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Faraday Cages, Your Electronics, and EMPs

Homeowners have a number of concerns with household safety and protection. While many of these concerns reflect mundane life, some concerns reflect the global economy and the state of tension between world powers. With modern technology, a nuclear war is not the only global catastrophe we may face.

Electromagnetic pulses (EMPs) are bursts of electromagnetic radiation that can be caused by nuclear explosions or fluctuating magnetic fields. [Note: There is no current evidence that the government has technology capable of producing this effect without using nuclear devices.] The EMP effect can be produced by warheads detonated on the Earth’s surface or from detonations occurring high above the surface. The effects from these detonations will vary greatly depending on altitude and interaction with local magnetic fields.

EMPs will disable modern technology within a certain radius of the originating blast. Those caught in its path will have their cell phones, computers, cars, and household electronics cut out, and it will cut out the power grid as well. There are few ways at present to protect ourselves from this type of threat. One potential method of protecting your electronics and alternative energy sources is by using Faraday cages.

Faraday cages were discovered by Michael Faraday, and these devices can protect anything inside of them from electrostatic shocks (up to and including lightning) and from EMPs. They are generally built as metal cages with mesh on the outside, and they must be grounded. The metal mesh conducts the electricity or electromagnetic energy around the exterior surface of the cage, protecting the cage’s contents from harm, and the energy runs along the ground and dissipates. We use several examples of Faraday cages in everyday life: microwaves and coaxial cable. Each of these conducts energy around a particular surface to protect its contents.

While it is possible to protect numerous objects by placing them in these cages, homeowners must consider the utility of doing so. Protecting an outdoor generator by placing it inside a Faraday cage presents little impediment to daily life; in contrast, placing a television and stereo or game system inside a cage would make it difficult to use these appliances. It’s also not practical to place a stove or refrigerator inside a Faraday cage — you can plan ahead and replace your stove with a wood-burning or a propane/natural gas unit to avoid losing use of it due to an EMP incident.

It’s impossible at this point to protect energy sources such as solar panels from EMPs, but it may be possible to protect the generator components of wind turbines and hydro units. This depends on the individual unit construction, and whether it’s possible to have the generator itself be connected to the unit rather than be an interior component, which cannot be protected without shielding the entire device.

Numerous online resources exist that describe various Faraday cages and their applications. It’s possible for people to build cages using plans found on some of these sites. A homemade Faraday cage can be constructed simply by using a wood frame covered with metal mesh. However, a mesh with wide openings will not be useful for protection. The best sets of construction plans make use of a very fine mesh to ensure protection.

Please note that Faraday cages must be grounded in order to properly protect their contents. Some websites claim you can build cages from anything (including cardboard boxes and tin foil), but most of these will not work. Tin foil, while metallic, is not thick or strong enough to resist EMPs. You must have a solid structure, a metal mesh (not tin foil), and the cage must be grounded. Even the common Faraday cages mentioned earlier utilize grounding: coaxial cable contains a grounding wire, and all microwaves make use of three-pronged (grounded) plugs.

Faraday cages can offer excellent protection if properly constructed and grounded, so please be very cautious when reviewing instructions on how to build them. Make sure to select a comprehensive plan that includes and explains how the grounding works, and follow the specifications to the letter to ensure optimum protection for your appliances and electronics. Finally, avoid any plans that instruct you to use flimsy materials such as cardboard, as these will simply leave you unprotected.

One final note: a popular online myth is that cars are Faraday cages on wheels. While this may have been true to some extent when our vehicles were made out of more metal than anything else, this is no longer the case with vehicles that involve more fiberglass than steel. A car may ground some energy and offer slight protection from a lightning bolt, but it will not offer protection from an EMP. Do not rely on them to protect your small electronics (cell phones, laptops, etc.) from harm in the event of an EMP strike.

For Further Reading:

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  1. Just a thought, I’m not sure if this would work, but maybe you or someone you know might.
    I’ve done a lot of stucco wire in my time and was thinking that 20 gauge wire (normal gauge) if covering the entire outside of a home and used in the roof construction as well and also grounded to the cement basement walls would work as a faraday cage therefore protecting the entire contents of your home. Of course the wire on the roof would have to be properly connected to the wire on the walls, and the wire on the walls would have to be connected to the concrete. The outside doors and windows would be holes in the cage, but would it work.
    Walter Smith

    • Based on everything I’ve read to date, large amounts of wire are counter productive as the act as a large antennae and actually attract the magnetic pulse. You need a really good ground as close to whatever cabinet, etc. you are grounding. Most are insulating a metal cabinet from the floor and walls, placing as close to an outside wall as possible (to keep ground cable short), and using an 8′ copper ground rod in the ground as close to cabinet location as possible. Your house wiring will act as an antennae, too.

