On 02/24/04 01:53 am w_tom put fingers to keyboard and launched the
following message into cyberspace:
Earthing for two separate reasons. First for human safety
which is what the National Electrical Code (NEC) addresses.
All safety grounds long ago have to be bonded together. In
days past, the typically was to city water pipe where it
entered earth or, if using well water, to a dedicated earth
ground rod. In the past decade, earthing via a water pipe is
not acceptable no matter what that water pipe currently is -
copper or plastic.
I am not sure what water pipe material is used outside the house. The
municpality was in the process of repairing or replacing the pipe from
the street to the house when we were looking at the house before buying
it. By the time we took possession everything was filled in again. There
is such a short length of pipe coming through the basement wall before
it connects to a brass or bronze fitting that I can't tell for sure, but
I think it's probably iron.
Code since 1990 demands a dedicated single point ground at
the service entrance which means where AC electric enters
building. Telephone, CATV, satellite dish and even exterior
TV antenna should make a connection to this ground (either by
hardwire or via a protector). Code demands services such as
phone make a less than 20 foot connection.
The telephone connection comes into the house at the opposite end from
the electric service entrance -- 60ft or more away -- so no way to
comply with the 20ft rule. The cable TV service (now used for Internet
only) enters at the back of the house, perhaps about 45ft from the
electric service entrance; there is a ground wire from the cable
company's box, but where it goes I have no idea. The satellite dish,
installed "professionally" about 3 months ago, is about the same
distance from the electric service entrance and with no sign of a ground
wire at all: the coax. cables come straight down from the dish and
through the wall of the house at a level just above the suspended
ceiling of the basement and, as far as I can tell, go straight to the
satellite box; if they do pass through a grounding block, I have no idea
to what that grounding block could be grounded.
Ground wires to pipes are for human safety - only to remove
electricity from those pipes. IOW wire once connected to city
water as an earth ground is now only to remove any electricity
that might leak into those pipes. Also required would be a
connection from hot water to cold water pipes at water heater
if pipes are metal; so that heater does not become part of the
grounding circuit. Water meter must also be bypassed so that
when water meter is replaced, then cold water pipes remain
connected to safety ground (meter man is not electrocuted when
changing meter).
The water meter is connected to two "arms" of a single brass or bronze
fitting in the line just after it enters the house, so there is a
permanent continuous electrical path even if the meter is removed.
But now if I want to ground the water pipe to the electrical supply
ground, can I run a wire to the ground bus in the panel located a few
feet away (in the laundry), or do I have to find a way of connecting
that wire to the ground at the service entrance panel (which has only
the main breaker and a breaker for the garage circuits) about 30ft away
on the garage wall? This would mean bringing the wire from the front of
the house (where the water line enters through the basement wall),
through the house (above the suspended ceiling of the basement), out
through the back wall, and around to the end of the garage where the
electrical service enters.
Any connection to a pipe for grounding or earthing (ie a
cable connected to exterior water faucet) is not legal. Again
connections made to pipes only to remove electricity.
Ground to gas pipe is really a domain of the local gas
company. Some want gas line bonded to AC electric so that
electricity is removed from gas pipe - so that gas pipe will
not be used as an electrical path to earth. In one location,
neutral wire on transformer failed. AC electric then used gas
line as a path back to transformer via earth. This
unacceptable ground path eventually caused gaskets on gas
meter to break down; house exploded. But again, that safety
ground to gas pipe is according to local gas authorities.
Exterior gas line has a wire that is not an earthing wire.
All pipes have a wire so that radio signals can be transmitted
through pipe. This is how underground utility pipes and wires
are located - radio waves. That wire on incoming gas line is
how the locator service puts a radio wave on that plastic gas
pipe. Wire is not for earthing.
A meter typically cannot report a good ground; meter can
only report a defective ground. A ground that measures good
may simply vaporize - is too small - when it must conduct
larger currents due to an electric power fault. Meter would
not detect an insufficient ground.
Agreed.
No replacement for visual
inspection. Furthermore, connections must be intended by the
designer to conduct electricity. A water heater was not
typically intended to connect hot water pipe to cold water
pipe. No matter what meter says, those two pipes still must
be bonded at that water heater (if metallic pipes).
The water heater was replaced two years ago, according to the "seller's
declaration," but I have no idea whether it was done "professionally"
and in accordance with relevant codes. It will be easy to bond the two
pipes together; I assume that #4 is OK? Stranded or solid, or doesn't it
matter?
volts500 wrote a good summary of bonding for human safety:
alt.home.repair entitled "Grounding Rod Info" on 12 July
2003:
http://tinyurl.com/hkjq
A lot of that I know in principle, but how to apply the principles to a
specific situation is not always obvious. E.g., when all these things
that are supposed to be bonded together are so far apart.
That covers safety grounds as required by NEC. Now second
reason is to enhance earthing for transistor protection.
Those safety grounds were defined by wire resistance.
Transient protection is about wire impedance. That means
connections to that single point ground must be short, direct,
and independent. No splices, no sharp bends, less than 10
foot connection from incoming utility to that single point
earth ground, and not inside metallic conduits or pipes. Phone
line connects directly to earth ground rod - not to AC power
earthing wire. IOW every earth ground wire must meet at same
single point location and should route separated from other
non-earthing wires. (non-earthing wire can suffer induced
surges if bundled with an earthing wire.) This technical note
demonstrates principles of earthing a tower and building:
http://www.erico.com/public/library/...es/tncr002.pdf
Building and tower are handled as if separate structures.
Each has it own single point earth ground. Any wire entering
each structure first connects to single point ground either by
direct connection or via components even sold by erico.com -
and others. Single point earthing for both structures is
interconnected by buried wire to enhance both earthings and
minimize potential differences.
One technique is to dig a shallow hole before driving
earthing rods. Buried wire connects each ground rod. A 4 or
6 inch plastic pipe placed in hole and backfilled so that
plastic cap can be removed to inspect wire bond to ground rod.
I like that idea, which I don't recall reading in any of the
radio-related publications.
Size of buried interconnecting bare copper wire, depth of
that wire, and spacing between multiple rods are defined by
NEC guidelines. However, effective earthing materials (ie
ground rods) must be deep enough into earth where earthing
will not freeze. Frozen earth is not conductive - not a good
earth ground.
One of the locals merely cut a groove in his yard with a power saw
(sacrificing a blade in the process, no doubt) and laid a ground wire in
that (but in conjuction with deep-driven rods, I think). Perhaps not
such a great idea?
MB