ERICO Practical Guide to Electrical Grounding - Manual (Page 102)

made below the liquid level. Pure fuel will not burn or
explode. It will burn or explode only when mixed with
oxygen (air) within certain ratios.
Codes & Standards. Section 80 of the 1994 Canadian
Electrical Code contains installation requirements for
impressed current cathodic protection systems. The section
includes requirements for the selection of wiring methods
for direct current conductors, splices, taps and connections,
branch circuit requirements and warning signs and drawing
requirements.
Interestingly, the NEC does not contain specific
requirements for the installation of cathodic protection
systems. The American Society of Mechanical Engineers
(ASME) publishes codes relating to the design and instal-
lation of pressure piping systems:
1. ANSI/ASME B31.8, Gas Transmission and
Distribution Piping Systems.
2. ANSI/ASME B31.4, Liquid Transportation
Systems for Hydrocarbons.
In both, under corrosion control, the code allows the
attachment of electrical leads using exothermic welding but
limits the weld metal size to:
1. CADWELD CA15 for steel pipe.
2. CADWELD CA32XF19 for cast, wrought or
ductile iron pipe.
These restrictions allow welding of a No. 4 AWG and
smaller conductor to steel pipe using CADWELD cathodic
Type CAHA connections and No. 6 AWG and smaller
conductor to cast, wrought or ductile iron pipe using Type
CAHB connections. When larger sized conductors must be
welded to pipes falling under these codes, several
alternatives are available:
1. Using a formed terminal bond, a No.2 AWG can be
welded to a cast, wrought or ductile iron pipe with
a CA32XF19.
2. Use a copper Bonding strap.
3. Use a CADWELD “Punched Strap” Bond.
4. Unstrand the larger conductor and make multiple
welds of one (or more) strands at a time.
RADIO ANTENNA GROUNDING
Antennas require grounding for both lightning protection
and electrical fault protection. However, depending upon
the frequency of the radio transmission, such as AM, a
ground plane also may be required for proper and efficient
transmission of energy. The ground plane may be made up
of radials, all bonded to the antenna base plate, and ending
at a set distance from the base. The radials are usually
spaced at 1 or 2 degree intervals. Ground rods and/or a
circumferential wire are commonly used at the ends of the
radials. (Fig. 6-7)
The ground plane also may be made using prefabricated
mesh around the antenna base with radials from the edge of
the mesh. (Fig. 6-8)
Some installations use copper tubing because of its
excellent high frequency characteristics and low cost
compared to other conductors having equal high frequency
characteristics. Although connections can be made on the
round tube, they are both costly and difficult to make.
Fig. 6-9 shows the preferred method. Since the tube comes
in different sizes and types (with different wall thickness),
the exact specification of the tube must be given.
In addition to copper tubing, wide solid copper strip is often
used as a low impedance conductor at high frequencies.
CADWELD connections of strip to strip and strip to ground
rods can be utilized as shown in Fig. 6-10 and 6-11. Thin
strip is usually recommended over tubing.
The transmission conductor must also be properly
grounded and equipped with surge protection. This,
however, is beyond the scope of this book.
The towers themselves are grounded using standard
connections to the tower legs and to the ground rod.
(Fig. 6-12 and 6-13)
Guyed towers also must have the guys and guy anchors
grounded. This can usually be accomplished by grounding
the anchor plate (Fig. 6-14) or the guy after it is terminated.
Do not weld or braze to any guy conductor that is (or will
be) under tension.
Since most communication towers, including broadcast
types, are located on the highest available site, the earth
resistivity is often very high. Extensive ground fields may
be required. The use of a ground enhancement material
such as ERICO GEM25™ may be a cost-effective method
of reducing system resistance. See the discussion on GEM
in Chapter 5.
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Practical Guide to Electrical Grounding
Grounding Book 4/14/99 10/5/99 6:02 PM Page 94 (Black plate)