Re: Electrical Grounding

What is the effect of having an electrical ground close to a telecom

> (telephone land line) ground and what is the recommended distance they > should be apart.

Once they did not even have to be the same earthing electrode. But transistors did not exist then. Others have cited wire resistance as a reason for short distance. However that voltage different would be still near zero if the distance was 20 feet or 200 feet. They are discussing a common ground for resistance.

However wire impedance is why wire distance must be short. Wire too long, with sharp bends, inside metallic conduit, or with splices would have little effect on wire resistance but would adversely affect wire impedance.

Code calls for a distance less than 20 feet. You really want a ground wire to common electrode of 'less than 10 feet'. Furthermore, you want that wire routed separate from all other non-grounding wires AND not meet other grounding wires until all meet at the earthing electrode.

Furthermore, if telco earth ground electrode is not same as earth> That said, the ground that you find in an outlet should not be

trusted, run a wire directly to a metalic water pipe (but not a > sprinkler), building steel, or back to the electrical system grounding > conductor. (IIRC, in some cases, which I'm not going to look up at > the moment, you're -required- to bond to the electrical system > ground.)

Do not connect a grounding wire to a water pipe. That connection is not permitted by code and suffers same problem of a grounding wire that is too long. Required connection to water pipe is only to remove electricity from that pipe for human safety.

But aga> Grounding is the intentional connection to earth through

a connection of sufficiently low impedance.

Impedance -- not resistance as others have posted. With impedance, transient current can result in voltages too far from zero. A shorter wire means less impedance - voltage closer to zero. Essential that all wires entering a building be at same voltage potential - for transistor safety and for human safety. That means all earthing (which is only one type of grounding) must be to a single point earthing electrode.

Impedance is also why grounding to wall receptacle safety ground is not sufficient for grounding telecom equipment. That telecom ground must be low impedance. AC electric safety (equipment) ground is low resistance -- but not low impedance.

Do not ground to water pipes. Once that connection was acceptable. Today grounding to water pipes is a violation and typically not a good low impedance ground.

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w_tom
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