ERICO Practical Guide to Electrical Grounding - Manual (Page 18)

The grounding electrode system is designed to provide
multiple electrical paths into the earth. As stated in the
Preface, grounding of electrical systems helps to ensure
personnel safety, provide equipment and building
protection and achieve electrical noise reduction. Section
250-81 requires that four components, if available, be
bonded together to form the grounding electrode system.
Notice the words “if available.” Contractors are not given
the choice of which components they want to bond
together. If they are available, all four must be used.
(Fig. 1-25)
The first component is the metal underground water pipe.
Metal water piping that is in direct contact with the earth for
10 feet or more must be part of the grounding electrode
system. Contractors should be aware that, with the
increasing presence of plastic in water piping systems,
these systems may not be suitable as grounding electrodes.
Note, however, that under the bonding requirements of
Section 250-80 (a) all interior metal water piping shall be
bonded to the service equipment enclosure or other
permissible attachment points as listed in the section. When
connecting the grounding electrode conductor to the metal
water pipe, use a UL listed clamp or other listed means to
make the connection. Ground clamps shall be listed for the
materials of which the metal water pipe is constructed and
not more than one grounding electrode conductor shall be
connected to each clamp unless the clamp is listed for
multiple connections (Fig. 1-26). One final consideration
when connecting the metal water piping to the grounding
electrode system: the point of connection must be located
within the first 5 feet of the point of entrance of the metal
water pipe into the building. This is to ensure that
downstream alterations of the piping system, such as the
installation of plastic fittings, doesn’t result in isolation of
the grounding electrode system. The NEC does not permit
metal water piping beyond the first 5 feet into the building
to be used as part of the grounding electrode system or as a
conductor to interconnect parts of the grounding electrode
system. Contractors should be aware that, because of the
uncertainty of the metal water pipe construction, the metal
water pipe is the only grounding electrode which must be
supplemented by an additional electrode. If the other
electrodes are not available, a “made” electrode will need to
be installed by the contractor to supplement the metal water
piping. Made electrodes are discussed on page 14.
The second component of the grounding electrode system
is the metal frame of the building. If the metal frame of the
building is effectively grounded, meaning it is intentionally
connected to the earth by means of a low-impedance
ground connection, it must be bonded to the grounding
electrode system. Once again the connection of the
grounding electrode conductor to the building steel must be
accomplished by the use of exothermic welding
(CADWELD), listed lugs, listed pressure connectors, listed
clamps or other listed means. See Section 250-115. If the
building steel is dirty or contains nonconductive coatings,
contractors are required by the NEC to remove coatings,
such as paint, lacquer and enamel, from contact surfaces to
ensure good electrical continuity. See Section 250-118.
ERICO has a full line of horizontal and vertical cable to
steel or cast iron connections that can meet any installation
requirements (Fig. 1-27).
10 Practical Guide to Electrical Grounding
Fig. 1-26
Structural
Steel
NEC 250-81 (b)
Water Supply (Street Side)
Ring Ground, NEC 250-81 (d) Rod/Pipe Electrode
NEC 250-83 (c)
Water
Meter
Bonding Jumper
NEC 250-80 (a)
Grounding Electrode
Conductor, NEC 250-94
Metal Underground
Water Pipe, NEC 250-81 (a)
(Must Be Supplimented)
To AC Service Entrance
Grounded Conductor (Neutral)
Water Supply (House Side)
Typical Electrodes
Fig. 1-25
Grounding Book 4/14/99 10/5/99 6:01 PM Page 10 (Black plate)