faraday cage

[HIG541]

does anyone know if an ammo can would work as a faraday cage? seems as if it would.

[TimRB]

Yes. If the box is magnetic (mild steel, for instance) it will also protect (somewhat) against magnetic fields, too.

http://en.wikipedia.org/wiki/Faraday_cage

Tim

[HIG541]

hmmmm. they are made of aluminium, so maybe not. thought they just had to be conductive. thanks for the link.

[TimRB]

An aluminum box will work as a Faraday cage. It will not protect against magnetic fields. Magnetic fields and electric fields are related but different.

Tim

[GrizzlyGuy]

Tim is correct, aluminum is fine. A few of mine:







The big toolbox has my most valuable stuff (2x HF ham radio stations, VOM, solar charge controllers, proto board, etc.) and I actually don't know if it is steel or aluminum:

[k1dude]

It will only work if you don't let the contents contact the metal of the container. Use a block of wood or some other non-conductive material to separate the contents from the container. The container must also be grounded. And the best way to ground is to connect the container via conductive cable to an actual metal stake in the ground. Just placing objects in a metal box won't do the job.

[Helpful_Cub]

does anyone know if an ammo can would work as a faraday cage? seems as if it would.

Are you trying to protect equipment from EMP?

[GrizzlyGuy]

It will only work if you don't let the contents contact the metal of the container. Use a block of wood or some other non-conductive material to separate the contents from the container. The container must also be grounded. And the best way to ground is to connect the container via conductive cable to an actual metal stake in the ground. Just placing objects in a metal box won't do the job.

It doesn't need to be grounded unless you are running wires into the container. From here on pg. 3-6: EP 1110-3-2, ELECTROMAGNETIC PULSE (EMP) AND TEMPEST PROTECTION FOR FACILITIES (31 DEC 1990)

(6) Grounding. Some form of grounding is required in any electrical or electronic system for protecting personnel from electrical shock, controlling interference, proper shunting of transient currents around sensitive electronics, and other reasons. (Grounding does not directly provide protection against EMP, but must be done properly to prevent creation of more serious EMP vulnerabilities.) Ideally, grounding would keep all system components at a common potential.

The "more serious EMP vulnerabilities" they are talking about are common mode currents and voltage differentials that can result from the inbound cabling serving as inadvertent antennas.

[C&Rtrader]

I was told that old microwaves work? any thoughts or comments?

work = protection from EMP etc

[Cnynrat]

I was told that old microwaves work? any thoughts or comments?

work = protection from EMP etc

I don't know about this for sure, but it does make sense. Microwaves are designed to keep microwave energy inside the unit.

Ammo cans or other metal boxes are probably cheaper though.

[k1dude]

It doesn't need to be grounded unless you are running wires into the container. From here on pg. 3-6: EP 1110-3-2, ELECTROMAGNETIC PULSE (EMP) AND TEMPEST PROTECTION FOR FACILITIES (31 DEC 1990)



The "more serious EMP vulnerabilities" they are talking about are common mode currents and voltage differentials that can result from the inbound cabling serving as inadvertent antennas.

I would rather believe the military rather than some obscure paper. Hardened electronics in the military use grounded faraday cage technology specifically for protection against EMP weapons and solar flares. There's LOTS of information on the internet from reliable sources that back up the need for grounding against EMP weapons. Your reference is the first I've ever seen to suggest otherwise.

Also, a well constructed Faraday cage is made of mesh, not solid walls.

EMP's effects are mostly theory. The only real world experience with weapons generated EMP's was a result of the "Starfish Prime" altitude detonations in the early 60's. Study what they found that worked and didn't work. Ham radio operators discovered quite a bit about the effects. I'll stick with what the military found out worked - they ground their equipment.

[TimRB]

Also, a well constructed Faraday cage is made of mesh, not solid walls.

It doesn't *need* to be made with solid walls. Mesh is lighter and cheaper, but solid conducting walls will also work just fine.

Tim

[k1dude]

It doesn't *need* to be made with solid walls. Mesh is lighter and cheaper, but solid conducting walls will also work just fine.

Tim

I didn't say it wouldn't work, I just basically said mesh is better.

And don't make the wire from your ground stake to your cage too long or it will act as an antenna.

[GrizzlyGuy]

I would rather believe the military rather than some obscure paper. Hardened electronics in the military use grounded faraday cage technology specifically for protection against EMP weapons and solar flares. There's LOTS of information on the internet from reliable sources that back up the need for grounding against EMP weapons. Your reference is the first I've ever seen to suggest otherwise.

Uhhhh... I assume you didn't even look at the document. Top of first page, this is who published it:

DEPARTMENT OF THE ARMY
U.S. Army Corps of Engineers
Washington, DC 20314-1000

You might want to read or at least skim through the rest. It is 467 pages describing how the military protects it's own stuff from EMP, lightning, etc. The rest of your post contains bad information. For example, read up on Maxwell's Equations and tell me if you still think that mesh is better than solid metal.

[jmancini]

I didn't say it wouldn't work, I just basically said mesh is better.

And don't make the wire from your ground stake to your cage too long or it will act as an antenna.

Where are you getting your information? Mesh is generally a lot worse at shielding, since any holes in the mesh must be smaller than the wavelength you're trying to stop. That's basic EE stuff.

Grounding isn't required for the Faraday effect, in fact, the high-voltage linemen at your local power company would be incinerated if the Faraday suits they wore were grounded.

It baffles me where all this misinformation comes from, when good information is so easy to get nowadays.