EMP Box or Faraday Cage?
A lot of preppers are looking for ways to protect equipment from EMP /CME /E-Bomb events. Discussions on-line almost always devolve into a moray of opinions on how to build a “Faraday Cage” to provide this protection. The assumption is that such a barrier will block all effects of the three events mentioned previously.
Faraday cages are good examples of the perfect conductor, in that the conducted charge is equally spread over the outer layer /mesh, from one side to the other on its way to a suitable ground. Because an EMP (used here on to stand in for all three) event is seen as an electronics killer due to high current and voltages frequently mentioned, the concept of a protective cage standing against the monster surges becomes an automatic connection in the minds of many. For those that don’t make the seemingly obvious connection, there are always others ready to supply it for them.
But, there is this little problem. You see, the energy from an EMP doesn’t directly correlate to as commo0nly known. There is no socket, no power strip and no extension cord connected to a power source with evil intentions for our electronics. We can not stand in where a current seeks to fry our gadgets, and direct it out and around. EMP energy is created and delivered in manners unrelated to a power company suddenly turned vicious with the electronics-taser-of-death. The currents themselves can often be propagated within the equipment itself.
This study covers much of how an EMP is generated. It takes but a little time to read to understand that this threat is a different beast altogether, and has only little resemblance to a 120v outlet short circuit applied to a computer, TV or phone.
The EMP Box
I hope that by now, you can see that a specialized protective container specifically suited for EMP survivability should be used in place of the Faraday cage. Fortunately, “designing” one does not require an electronics engineering degree. The specifics regarding an EMP Box are few, but important.
- The EMP Box should be as close to an enclosed container as possible. No gaps, holes or slots.
- It should not be grounded if a true EMP event is its reason for existing. A CME or E-Bomb *might* benefit from grounding. A manual discharge before opening the container would be sufficient.
- Protection by means of complete and nu-penetrated enclosure is far more important than the ready ability to open the container.
The Ammunition Can EMP Box
Ammo cans are just about everywhere a prepper normally looks for surplus supplies. They are sturdy, can take a beating and do their job well. Storing ammunition in a dry and air tight environment is no problem for them. Keeping equipment safe from an EMP is something else entirely. Left as built, they will not protect most equipment.
All genuine ammo cans use a rubber gasket between the lid and body flange to create the air tight seal. This gasket is trapped in the lid, and when the can is closed, it serves as a stand-off between the body and lid mating surfaces. This stand off creates an nearly perfect uniform gap that is transparent to the pulse effect. Depending on the environment, it might even act as a slot antenna, which will actually assist a pulse in penetrating the can.
To change the can to serve as an EMP Box, the modifier must:
- Remove the rubber gasket.
- Remove paint from the gasket seat in the lid.
- Remove paint from the lip of the can about 1/8″ down both the inside and outside.
- Create and install a “crush gasket” to occupy the space left after the rubber gasket seal is removed.
- Seal the outside of the joint. Optional, but helpful.
- Seal any other penetrations to the can.
Sealing the gap is the key. Without that step, you might as well leave the rubber gasket in place. There are many conductive and pliable gasket you can buy and use in this case. If you go that route, consider the operating specs for the gasket, and be sure the one you buy will operate as designed within the gap you place it.
An alternative to a commercial gasket, which will need to form a solid union where each end comes together, is a home built crush gasket. Aluminum foil, folder over and over, with enough material to lay over the edges of the can, will work. When rolled correctly, it will crush and resist crushing – pressing up against the lid and forcing you to apply a good amount of downward pressure just to close it. It will “spring back” some when opened. It may not be reusable without a reforming, so be careful about opening the can to inspect things.
A second method is to flip the EMP Box over onto it top, and melt plumber’s solder into the gap. This can be messy, as the solder will try to run into the can through the gap. If you lay a solder wire along the gap as a barricade, it will help hold the melting solder near where it should be, and join into the effort. This one takes practice. But the end result is a PERFECT seal that will allow you to use a desiccant in the can to control moisture.
A third method allows you to get into the box quickly, but might not work against a very strong pulse. Aluminum tape. After the box is closed, with its rubber gasket remaining in place, tape the box closed with 2″ aluminum duct tape. This metal tape can hold its shape well, is very sticky, and doesn’t deteriorate. The glue, however, prevents a true metal-to-metal contact. In effect, the tape is held slightly above the can’s surface by a measurement equal to the thickness of the glue. That dimension is tiny, but will allow wavelengths short of it to pass. Wider tape might make things more secure. If you wish to go one extra mile, remove the paint between the lid and body just outside the rubber gasket, press rolled foil into that space, and seal with the tape.
What you want is as much a perfectly sealed metal box as possible.
I’ll get into the packing methods in a later post.