Building an Effective Faraday Cage to Protect Against Lightning Strikes

[St. Elsewhere]

Originally Posted by Ozbullwinkle

There is obviously a market opportunity for a small Faraday Cage for the boating community. Which makes me wonder why one is not available?

The market for boating products is very small compared to most other items such as cars, toasters, etc. A very small subset of the boating public would buy a faraday cage, so there is no money to be made from them. Also, they are easily improvised. The fellow was right about using an old muffin tin.

[teejayevans]

To test if your faraday cage works, simply put a cell phone in it and then call the cell phone, if it rings, its not a faraday cage.
Tom

[bazzer]

Faraday cages in the Royal Air Force were no more than chicken wire. Worked well with powerful transmitters inside them. Couldn't rx much from the inside either.
Did anyone here watch The Mythbusters sitting in a car when subject to a simulated lightening stoke ? They lived. Any closed metal box or wire cage will work

[mikereed100]

Originally Posted by mikereed100

I experimented with this and it protected my electronics from lightning very well, but when I pullled the trap up the salt water had ruined everything.

I posted this tongue-in -cheek but when my wife saw it she said;
"why wouldn't that work?"
I patiently explained to her about salt water immersion and electronics to which she replied;
"I know that, numbnuts (she means that in the nicest possible way), but why couldn't you put everything in a weighted, watertight container and lower it over the side until the storm has passed?"
"Because, well, damn..."

Is she onto something?

Mike

[Nicholson58]

You wouldn't need anything as bulky as a metal box. If you don't have an oven or microwave, both known effective methods, you could use a chain-mail.

ThinkGeek :: Chain Mail Shirt



THis is too fun. Google chain mail bags and be entertained for hours. There were chain mail brazires - hopefully not for protection from lightning.

[teejayevans]

Originally Posted by mikereed100

I posted this tongue-in -cheek but when my wife saw it she said;
"why wouldn't that work?"
I patiently explained to her about salt water immersion and electronics to which she replied;
"I know that, numbnuts (she means that in the nicest possible way), but why couldn't you put everything in a weighted, watertight container and lower it over the side until the storm has passed?"
"Because, well, damn..."

Is she onto something?

Mike

I would double bag it....just in case, and make sure its well below the surface.
Tom

[Ocean Girl]

Originally Posted by teejayevans

To test if your faraday cage works, simply put a cell phone in it and then call the cell phone, if it rings, its not a faraday cage.
Tom

Is this true?

And will making a small chainmail duffle bag really work? Will it still need another box?

I'm uh er , electrically challenged, so what is the most reliable, simple to assemble, faraday cage?
thanks,
Mrs. Rain Dog

[colemj]

Originally Posted by Ocean Girl

Is this true?

And will making a small chainmail duffle bag really work? Will it still need another box?

I'm uh er , electrically challenged, so what is the most reliable, simple to assemble, faraday cage?
thanks,
Mrs. Rain Dog

Testing a cell phone is not an indication of a good Faraday cage for lightning. It is an indication of a good Faraday cage for microwave transmission. I suspect a chain mail duffle will not block microwaves, but it may block lightning frequencies - depends on the size of the holes and how well the links contact each other. The latter point will be a big challenge for chain mail.

But test the brazier and report back on its lightning protection!

Mark

[LakeSuperior]

I am under the impression that the Faraday cage does great for the electro part of the pulse but there is also a changing magnetic field that will induce damaging current in device conductors. This is the M part of EMP in a lightening strike.

The Faraday cage will not protect the electronics from the magnetic pulse. Consequently, your electronics will still get fried.

[Lagoon4us]

The microwave worked a treat, in our case that's good info thanks....

[bazzer]

How aircraft which are frequently struck by lightening do not have their electronics"fried"? Just like the car electronics in Mythbusters everything including the occupant was fine.
Now, the solar flare due tomorrow is another thing. A big one in the late 1800 hundreds caused telegraph wires to glow and work without batteries! I'm hoping smart meters and drivers cell phones get it

[St. Elsewhere]

Originally Posted by bazzer

How aircraft which are frequently struck by lightning do not have their electronics"fried"? Just like the car electronics in Mythbusters everything including the occupant was fine.
Now, the solar flare due tomorrow is another thing. A big one in the late 1800 hundreds caused telegraph wires to glow and work without batteries! I'm hoping smart meters and drivers cell phones get it

Commercial airliners use twisted shielded wiring on some circuits, but do not employ the braided shielding over entire harnesses to the extent that has been done on military aircraft. My information dates back a couple of decades, but I believe that the H fields of a lightning strike are sufficiently less than from an EMP from a nuclear detonation to allow airliners survive routinely.

[teejayevans]

Originally Posted by LakeSuperior

I am under the impression that the Faraday cage does great for the electro part of the pulse but there is also a changing magnetic field that will induce damaging current in device conductors. This is the M part of EMP in a lightening strike.

The Faraday cage will not protect the electronics from the magnetic pulse. Consequently, your electronics will still get fried.

Sure it will, it will induce a current into the faraday cage and not your electronics, but of course this creates a magnatic field which induces a current into the electronics, so you would need a nested faraday cage, but we're not talking about a EMP from a nuclear blast. Also the faraday cage needs to be grounded.
You could use aluminum foil, which has no gaps.
Tom

[hpeer]

The 'magnetic' part requires some magnetic type material to shield it from the H fields, think mild steel. Aluminum will not work against the H (magnetic) fields.

That is not to say that there is no value in wrapping something in aluminum.

Frankly the fields and frequencies you get from a lightning strike vary so much that many freak things can happen. I don't think that there is an 'sure' solution even though many of the things proposed above are surely better than nothing.

Yes you need grounds, and they should be straight and direct and short as possible. Nice neat wiring with 90's cause self inductance which works against the grounds effectiveness.

I don't want to get into any kind of peeing contests here over the right and wrong way to do things. Perfect is the enemy of the good. If you do something, then you are probably in the top 10% of folks. If you worry about it, you probably need a counselor.

If you are a obsessive, compulsive, nut case....buy a steel boat.