On Tue, 09 May 2006 10:41:48 -0500, jakdedert
wrote:

I've read a good deal about the above. Ideally, the grounds for various
(telephone, cable, power) electrical utilities should all be common; and
the service entries for those sundry services should be located within
15' of each other.

If I ever build a new house, I will take that into account.

However, it's not practical at this time to realize the ideal. What I
have currently is as follows:

The phone drop (two lines) comes in on one side of the house and is
grounded to the water supply line which comes in the front of the house
(about of 20' of wire clamped to the pipe where it comes through the
foundation into the unfinished basement).

The power drop (100 amp 220v single-phase) enters at the back of the
house, about 30' diagonally from the phone service. A ground wire
snakes from the panel (inside a utility porch) around a couple of
corners and through the floor to a ground post of unknown length/depth
in the crawl space beneath the adjacent kitchen...approximately 20 feet
of wire with at least two 90 degree bends.

The cable drop is around 15' feet from the power service entrance, and
grounded to an adjacent outside faucet a couple of feet away (all
plumbing in the house is copper).

Over the years, we've had a good deal of surge and lightning related
damage to devices in the house...most recently a DSL modem.

Would I derive any advantage by driving a new ground post outside,
adjacent to the power drop and to run all the various service grounds to
it (around 15' for cable, 25' or so for phone)?

Alternatively, I could move the telephone ground wire to the existing
power drop ground post (probably using the same 20' wire), and also
extend cable ground to this point. That would give me a 'star'
configuration with all utilities having around 20'-30' of wire from each
drop to ground.

Moving the phone service drop at this time (the ideal) is not practical.

I'm assuming the DSL modem and computer are plugged into the same
outlet . . .

It sounds like you have two unknown grounds that are far from the
ideal. You don't say what the failure mode of the equipment is and
how severe - I'm guessing it is probably common-mode developing
between the two ground systems. If you get something like bridge
rectifiers in power supplies shorting - that could indicate a
differential voltage spike.

Or, better yet, start at the beginning . . .Check the power
transformer. There should be a lightning arrestor for the transformer
- a kind of insulator that sits off to the side of the can that is
clamped to the can and has a small 1/2"-1" air gap between it and the
HV terminal. (designs vary quite a bit but it should be there in some
form - a collection of broken porcelain around the base of the pole
and some carbon blocks means it is done its job once too often)

The transformer pole and transformer must be grounded. There should
be a thick soft copper wire running from the transformer down the
length of the pole and into the ground. Usually the wire is wrapped
in a spiral and nailed to the bottom of the pole.

Without the transformer grounded - anything you do may be wasted
effort. I had no problem getting a neighbor's lightening arrestor
replaced with just a call to the power company and, in another
instance, a pole ground wire replaced - they are subject to being
stolen by people trying to salvage the copper. Two different power
companies and no arguments - they just went out and fixed it.

Your best option is probably to get the grounds on the same circuit.
I'd sink a ground and wire to it, so I knew what its condition is
like. (ten foot length of half inch dia copper water pipe washed into
the soil is better than anything you're likely to drive into the
ground) Braze or solder the heavy wire on. Put it at the power
entrance as directly under the power meter as you can with no bends in
the heavy wire. Five or six feet to ground if you can manage it with
no bends. Use a large radius bend if you go around an obstacle. It
may not be practical, but do the best that the conditions allow.

What to do about the telephone line and power line separation? Sink
a separate ground for the phone line and just use it for the
lightening arrestor on the line and make sure it is bonded to the main
power ground. There was some good stuff in an ARRL article some years
ago that mentioned a similar problem. He solved it by adding a ground
for the phone line directly under the phone's entrance box to the
company supplied arrester then added a set of gas filled spark gaps in
addition to the arrester.

Cold water pipes are iffy - they can be excellent grounds or very poor
grounds. Too many variables - you'd have to know the material and
condition of the pipe, how straight the run to ground is, and what the
joints are like electrically. Some old systems used cast iron pipe
and the joints are not connected electrically. Some really old cities
still pull up a wooden water main from time to time . . . Galvanized
threaded joints are usually pretty good if the pipe was clean when the
pipes where joined and someone didn't get carried away with Teflon
tape.

Beyond that you can still get fancy with isolation transformers or
optical links.

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