000W dc inverter tucked away on a shelf. It will still get zapped by 100,000 volts, but that induced energy potential doesn’t go anywhere until that energy potential is great enough to overcome the resistance of air(!) to get to Ground. And since we know from the paragraphs waaaay up there at the beginning that lighting can arc through air at somewhere around 10,000, we’re still turning that nice 1000W inverter into a paperweight as that induced energy somehow, someway discharges itself to ground. Or it might not immediately, and stay at 100,000 volts potential; but then you touch it… ouch, or plug it in.. ‘poof’.
“But I want my eyes even further crossed – what else you got?” You are masochistic, my friend. Let us continue to Shielding.
Electromagnetic radiation wants to go to earth Ground – it is its destiny, that’s its sole purpose in the universe, its feelings would be hurt if it couldn’t. To protect equipment we either need to “hide” it ten feet or more underground or “shield” it before the energy waves find it. Hiding doesn’t mean putting it in the basement or the storm cellar – you need at least ten feet of earth above your abode; we’re talking underground bunkers here.
By surrounding it with – but not touching – a grounded conductive enclosure the electromagnetic waves and/or static discharges are harmlessly shunted around the sides of the enclosure. Some dead dude name Benjamin Franklin (I’ve never heard of him either) noted as the discoverer of this but some other dead dude named Faraday codified it, thusly the Faraday Cage.
Almost anything can be made in to an effective faraday cage, provided it is:
- conductive (“Yay!” screams the tinfoil hat crowd),
- properly Earth Grounded (“Hissss!” boos the tinfoils),
- adequately surrounds whatever is trying to be enclosed (“Hey, we need to breathe yo!” the tinfoils’ excuse is),
- whatever is inside is sufficiently insulated from this cage. (“I got nothing.” Me either.)
Microwave ovens are designed and built as faraday cages and continue to function as such even if it doesn’t work anymore. Ever loose cell phone reception in an elevator? That is the faraday cage effect my friend. A grounded safe or vault. Properly grounded tinfoil around a box. You can use a military surplus ammunition can, drill and tap a hole, screw in a lugged ground wire and clip it to the metal shelf support next to the other ammunition cans you’re using as such, and tie that shelf into earth ground.
“But what about using bird cages, chicken wire, and/or DW’s heirloom spaghetti strainer bowl?” Depends, and this is where the lack of public information comes in to play. The spacing of the electromagnetic permeable conduits acts as a wave-guide of sorts and determines what frequency of electromagnetic radiation is rejected, attenuated or passed. WAIT- Please don’t leave, I didn’t mean to get too technical! Think of an EMP burst as a golf ball passing through a faraday minefield of putting holes of different sizes – too small a hole and the ball will roll over it and too big a hole the ball will bounce out and continue on.
Complicate that further by not knowing what size of the golf ball is to begin with. So it might just be that the hole spacing in a bird cage and chicken wire won’t be able shield out enough of the EMP. I can’t say for sure that these materials would be 100% effective against EMP or CME events, but something is better than nothing and this something is *significant*. I use chicken wire over certain things I’ve got in the shed; if you think the holes are too widely spaced then add another wrap around it.
There is no Prepper Law that says you can’t have DW’s spaghetti strainer covered by chicken wire over a bird cage. Solid cage is best, next is the smaller the spacing of the holes the better off you are. Just make sure whatever you use is properly grounded to earth ground.
“So what does properly earth grounded mean?” A good earth ground is a conductive rod that is driven into the ground 10 feet or so – and the depth is dependent on where the damp earth starts; Texas building code is 10 feet so that’s what I stuck to. The licensed electricians I work with say some houses have copper plumbing that acts as the earth ground. The shield has to be connected to it and you need to make sure the grounding wire is thick enough to handle the ‘funneled’ energy (if you’re covering an entire safe room then tiny 24ga speaker wire will not be sufficient – use a battery jumper cable) and makes a good, solid contact to whatever earth ground you are using as well as the shielding material.
“Properly insulated?” If the equipment you want to shield is actually touching the cage then there is a conductive path for the energy burst to follow that could compromise your equipment; it becomes part of the shield therefore it is fully exposed. Put that inverter in a cardboard box, wrap it in a garbage bag, then put it in that properly grounded junky microwave. Throw in a desiccant bag for good measure.
“’Conductive’; you keep using this word. I do not think it means what you think it means.” Copper is the best common material that conducts electricity and the higher the content of the copper in the conductor the better it does that job. Aluminum (probably the worst), steel, brass, tinfoil and other commonly available alloys do work but are not as efficient as copper. But those *do* work as conductors, so don’t disregard them if that’s what you’ve got available.
EMP or CME related puns welcome in the comments; I enjoy electrifying conversations. (<- see what I did there? Hah! I kill me!)