    • The EMP consists of multiple pulses at varying time lags from the initial source, whether a detonation or solar flare. Each pulse may have a different intensity, frequency, and duration. That makes it difficult to design a single cage to address all scenarios. Finer mesh will disrupt pulses whose wavelength is greater than 1/2 the mesh mean diameter, so finer meshes are preferable. Airborne pulses are measured in watts/square meter, joules/m2, or similar, so you may be able to protect a large area from certain airborne pulses with the right Faraday cage design. However, incoming pulses may also travel on electrical grid wiring or any external wiring source that enters the home and bypasses your Faraday grid. The weak spot on most grounding systems that I’ve noticed over the years is the earth to ground connection. Without a good ground coupling, your system is useless. An 8 foot copper clad rod may or may not be adequate, but probably won’t be for an EMP. You should have multiple grounding sources, including a water well casing if available, metal water lines lines, ground rod or rods, and the rebar grid of your home or driveway. Rebar in concrete can be an excellent grounding path if large enough and well-bonded. Bond everything together (eutectic or thermal welding is the best, if it can be done). Otherwise use electrical split bolts or other approved electrical methods, with anti-oxidation compounds and protection from moisture. Final system should have less than 1 ohm resistance to ground if done correctly (the NEC only requires 25 ohms to ground for residential, but your Faraday cage should be done to a better standard).

  2. As the article suggests, there is a lot more to Faraday cages than simply putting a metal screen around an object. And, as the article suggests, everyone has a light-weight (read inadequate) Faraday cage in their house already in the form of your microwave oven. Have you ever wondered why your normal oven has a glass window, but your microwave has that weird screen you can’t see through? That’s the Faraday cage which keeps the microwaves contained inside the oven.

    With that said, one must remember the very high power levels with an EMP strike. The grounding wire on your microwave likely won’t carry the EMP power to ground. REAL Faraday cages for EMP protection have huge… HUGE… grounding cables. The idea is to provide a large enough “pipeline” to carry all the power to ground before it does any damage.

    As for the suggestion about stucco wire, another characteristic of Faraday cages is the gap size between wires. The wave size of EMP strikes is much smaller than, say, chicken wire. So, you would need a heavy gage, small mesh wire that is completely connected around the structure. Your doors and windows would need to be covered with this mesh wire, as well as all utility openings, garage doors, etc. Not realistic for more normal homes. There are buildings which are Faraday cages, but they were designed that way to make sure the wire mesh is well connected across doorways and typically minimizes windows.

    I have intentionally not provided details. Details on mesh sizes, wire gages, etc. are available from better sources than me. Check some military construction manuals online and consult an electrical engineer for more help.

  3. My home, built 20+ years ago with insulated steel forms is a sort-of faraday set up. Hopefully we won’t have to find out. Good article. Thanks

  4. Just reading along with the article some thoughts . EMP CAN be generated without a nuclear explosion and has been by the government and others for years .It is possible to protect solar panels from EMP in a manner like what is used in microwave ovens Phone lines and cabel can be protected in the home/office though may fry the network when not fiber optic ..Generators, wind turbines, and hydro electrics can be protected .It is not the grounding as much as it is the conductor geometry and conductivity versus the wave lengths of the EMP .My back ground nuclear supervisor submarines, USEPA HAZMAT ERT NUCLEAR CHEM BIO , Hi FEQ/HI Voltage , Plasma Generation, Remote Monitoring and Trend Analysis, R&D support CDC-GATECH-DARPA-Vandy=other research labs . Pardon the entry here having some eye problems . .

  5. To test your microwave to see if it is an effective faraday cage, simply put your cell phone inside and have someone call it, if it doesn’t ring it will be an effective cage. We have one downstairs in our basement that quit working so we cut the cord and now use it to store spare electronics in.

    • Mindy says: To test your microwave to see if it is an effective faraday cage, simply put your cell phone inside and have someone call it, if it doesn’t ring it will be an effective cage. We have one downstairs in our basement that quit working so we cut the cord and now use it to store spare electronics in.

      If you cut the cord off aren’t you negating the protection?? I thought the Faraday cage has to be grounded very well. Also, I am with Steve – there isnt a lot of info to assure proper protection. We need a source. My wife and I have been discussing short wave or ham radio as an effective communication technique to reach our family. Has anyone given any thought to protecting these inside a Faraday cage microwave or some such for later use as a communication tool? Any input is helpful. Thanks

  6. “[Note: There is no current evidence that the government has technology capable of producing this effect without using nuclear devices.] ”

    While there may be no evidence, the technology is easily available. Small-scale EMPs are produced in plasma research labs on a regular basis. The collapse of a double-layer in a plasma z-pinch or theta-pinch is a very efficient method of producing a high-powered, broad-spectrum EMP. With the right budget, anything is possible, and I would bet the farm that a large-scale device of this sort is sitting in some government black-ops research facility, just waiting to be used.


