TELECOM Digest OnLine - Sorted: Re: Electrical Grounding

Re: Electrical Grounding

Bob Vaughan (
Fri, 17 Nov 2006 04:02:37 UTC

In article <>,
Dan <> wrote:

> 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.

The grounds for all utilities should be the same point. This is
required by the NEC (article 250, 800, 810, 820, and 830). The
maximum distance allowed is 20' before supplemental grounding in
required, which must be tied into the grounding system.

The reason for this is that the resistance of the earth varies, and by
using the same grounding point, we can make sure that the electrical
relationship between the grounded devices is maintained within the

Within any building, the goal is that (ground) = (ground) = (ground),
and not (ground) = (ground +2 volts) = (ground +4 volts).

Voltage differential between grounds = current flow = electrical noise
when grounds are connected together thru the connected equipment.

If the voltage differential is high enough, damage to equipment can
occur, or injury to humans can occur if they are connected between

For this reason, all utilities (water, gas, electrical, telephone,
catv), and all other metallic cabling (antennas, etc) should all be
grounded to the main building ground, which may be multiple grounds
tied together as a common ground system.

-- Welcome My Son, Welcome To The Machine --
Bob Vaughan | techie @ |
| P.O. Box 19792, Stanford, Ca 94309 |
-- I am Me, I am only Me, And no one else is Me, What could be simpler? --

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