Letter Re: Metal Building as a Faraday Cage

Metal Building as a Faraday Cage


I will be building a small building to house electronic equipment (batteries for off-grid) and want to protect it from any EMP type of conditions. If we use metal roofing and clad the outside in corrugated metal would that be satisfactory protection? There will have to be ventilation for it too. The equipment will have to be well grounded.

HJL’s Comment:

If the panels are bonded together well (meaning more than just the 1 screw every 4 feet) and you have some form of conductive flooring also bonded to the building, then yes, it would work. Most metal building will not work well because of those two deficiencies.

Letter: EMP Foil Wrap

EMP Foil Wrap

Good morning, Hugh and James,

I’ve posed questions before RE: EMP protection, and now I have one or two more.

Survival blog had a recent series of posts about how to EMP-proof steel ammo cans; I found them enlightening. but they sparked some questions.

A Faraday Cage

The purpose of a Faraday cage is to completely enclose the item one wishes to protect with a conductive material. This will not permit passage of electromagnetic energy of certain wavelengths. The usual approach to Faraday cages is to exclude all wavelengths of electromagnetic energy. Different electronic components may also be susceptible to energy of different wavelengths. An EMP event may include myriad wavelengths of electromagnetic energy. This creates the preference for solid material, rather than mesh, EMP protection.

Protecting Electronics in Metal Military Surplus Ammunition Cans- Part 3, by J.T.

Faraday cage gasket

I am sharing a better solution for protecting sensitive electronics stored in metal military surplus ammunition cans made into a Faraday cage. In the Part 1, I talked about the ammunition cans that can be used and began the instructions for building ammunition can gaskets by listing the materials and tools required. Part 2 of this series consisted of the bulk of the instructions of how to make and assemble the RF and EMP shielding gasket, and we are continuing with these today, in Part 3. The following instructions are for a 20mm M548 ammunition can.

16. If you want to “belt-n-suspender” the conductivity between the sheet metal gasket and the lid, then remove some of the paint to reveal bare metal so that you have a good bare metal contact between the sheet metal gasket and the lid.

The sheet metal gasket with the copper mesh tape will be … Continue reading

Protecting Electronics in Metal Military Surplus Ammunition Cans- Part 2, by J.T.

Lid Gasket

I am sharing a better solution for protecting sensitive electronics stored in metal military surplus ammunition cans made into a Faraday cage. In the Part 1, I talked about the ammunition cans that can be used. We then began the instructions for building ammunition can gaskets by listing the materials and tools required. Now, let’s move on.

Making and Assembling the RF and EMP Shielding Gasket

The following instructions are for a 20mm M548 ammunition can, which is my preferred can size. If using another ammunition can, you will need to make adjustments in measurements within these directions to adjust for your ammo can’s size. I’ll give some guidance along the way for doing so.

1. Cut the sheet metal into a 7” by 16¾” rectangle, for the 20mm can.

But always start out by taking a good measurement. You know the old saying of “measure twice, cut once” still … Continue reading

Protecting Electronics in Metal Military Surplus Ammunition Cans- Part 1, by J.T.


In this multi-part article, I am sharing a better solution for protecting sensitive electronics stored in metal military surplus ammunition cans. There are many references for making a Faraday Cage on SurvivalBlog. Some references go back as far as 2005. One solution was proposed in 2006 that required the removal of the rubber gasket on ammo cans and replacing the seals with a conductive material (stainless steel or steel wool). Other articles suggested the use of a galvanized garbage can that is sealed up with conductive metallic tape, or an open head steel drum, or using an old microwave oven and a metal cabinet. I have read and researched many great comments and feedback on the effectiveness of these EMP protection measures.

Previous Proposals

All of the proposed solutions are more or less effective. … Continue reading

Letter: Faraday Cage Question

Faraday Cage

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…. Continue reading

Letter: Advice for Disabled Suburban Retiree Preppers

HJL and JWR,
I’m seeking links or tips on how a 77-year-old disabled person can defend his property in case there’s TEOTWAWKI. My wife is 72.

We live in a middle class subdivision 45 miles from Cleveland, Ohio. Because of physical disabilities (neuropathy, bad knees and legs) I am not very mobile.
I use walker/cane most of the time.

We are moderately prepared (food, guns, ammo, junk silver, etc. A retired Marine lives at the other end of the block but says he will bug out if SHTF.
Nobody else on the block seems even to be aware of the dangers of a potential disaster (natural or man-made).We are one block from main artery, one mile from an interstate.

Finally, where is the best place to shop for potassium iodide?

Thank you for what you do on the blog.  We have been … Continue reading

Letter: Using Military Ammo Cans for Faraday Shielding

Dear JWR:
The use of military surplus ammo boxes as Faraday shields was recently mentioned again in SurvivalBlog.  But readers should be reminded that these cans will not work in the configuration where they are normally purchased.  This is because the boxes have a rubber gasket to seal the lid from water and that makes the lid not in [electrical] contact with the body of the can, thereby losing the [EMP] shield effect.  Regards, – Dave X.

