What is a Faraday Cage?

The discovery and application of the principles of electricity surely made our lives a thousand times more convenient. But what if I tell you that one mishap can fry every electronic device there is? Yes, you are reading it right. Imagine that! One day, you wake up but not from your phone’s alarm clock but from the rooster’s morning call. You instinctively grab your phone and check for messages, but the fully-charged phone will not even turn on. Then, you try to stand up and turn the TV on. But no, the TV won’t turn on. No phone, no radio, no television, and no Wi-Fi. That’s no ordinary brownout. How well will you fare without the aid of electronics?

 That’s why Be it by a natural phenomenon or by an intended attrition, we can all be sent back to the stone age in the blink of an eye (at least temporarily). This fact alone is enough reason to build a faraday cage.

What is a Faraday Cage?

Ever wondered why passengers and equipment are not fried when a lightning hits a plane? Have you ever pondered why elevators are usually cellphone signal “deadzones?” Those two phenomenon can be attributed to the fact that airplanes and elevators act like Faraday cages.

Faraday cages are your savior when EMPs knock the grid out. Therefore, faraday cages are enclosures that shield their contents from external magnetic fields.

Applied use of Faraday Cage

Today, faraday cages have thousands of practical applications. For example research, medicine, counter-espionage, security, forensics and many others. You can see faraday shields in a day-to-day basis. *coughs* microwave oven *coughs*

Here is a list of some non-prepping applications of Faraday Cages:

  • Booster Bags – shoplifters use such bags to steal RFID tagged items without causing detectors to raise an alarm
  • Chemistry– Faraday cages are used to isolate subjects while doing sensitive measurements
  • Faraday Suits – these are conductive clothing that acts like Faraday cages which help linemen work on live power lines
  • MRI – the scan room of MRI machines are designed to act like faraday cages so that RF signals will not interfere with the output image. As a prepper, you will be interested in building a Faraday cage to

Why Build a Faraday Cage?

As a prepper, you should be interested in building a Faraday cage because of natural and unnatural events that can fry electronic systems. Take note, however, that there are both true and fallacious claims about which events you should prepare for.

Solar Flares and Geomagnetic Storms

sun emitting solar flares

Contrary to popular belief, solar flares cannot fry your electrical systems.

Solar flares are astronomical events that is characterized by a sudden spike in brightness of a certain area of the sun. Normally, solar flares will not interfere with our planet’s magnetosphere to an extent that terrestrial-based electronics will be messed up, especially when the flare is not directed to our planet. However, X-class flares and beyond can be accompanied by a CME (Coronal Mass Ejection) which release significant amounts of plasma producing a magnetic field. If such a solar flare is directed to Earth, then the magnetosphere can be temporarily “deformed” as it is assaulted by a geomagnetic storm.

Recall your basic physics. Electrical current is produced when a magnetic field moves about a conductor, right? Now, imagine that the Earth’s magnetic field moves constantly due to deformation. This means that there are magnetic fields moving around every terrestrial conductor, producing geomagnetic current everywhere! Power grids will shut down as their load thresholds are breached. Mile long transmission wires will build up current and damage the grid as they cause a power surge. Your appliances can devices can be damaged too if they are plugged.

Carrington Event

While this may all sound taken straight from a science fiction novel, this calamity can happen in real life. In fact, the solar storm of 1859 (aka Carrington Event) fried Telegraph lines, electrocuted operators and even caused fires. Thankfully, surge protection, circuit redundancies and overload protections like provide better protection nowadays. In addition, space agencies like NASA are capable of detecting CMEs in advance so CMEs will not catch us off guard.

If you think that the Carrington Event is merely a coincidence, then think twice. In 2012, a CME near-miss occurred.[1] Back then, a CME hit Earth’s orbit. Fortunately, Earth is no longer in that position when the phenomenon occurred.

Safety First

Consumer electronics and digital vehicle control systems are quite safe from being toasted since they will not generate enough current to damage themselves, unlike the transmission wires that span miles long.

Be wary when people say “hey buy this, it will save your electronics during a solar flare”. Why need a lifeguard when there is no water at all, right? Keep in mind that solar flares will damage the grid and interfere with communications, gps and radio signals but it will not damage electronics. Faraday cages won’t save you here.

Nuclear EMP (HEMP or High-altitude EMP)

The world of geopolitics is slowly heating up. As the major powers struggle for dominance and self-preservation, advance warfare tactics and technologies that prey on both military and civilian technologies are being developed. Nuclear warheads belong to such technologies.

If a nuclear warhead is detonated in an altitude high enough to not cause casualty but low enough to let the electromagnetic pulse it produce to interact with electronics, major damage can be done to the entire grid. Unlike CMEs, Nuclear EMP can damage even consumer electronics.

Nuclear Explosion

A nuclear explosion can generate an electromagnetic pulse which can RAPIDLY alter magnetic field in its vicinity, causing arcing and generating voltage surges in electronic devices. If the surge protectors from your electronic devices can resist the little-to-no-effect of a CME, they won’t be able to save your devise and appliances from a Nuclear EMP. The first pulse of a nuclear blast, E1, is too fast to be resisted by ordinary surge protectors so rest assured that you can kiss your Television goodbye even if you use surge protectors unless you get your hands on a military grade one.

The second pulse of a nuclear blast, E2, bears similarities to a lightning. Hence, it is not much problematic than the first blast thanks to the fact that most designs consider lightning protection. The third blast, E3,  (Surprising, really) can last for thousands of seconds. This last pulse is similar to a geomagnetic storm. Just imagine CMEs, except that it is a lot closer to you than a CME that accompanies a solar flare. Simply put, the third pulse from a nuke can induce geomagnetic currents in very long wires and eventually overload an entire power grid.

