DIVISION 2
PROPERTIES AND SPLICING
OF CONDUCTORS
Electrical Conducting Wires and Cables . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1
Cable Joints and Terminal Connections . . . . . . . . . . . . . . . . . . . . . . . . . . 2.61
Aluminum-Building-Wire Installation Practices . . . . . . . . . . . . . . . . . . . . 2.100
Termination and Splice Kits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.144
ELECTRICAL CONDUCTING WIRES AND CABLES
1. Electrical conducting wires and cables are available in a great variety of types
and forms of construction. To cover this one subject completely would require a large volume. The aim of the authors has been, therefore, to include in this division sufficient general information with respect to the materials employed, method of construction, and types
available so that the reader can select intelligently the proper cable for a given application.
At the end of the section, more detailed tabular information is included for the types of
cables that the average worker will use most frequently.
2. Electric Wire and Cable Terminology
Wire. A slender rod or filament of drawn metal. (This definition restricts the term wire to
what would ordinarily be understood by the term solid wire. In the definition the word slender is used in the sense that the length is great in comparison with the diameter. If a wire is
covered with insulation, it is properly called an insulated wire, although the term wire
refers primarily to the metal; nevertheless, when the context shows that the wire is insulated, the term wire will be understood to include the insulation.)
Conductor. A wire or combination of wires not insulated from one another, suitable for
carrying a single electric current. (The term conductor does not include a combination of
conductors insulated from one another, which would be suitable for carrying several different electric currents. Rolled conductors, such as busbars, are, of course, conductors but
are not considered under the terminology given here.)
Stranded Conductor. A conductor composed of a group of wires or any combination of
groups of wires. (The wires in a stranded conductor are usually twisted or braided together.)
Cable. (1) A stranded conductor (single-conductor cable) or (2) a combination of conductors insulated from one another (multiconductor cable).
The component conductors of the second kind of cable may be either solid or stranded,
and this kind may or may not have a common insulating covering. The first kind of cable
is a single conductor, while the second kind is a group of several conductors. The term
2.1
Copyright © 2009, 2002, 1996, 1992, 1987, 1981, 1970, 1961 by The McGraw-Hill Companies, Inc.
Click here for terms of use.
2.2
DIVISION TWO
cable is applied by some manufacturers to a solid wire heavily insulated and lead-covered;
this usage arises from the manner of the insulation, but such a conductor is not included
under this definition of cable. The term cable is a general one, and in practice it is usually
applied only to the larger sizes. A small cable is called a stranded wire or a cord, both of
which are defined below. Cables may be bare or insulated, and insulated cables may be
armored with lead or with steel wires or bands.
Strand.
One of the wires or groups of wires of any stranded conductor.
Stranded Wire. A group of small wires used as a single wire. (A wire has been defined
as a slender rod or filament of drawn metal. If such a filament is subdivided into several
smaller filaments or strands and is used as a single wire, it is called stranded wire. There is
no sharp dividing line of size between a stranded wire and a cable. If used as a wire, for
example in winding inductance coils or magnets, it is called a stranded wire and not a cable.
If it is substantially insulated, it is called a cord, defined below.)
Cord. A small cable, very flexible and substantially insulated to withstand wear. (There
is no sharp dividing line in respect to size between a cord and a cable and likewise no sharp
dividing line in respect to the character of insulation between a cord and a stranded wire.)
Concentric Strand. A strand composed of a central core surrounded by one or more layers of helically laid wires or groups of wires.
Concentric-Lay Conductor. A conductor composed of a central core surrounded by one
or more layers of helically laid wires. (Ordinarily it is known as a concentric-strand conductor. In the most common type, all the wires are of the same size, and the central core is
a single wire.)
Concentric-Lay Cable. A multiconductor cable composed of a central core surrounded
by one or more layers of helically laid insulated conductors.
Rope-Lay Cable. A cable composed of a central core surrounded by one or more layers
of helically laid groups of wires. (This cable differs from a concentric-lay conductor in that
the main strands are themselves stranded and all wires are of the same size.)
Multiconductor Cable. A combination of two or more conductors insulated from one
another. (Specific cables are called 3-conductor cable, 19-conductor cable, etc.)
Multiconductor Concentric Cable. A cable composed of an insulated central conductor
with one or more tubular stranded conductors laid over it concentrically and insulated from
one another. (This kind of cable usually has two or three conductors.)
N-Conductor Cable. A combination of N conductors insulated from one another. (It is
not intended that the name as given here be actually used. One would instead speak of a
3-conductor cable, a 12-conductor cable, etc. In referring to the general case, one may
speak of a multiconductor cable, as in the definition for cable above.)