    • I guess that nobody told the writer about the EMP Tomahawk missiles that were used during the wars in Iraq? Seems that the technology to cause an EMP is quite advanced, indeed.

  7. rhythmforcedmelody

    credible or not, the American government tested microwave weaponry years ago folks…and from what I understand, there were a number of incidences involving the local population sustaining internal burns.

  8. From the article, second paragraph…”Note: There is no current evidence that the government has technology capable of producing this effect without using nuclear devices.” WRONG !!! I remembered Popular Mechanics, Sept 2001 edition, as shown on the front cover, detailing inside how a non-nuclear EMP bomb is made. See Perhaps the author of this article doesn’t Google.
    From an article in an amature radio magazine”QST”, an air burst over the center of the US would create a 10,000 volt/meter electric charge over the whole lower 48. That means 10Kv potential difference from one end of a metal conductor to the other, only one meter long (or wide). Your car…3 meters long, 30,000 volts potential. Your line cord to the microwave, 1 meter…10,000 volts. Line cords, tv cables, phone cords, house wiring, stereo wiring, as well as all metal surfaces, are all succeptable.
    The people that will be uneffected immediately are the ones without technology. GFL !!!

  9. Just wondering how I would begin to protect the photovoltaic arrays on my roof from an Electromagnetic Pulse or Coronal Mass Ejection or similar event. Even lightning, which is very common during about 9 months of the year here, is a concern. Any suggestions would be appreciated.

  10. Endless black op talk is of no use. No one should care if some group has a capability. What everyone should be concerned with is a scientific approach to building a HEMP/EMP/CME proof container that is large enough to protect whatever components you wish to save.

    There doesn’t seem to be any consensus on construction. I do not see any place on the net except very large corporate entities building Faraday enclosures for military or medical situations and of these there is no in depth construction technique described. It certainly isn’t tin foil or garbage cans tested with cell phone reception as the end all test. On top of this. grounding opinions are all over the spectrum with some saying absolutely necessary while others saying the opposite.

    There are three components of a EMP/CME,how do you protect against these very low to extremely high frequencies?
    Is a solid conductive container,as in a copper, with conductive gaskets around the opening,wood lined interior, be all that is necessary?
    If a nested/laminated container were constructed with multiple layers of copper screen/insulation , provide better protection?
    Do nested,layered /laminated shielding need to be connected to each other?
    Does the conductive gasket have to be of a one piece construction or can they be butted together?
    How tight does the cover for the opening need to be?
    What if any does the size of the container mater in calculating the amount of shielding?
    If grounding is necessary what size conductor for the ground?
    Why would’t the ground act as an antenna with distructive results?

    Lot of questions but if one is not fooling themselves and wants to build something that will work they better get some answers.

    Your answers?

  11. I have a metal underground survival shelter. I hope that it will protect my electronics! It is thick metal, and very well grounded.

  12. I have been trying to understand the whole EMP/Faraday cages idea. I have just one question at this time, if a piece of electronic equipment is not plugged in or turned on, it is merely sitting in the box you bought it with or sitting on the shelve, then how can a EMP or solar flare burst destroy the item ??? Thanks, Steve

    • EMP can be HUGE. It doesn’t involve your electrical system. Think of setting a huge magnet on top of one of the old floppy disks. That’s how you securely wipe a disk – even a hard disk if the magnet is large enough. The magnetic pulse creates an electrical pulse in the air so anything not protected by a device to capture and divert that pulse safely to ground will be toasted. The device sitting in a box on a shelf still has capacitors, resistors, and circuits connecting them. It is those connecting circuits that will pickup the EMP out of the air – kind of like your cell phone picks up electrical pulses out of the air.

  13. A nuclear detonation is not required to generate EMP. The article at the following link is from the September 2001 issue of Mechanics Illustrated. Realise the issue was put together before 9/11/2001. In fact they have removed some parts that were published in the original article but it basically says that anyone with $400, access to the materials, and the knowhow can create an EMP bomb. See page 51 at the below link.

  14. I have been reading and reading about EMP’s and Faraday Cages on the web, and am lost and confused. I am not mechanically inclined and therefore lack the understanding of knowledge to determine what will work and what will not? If I purchased a microwave oven cut the cord and buried it in my backyard would this protect the enclosed batteries, radios, etc. from the damage of an EMP? If grounding is needed could someone please explain in detail how to do so?

