On 11/3/2014 10:19 PM, josephkk wrote:
On Fri, 31 Oct 2014 12:55:14 -0600, bud-- wrote:

On 10/30/2014 11:46 PM, Michael A. Terrell wrote:

junebug1701 wrote:

On Thursday, October 30, 2014 8:20:06 AM UTC-5, Robert Macy wrote:
Actually, sharing with you all, but English, what can I say?


this started after the famous flooding here - covered in the national news.
PROBLEM:
outgoing calls: NO problem, clear voice line and dial up modem within 95%
of 'normal' [seen slower rates before with damp weather]
incoming calls: the ring sounded anemic, like a single tinkle, not to be
repeated. Pick up phone, and someone was there?! albeit the connection
sounded like old fashioned long distance.

This reminds me of a strange service call I had when I worked as a Bell System repair technician. It was a rural area and the customer complained that none of her phones would ring, but that she knew somebody was calling whenever her dog howled. Sounded crazy to me, but it turns out that she was on a party line which requires a good earth ground on the third (yellow) wire for the ringers. Well, the unlucky dog was chained to a poorly grounded water pipe which also held the ground clamp and wire for the telephone protector. Whenever she got a call the poor dog got a 90VAC jolt! That's one of the reasons the telcos quit grounding to water pipes in favor of the electrical power neutral.

(US practice.)

You mean the service "ground", not the neutral.

Phone techs had better not be connecting anything inside the service panel.

A convenient point of connection is the wire to the earthing electrodes,
but it is not the only place the connection can be made.

Recent services have an "intersystem bonding termination" where phone
and coax entry ground connections must be made.


The reason that they switched was that the NEC required them to. Some
fools couldn't tell the difference between a water and a gas pipe.


The NEC did not require them to.

Water pipes (10 or more ft of metal in contact with the earth) must
still be used as one of the power system earthing electrodes.

I don't know what version of NFPA 70 (NEC) you are talking about; but
recent editions of the NEC requires a grounding electrode (rod) with at
least 10 feet in direct earth contact; plus bonding to water pipe and gas
pipe when metallic. Also bonding to the structural steel if there is
significant steel above ground. Enforcing article 250 et seq. has been
part of my job for the past 8 years.

There may be requirements other than the NEC where you are working.

The NEC requirements a

- Power earthing may have one or many electrodes that are connected
together as an earthing system (250.50).

- A metal water service pipe MUST be used as one of the earthing
electrodes. It has been so since time began. Exact requirements have
changed over time as more water services use plastic pipe. The
requirement for many years is that a metal water service pipe in contact
with the earth for 10 ft MUST be used as an earthing electrode. (250.50,
250.52)

- If the water service pipe is NOT metal-10ft, then the interior metal
water pipe must be "bonded" to the power ground system (250.104-A). The
connection as an earthing electrode (above) is more stringent than
"bonding".

- Since a metal water service may be replaced by plastic, a
"supplemental" electrode has been required for many years. Many kinds of
electrode can be used (250.53-D). Often it has been a ground rod because
they are easy to install.

- Gas piping must be "bonded" to the building ground system. The size of
the bonding wire is determined by the current rating of the circuit that
is likely to energize the pipe. In a house this is likely the feed
circuit for a furnace, or similar device. "The equipment grounding
conductor for the circuit that is likely to energize the piping shall be
permitted to serve as the bonding means." (250.104-B)

- Gas service pipe may not be used as an earthing electrode.

- Structural steel may be required to be used as an earthing electrode
(250.50, 250.52). Else it is required to be "bonded" (250.104-C).
Connection as an earthing electrode is more stringent than "bonding".

- For new construction, if there is a concrete foundation or footing, a
"concrete encased electrode" is required (250.50, 250.52) These are
commonly called a "Ufer" ground. They are a good electrode (far better
than a ground rod) and are used as the "supplementary" electrode for a
water service pipe where both are present.

- Ground rods are required to be used as an earthing electrode "where
present". They won't be present unless someone installs one. Installing
one is not required. (250.50)
Rods are 8 ft min, and the types used are 5/8" diameter. They must have
a resistance to earth of 25 ohms or less, or else 2 can be used and
there is no requirement (250.53-A-2).

Ground rods are among the worst earthing electrodes. If you connect a
120V circuit to a code compliant 25 ohm rod will it blow a 15A fuse?

If the only earthing electrode is a ground rod (which is compliant is
some places), and the rod has a near miraculous resistance to earth of
10 ohms, and there is a surge to earth of 3,000A, the potential of the
building "ground" is 30,000V above 'absolute' earth potential. In
general, 70% of the voltage drop away from the rod is in the first 3 ft.
Over 3 ft from the rod is at least 21,000V from the building "ground"
system. If you have a rooftop TV antenna that is earthed only to a
separate rod the coax will be over 21,000V from the power "ground". You
may also get that on a metal gas service pipe, which is why very
thin-walled CSST can be a problem.


What I wrote is consistent with NEC requirements.
Installing earthing systems has been part of my job for the past
....um... lots of years.


That metal water pipe can still be used as the ground for phone entry
protectors (if there is no intersystem bonding termination). In the past
the connection could be anywhere. Now it must be within the first 5 ft
inside the building. That is the same place the connection must now be
made for the water pipe as an earthing electrode.

Gas pipes are grounded at locations like furnaces.

Corrugated stainless steel tubing (CSST) is often used for gas piping
inside a building because it is flexible. There have been fires and
explosions, and I think all manufacturers now require the stuff to be
connected to the earthing system near the building entry. (There have
been fires where the stuff was grounded to manufacturer's specs. An
electrical inspector recommended electricians not make the ground
connection, then they will not be involved in the lawsuit. I would not
use CSST.)