N-Conductor Concentric Cable. A cable composed of an insulated central conducting
core with tubular stranded conductors laid over it concentrically and separated by layers of
insulation. (Usually it is only 2-conductor or 3-conductor. Such conductors are used in carrying alternating currents. The remarks on the expression “N-conductor” in the preceding
definition apply here also.)
PROPERTIES AND SPLICING OF CONDUCTORS
2.3
Duplex Cable. A cable composed of two insulated single-conductor cables twisted
together with or without a common covering.
Twin Cable. A cable composed of two insulated conductors laid parallel and either attached
to each other by insulation or bound together with a common covering.
Twin Wire. A cable composed of two small insulated conductors laid parallel and having
a common covering.
Twisted Pair. A cable composed of two small insulated conductors twisted together without a common covering.
Triplex Cable.
together.
A cable composed of three insulated single-conductor cables twisted
Sector Cable. A multiconductor cable in which the cross section of each conductor is
approximately the sector of a circle.
Shielded-Type Cable. A cable in which each insulated conductor is enclosed in a conducting envelope so constructed that substantially every point on the surface of the insulation is at ground potential or at some predetermined potential with respect to ground under
normal operating conditions.
Shielded-Conductor Cable. A cable in which the insulated conductor or conductors are
enclosed in a conducting envelope or envelopes, so constructed that substantially every
point on the surface of the insulation is at ground potential or at some predetermined potential with respect to ground.
Composite Conductor. A conductor consisting of two or more strands of different metals, such as aluminum and steel or copper and steel, assembled and operated in parallel.
Round Conductor. Either a solid or a stranded conductor of which the cross section is
substantially circular.
Cable Filler. Material used in multiconductor cables to occupy the spaces formed by the
assembly of the insulated conductors, thus forming a core of the desired shape.
Cable Sheath.
Protective covering applied to cable.
Insulation of a Cable. The part of a cable which is relied upon to insulate the conductor
from other conductors or conducting parts or from ground.
Insulation Resistance of an Insulated Conductor. The resistance offered by a conductor’s insulation to an impressed direct voltage, tending to produce a leakage of current
through it.
Lead-Covered Cable (Lead-Sheathed Cable). A cable provided with a sheath of lead to
exclude moisture and afford mechanical protection.
Serving of a Cable. A wrapping applied over the core of a cable before the cable is leaded
or over the lead if the cable is armored. Materials commonly used for serving are jute, cotton,
and duct tape.
2.4
DIVISION TWO
Resistive Conductor.
resistance.
A conductor used primarily because it possesses high electric
3. Wire sizes. The size of wire is usually expressed according to a wire gage, and the
different sizes are referred to by gage numbers. Unfortunately several systems of gages
have been originated by different manufacturers for their products. However, it has become
standard practice in the United States to employ the American wire gage (AWG), also
known as the Brown and Sharpe (B&S), to designate copper and aluminum wire and cable
used in the electrical industry. The names, abbreviations, and uses of the most important
gages employed for the measurement of wires and sheet-metal plates are given in Table 4. A
numerical comparison of these gages is given in Table 85. In most cases the larger the gage
number, the smaller the size of the wire.
4. Names, Abbreviations, and Uses of the Principal Wire and Sheet-Metal
Gages
Col.
no. in
Table 85
Names and abbreviations
Usual
Others
1
American
wire gage
(AWG)
Brown and Sharpe
(B&S)
2
Steel wire
gage (SWG)
3
Birmingham
wire gage
(BWG)
Roebling, American Steel
and Wire, Washburn &
Moen, National, G. W.
Prentiss
Stubs iron wire gage, iron
wire gage
4
Stubs steel
wire gage
British
standard
wire gage
(SWG)
5
6
7
8
9
10
.................................................
Imperial standard wire gage,
standard wire gage,
English legal standard
Steel music
Hammacher, Schlemmer,
wire gage
Felten & Guilleaume
(MWG)
U.S. Standard Gage .................................................
(USG)
Manufacturers
.................................................
standard gage
(MSG)
American zinc
.................................................
Birmingham
.................................................
gage (BG)
Ordinarily used for
measuring
Copper, aluminum, copperclad aluminum, and other
nonferrous wires, rods,
and plates. Wall thickness
of tubes
Iron and steel wire. Wire
nails. Brass and iron
escutcheon pins
Galvanized iron and steel
wire. Iron and copper
rivets. Thickness of wall of
nonferrous seamless tubing
Drill rod
Legal standard wire gage for
Canada and Great Britain;
used sometimes by
American telephone and
telegraph companies for
bare copper line wire
Steel music wire
Stainless steel sheets
Legal standard for iron and
steel plate. Monel metal.
