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Re: May I comment?

"However, noise can be caused also by interwiring neutral and ground in outlets. It's a very common problem"

It's an electrical code violation in the US and can easily be checked for with a $5 receptacle checker availabe at RS and many other stores. It is of course not only a problem for noise but a serious safety hazard which should be corrected ASAP. You don't ever want neutral current flowing through the ground circuit, it's a real shock hazard. NEC proscribes that a voltage source (transformer secondary) can only have its neutral grounded at one point, usually at the transformer itself. This became a bone of contention between me and one electrician I had a great deal of respect for. He insisted it be grounded at the first distribution panel.

"Does an earthground really stop noise? Think about all the electronics in a 747 ...
It is a marketing hype argument, not a solid one. On the contrary, everything is well grounded on a plane. It carries its earthground reference with it, but it's a real neat ground. In many areas, even done in order to let a lightning stroke pass through it without melting anything away."

The ground plane/ground window concept is de rigeur in the American telephone industry. It provides an excellent "quiet" signal ground. It usually consists of a massive copper bar or plate. Interestingly, an imaginary line is drawn down the center and one side is arbitrarily defined as "clean" ground and the other as "dirty" ground. I found this very strange and I pointed out that in order for a sufficient voltage to be developed between one extreme corner and the other, given its low impedence, sufficient current would have to be developed through it to melt the bar. Nevertheless, this is the standard in the US. As for lightening strikes, it's interesting that a roof mounted lightening rod with ground wire network is not intended to absorb an actual strike but to discharge static electricity in the air just prior to a likely strike. Lucky me, I've got a neighbor about 200 feet away who is on slightly higher ground and has a flagpole. It's abiltiy to attract and discharge a stroke has served me well. On buildings which had roof mounted systems, I've seen lightning hit the building and blow chunks directly out of the brick masonary exterior. The path through which lightening will discharge through a steel structure building has been well studied and apparantly the favored path is vertical. I was once caught on an audit where the ground connection to building steel was to a horizontal member and that was considered a finding (BTW, this was a laboratory building, not a Central office.) The preferred method to ground the ground plane in a CO to earth is with a 750 mcm bare copper conductor with NO bends. It is believed that if the wire is bent, the lightning could actually fly off the condctor and discharge to earth through another path.

While NEC states specifically that Utilities are NOT required to adhere to the code in facilities dedicated to delivering the product or service which is their primary business (same for electrified railroads) adoption of NEC by the Bell System (or what's become of it) is their standard and compliance in all cases is manditory company policy. And you should have seen the crazy violations.

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