Sounds like we didn't catch the whole question on this subject
originally. Check an email sent to one of the authors of this
site Don Kerr. He asked me to try and answer the questions in
hope everyone could get a more detailed answer to the extra
questions concerning this subject. Check below a copy of the more
clear question of the original post and then the reply that we
emailed to Buck;
DK,
Earlier today I posted a question that may not have been
understood by some of your readers. In my area, they're suppose
to run a jumper wire across the water meter. The new house I
just bought has it jumpered across as follows: a #4 bare wire
from the neutral buss in the panel to the street side of the
meter; and then jumpered across the water meter to the house
side. I'm just wondering if this is hooked up properly.
Can you help?.........Thanks......Buck
Tom [Buck]
Your email sent to Don Kerr was referred to me hoping that I
could better answer the question you have.
As I understand you situation, you have a fourth equipment
bonding conductor sized 4 awg cu. installed between the meterbase
and the main service rated panel. Then you have a 4 awg cu.
conductor as a main bonding jumper that links your plumbing
across your water heater meter.
The following are copies of the rules that apply. Then I will
issue an interpretation adapting those rules to your situation
with a few ifs.
250-50. Grounding Electrode System
If available on the premises at each building or structure
served, each item (a) through (d), and any made electrodes in
accordance with Sections 250-52(c) and (d), shall be bonded
together to form the grounding electrode system. The bonding
jumper(s) shall be installed in accordance with Sections 250-64
(a), (b), and (e), shall be sized in accordance with Section 250-
66, and shall be connected in the manner specified in Section 250-
70.
An unspliced grounding electrode conductor shall be permitted to
be run to any convenient grounding electrode available in the
grounding electrode system or to one or more grounding electrode
(s) individually. It shall be sized for the largest grounding
electrode conductor required among all the electrodes connected
to it.
The grounding electrode conductor shall be unspliced or spliced
by means of irreversible compression-type connectors listed for
the purpose or by the exothermic welding process.
Interior metal water piping located more than 5 ft (1.52 m) from
the point of entrance to the building shall not be used as a part
of the grounding electrode system or as a conductor to
interconnect electrodes that are part of the grounding electrode
system.
Exception: In industrial and commercial buildings where
conditions of maintenance and supervision ensure that only
qualified persons will service the installation and the entire
length of the interior metal water pipe that is being used for
the conductor is exposed.
FPN: See Sections 547-8 and 547-9 for special grounding and
bonding requirements for agricultural buildings.
(a) Metal Underground Water Pipe. A metal underground water pipe
in direct contact with the earth for 10 ft (3.05 m) or more
(including any metal well casing effectively bonded to the pipe)
and electrically continuous (or made electrically continuous by
bonding around insulating joints or sections or insulating pipe)
to the points of connection of the grounding electrode conductor
and the bonding conductors.
(1) Continuity. Continuity of the grounding path or the bonding
connection to interior piping shall not rely on water meters or
filtering devices and similar equipment.
(2) Supplemental Electrode Required. A metal underground water
pipe shall be supplemented by an additional electrode of a type
specified in Sections 250-50 or 250-52. Where the supplemental
electrode is a made electrode of the rod, pipe, or plate type, it
shall comply with Section 250-56. The supplemental electrode
shall be permitted to be bonded to the grounding electrode
conductor, the grounded service-entrance conductor, the
nonflexible grounded service raceway, or any grounded service
enclosure.
Exception: The supplemental electrode shall be permitted to be
bonded to the interior metal water piping at any convenient point
as covered in Section 250-50, Exception.
Where the supplemental electrode is a made electrode as in
Section 250-52(c) or (d), that portion of the bonding jumper that
is the sole connection to the supplemental grounding electrode
shall not be required to be larger than No. 6 copper wire or No.
4 aluminum wire.
(b) Metal Frame of the Building or Structure. The metal frame of
the building or structure, where effectively grounded.
(c) Concrete-Encased Electrode. An electrode encased by at least
2 in. (50.8 mm) of concrete, located within and near the bottom
of a concrete foundation or footing that is in direct contact
with the earth, consisting of at least 20 ft (6.1 m) of one or
more bare or zinc galvanized or other electrically conductive
coated steel reinforcing bars or rods of not less than ½-in.
(12.7-mm) diameter, or consisting of at least 20 ft (6.1 m) of
bare copper conductor not smaller than No. 4. Reinforcing bars
shall be permitted to be bonded together by the usual steel tie
wires or other effective means.
(d) Ground Ring. A ground ring encircling the building or
structure, in direct contact with the earth at a depth below the
earth’s surface of not less than 2½ ft (762 mm), consisting of at
least 20 ft (6.1 m) of bare copper conductor not smaller than No.