Galvanized sheets
Sheet zinc
Legal standard for iron and
steel sheets in Canada and
Great Britain
PROPERTIES AND SPLICING OF CONDUCTORS
2.5
5. How to remember the AWG or B&S wire-gage table (Westinghouse Diary).
A wire that is three sizes larger than another wire has half the resistance, twice the weight,
and twice the area. A wire that is 10 sizes larger than another wire has one-tenth the resistance, 10 times the weight, and 10 times the area. Number 10 wire is 0.10 (more precisely
0.102) in (2.6 mm) in diameter; it has an area of 10,000 (more precisely 10,380) cmil
(5.26 mm2); it has a resistance of 1 /1000 ft (304.8 m) at 20C (68F); and it weighs 32
(more precisely 31.4) lb (14.24 kg)/1000 ft (304.8 m).
The weight of 1000 ft (304.8 m) of No. 5 wire is 100 lb (45.36 kg). The relative values
of resistance (for decreasing sizes) and of weight and area (for increasing sizes) for consecutive sizes are 0.50, 0.63, 0.80, 1.00, 1.25, 1.60, 2.00. The relative values of the diameters of alternate sizes of wire are 0.50, 0.63, 0.80, 1.00, 1.25, 1.60, 2.00. To find resistance,
drop one cipher from the number of circular mils; the result is the number of feet per ohm.
To find weight, drop four ciphers from the number of circular mils and multiply by the
weight of No. 10 wire.
6. Wire-measuring gages (Figs. 2.1 and 2.2) are made of steel plate. With the kind
shown in Fig. 2.1, the wire being measured is inserted in the slots in the periphery until a
slot is found in which the wire just fits. The wire’s gage number is indicated opposite the
slot. A measuring gage like that of Fig. 2.1 indicates the numbers of one gage or system
only. A gage like that of Fig. 2.2 indicates the numbers of four gages but has the disadvantage that, to use it, the end of the wire must be available to be pushed through the slot. The
wire is pushed as far toward the small end of the slot as it will go, and its gage number is
then indicated opposite the point where the wire stops. The gage of Fig. 2.2 is arranged to
indicate gage numbers for the American standard screw gage, English wire gage, and
American wire gage, and one scale is divided into 30 seconds of an inch.
FIGURE 2.1 Standard wire gage (greatly reduced).
FIGURE 2.2 Angular wire gage (greatly reduced).
7. A micrometer is frequently used to determine the size of a given wire or cable. It
provides an accurate means of measuring the diameter of the wire or cable to thousandths
of an inch and of estimating to ten-thousandths. After the diameter has been determined,
the corresponding gage size may be ascertained by referring to a wire table. The wire to be
measured is placed between the thumbscrew and the anvil (Fig. 2.3), and the screw is turned
until the wire is lightly held between the screw and the anvil. The screw has 40 threads to
the inch, so that one complete turn of the screw in left-hand direction will open the micrometer 1/40 in. On the edge of the collar is a circular scale divided into 25 divisions; hence,
when the screw is turned through one of these divisions, the micrometer will open 1/25 1
/40 in 1/1000 in. The shaft on which the collar turns is marked into tenths of an inch, and
each 1/10 is subdivided into four parts. Each of these parts must be equal to 1/10 1/4 in 2.6
DIVISION TWO
FIGURE 2.3
A micrometer caliper.
/40 in 0.025 in. Therefore, a complete rotation of the collar or 25 of its divisions will
equal one division of the shaft, or 0.025 in.
1
8. To read a micrometer (see Fig. 2.4 and the paragraph above), note the number
on the circular scale nearest the index line. This indicates the number of thousandths.
Note the number of small divisions uncovered on the shaft scale. Each one of these small
divisions indicates 0.025 in (25/1000). Add together the number of thousandths indicated
on the circular scale and 0.025 times the number of small divisions wholly uncovered on
the shaft scale. The sum will be the distance that the jaws are apart. Examples are shown
in Fig. 2.4.
FIGURE 2.4
A micrometer caliper.
9. Classification of wires or cables. Electrical conducting wires and cables may be
classified in several different ways, depending upon the particular factor of consideration
as follows:
1.
2.
3.
4.
5.
6.
According to degree of covering of wire or cable
According to material and makeup of electrical conductor
According to number of conductors in cable
If insulated, according to insulation employed
According to protective covering
According to service
PROPERTIES AND SPLICING OF CONDUCTORS
2.7
10. Classification according to degree of covering. Probably the broadest classification of electrical wires and cables is according to the degree of covering employed, as
follows:
1. Bare
2. Covered but not insulated
3. Insulated and covered
In many cases bare conductors without any covering over the metallic conductors are
employed for electrical circuits. The conductors are supported on insulators so spaced,
depending upon the voltage of the circuit, that the length of the air space between the conductors will provide sufficient insulation. Bare conductors are employed for most overhead
transmission lines. They are also used for certain overhead telephone and telegraph circuits.