    Thank you!!

    • All I can tell you about burying it is this… the ground is where all electricity goes. I’m no physicist but you probably want to avoid that chapter. As far as a microwave, you would need the cord to ground out the electricity, so don’t cut it, in fact leave it plugged in… in fact leave it in the kitchen. But don’t expect particularly good protection from an EMP.

  15. i am wondering if a 20ft. container grounded and burried will work as a cage ?

  16. I have noticed that the when closed a MacBook Pro and a Mac Mini are solid blocks of aluminum that cover their insides more completely than a Faraday cage. Am I correct in assuming that they would only need a grounding cable to protect a MacBook Pro? Of course, a Mac Mini would be pretty useless without a protected mouse, keyboard, and monitor.

  17. So here is my two cents of this subject.

    There sure seems to be a whole bunch of conflicting information on this subject.

    I admit that I don’t know much about this except what I have read which is not much but I have a lot of questions.

    Why did not the bombing of Japan not cause an EMP? I have not found any answers to this question.

    It is reported that US Nuclear testing the South Pacific knocked out street lights in Hawaii and affected radio communications in Australia. It is reported that Russian nuclear testing showed similar result and this resulted in both countries going to underground nuclear testing. You could conclude that the bombing in Japan should have effected other areas with EMP.

    There are quite a few videos of people making Faraday cages on YouTube. A favorite way of testing them is to put an FM radio or cell phone in the cage and see if it works. I have no idea if this is a good way to test a Faraday cage. If it is, then the ground question comes into play because there are many that are not grounded and they seem to work. I have also read that a ground wire could act as an antenna for the EMP and make the problem worse.

    Until someone shows a de-facto way of testing a Faraday cage we may not know what is the real answer. I also read that the only way to really test is to creat a real EMP.

    I have seen on YouTube a Faraday cage made out of metal window screen. It seemed to work. Tesla and some other experimenters made Faraday cages that looked like a metal cage that would house a wild animal. You have probably seen the photograph of the Tesla Coil generating lighting bolts to a cage where some body like Tesla is sitting reading a newspaper. Therefore you could conclude that wire mesh such as the chicken wire which is used when stuccoing the outside of a residential house could be used as part of a Faraday cage if windows, doors, ceilings are treated. I would also question the effect of electrical and HVAC entering the room the affect.

    If window screen works, will chicken wire work or some other size of wire mesh or metal wire fencing and what size will not work.

    But, I also saw a video on YouTube of a guy that acquired a metal cabinet. It was probably 6 feet tall and 3-4 feet wide. Testing it with an FM radio showed it leaked until the door seams were covered with metal tape used by the HVAC industry and available at your local home improvement store. The door gap was probably less than ¼ inch. So my question is why do metal cages work when a metal box with small door gaps do not. Maybe it has to do with grounding. According to the video, the cabinet was not grounded.

    The Popular Mechanics article mentions India has done some research because of concerns about Pakistan’s nuclear weapons. They claim we (the west) don’t know about “high-frequency pluses… that can worm their way around vents of a Faraday Cage”. Another new issue is “late-time EMP effect”.

    So I have few question but no answers.

  18. About testing a faraday cage by seeing if it will block a cell phone signal. If you’re only trying to keep out cell phone signals, fine. But EMP is likely to overwhelm such flimsy protection. A cell phone signal compared to the pulse generated by a nuclear blast is a bit like comparing ordinary waves on the beach to a tidal wave.

  19. KISS
    Keep It Simple St****. and keep it cheap the best faraday cage is a steel trashcan with a tight fitting lid

  20. hey folks,as if we don,t have enough to worry about and we,ve known for sometime about the sun for a while as far as the coronal disharges,well i live out in the country and have a old house with sections of steel roofs,so how that play out, as far as making the roofs with ground cables on each corner going into the ground from the house? as far as the power that goes to your house pull the main breaker for electron pulse,not to damage wiring in the house? and all the electronics in steel trash can?,as far as i configure, a question of individuals needs if big pulse did hit we would be back in the stone age for a while as how many companys that supplly power for all our electronics and such,have thir sytsems emp proofed i think not many now,thats another burning question? good luck to all and a good christmas i remain optimistic as far humanity any answers out there.Walker

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  23. My father has a 40ft. REEFER Container and has all of his solar equipment stored inside of it “Panels are outside of course” will this container keep the electrical equipment protected inside of it or do we have to do more to keep it protected??

    Thanks for any advise!

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