Glass-fronted Faraday box?

Danny Jo

Danny Jo

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One reads advice about protecting electronic gizmos like hand-held GPSs during thunderstorms by putting them in the oven, in the expectation that it will act like a Faraday box in the event of a lightning strike. An example is Richard Wood's article in PBO, which is available here.

The oven pictured in the PBO article looks suspiciously like a glass fronted one. I have two questions:

Doesn't the glass front make it a Faraday box with a socking great hole in it?

Is wrapping in aluminium foil as effective as placing in an all-metal box?

Apologies if there has been recent discussion of this issue - I did a forum search on "lightning" and got not hits.
 
Sorry, just had to smile at this one.
I could just imagine everyone running around, removing all their electrical goodies and placing them in the oven if a storm broke out.
Then SWMBO decides to light and preheat the oven ready for dinner /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
 
Have you been in a real storm? You will do anything that you feel might improve your chances! The most scariest event in my life. Hours of just survival situation with strikes and lighting all around. No direct strikes but we lost the SSB tuner and one instrument just from the generated fields from nearby strikes.

A microwave over would be better than a glass fronted oven at least that has the metal microwave filter in the glass.
 
2 years ago we were in the mouth of the Shannon Estuary when the remains of hurricane Alex, now just a depression belted in with imense lightening storms. It flashed and banged all around us, and then to our amazement and before our eyes, two dark sprialling cones formed at the base of clouds about 3 miles away, and they grew, and grew, and started to stretch down towards the sea. Pinched ourselves and convinced that as we were not anywhere near texas and these were not suddenly going to develop into F4s. Made us feel pretty vunerable out there in a little boat! They didn't ground but it was fascinating to see them develop in real time. There are about 1500 mini tornados that hit the British Isles and Ireland every year, most go unnoticed, or just knock dustbins over! /forums/images/graemlins/wink.gif

It did occur to me at the time to stick the hand held VHF and hand held GPS in the microwave - just in case.

Much safer in a steel boat than GRP. GRP will literally delaminate and explode at point of contact with lightening. One of the worries about the use of composites for aircraft skins, metal skins cope with lightening strikes, composites are destroyed. North sea helicopters no longer have composite materials in the main or tail rotors as a result of a strike some years ago to a platform helicopter when the blade shattered.
 
His article refers to a "well grounded" Faraday cage. An oven without proper grounding as described in his article is not going to be fully effective as a defence aginst electromagnetic radiation. Having one side that is transparent to electromagnetic radiation renders it even less effective.

If you're really concerned, wrap it in aluminium foil and put it in the oven, making sure that the foil is touching the metal lining. However don't assume that this will be 100% effective.
 
The oven should not be grounded. It is better if it is free of any connections. You do not want a current to pass through the walls of the oven. If the oven can "float" electrically it will just reduce the field strength on its inside.
 
Off-topic, hope it doesn't spoil your thread. I am most impressed with the Zinio magazine service, haven't seen it before. I can't see PBO on their lists yet you seem to have found it. Being in Spain this service is very interesting, can you explain about PBO and tell me what you think of the service?
 
[ QUOTE ]
Have you been in a real storm? You will do anything that you feel might improve your chances! The most scariest event in my life. Hours of just survival situation with strikes and lighting all around. No direct strikes but we lost the SSB tuner and one instrument just from the generated fields from nearby strikes.

A microwave over would be better than a glass fronted oven at least that has the metal microwave filter in the glass.

[/ QUOTE ]

Depends what you consider as a real storm.
Been a boat fisherman for many years, some large boats, some small. Been out at sea when storms have passed over, watched the lightening hitting the water, but the fishing continued. Was out in a terrific snow storm once, in a 17ft boat and we had to keep emptying the snow out of the cockpit and washing off the decks with salty sea water.
Apart from being a bit chilly and almost zero visibility, everything was OK.
 
[ QUOTE ]
Have you been in a real storm?