There is a definite distinction between the meanings of the words bare, covered, and
insulated in electrical-cable terminology:
Bare. Designating a conductor having no covering or electrical insulation whatsoever.
Covered. Designating a conductor encased in material whose thickness or composition is not recognized by the National Electrical Code® (NEC) as electrical insulation.
Insulated. Designating a conductor encased in material whose thickness or composition is recognized by the Code as electrical insulation.
Insulated wires and cables consist of an electrical conductor covered with some form of
electrical insulation with or without an outer protective covering. With covered wires the
conductor is protected against mechanical injury by some form of covering applied directly
over the conductor. This covering, however, does not provide insulation of the wet conductor to any great extent and often even becomes a fair conductor itself when moist. The
covering therefore cannot be relied upon to afford consistently any insulation beyond that
of the air spacing between the conductors.
Weatherproof wires may be divided into two general classes, those with fibrous coverings and those with homogeneous coverings (Sec. 12).
11. Weatherproof-covered wire with fibrous coverings is available in two
types. Both are designated as URC and are manufactured according to specifications recommended by the Utilities Research Commission. The two types are distinguished by at
least one manufacturer as O.K.-URC and Peerless URC. The O.K. is the more common
type. The wire is covered with two or three weatherproof cotton braids, which are applied
directly over the conductor. The braids are saturated with a black asphaltic compound. The
outside surface of the outer braid is coated with mica flake to provide a smooth surface free
of tackiness. The Peerless type, a better-grade covering, not only is longer-lived but
provides some degree of overall electrical insulation to the conductor. The construction
consists of a compacted pad of unspun cotton wrapped helically directly around the conductor and filled with asphalt. This pad provides a homogeneous wall of insulation without
the usual braid interstices encountered in ordinary weatherproof-covered wire. The asphaltimpregnated pad is covered with a standard outer weatherproof braid. Peerless wire is made
in two types, designated as double braid and triple braid. Actually there is only one braid in
both types, but the combination of the cotton pad of different thicknesses and the braid
gives a covering which is equivalent in thickness to the regular double- or triple-braid O.K.
wires. Weatherproof-covered wire is available with the conductor material consisting of
copper, solid copperweld, solid bronze, composite copper-copperweld, all aluminum, or
steel-reinforced aluminum.
2.8
DIVISION TWO
12. Weatherproof-covered wire with homogeneous covering is available in
two types, neoprene and polyethylene.
The neoprene type has a homogeneous covering which consists of a tough and durable
vulcanized neoprene compound. This type has the following advantageous characteristics:
1. Highly weather-resistant.
2. Not brittle under extremely low temperatures. It will not migrate under abnormally high
temperatures.
3. Preventing normal moisture ingress to conductor, thus permitting maximum continuity
of service under storm conditions.
4. Tough, with excellent resistance to mechanical abuse.
5. Light in weight and smooth-surfaced, with adhesion to the conductor. It can be handled
and installed without special precautions.
The polyethylene type has a homogeneous, seamless thermoplastic covering which is
applied by extrusion. Its more important characteristics may be summarized as follows:
1.
2.
3.
4.
5.
6.
Highly resistant to weathering, being both weather- and sun-resistant
Physically strong
Resistant to abrasion
Inherently tight on the conductor
Possessing a wide temperature range, 94F (70C) to 176F (80C)
Light in weight
13. Material and makeup of electrical conductors. The conductor may consist
of a single solid wire or a stranded cable made up of several individual bare wires twisted
together. Stranded conductors are more flexible than a single solid wire. The flexibility of
the cable increases with the number of strands and also depends upon the arrangement of
the individual strands in the makeup of the conductor. Solid wires are used for conductors
of the smaller sizes and stranded cables for the larger sizes. In the intermediate sizes both
solid and stranded conductors are available.
Wires more finely stranded than class C require special provisions at terminations, as
covered in Sec. 163. Although finely stranded conductors are readily available, they are
commonly designated welding cable. Even if rated “600 V” the welding cable designation
only means that these wires are listed for use in the secondary circuits of electric welders,
as covered in Part IV of Article 630 in the NEC. Unless provided with additional or other
markings, they are not listed for use in conventional building wiring. Building wire will
have one of the designations in NEC Table 310.13(A) such as RHH or RHW or THW or
XHHW, etc.
Electrical conducting cables are made of copper, copper-clad aluminum, aluminum,
steel, bronze, or a combination of either copper or aluminum with steel. Because of its high
conductivity, copper is the material most commonly employed. Practically all insulated
wires and cables employ copper or aluminum conductors. Aluminum or steel wires and
cables are frequently found to be more economical for certain classes of aerial construction.
