Last week we talked about electromagnetic pulses (EMPs)—potentially one of the most threatening forces to our modern way of life. Under the right conditions, a solar EMP could wipe out power over large swaths of the US in a blackout that lasted for months.
It doesn’t take much imagination to picture how devastating that would be.
The good news is that it's not too late to prepare! With some relatively simple steps, you can protect your important devices from EMP damage. The cheapest and most effective of these is the Faraday cage.
What Is a Faraday Cage?
Also known as a Faraday shield, radio frequency cage, or EMF (electromotive force) cage.
Simply put, a Faraday cage is an enclosure built to protect electronic devices from electromagnetic pulses (EMPs) that can overload and fry them.
A Faraday cage be anything from a small box to a large room, covered with conductive metal or wire mesh, which prevents surges from damaging the equipment inside.
Devices a Faraday Cage Will Protect
There are a variety of personal electronics that can be protected by a Faraday cage.
Typical items that can be stored in a Faraday cage include:
The History of the Faraday Cage
The Faraday cage actually outdates modern electricity by quite a few years.
The device is named for Michael Faraday, who observed in 1836 that the excess charge from a conductor remained on the outside of a container and had no effect on the interior contents.
He experimented by building a room coated with metal foil, and then he allowed high-voltage discharges from a generator to strike the outside of it. He used an electroscope to show that there was no electric charge present on the inside of the room’s walls.
Though the device bears Faraday’s name, Benjamin Franklin is believed to have been the first to discover the principle.
Faraday Cages in Unexpected Places
Faraday cages are found in lots of places, from some protective work clothing to cars (especially older metal vehicles can be Faraday cages with wheels).
Faraday cages or shields are used all over the world and show up in lots of places you might not expect.
MRIs – Faraday shields are used in the scan-rooms of MRI machines, in which the “cage” effect prevents radio frequency signals from being added to the data from the patient’s image.
Protective work clothing – Some electrical linemen wear “Faraday suits” when working on live, high-voltage power lines to prevent accidental electrocution.
Cone of silence – Military planners and politicians who have reason to keep their communications private often meet in Faraday-protected rooms that are impervious to electronic eavesdropping.
Personal privacy – Many people buy Faraday bags to protect their cell phones and laptops both from electrical surges and from unwanted surveillance or tracking.
Cars – According to the National Weather Service, an automobile is essentially a Faraday cage, and it’s the metal surrounding you, not the rubber tires, that protects you from lightning (as long as you’re not touching metal inside the car).
A smaller example is a microwave oven, which is a Faraday cage in reverse, trapping the waves inside the device instead of keeping them out. In fact, an old microwave oven makes a good Faraday cage for small electronics!
Why You Need a Faraday Cage When Everyone Else’s Devices are Down
Why, you may ask, would it do any good for you to have working electronics when everyone else’s would be down or destroyed?
First of all, you might still be able to communicate with people outside the affected area (and it may be very difficult at first to determine how large that affected area is).
Second, you won’t be the only “techie” who thought to protect valuable electronics in a Faraday cage. Some preppers do this as a matter of course, and eventually you would probably be able to communicate with them. (Cell towers, however, would likely be “fried” and need to be rebuilt.)
Back Up Devices in a World Without Electronics
Many ham radios could survive an EMP event.
Communication at such a time would be extremely valuable.
Unless there had been well-publicized warnings of impending CMEs in the days before the event, many people would have no idea what had happened to our world.
Ham radio operators, who could communicate with other Hams around the globe, might become the new heroes of the day.
Many AM/FM and shortwave radio stations believe that they’ll still be able to broadcast after an EMP or CME event. And without all the usual “noise” of our plugged-in society, their waves may be able to travel farther than they do now. Hopefully there would be Faraday-protected radios out there to receive their signals!
There is, however, a likelihood that the earth’s electromagnetic field would be seriously disrupted by such an event, and it might take quite a while for things to settle down and not cause static on the airwaves.
How to Make a Faraday Cage
You can make a Faraday cage from lots of different receptacles. More important than the shape or size is what they’re lined with.
To be effective, a Faraday cage must:
Be covered with conductive metal or mesh. Copper is the most conductive metal, followed by aluminum. (Well--gold and silver are better, but we assume you won’t be covering your cage with those!)
Be properly grounded (according to some experts, to prevent shocks when touched)
Adequately surround whatever it’s protecting.Be adequately insulated from the cage itself, such as being placed on wood, in a cardboard box, or on a rubber mat so that it doesn’t touch any metal.