2.
250-52. Made and Other Electrodes
Where none of the electrodes specified in Section 250-50 is
available, one or more of the electrodes specified in (b) through
(d) shall be used. Where practicable, made electrodes shall be
embedded below permanent moisture level. Made electrodes shall be
free from nonconductive coatings such as paint or enamel. Where
more than one electrode is used, each electrode of one grounding
system (including that used for air terminals) shall not be less
than 6 ft (1.83 m) from any other electrode of another grounding
system. Two or more grounding electrodes that are effectively
bonded together shall be considered a single grounding electrode
system.
COMMENTS
If you have a metal water pipe entering that home that is in
direct contact with the earth for at least 10' then you must use
that metal water pipe as your main grounding electrode. The
connection of that main grounding electrode to that water pipe in
direct contact with the earth must be installed within 5' of
where that water pipe enters the dwelling.
A main bonding jumper must be installed across the water meter to
ensure a solid electrical path through that water meter. This
bonding jumper is used to ensure that all the metal water pipes
in the house is also bonded to this grounding electrode [water
pipe in direct contact with the earth].
If the water meter is within 5' of the entry of the dwelling you
may connect the grounding electrode conductor between the water
pipe and the main service rated panel on either side of that
meter, it does not matter as long as that connection from the
panel to that water pipe in direct contact with the earth for a
minimum of 10' is within 5' of the entry of the dwelling of that
metal water pipe.
If you have the metal water pipe in direct contact with the earth as your required main grouding electrode then
you must also install a supplemental grounding electrode as listed above. Made electrode is common but the
weakest choice from the rules and choices in the code section copied above. This supplemental grounding
electrode is required to protect you from a plumber changing to plastic and you losing your grounding electrode
system.
If you install the 4 awg from the main service rated panel to the water pipe between the water meter and the
entry of that pipe into the dwelling then the jumper across the meter bonds the rest of the house metal plumbing
making it one entity with the grounding electrode system for your safety.
If you have plastic plumbing throughout the dwelling with short pieces of metal water pipes only then you can
ignore bonding those short pieces of water pipe.
If you have plastic coming into the dwelling but metal water pipes that are not in direct contact with the earth for
a minimum of 10' to the earth then you must still install that 4 awg ground wire to those metal water pipes to
make them one entity with the grounding electrode system for your safety.
Now you second question seems to be a fourth wire connected between the meterbase and the main service
rated panel. This is allowed by the NEC. However my personal feelings on that fourth wire is it is not a good
idea. You are creating a circle or parallel between the neutral [white or grey] wire and the bare or green wire
that is much smaller than the larger neutral conductor between that meterbase and main panel. If you lose
contact with the larger neutral then that little 4 awg grounding conductor will try to take over as the neutral
conductor carrying the unbalanced load back to the transformer. This would be like a pony carrying the load of a
large work horse. Dangerous in my mind. The parallel should be avoided, yet the NEC still allows it between the
meter base and main panel. Check the NEC copy below that was changed in the 99 NEC allowing the neutral
conductor to be used as a dual purpose wire on the line side and within the main service rated panel to the
meterbase. This in my opinion is the better design. I suspect the NEC will soon forbid that fourth wire between
the meterbase and the main service rated panel in future Code versions of the NEC. Check the two Code
sections below that should apply allowing you to remove that fourth wire. Just make sure you local electrical
inspector approves first. Remember, he is the authority having jurisdiction and the last answer to what you can
do.
250-24. Grounding Service-Supplied Alternating-Current Systems
(a) System Grounding Connections. A premises wiring system that is supplied by an ac service that is grounded shall have at each
service a grounding electrode conductor connected to the grounding electrode(s) required by Part C of this article. The grounding
electrode conductor shall be connected to the grounded service conductor in accordance with (1) through (5).
(1) General. The connection shall be made at any accessible point from the load end of the service drop or service lateral to and
including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.
250-142. Use of Grounded Circuit Conductor for Grounding Equipment
(a) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground noncurrent-carrying metal parts of equipment,
raceways, and other enclosures at any of the following locations:
1. On the supply side or within the enclosure of the ac service-disconnecting means
2. On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in Section
250-32(b)
3. On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system
where permitted by Section 250-30(a)(1)
Hope this hits what you wanted to know.
I carried a copy of this email onto the forum as a reply to your original question so others can learn and understand or make
comments with their opinions.
Good luck and let us know on our forum as a reply to your original question how you come out.
Thank you
Wg
This is 1 item from the Home Wiring
Forum Archives, to go to the main page of the forum archives then click HERE.
To go to the main page of the Home
Wiring Site , click HERE.