All-steel conductors are employed for telephone and telegraph work and certain rural distribution lines with light load densities. Steel-copper conductors are employed for longspan river crossings of power lines and for certain rural distribution lines.
A classification of electrical conductors with respect to standard materials and makeups
available is as follows:
PROPERTIES AND SPLICING OF CONDUCTORS
A. Copper
1. Solid
a. Round
b. Grooved
c. Figure eight
d. Figure nine
e. Square or rectangular
2. Standard concentric stranded
a. Class AA
b. Class A
c. Class B
d. Class C
e. Class D
3. Standard rope stranded
a. Class G
b. Class H
4. Bunched stranded
5. Bunched and rope stranded
a. Class J
b. Class K
c. Class L
d. Class M
e. Class O
f. Class P
g. Class Q
6. Annular concentric stranded
7. Special stranded
2.9
8. Compact stranded
a. Round
b. Sector
c. Segmental
9. Hollow-core stranded
10. Tubular segmental (type HH)
B. Iron or steel
1. Solid
2. Stranded
C. Copper-steel
1. Copperweld
a. Solid
b. Stranded
2. Copperweld and copper
3. Copper and steel stranded
D. Aluminum
1. Solid
2. Stranded
3. Compact stranded
E. Copper-clad aluminum
1. Solid
2. Stranded
F. Aluminum and steel (ACSR)
G. Bronze
Refer to Table 86 for illustrations and applications of different makeups. Refer to
Table 87 for a guide to applications of conductor materials.
14. Copper wire is made in three grades of hardness, known as hard-drawn, mediumhard-drawn, and soft or annealed. Hard-drawn wire has the greatest tensile strength and the
least amount of elongation under stress and is the stiffest and hardest to bend and work.
Soft-drawn or annealed wire has the lowest tensile strength and the greatest elongation
under stress and is very pliable and easily bent. Medium-hard-drawn wire has characteristics intermediate between those of hard-drawn and soft-drawn wire. The conductivity of
copper wires decreases slightly as hardness increases, but there is relatively little difference
in the conductivity of the different grades.
Hard-drawn wire is used for long-span transmission lines, trolley contact wires, telephone
wires, and other applications for which the highest possible tensile strength is desirable.
Medium-hard-drawn wire is employed for such applications as short-span distribution
circuits and trolley feeders, for which slightly lower tensile strength is satisfactory and
greater pliability is desired.
Soft-drawn or annealed copper is used for all covered or insulated copper conductors
except weatherproof-covered cables. Wires with this covering are available in all the three
grades of hardness. Bare or weatherproof-covered soft wire is used only for short spans.
Copper wire used for rubber-insulated cable must be tinned by coating with pure tin to
protect the copper against chemical action caused by contact with the rubber.
2.10
DIVISION TWO
15. Makeup of copper conductors. Copper conductors are manufactured in various forms of makeup as listed in Sec. 13, depending upon their size and application. An
understanding of the construction of the different makeups and their applications can be
gained from Table 86. The employment of solid or stranded conductors and the choice of
the class of stranding depend upon the degree of flexibility desired. For very flexible cables
for special applications, special strandings are employed. There is no fixed standard for
these special strandings—practice varying with different manufacturers. Data for bare copper conductors of the different standard makeups are given in Tables 88 to 94.
16. Iron or steel electrical conductors. All-steel conductors for power circuits are
made from special low-resistance, high-strength steel stock. They are available in both
solid and three-strand construction. Each wire is protected by a heavy galvanized coating
of zinc. Since all-steel conductors can be applied economically only for light electrical
loads, these conductors are manufactured in only three standard sizes. Stranded conductors
are used in preference to solid wires for longer-span construction because their inherent
damping capacity reduces the amplitude of vibration in strong lateral winds.
Commercial galvanized-iron wire for telephone and telegraph circuits has been made
for many years in three types designated as extra best best (EBB), best best (BB), and steel.
These designations are somewhat misleading. Adopted many years ago, they refer to the
electrical conductivity of the different grades. All three types are made from high-grade
materials and meet the same standard of galvanizing.
Extra best best wire has the best conductivity but the lowest tensile strength. Its weight
per mile-ohm is from 4700 to 5000 lb. This wire is uniform in quality, pure, tough, and pliable. It is used largely by commercial telegraph companies, in railway telegraph service,
for tie wires, and for signal bonding.
Best best wire has a lower value of conductivity but greater tensile strength. Its weight per
mile-ohm is from 5600 to 6000 lb. This grade is used very largely by telephone companies.
Steel is a stiff wire of high tensile strength and low conductivity. It is very difficult to
work but is used on short lines which must be erected at low cost and for which conductivity is of little importance. Its weight per mile-ohm is 6500 to 7000 lb.
