Letter: Faraday Cage Question

Good afternoon!

I have a question on adapting a homemade Faraday cage. I am getting a little paranoid about these two North Korean satellites in orbit over our country.

Would a metal mailbox, such as can find at the local hardware store, be acceptable protection? I am trying to put together something simple for really, really cheap! It has a larger size and is easier to obtain. It is also cheaper than some of the other options I have been reading about on constructing a Faraday cage.  T.B.

HJL’s Comment:

Most any metal container will work as a Faraday cage with a few simple preparations. The metal needs to have a good electrical connection between the various parts. If you are using painted metal, you will have to remove the paint where the electrical connection needs to exist. Galvanized metal works really well. If a metal mail box is not large enough, you can consider a 30 gal trash can with a metal lid.

Once you have placed your objects inside, use a good aluminum foil tape to completely seal any seam. The aluminum tape must make a good electrical connection and an inexpensive digital multi-meter works well to verify. Also, if you are having issues with the electrical connection, you can use an alarm foil splicing tool to ensure that connection.

While this will give you good EMP protection, it also means that every time you open the container, you will have to reseal it. To make a container that can be regularly opened is more difficult due to the requirement of the good electrical connection seal.


  1. A couple of years ago I did some research on this very thing. I happened upon http://www.futurescience.com/emp.html

    I also spoke with the engineer that runs the site. He gave me some very good advice:
    Make nested Faraday cages. This is how I protect the electronic and electrical items I want to survive an EMP event.
    I use either the box the item came in or a small box on hand, I wrap in heavy duty foil, then I use parchment paper or heavy duty paper over the foil and then another layer of foil and repeat this. I do this several times to form a nest over the item. I also purchased a few Faraday bags and nested within these for the more valuable items ( NV, FLIR and some radios) Also in my work shop built a Faraday cage, using a layer of aluminum screen and then galvanized sheet metal, I made a door gasket using the aluminum screen rolled up and attached so that it is crushed in the door opening. I am not sure anyone truly knows what will survive and what will not as there is a lot of guessing going on. I go as many extra steps as I can afford in hopes that if an EMP event was to happen my family will have some items that will increase our odds of survival. Another thing I found useful is the heavy duty aluminum cooking pans with lids, again I nest everything inside of this. it works great for smaller items and these are fairly cheap.
    Some of the items I have also protected: Multi meters, SSB radios, Cordless drills and chargers, solar panel controllers and some higher end LED lights.
    I hope this was helpful as I think we all need to have a level of preparedness that allows us to protect and provide for your families.

  2. It is also important to insulate the contents from contact with the metal skin of the Faraday cage. You can use bubble wrap, cardboard, shipping foam or some other non-conductive material to keep the electronics separate from the skin.

    1. I don’t believe that is true. If the inner skin of the metallic enclosure has any electric potential that means there is an electric field inside the Faraday cage, and therefore the cage has failed. I remember in my electromagnetic classes we were taught that only the outer skin is exposed to exterior EM fields. The inner skin is safe. Anyway, my two cents worth.

  3. Other containers could include paint cans. I’ve seen empty paint cans for sale. They would be air tight and seal would be metal to metal. Spatter with a few paint splotches on it and you could hide among all those other paint cans on the shelf.

  4. If you can put your cell phone in your microwave and call it, then some electromagnetic energy is getting through. A metal garbage can is pretty good and affordable. The foil tape is still needed

  5. Back in the 70s I was tasked with designing a replacement for the standard S280 van for the military. The new unit was to be fiberglass foam sandwich construction. We were required to withstand the EMP from an 20 meg Ton Hydrogen bomb within 20 miles. This was an almost an impossible task. Seams were very difficult to secure from an EMP.

    You can do a search and find door seals and windows designed for these applications.

    EMP was a huge threat to inductors as well as solid state components.
    We used the door seals along the floor and wall seams. We flame sprayed copper to the inside of the outer skin and flame sprayed copper in the outer side of the inside skin. Then we grounded both of these layers to a common grounding system.

    Your trash can scheme requires the lid to be securely fastened to the lower section with conductive jumpers. Bonding techniques would be required to secure the contact.

    I might suggest MIL-STD-188, MIL-STD-464 and MIL-STD-461 as good reference.

  6. Everybody wants their items to survive an EMP. They will retrieve their Faraday protected items and some critical things will be ok. EXCEPT there will be more than one EMP because every surviving nuclear power (except Britain and France) will light us up with an EMP a second and third time and every six months or so in order to keep us from ever recovering. That’s what enemies are for. To protect yourself against EMP you must be able to live without any electronics. Think horses and mules, steam engines, diesels with hand crank start and no electronic fuel pump or controls, etc. An EMP attack will be a true disaster and we may only be able to recover to the extent of pre-1900 technologies. The Federal government should stockpile steam locomotives, steam tractors, steam boats, steam machinery as well as non electronic diesels and protect the grid as well as possible. They do not appear to have done so. Farmer/Preppers should have horses and mules and plows and implements for them. IMHO an EMP is the greatest threat to our way of life and our life itself.

  7. when visiting London and seeing several museums I realized that Great Britain had a full industrial civilization built on steam, with electricity only in their telegraphs. Thats the way to go.

    1. That would only work on the relatively low frequencies of an EMP. Because the EMP is made up of broad spectrum energy, the higher frequencies would pass right through with little to no attenuation. Most larger Faraday cages are built with copper screening with holes about the size of window screen, but even that struggles when you get above microwaves. Solid is best. The larger the holes, the more high frequency stuff gets through.

  8. TICK TOC- TICK TOC keeping time after emp,,, most use a watch or cell phone NOW for a time piece but they all will be exposed and may not work. old school windup with no power may be the solution. when someone needs to wait 30 min or meet someone at 3:30 pm at some location how will anyone know what time it is without working timepiece ? also buy windup manual alarm clock for wake ups or work shifts or timer .

  9. A previous owner of our house left a circa 1960 refrigerator in the basement when we bought the house. It sucks massive amounts of electricity, but I’ve now lined it with castoff foam mats from the local gym, covered the exterior seams & around the door gasket with foil tape to make a wonderful Faraday cage. The first time I tried it a cell phone inside got no reception whatsoever. Y9u can find castoff fridges at every garbage dump in the US & Canada for free & the foil tape is relatively inexpensive.

  10. Another question from me: My All American Pressure Canner, which has no gasket, sits unused about 363 days a year. Does it meet the criteria for use as a Faraday cage? There is one heavy gage tube opening, interior diameter about 1.5 millimeters, exterior diameter about 10mm. If I have the insulated bag inside with electronic gear (such as handheld radios, etc.) inside and the top cranked down is it enough protection?

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