[/ QUOTE ]

Yepo. left Chi marina in a thunderstorm this year, I was asked whether I really wanted to go out through the lock. Yes, I said as the storm was behind me at that time. Later in the Solent it was to the SE of me and I was headind West. Really impressive seeing the lightning flashes, wouldn't have missed it for the world. Reckon I've gor more chance of winninga million on ERNIE than getting hit by lightning /forums/images/graemlins/grin.gif
 
Does the glass in a microwave act differently. To retain the electromagntic field. It seems to have some wire in it. Am I wrong? Is it my imagination? Am I drunk?
 
If you see flashes but no strike to water it is miles away.
If you see the strike to water and hear the bang after 4 seconds (as opposed to a rumble) it is a mile away.

If you just get a funny effect where your night vision goes, along with a crackling effect, you are IN the storm.

Looking up and seeing flashes across the bottom of a cloud directly above you confirms it.

The good thing is that most isolated storms can be missed easily. Just treat it like a ship and watch for a constant bearing. It is only continuous lightning storm fronts that can not be avoided. Very rare in the UK.
 
Been in a lightning area that stretched half the length of the Baja. Absolutely no wind and a really no danger. They all stayed very still for 24 hours of entertainment!

Completely different. We could see 30 or so clouds flashing and 10 or so striking to the sea. No rain, no wind and hot sun between the clouds. Also no Visa so we could not turn back!

I cannot comment on your ability to refuse alcohol, but the wire screen in a Microwave will refuse to let the field propagate into the oven. A glass oven door might have a metalized heat reflector coating, but plain glass will allow the field lines to curve into the oven compartment.
 
Just picking up on your comments re steel boats are safer.
If you are going to be hit by lightning you have to manage huge electric currents to ground (or just in the path of the strike as in a helicopter.) Steel can carry a lot of current and having fairly low resistance it does not get too hot. (hopefully)
Stainless steel has significant resistance so gets very hot with high current. The resistance is low enough to attract a strike but high enough to melt or loose its temper (heat reatment not state of mind) so rigging is at real risk in a strike. Aluminium no prob very low resistance.
Now fibreglass has very high ressitance so it does not try to conduct. Unless it is saturated with water, in which case like a tree trunk it will explode with boiling the moisture.

Re helicopter blades they are made mostly of carbon fibre reinforced plastic which has a lowish resistance abit like SS. Modern design standards for aircraft require ressitance to lightning damage which is usually achieved by puting in a layer of conductive wire mesh near the surface. Certainly huge amounts of carbon fibre are used in aircraft skins now days and I understand a transport jet aircraft is struck by lightning average once in 12 months. It is unusual to find noticeable damage in a lightning strike on an aircraft.

So back to the original question, the oven even with non conductive glass door is probably better than nothing in a strike but I feel that current induced voltage damage to sensitive portable electronics might be only a remote possibility.(gear connected to wiring in the ship is very susceptible)(hence pull the plugs out) However I do understand that a nearby lightning storm can be frightening and it must be good to have something you think you can do to help. I might however want to keep the hhvhf and the gps nearby in case of abandon ship in a hurry. I would be trying to provide a good earth(to water) to the mast if I could. olewill
 
Lemain, I think that many magazines use the Zinio software to download their articles. I know that I subscribe to Cruising World and Sail magazine and receive them each month as a Zinio download. You get the software when you take out an electronic subscription to their ezine service. Great way to get the mags you want, anywhere.
 
Is my understanding too OleWil that a commercial aircraft averages getting hit once per year.

I have only been on one when I have known for sure it was struck (a 737) but been on a few when I suspected maybe. In the definite occasion was a flash and metallic twang sound both together.

The flight arrived home late evening and my car was parked in one one of my client's secure parks in an office building basement - my swipe caccess card to was erased and I could not get in (a problem late at night /forums/images/graemlins/frown.gif). I had been in a window seat on the aircraft and the card was in my briefcase lying against the cabin lining - so a coincidence or did the card get zapped by the lightning? I don't know. Maybe I should have taken an oven to put it in /forums/images/graemlins/smile.gif.

John
 
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