17. Copper-steel conductors. Electrical conductors consisting of a combination
of copper and steel are frequently employed for certain types of circuits (see Sec. 13 and
Table 87). Three general types of construction are listed in Sec. 13 and are illustrated in
Table 86.
Copperweld wire is composed of a steel core with a copper covering thoroughly welded
to it by a molten welding process. This process produces a permanent bond between the two
metals which prevents any electrogalvanic action and which will withstand hot rolling, cold
drawing, forging, bending, twisting, or sudden temperature changes. This wire is made in
three grades: 30 percent conductivity, extra-high strength; 30 percent conductivity, high
strength; and 40 percent conductivity, high strength. Solid conductors are made in sizes
from 12 to 4/0 AWG. Concentric-stranded cables are available in sizes with outside diameters from 0.174 to 0.910 in (0.442 to 23.1 mm.). Weatherproof-covered copperweld solid
wire is made in sizes from 12 to 2 AWG. Rubber-insulated twisted-pair cables in sizes 14
and 17 AWG are made for telephone, telegraph, and signal work. Single-conductor rubberinsulated wire may be obtained in any size. Rubber-insulated parallel drop wire is made in
one size only, 17 AWG.
Composite cables (copperweld and copper) consisting of a combination of certain strands
of copper wire with a number of strands of copperweld wire often are economical for aerial
circuits requiring more than average tensile strength combined with liberal conductance.
PROPERTIES AND SPLICING OF CONDUCTORS
2.11
Copper and steel cables consist of a combination of copper and steel wires stranded
together. The strands of the different materials are not intended to serve in any dual capacity, and the conductivity of the cable is determined by the sectional area of the copper
strands. The size of the cable is designated according to its total sectional area of copper,
not according to the total sectional area of the whole cable. For instance, a cable designated as No. 4, consisting of two copper and one steel strands, has a total sectional area of
62,610 cmil (31.7 mm2) and a sectional area of copper of 41,740 cmil (21.1 mm2). The
area of the copper, 41,740 cmil, corresponds to the area of a No. 4 wire. The cable is therefore designated as a No. 4 cable, although its total sectional area of copper and steel is
between No. 3 and those of No. 2 wire.
These copper and steel cables are available in sizes from No. 2 to No. 12. All sizes
except Nos. 10 and 12 consist of two plain hard-drawn copper wires and one extragalvanized-steel wire. Wire cables of sizes 10 and 12 consist of one galvanized hard-drawn
copper wire and two extra-galvanized-steel wires.
18. Copper-clad aluminum. Copper-clad aluminum is the newest conductor material on the market. A copper-clad aluminum conductor is drawn from copper-clad aluminum
rod, the copper being bonded metallurgically to an aluminum core. The copper forms a
minimum of 10 percent of the cross-sectional area of the solid conductor or of that of each
strand of a stranded conductor.
Although copper-clad aluminum contains only 10 percent of copper by volume
(26.8 percent by weight), its electrical performance is equivalent to that of pure copper.
It is lighter and easier to handle, and the price advantage, which reflects the value of
the copper content, can be as much as 25 percent when copper peaks to one of its
periodic highs. Detailed studies by Battelle Laboratories have shown that copper-clad
aluminum and copper have the same connection reliability.
Because the electrical industry consumes 60 percent of all copper used in the United
States, it is critically affected by copper’s fluctuating costs and uncertain supply. Until
recently, however, aluminum was the only alternative to copper.
Aluminum, in the more than 70 years since its introduction as an electrical conductor,
has significantly penetrated such areas as electric power transmission lines, transformer
windings, and telephone communications cables. On the other hand, it has received relatively limited acceptance in nonmetallic-sheathed cable and other small-gage building
wires. The reason has been a lack of acceptable means of connecting or terminating aluminum conductors of 6 AWG or smaller cross-sectional areas.
Connector manufacturers, the National Electrical Manufacturers Association (NEMA),
Underwriters Laboratories (UL), and aluminum companies have devoted much attention
to this connection problem. The most significant advance in aluminum termination has
been the institution of UL’s new requirements and testing procedures for wiring devices
for use in branch-circuit-size aluminum conductors. Devices which meet the revised UL
requirements are marked CO/ALR and carry that mark on the mounting strap. Only
CO/ALR switches and receptacles should be used in aluminum 15- and 20-A branchcircuit wiring.
Copper-clad aluminum is now available to counter the disadvantages of high price and
lack of availability of copper and the problems of connection reliability of aluminum. It is
a product of a metallurgical material system, i.e., a system in which two or more metals are
inseparably bonded in a design that utilizes the benefits of each component metal while
minimizing their deficiencies. In copper-clad aluminum conductors, the electrical reliability of copper is combined with the abundant supply, stable price, and light weight of aluminum. Copper-clad aluminum is already being used for building wire, battery cable,
magnet wire, and radio-frequency (rf ) coaxial cable.