Needless to say, Faraday cages will help you save your electronics from a nuclear EMP.

How do I Build a Faraday Cage?

Principles Behind a Faraday Cage

Don’t frown just yet! We won’t do dot multiplication or anything that involves vector analysis. Let’s keep things simple and say that a Faraday cage cancels out the net electrical charge inside it thus making EMP useless. Once an electromagnetic wave hits a Faraday cage, an electrostatic induction is triggered, pushing all the negatively charged particles (electrons) which will pile up in one side, leaving all the positively charged particles (absence of electrons, aka holes) on the other. This makes the center electrically neutral. Hence, when an EMP hits a Faraday cage, the pulse is simply cancelled out.

Judging from this principle, we can conclude that all we need is an enclosed conductor, but don’t clap out of excitement yet. Before we actually build a Faraday cage, we have some more things to consider and myths to debunk.

Things to Consider When Building a Faraday Cage

A Faraday Cage Do not Have Be Grounded

Most Youtube videos and random blog DIY instructions in the net will tell you that a Faraday Cage should be grounded, unless you want to damage the contents. Candid rebuttal; NO. Grounding is not necessary, but it won’t hurt to have them. You’ll only need to ground a Faraday cage if you will use it for a fancy “electricity-will-not-kill-me-while-I-am-inside-this-cage” roadshow, or if you will use it to house a device that can generate electricity by itself. In any case, the grounding is used for protecting you from electrocution. With a grounding, only a negligible amount of current will flow through you and the rest will flow through the grounding, as per the Ohm’s law. If you ground a small scale Faraday shield (like the one we will build), chances are, the ground will serve more as an antenna for EMP thus doing more harm than good.

Mesh Faraday Cages are not useful against EMP Attacks

It is true that Faraday cages made of chicken wire mesh can disrupt both AM and FM radios, but that does not necessarily mean that they can repel electromagnetic pulses as well. The frequency of an electromagnetic pulse is way higher than the frequencies of AM and FM. EMP can range from 100 MHz to 100 GHz while FM and AM frequencies only range from 88-108 kHz and 540-1600kHz, respectively. Higher frequencies will require less space to pass through a Faraday cage, hence EMP can pass through small spaces. This means that we’ll have to use totally enclosed space.

Size Matters

Consider what you want to store in your Faraday Cage. Will you store mobile phones (which will be useless because the grid will be down anyway)? How many of them? Or will you stash a couple short-wave radio (and you need to stash them)? And what about your trusty laptop? Will you store an extra solar inverter as well? Consider this before you actually decide the materials you will use for you Faraday cage.

There is no Truth in “The Thicker the Better”

While it is quite tempting to stack multiple layers of aluminum foil in the surface of your cage, the “skin effect” makes attenuation less effective when a certain thickness is reached. We will not go in depth with the skin effect, just keep in mind that alternate layers of conductor and insulator works much better than multiple stacks of conductive layers.

Sealing the Lid of a Container Can Make it more Vulnerable than Stronger

Some DIY blogs will instruct to seal the lid with duct tape, plastic or any insulating layer. NEVER DO THIS. If you cut off the electrical connection between the lid and the container, EMP hitting the lid will be projected directly inside causing more harm than good. If you try to seal a lid, seal it with a conductive material such as aluminum foil. This will not disrupt the connection between the lid and the body.

The DIY Cage you will do will NEVER be perfect

Contrary to what most blog say, there’s no way we can completely fend off a nuclear EMP using DIY cage. Even industrial grade Faraday shields will hard time doing so. Nevertheless, a Faraday cage is critical for attenuating an EMP attack so signals will not be strong enough to toast your electronics.


A Faraday cage should have two main components: the insulating layer and the conductive cage. The cage will decide the size and penetrability of the entire Faraday cage. Make sure that the caging material you use is conductive and has no spaces in between. If you can’t find a good conductive cage, then you can use any enclosed material and wrap it in nested aluminum foils.

You will need the following materials:

  • Enclosed conductive material
  • Heavy duty plastic bags
  • Cardboard
  • Adhesive material
  • Conductive sheets like aluminum or copper mesh

I won’t lay out a detailed instruction since it is pretty straightforward, but here is a summary of steps:

  1. Choose a container
  2. If the container is not a conductive material, wrap the container in heavy duty aluminum foils.
  3. Seal the lid using a conductive  material (like aluminum foils, copper sheets etc)
  4. Stick cardboard boxes in the inner faces of the container.
  5. Wrap the device you will store with a heavy duty plastic bag. Then, wrap the plastic bag with a conductive material. After this, add another layer of insulation. It will be ideal if you add a mix of aluminum and copper mash as conductors.


You’ll never know when you will need Faraday cages. Nevertheless, it will always be wise to prepare for anything possible. No. Saying a Nuclear EMP attack is possible is underrated. Given the complications in today’s political arena, the term to use is “likely”.

 Learn what to prepare for. Distinguish the myth from the fact.

Phillips, Dr. Tony (July 23, 2014). “Near Miss: The Solar Superstorm of July 2012”. NASA

Ott, Henry (1976), Noise Reduction Techniques in Electronic Systems, Wiley Interscience, ISBN 0-471-65726-3. Ott (1976, figure 6-13)

What do you think?

0 points
Upvote Downvote

Written by Jake Obguia

I love the outdoor life! I grew up in a city and never went out that much. When I was 13 years old, we moved to the countryside. Right then, I found a lifestyle that I loved. I made friends with country boys and they taught me how to fish, raise livestock, pick fruits and plants without the aid of technology. I now enjoy exploring mountains, looking for majestic lakes or river to swim, and camping out.

homesteading off the grid

4 Essential Things To Do When Homesteading Off the Grid

How To Store Fuel at Home

The Ultimate Guide To Store Fuel at Home