Faraday Box # 1—The Galvanized Trash Can
A trash can with a tight fitting lid makes an effective Faraday cage.
- A galvanized metal trash can with a tight-fitting lid
- Several boxes of heavy-duty aluminum foil
- Enough metal screening or mesh to wrap around the top of the can and fit over the lip
- Cardboard boxes of assorted sizes that fit inside the can
- Plastic garbage bags or plastic wrap
- Cloth pieces to wrap items
Wrap the items you wish to protect first in cloth, then plastic, then 3-4 layers of heavy-duty foil, being sure that the foil is molded to the shape of the item and that each layer completely covers the previous one, with no tears or holes.
Place your wrapped items in cardboard boxes. Tape shut, then wrap the entire box with 2 layers of foil. Line the trash can with cardboard, including the bottom, making sure there are no gaps. The foil-wrapped boxes must not touch the metal of the can.
Set the can on wood or cardboard, not touching any other metal. Several experts say that simply putting the lid on the can, even if it fits tightly, is an insufficient seal. They suggest folding a sheet of metal screening around the top of the can and over the top lid and then forcing the lid over that to maintain a constant, tight-fitting metallic connection.
KEEP IN MIND...
Not for daily use — Remember, this is for long-term storage of the appliances inside, not something that you can take your appliances out of to use and then return to the container without a great deal of trouble.
Look for duplicates — A good idea is to look around for good deals on duplicates of things you use every day.
Don't forget your chargers! — Another important thing to remember is that you will need some type of charger—hand-cranked or solar-powered—to power up your devices once a crisis has passed. If you can wrap and store one of these in a protected Faraday container, you’ll be glad to have it.
Faraday Cage # 2—A Metal-Clad Box
Ammo boxes and tool boxes, with a tight enough seal, can make great faraday cages.
Any box made of non-conductive material such as plywood, and then totally covered with metal, metal mesh, or metal screening can serve as a Faraday cage.
Close all openings — The metal must touch at all the corners and over and all around any opening for the protection to be complete, as an electrical charge will Replace its way through any gaps or crevices in the construction.
Metal mesh — The smaller the holes in the mesh or screen, the better the protection—but either mesh or screen is believed to work better than solid metal. The metal can be attached to the wood with staples or screws, whichever seems to work best for you.
You might consider applying the metal mesh so that it folds around the corners. Then let the next piece overlap the edge of the first, securely fastening them together and to the wood so that there is no break in the conductive shield.
Or Just Purchase a Faraday Cage
With 210D nylon ripstop material, this waterproof 5-liter Faraday bag is a super convenient option for protection.
The problem with lots these free options is that they can be cumbersome and tough to haul around.
For a study, super-portable Faraday cage to carry on the go, you might want to look at some manufactured options, like a 5-liter Faraday cage bag.
They’re made with waterproof, 210D nylon ripstop material. Of course they’re EMP-proof, and actually block cellular signals too, to protect against hacking and tracking.
So there you have it: our in-depth guide to Faraday cages.
Are Faraday cages part of your emergency supply? Have you had a chance to see them in action? Let us know in the comments below!
For more DIY projects, check out the articles below:
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How to build a faraday cage in a few easy steps
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Bonnie, we have seen large Faraday bags specifically sized for generators. If you still have the original box you could also wrap it in multiple layers of heavy-duty aluminum foil. You could do the same thing with any sufficiently large box. Hope this helps!
You forget that if you are using your devices (car, comuputer, laptop, phone, etc) at the time of the attack you won’t have it in a Faraday cage.
I have a portable solar generator. It’s too heavy to lift into a galvanized can. It’s on a two wheeled luggage carrier. Also the solar panel that connects for charging. I can remove the connecting cords. How do I protect these two items?
What about a steel fireproof safe that is bolted to a concrete floor?
A couple of notes: For metal containers, weld a bolt to each piece (e.g. can and lid) to attach a ground wire for a more secure ground path. Attach the other end to a cheap ground rod. If you don’t weld it on, at least make sure you sand off any paint and get the bolt attached to bare metal for an adequate connection.
Also, old microwave ovens are not good for wide spectrum. If any doubt, put your cell phone in one then call your number. If it rings it is electrically vulnerable.
55 Gal. drums can work well, but remember the gasket on the lid as a leak. Cardboard can also hold moisture which can corrode things and aid in conductivity. I wouldn’t use that.