2.12
DIVISION TWO
The ampacity (current-carrying capacity) of copper-clad aluminum conductors is the
same as that of aluminum conductors. It is required that the wire connectors used with
copper-clad aluminum conductors be recognized for use with copper and copper-clad aluminum conductors and be marked CC-CU or CU-AL, except that 12-10 AWG solid
copper-clad aluminum conductors may be used with wire-binding screws and in pressureplate connecting mechanisms that are recognized for use for copper conductors. Copperclad aluminum conductors are suitable for intermixing with copper and aluminum
conductors in terminals for splicing connections only when the wire connectors are specifically recognized for such use. Such intermixed connections are limited to dry locations.
19. Aluminum and aluminum steel-reinforced conductors often are economical for transmission and rural distribution circuits. Commercial hard-drawn aluminum wire
has a conductivity at 20C of 60.97 percent or a resistance of 17.010 /cmil ft. Its weight is
0.000000915 (91.5 10–8) lb/cmil ft. An all-aluminum wire for equal conductivity must
have a diameter 126 percent and an area 160 percent of that of a copper wire. All-aluminum
conductors are available in bare, weatherproof-covered, rubber-insulated, and thermoplasticinsulated constructions. Aluminum steel-reinforced conductors, owing to their high tensile
strength, are frequently used for long spans and for high-capacity lines requiring heavy conductors. They consist of a concentric-stranded aluminum cable with a reinforcing steel core.
Except in the smaller sizes, the steel core is made up of several steel strands. Aluminum steelreinforced conductors are available either bare or weatherproof-covered.
20. Number of conductors. Bare or covered (not insulated) cables must, of course,
always be single-conductor. Insulated cables are manufactured with one, two, three, or
even more conductors per cable. The choice between single- or multiconductor cable is
affected by so many factors, which vary with the particular installation, that only general
suggestions can be made here. The selection will be influenced by practical field conditions
and facilities of installation, cost of cable and enclosure, physical dimensions of the cable
and of the available enclosure, electrical load requirements, and voltage and type of power
supply system. The use of multiconductor cables usually results in lower cable cost, smaller
voltage drop, and more economical utilization of duct space. On the other hand, singleconductor cables are more flexible and are easier to splice and install. For underground
transmission and primary distribution applications, single-conductor cable is generally
used when the voltage exceeds 35 kV or when the load is 50,000 kVA or more. For all other
underground transmission and primary distribution applications, both single-conductor and
multiconductor cables are employed. In the past the use of multiconductor cable was most
common, but the use of single-conductor cable in this field is rapidly growing. Singleconductor cable is generally preferred for secondary distribution because of the ease in
making taps. For interior building wiring, single-conductor cable is most commonly
employed in raceway systems.
21. Cable assembly. For the application of electrical conducting wires and cables, it
is essential to have a general knowledge of the materials employed in their manufacture and
also of the manner of assembling the component parts in the formation of the finished cable.
For a bare wire the assembly is, of course, very simple, consisting only of the solid or
stranded wire of the conductor. For insulated cables and especially for multiconductor
cables, the use of many materials and different forms of assembly is involved. The component parts of the more common insulated cables, in the order in which the parts are
employed in the manufacture of the cables, are as follows:
PROPERTIES AND SPLICING OF CONDUCTORS
A. Single-conductor cables
1. Conductor
2. Insulation
3. Protective covering
B. Multiconductor cables
1. Without shielding or belting
(no insulation around group of
conductors)
a. Conductor
b. Conductor insulation
c. Conductor covering
d. Fillers
e. Protective covering
2.13
2. Belted type (insulation around group
of conductors)
a. Conductor
b. Conductor insulation
c. Conductor covering
d. Fillers
e. Belt insulation
f. Protective covering
3. Shielded type
a. Conductor
b. Conductor insulation
c. Conductor shield
d. Fillers
e. Binder tape
f. Protective covering
22. Electrical shielding is often necessary on power cable to confine the dielectric
field to the inside of the cable insulation so as to prevent damage from corona or ionization.
The shield usually consists of a thin (3-mil, or 0.076-mm) conducting tape of copper or aluminum applied over the insulation of each conductor. The shielding tape sometimes is perforated to reduce power losses due to eddy currents set up in the shield. Sometimes
semiconducting tapes consisting of specially treated fibrous tapes or braids are used. These
semiconducting tapes are frequently employed for the shielding of aerial cable, since they
adhere more closely to the insulation and thus tend to prevent corona.