JWR Replies:  You are correct.  As mentioned previously in SurvivalBlog, the best approach is to remove the rubber gasket,  rough up the metal on both the top edge of the can lip and in the gasket groove (with sandpaper, a wire brush wheel, or a Dremel tool rotary stone) and replace the thickness of the gasket with stainless steel wool which is tacked in place with small globs of epoxy … Continue reading

Letter Re: EMP Telltale


Whenever the power goes out wherever I am, the first thing I do is see if my battery-operated watch is still working. I suspect one of these times, the screen will be blank or just chaos. – Sid, too near Niagara Falls

HJL Comments: As technology advances, the gate sizes grow smaller making such electronics more susceptible, but at the same time manufacturers recognize that they are more susceptible to static electricity as well. As a result, manufacturers almost always include some basic protection in the on-board circuits. Add to that the concept that the amount of energy absorbed by these electronics is directly related to the amount of “antenna” on the circuit board and you end up with practically no idea whether your watch will survive or not. The circuits are so small that the antenna lengths are negligible (unless you happen to be plugged in charging the … Continue reading

Using EMP-Hardened HF Ham Radio to Send/Receive E-Mail During Nationwide Outage- Part 1, by PrepperDoc

There are multiple possible scenarios that may result in a regional an/or national combined loss of Internet connectivity and cell/telephone service, during which you would probably wish to maintain communications to loved ones and others. EMP may destroy routers, cell towers, and power sources; solar coronal mass ejection (CME) may remove power from all communications systems; cyber warfare may have similar outcomes. Travel in some of these circumstances will be difficult, or dangerous to impossible.

Ham radio VHF/UHF repeaters may go down, due to power outages or EMP. Direct, point to point simplex VHF Ham radio will still work (even after an EMP, if hand-held radios were at all hardened or protected) over modest distances. Long range HF direct Ham radio communications will work (possibly after a delay of any EMP), presuming you had protection (if EMP) and have your own power. However, they will be of less usefulness … Continue reading

Letter Re: Shielding Electronics From EMP

Another point on electromagnetic pulse (EMP) and Faraday cages is even something simple can be protective. There are 30 Gallon galvanized steel trash cans with lids (made in the USA!) available at my local farm and ranch store for $22. This makes for affordable and easy storage, and you can wrap things in common aluminum foil. Or even something like a steel cabinet or vault, but generally try to avoid gaps or spaces. It doesn’t have to be zero signal, but reduce the field strength enough to prevent damage.

Vehicles have some protection for many years. In the early days of electronic ignition systems, truckers with CB linear amplifiers were causing police vehicles to stall. And driving near powerful radio towers also caused some glitches. The protection added since the early 1970s isn’t military grade, but realize if your vehicle doesn’t even hiccup when it is next … Continue reading

Two Letters Re: EMP Effect and Pacemakers

While case-by-case circumstances can effect the practicality of many alternatives, there are external pacing and monitoring options. The Zoll Company for example has just released a type of vest, worn similar to a brassiere with a fanny pack (battery pack). This device consistently performs cardiac monitoring and when a shockable rhythm presents itself the device does just that. More archaic methods would involve adhesive defibrillation or subcutaneous pacing patches and a cardiac monitor, while the monitors can be significantly expensive, older models are available at online auction sites. Both the aforementioned devices can be recharged, and more importantly, stored in a Faraday cage to protect them from an EMP. Neither would be as convenient as implanted devices but in a pinch could be just the thing to keep that ticker going.  – John, EMT-P.

Dear Editor:
You aren’t safe even when it is not an … Continue reading

Letter: EMP Effect and Pacemakers

I have an implanted cardiac device (a pacemaker and defibrillator) and, after reading the letter about possible effects of electromagnetic pulse (EMP) on batteries, became curious as to how an EMP or maybe a strong solar flare could affect my device. I searched SurvivalBlog’s archives and saw that such an event could possibly damage the implanted cardiadefibrillator (ICD). Is there any firm evidence as to what may actually happen to an ICD or similar device in the human body and anything that can be done to counter the effects? It seems it will be a bleak future for the millions of people whose life depends on some form of technology in the event of a worse-case scenario, but, God willing, I still plan on having a long life. Thanks. – J. “Doc” Holiday

Hugh Replies: Yes, this is a troubling issue. Integral pacemakers with defibrillators have leads … Continue reading

Letter Re: EMP Question


I’ve asked Matt Bracken this question, and he didn’t know. I’ve read all of your EMP-related data, but none of them answer the question of whether batteries, particularly the small D, C, AAA, AA types need to be shielded to protect them from EMP. All authors make much of electronics in devices but never mention separate stores of batteries or the dangers of batteries stored in electronic devices like radios, sights, et cetera. Your advice would be greatly appreciated. – S.D.

Hugh Responds: There is much FUD in the online world (and in books) about EMP. Some of it is well deserved, and some of it is simply because of ignorance about how such forces work. There are two interrelated factors that are critical in determining how destructive an EMP would be towards electronics:

  • Peak impulse energy
  • Length of the reception antenna
  • The peak impulse … Continue reading

    Two Letters Re: The OTHER Electrical Grid Failure Problem


    I just retired from 24 years of bouncing around the nuclear plants in the U.S. and abroad. For work planning, fire stop penetrations, and OSHA worker safety, every nuclear plant in the world has at least 20 electricians on-site 7/24. During a refueling outage, add 100 to that number. – K.G.

    o o o

    Hello Hugh,

    I read the comments about electricians at nuclear plants and the inability to have more than one or two there in an emergency situation. While I am not disputing that possibility, the entire situation should be told. Electricians are support staff at any nuclear station. I have been an electrician at a dual unit nuclear station for over eight years after years of being a contractor. We work for the Operations Department, which is there 24/7/365, and they are required per NRC Tech Specs to maintain minimum staffing at all times. So there … Continue reading