My $ .02
For definitive answers on EMP’s, watch Dr. Arthur Bradley’s YouTube videos. He conducts actual tests on the video and disspells many false ideas while giving correct info. He is an electrical engineer at NASA in Houston and has a PhD in electrical engineering. His website is disasterpreparer.com
What about a well sealed mylar storage bag ?
So when exactly do you place your electronics into a faraday cage?
When it comes to automobiles/trucks/vehicles, your best bet would be either to store vital automotive electronics in a Faraday cage, but this would be a very expensive proposition.
A better option would be to own one or more older vehicles with "point & plug" ignition systems. Usually, the only vulnerable parts of these ignition systems are the condenser (usually located inside the distributor cap) and a ballast resistor (usually mounted on the firewall). Both of these parts are inexpensive, common, and resistant to EMP-type anomalies. Buy spares, and store them in the Faraday cage.
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Here’s what Sharon, one of our bloggers (and the writer of this post) had to say: Microwave ovens appear to be the perfect Faraday cage, as they are lined with a mesh or metal screen with small holes that keeps the microwaves safely inside the oven. It would seem to follow that they could also keep strong electronic charges out of the interior. Whether or not they really do so is a matter of debate, and may vary from oven to oven. Whatever you choose to protect your electronics, remember that they must be insulated or placed on wood, thick cardboard, Styrofoam, foam rubber or some other non-conductive material. Most seem to agree that car batteries could withstand an EMP or Carrington Event—but electronic ignition systems in cars would not. “Lone” batteries that are not connected to anything would seem to be safer than those in service where a circuit would be completed, and which are connected to metal.
The fact is that we do not know exactly what would happen in an EMP or a really destructive solar flare (and hope we never will!)—and it may vary according to how far away we are from the center of the event—so the above is based on the “best guess” and best science available.
I went onto Google shopping and found a couple of commercially produced Faraday cages. You can check that google shopping or amazon to get more information. There is a company called Corstat that makes faraday boxes and they seem to be coming up in a lot of the searches I’v done. Unfortunately, we do not sell faraday cages ourselves.
Lawrence C. Muhr
Are any cages being commercially produced? If so, do you have an address/phone #? I believe many people would purchase some if they are available.
Why not just get several old microwaves and put them in the garage? The contents would be accessible at any time, right? Also, I wonder if batteries need to be protected.
Remember to ground the metal cans or what ever you use to earth. You need a place for the charge to go to ground at.
To test this out if this is really EMP proof, drive up to your local radio station with an FM radio inside your faraday cage. If you still get reception it DOES NOT work.
Another effective faraday cage for small electronics such as an HT ham radio is to wrap the item in something non-conductive such as a wash cloth or bubble wrap then place inside a ziplock bag. Create a tight fitting bag of copper mesh that you then place the ziplock into and sew hue mesh bag shut with copper wire. Small, portable and easy to access.
With any container being used as a Faraday cage, the metal must be uncoated. So of you have a painted ammo can or trash can, etc you would need to scrape the paint off where the top and bottom join to shut the box so that the metal from the lid is in continuous contact with the metal of the main portion of the cage. Best regards.
An ammo can, as theory goes would work but the rubber seal in the cans might be an electrical way in. My suggestion with these cans is insulating the inside and after putting in the contents put fine mesh/screen over the opening and then put the lid on. I like the idea on a can inside a can.
Yes, a Metal Ammo Can could work as a Faraday Cage as well. You just have to be sure that it’s sealed well.
Wouldn’t metal ammo cans work well as a Faraday cage?
Thanks Sharon. I thought that. It needs total enclosure.
As far as we can tell, a grounded metal roof might help to protect your house from lightning strikes, but as with a small Faraday cage, we think the conductive metal would need to be built in around all sides of the house (including doors and windows) in a continual (oroverlapping) manner to protect any electronics within the shelter against EMP surges or CMEs, which would seek entry at all possible gaps. A house as an effective Faraday cage would be tricky to construct.
As far as we can tell, the initial destruction of an EMP attack or CME incident would happen in-no pun intended-a flash, and bringing out protected electronics would be safe after just a few minutes. A possible exception would be multiple incidents, which could happen, especially with CMEs, in which one impulse might follow shortly after another. The problem, of course, would be with the infrastructure—cell phone towers, radio and tv stations, etc., which would be rendered non-functional.
If the house has a metal roof, could grounding rods make it into a Faraday Cage?
Good overview. Now that you’re on-board with the EMP threat, did you notice how quickly "after" an EMP hit has
occurred is it safe to expose our sensitive electronic equipment?