ERICO Practical Guide to Electrical Grounding - Manual (Page 91)

This type of electrode is commonly called a “Ufer
Ground”. (A plastic sheet must not be used to
separate the concrete from the earth.) Figure 5-1
shows a #4 AWG or larger copper wire imbedded in
the concrete foundation. Figure 5-2 shows a #4
(1/2”) or larger rebar imbedded in the concrete
foundation. CADWELD Connections are used to
make permanent connections to either the copper
wire or the rebar.
3. The copper wire ground ring encircling a building
or structure must be #2 AWG or larger, at least 20
feet (6 m) long and buried at least 2 1/2 feet (.76m)
in the earth.
4. Rod or pipe electrodes shall be at least 8 ft long with
a minimum of 8 feet in contact with the earth,
installed vertically except where rock is
encountered, in which case they may be driven at a
45
o angle or buried in a trench 2 1/2 feet deep. The
upper end of the rod or pipe must be flush or below
grade unless the top end and the connector are
protected from damage. Pipe electrodes shall be 3/4
inch trade size or larger and shall have their outer
surface galvanized or another metal coating for
corrosion protection. Rod electrodes shall be 5/8
inch diameter if of iron or steel. Stainless steel rods
less than 5/8 inch and nonferrous rods, including
copper clad steel rods, shall be listed and not less
than 1/2 inch diameter.
5. Plate electrodes must be at least 1 square foot
(0.093 square meter) and 1/4 inch (6.3 mm) thick if
steel or 0.06 inch (1.5 mm) thick if nonferrous.
Note the plate thickness required by the NEC is
different than that required for lightning protection.
Burial depth is not specified by code. If used, we
suggest that to get the best performance, it be
installed on edge and with the top at least 18 inch
(460 mm) below grade. Plate electrodes, however,
are not as efficient as most other types of electrodes
and are usually used only in special conditions
where other types of electrodes cannot be used.
Recommended practice is to install the electrodes and
interconnecting conductors 18 inches (460 mm) beyond the
roof drip line. This provides additional moisture to reduce
resistance.
The electrodes used to ground lightning protection systems
shall not be the same ones used for the electrical system
ground electrodes but the electrodes from both systems
must be bonded together. Not only required by the NEC
but also required for safety of all who may come in contact
with the electrical system, all grounding electrodes must be
interconnected. Separate and isolated ground systems are
dangerous and are not permitted! While separate and
isolated ground systems were once specified for many
electronic systems, this practice has been shown to corrupt
the data, damage the equipment and in addition can be
extremely dangerous.
GROUND RODS
Ground rods are commonly available as copperbonded steel
and galvanized steel. Solid stainless steel, solid copper and
occasionally plain steel are also utilized. Rods are also
available with a factory welded pigtail (Fig. 5-3). While
copper bonded steel rods have a slightly lower electrical
resistance than galvanized or plain steel rods, they are not
chosen for their lower electrical resistance but rather for
their resistance to corrosion. Copper is a more noble metal
than steel and will therefore resist corrosion much better
than steel, or even galvanized steel in most soils. (Fig. 5-3)
83 Chapter 5: Selection of Components Used In Grounding
Fig. 5-1
Fig. 5-2
Grounding Book 4/14/99 10/5/99 6:02 PM Page 83 (Black plate)