# grounded and not grounded Faraday cage - what's the difference?

**URL:** <https://boards.straightdope.com/t/grounded-and-not-grounded-faraday-cage-whats-the-difference/533955>\
**Category:** Factual Questions\
**Created:** [March 26, 2010, 10:51pm UTC](https://boards.straightdope.com/t/grounded-and-not-grounded-faraday-cage-whats-the-difference/533955 "2010-03-26T22:51:09Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\
**Post date:** [March 31, 2010, 6:22pm UTC](https://boards.straightdope.com/t/grounded-and-not-grounded-faraday-cage-whats-the-difference/533955/21 "2010-03-31T18:22:59Z")

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Neither a house nor a car makes a really good Faraday cage. From experience, I can aver that holes to the outside world can be insidious and elusive. While repairing a broken Faraday Cage – whose walls were double thicknesses of copper mesh – I carried my cell phone and a radio into it and turned them on. They still worked perfectly, despite the fact that I was almost completely encased in apparently seamless mesh. Carrying them around I soon found out where tears and breaks in the mesh were, and was able to repair them. When I was finally finished, my radio didn’t work any more, and neither did the cell phone. But it wasn’t easy to find and repair all the holes – some of which were linear rips in the mesh.

By comparison, the windows in a metal-covered house or a car are enormous. If a tear so small you can’t see it can let signal leak in, any gap as big as a window you can easily see through is hopeless, and the “Faraday cage” with that big a gap will leak signal like a sieve.

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**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\
**Post date:** [March 31, 2010, 9:36pm UTC](https://boards.straightdope.com/t/grounded-and-not-grounded-faraday-cage-whats-the-difference/533955/22 "2010-03-31T21:36:35Z")

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> [@engineer\_comp\_geek](#):
>
> The earth isn’t that bad of a conductor. If you just stick the ends of a multimeter into the soil you aren’t going to get a very good reading, but power systems back in the old days sometimes used the earth as their return wire (saved quite a bit on wiring costs).

Isn’t the old power system method reliant on an enormous impedance shift for transmission? That is, at least today, transmission systems work with impedances maybe a million times higher than end users. I mean, my appliances consume power at 120 volts, but there are long distance transmission lines operating at over 120,000 volts, and my share of the load is drawing 1000 x fewer amps at that voltage too.

If you tried to transmit 120 volt power for appliances using dirt for the return, it probably wouldn’t even work an inch away from the power station.

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [April 1, 2010, 12:58pm UTC](https://boards.straightdope.com/t/grounded-and-not-grounded-faraday-cage-whats-the-difference/533955/23 "2010-04-01T12:58:55Z")

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Sigh, the grounded Faraday cage may **not** go to the Prom this weekend.  
The not grounded Faraday cage **may** go to the Prom this weekend, but if it comes home at 3AM, with a [Hickey](http://www.romanceclass.com/miscr/howto/hickey.asp), it will quickly find itself grounded too.

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