Does the oven work as a Faraday cage if hit by lightning

[tudorsailor]

Up until now, whenever lightning has been nearby, I have put mobile phones, h/h GPS and laptop in the boat's oven (not turned on of course). I thought that the metal oven would protect the electronics by acting as a Faraday cage. I now wonder if I am deluded as the oven has a large glass window! Unlike a microwave there is no mesh
So am I wasting my time? Would it help to put foil across the window?


TudorSailor

 

[sarabande]

Here's a UK company which weaves a metal mesh for the purpose.

http://www.wiremesh.co.uk/woven-wire-mesh-applications/emi-and-rfi-shielding

You could line a locker with the mesh, and store your sensitive kit in it when you leave the boat, as well as in thunderstorms.

I am trying to find out if such a locker should be connected to the anode/earth system.

 

[macd]

You could line a locker with the mesh, and store your sensitive kit in it when you leave the boat, as well as in thunderstorms.

I am trying to find out if such a locker should be connected to the anode/earth system.

I don't think earthing is necessary, but know little about the science. I seem to recall Jumbleduck's writing knowledgeably on the subject some time ago.

The Wiki page on Faraday cages, which I daresay you've checked out, has this tantalising piece of information:
"Plastic bags that are impregnated with metal are used to enclose electronic toll collection devices whenever tolls should not be charged to those devices, such as during transit or when the user is paying cash."
Maybe 'Faraday' plastic bags might be the most convenient answer for boat equipment. (And, inter alia, their use rather suggests no need for an earth, at least in the context of toll devices.)

 

[tudorsailor]

Come to think of it, the over (Force 10) is open at the back - so I have probably been wasting my time

Lining a locker or drawer seems a good idea. I will email the company

Of course if I had a microwave on board, that might work as its designed to stop microwaves escaping. But only microwaves of a certain size

TS

 

[bedouin]

I am trying to find out if such a locker should be connected to the anode/earth system.

A long time since I studied Physics but I am pretty sure the answer is "no". The purpose of a cage is that any charge flows round the outside of the cage, and anything inside remains unaffected

 

[davidej]

I did a transat with a skipper who insisted on doing this.

My opinion was that he was much more likely to roast the GPS when he forgot to take it out than have it destroyed by lightning.

 

[mjcoon]

You could line a locker with the mesh, and store your sensitive kit in it when you leave the boat, as well as in thunderstorms.

I am trying to find out if such a locker should be connected to the anode/earth system.

I think the locker should be left floating. Currents flowing through the cage will still generate voltage, so minimising the current is still beneficial.

BTW Although I keep hearing about people having their high-end cars stolen by crooks amplifying and relaying the key-fob's signal within the house to the car outside, no-one suggests putting the key-fob in a biscuit-tin indoors to foil the crooks. (Or tin-foil the fob!)

Mike.

 

[tudorsailor]

BTW Although I keep hearing about people having their high-end cars stolen by crooks amplifying and relaying the key-fob's signal within the house to the car outside, no-one suggests putting the key-fob in a biscuit-tin indoors to foil the crooks. (Or tin-foil the fob!)

Mike.

I have a new car with a wireless fob. I now keep the key in a little tin at night to stop thieves using an amplifier! Certainly it works as I cannot open the car with the key in the tin and right next to the car

TS

 

[mjcoon]

I have a new car with a wireless fob. I now keep the key in a little tin at night to stop thieves using an amplifier! Certainly it works as I cannot open the car with the key in the tin and right next to the car

TS

I bet you thought of the solution, and the test for efficacy, yourself. But I also bet a lot of people (targets for thieves!) need a big hint...

Mike.

 

[sarabande]

The world of ebay is far ahed of you !

Wallets and bags that jam car keys...

https://www.ebay.co.uk/sch/i.html?_...ag.TRS0&_nkw=metal+mesh+car+key++bag&_sacat=0

 

[tudorsailor]

Not that I am obsessed, but yes I do use a wallet that blocks RFID on my cards!

TS

 

[KellysEye]

There are those that say the glass will stop the oven being Faraday cage but is not true, we know long distance sailors who have used it for that and one who didn't. He tied up next to us all his instrument, worth thousands and no insurance, were destroyed ad there was a burn on the UK flagon the backstay.

The closest we came was sailing north to Mustique when lighting hit the water about 30 yards in front of us, we had Elmos fire crackling in the rigging but no damage. The other one was I was watch at night of the Venezuelan coast and there was lightning all around us, I heard the loudest bang I have ever heard, the brightest flash ever and the smell of ozone, it was overhead. Fortunately it was cloud to cloud.

 

[rogerthebodger]

Up until now, whenever lightning has been nearby, I have put mobile phones, h/h GPS and laptop in the boat's oven (not turned on of course). I thought that the metal oven would protect the electronics by acting as a Faraday cage. I now wonder if I am deluded as the oven has a large glass window! Unlike a microwave there is no mesh
So am I wasting my time? Would it help to put foil across the window?


TudorSailor

A couple of points to consider.

1) when an EPIRB is tested by the service agent, the EPIRB is placed inside faraday cage to prevent the EPIRB signal from escaping and reaching the satellite.

