I was at a police dispatch center today. The builder had mounted, about 9’ up the wall, a 1/4 or 3/8" copper cable on brackets around the entire perimeter of the room and adjoining offices. Above that was drop ceiling.
At first, I didn’t see it in its entirety, and assumed it was a ground for something (maybe a radio antenna.) Still seemed strange to run it indoors. After I noticed the circuit, I asked what it was for and was told that it was to protect the facility from lightning strikes…not only that, but the room that housed the majority of the telephone and radio equipment was outfitted similarly.
I understand that a room or facility that houses sensitive electronic equipment may be protected from electrical interference by a Faraday cage…but a single copper wire?
Is there an explanation for this, or is this copper decoration as pointless as it seems?
That’s called a “halo ground” (if it were outside the building it would be called a “ring ground”).
If you understand a Faraday cage, then you probably understand that if you take a coil of wire and move it through a magnetic field it will generate a current. That’s how electrical generators work. A halo ground or ring ground takes advantage of this and takes the energy from a moving magnetic field and shunts the resulting current to earth ground, thereby attenuating the magnetic field and protecting the equipment in the room or building.
engineer_comp_geek, do you have some links that could provide a more detailed explanation?
Thanks.
There doesn’t seem to be a whole lot online about them. I did manage to find these by googling halo ground and ring ground:
http://www.comm-omni.com/polyweb/halogrounds.htm
http://www.asgmt.com/default/papers/asgmt2007/docs/072.pdf (warning - PDF)
I also found an awful lot of links about the video game Halo. 
Thanks. Yeah, I Googled images for halo ground–90% of those images were you-know-what…
Thanks for the answer and links!