2) the metal body of a jet aircraft protects the people inside at if there is a lighting strike the lighting flows around the metal shell acting as a faraday cage, so no damage to the passengers inside. Also the electronics of aircraft also do not seem to be affected so unless the electrics have special shielding inside a faraday cage should protect all the electronics.

here are some examples of faraday cages


Faraday cages are routinely used in analytical chemistry to reduce noise while making sensitive measurements.

Faraday cages, more specifically dual paired seam Faraday bags, are often used in digital forensics to prevent remote wiping and alteration of criminal digital evidence.

The US and NATO Tempest standards, and similar standards in other countries, include Faraday cages as part of a broader effort to provide emission security for computers.

Automobile and airplane passenger compartments are essentially Faraday cages, protecting passengers from electric charges, such as lightning

A booster bag (shopping bag lined with aluminium foil) acts as a Faraday cage. It is often used by shoplifters to steal RFID-tagged items.[5]

Similar containers are used to resist RFID skimming.

Elevators and other rooms with metallic conducting frames and walls simulate a Faraday cage effect, leading to a loss of signal and "dead zones" for users of cellular phones, radios, and other electronic devices that require external electromagnetic signals.

During training firemen and other first responders are cautioned that their two-way radios will probably not work inside elevator cars and to make allowances for that. Small, physical Faraday cages are used by electronics engineers during equipment testing to simulate such an environment to make sure that the device gracefully handles these conditions.

Properly designed conductive clothing can also form a protective Faraday cage. Some electrical linemen wear Faraday suits, which allow them to work on live, high-voltage power lines without risk of electrocution. The suit prevents electric current from flowing through the body, and has no theoretical voltage limit. Linemen have successfully worked even the highest voltage (Kazakhstan's Ekibastuz–Kokshetau line 1150 kV) lines safely.[citation needed]

Austin Richards, a physicist in California, created a metal Faraday suit in 1997 that protects him from tesla coil discharges. In 1998, he named the character in the suit Doctor MegaVolt and has performed all over the world and at Burning Man nine different years.

The scan room of a magnetic resonance imaging (MRI) machine is designed as a Faraday cage. This prevents external RF (radio frequency) signals from being added to data collected from the patient, which would affect the resulting image. Radiographers are trained to identify the characteristic artifacts created on images should the Faraday cage be damaged during a thunderstorm.

A microwave oven utilizes a Faraday cage, which can be partly seen covering the transparent window, to contain the electromagnetic energy within the oven and to shield the exterior from radiation.

Plastic bags that are impregnated with metal are used to enclose electronic toll collection devices whenever tolls should not be charged to those devices, such as during transit or when the user is paying cash.

The shield of a screened cable, such as USB cables or the coaxial cable used for cable television, protects the internal conductors from external electrical noise and prevents the RF signals from leaking


Read more about it here

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

 

[johnalison]

I would imagine that in the case of a boat oven it is a matter of degree. Clearly, a Faraday cage doesn't have to be complete in order to function, so in the case of the oven it is a matter of how large the glass aperture is, and perhaps how near the aperture the contents are. I would look on it as an imperfect cage but a lot better than nothing.

 

[tudorsailor]

Unscientific I realise but I have done a test with my mobile phone. I placed it in sequentially a microwave, my home oven with glass window. inside loose fitting foil tins and in a proper metal cake tin with lid. I rand the phone with my landline and it rang in every location. Must be related to the wavelength of 3G frequency! So all equally ineffective in blocking a phone signal
TudorSailor

 

[Sandy]

I have a friend who is a researcher on lightning protection on composite material aircraft, I'll ask what he thinks.

 

[lw395]

Unscientific I realise but I have done a test with my mobile phone. I placed it in sequentially a microwave, my home oven with glass window. inside loose fitting foil tins and in a proper metal cake tin with lid. I rand the phone with my landline and it rang in every location. Must be related to the wavelength of 3G frequency! So all equally ineffective in blocking a phone signal
TudorSailor

Mobile phones have a huge dynamic range.
Your metal cake tin might provide (wild guess) 40dB of protection. That's 10,000:1 as a ratio of power.
It's also possible the phone was dropping back to 2G or whatever strongest signal is available.
Some phones in some places have 4 or even more bands to pick the best from.
I've worked in screened rooms, which are basically a metal shed with all apertures screened.
I often try my phone in there to check it's all sound. You need good contact all around the door and metal honeycomb on the vents to keep vodafone out.
Also there are filters on the mains wiring and any signal cables.
ISTR the chamber was supposed to be good for 80dB or so.

Even 20dB might make the difference between cooking your electronics or not.


(A faraday cage is not quite the same thing as a screened chamber/enclosure when you are talking about enclosures bigger than some fraction of a wavelength or high energy effects like lightning where linearity is out of the window.)

 

[Daydream believer]

If you want to kill a mobile phone signal you do not need a cake tin. Just live in a 4 mile radius of our village

 

[tudorsailor]

I have carried on looking on the web. I discovered that there are numerous discussions about faraday cages and protection against EMP on websites devoted to "Preppers". They are people preparing to survive a disaster which includes a nuclear strike it seems. I'd rather be far away on my boat!

TS

 

[lw395]

I have carried on looking on the web. I discovered that there are numerous discussions about faraday cages and protection against EMP on websites devoted to "Preppers". They are people preparing to survive a disaster which includes a nuclear strike it seems. I'd rather be far away on my boat!

TS

Who will they phone after the apocalpyse anyway?