23. Fillers are used in the manufacture of most multiconductor cables. Their purpose
is to fill the spaces between the conductors to produce a solid round structure for the complete cable. The materials commonly employed for these fillers are saturated jute, asbestosbase caulk, rubber, and, in some cases, cotton.
24. Binder tapes are used in the construction of many multiconductor cables to bind
conductors, shields, and fillers together in proper form during the addition of the protective
covering. The more common types of binder tapes are rubber-filled cloth tape, combinations of cotton cloth and rubber compounds, steel, and bronze.
25. Insulation of electrical conductors. Except for aerial construction, interior
exposed wiring on insulators, and special cases of interior-wiring feeder circuits, electrical
conductors must be covered with some form of electrical insulation. An ideal insulating
material for this purpose should have the following characteristics:
1.
2.
3.
4.
5.
Long life
Long-time high dielectric strength
Resistance to corona and ionization
Resistance to high temperature
Mechanical flexibility
2.14
DIVISION TWO
6. Resistance to moisture
7. Low dielectric loss
It is impossible to find any one material that is best when all these essential characteristics are considered. For instance, impregnated paper has the highest electrical breakdown strength coupled with the longest life of all the materials employed for the
insulation of conductors. On the other hand, it is not moisture-resistant, is not so flexible
as some other materials, and will not withstand such high temperatures as asbestos.
Several different types of insulation are therefore employed. The insulation whose overall characteristics best meet the conditions of service for the particular application should
be selected. Tables 76, 99, and 101 classify the different types of insulation with respect
to temperature.
26. Rubber insulation. With respect to insulation, rubber is the word used to designate insulations consisting of compounds of natural rubber or synthetic rubber, or both,
combined with such other ingredients as vulcanizing agents, antioxidants, fillers, softeners, and pigments. These natural-rubber and synthetic rubberlike compounds are used
more than any other material for the insulation of electrical conductors. They have the
desirable characteristics of moisture resistance, ease of handling and termination, and
extreme flexibility. On the other hand, they will not withstand such high temperatures or
voltage without deterioration as will some other types of insulation. The different ingredients of each compound are combined by the process of vulcanization into a single homogeneous material.
A large variety of rubber compounds are available, with different characteristics that
depend upon the particular service conditions for which they have been developed. It is feasible to include here only those in most common use. For applications which require special characteristics, experts of the cable manufacturers should be consulted for advice on
the best available compound.
In general, the physical and electrical properties of a compound increase with the rubber content. However, rubber alone would not provide suitable insulation. The proper
choosing and proportioning of the other ingredients are important in obtaining the desired
characteristics.
Heat-Resisting Rubber Compounds. These compounds, which will withstand considerably higher temperatures than the Code-grade rubber compound, have been developed.
Such compounds meeting Underwriters Laboratories specifications are designated as Type
RHH insulation.
Moisture-Resistant Rubber Compounds. These compounds are available for installations in which the wire will be subjected to wet conditions. They are called moistureresistant and submarine compounds.
Moisture- and Heat-Resistant Compounds. These compounds combine the temperatureand moisture-resistance characteristics of Type RHH and Type RHW insulations. They are
recognized by the Underwriters Laboratories designation of Type RHW, which is approved
for use in wet or dry locations at a maximum conductor temperature of 75C and RHW-2
for 90C.
Type SA Wire. It is insulated with a silicone rubber compound. The outer covering of this
type of wire must consist of heavy glass that is impregnated with a heat-, flame-, and
moisture-resistant compound.
PROPERTIES AND SPLICING OF CONDUCTORS
2.15
Many wire and cable manufacturers have a rubber compound for use on general power
cables which is of a higher quality than required by the Underwriters Laboratories’ specifications. These especially high-grade rubber compounds are designated by the individual
manufacturer’s trade name. Several other nonstandardized compounds, designated by the
individual manufacturer’s trade name, are available to meet special conditions of service,
such as resistance to chemicals, ozone, and corona.
A low-voltage compound called neoprene, although not a rubber compound, is recognized by the Underwriters Laboratories as an approved insulation for Type RHW building
wire without additional covering over the insulation. It is also widely used in many applications for which its superior mechanical properties are needed, such as self-supporting
secondaries for services and service-drop cables, overhead line wires, and motor and appliance lead wires.
27. Thermoplastic insulation. Thermoplastic compounds have been developed for
insulations of electrical wires. Those meeting the specifications of the Underwriters
Laboratories are designated as Type TW, THW, THWN, THHN, THHW, TBS, or MTW.
Type TW, THW, or THWN is moisture-resistant and can be used in wet locations. Type
THW or THWN is both moisture- and heat-resistant and is approved for use in wet or dry
locations at a maximum conductor temperature of 75C. Type THHW is moisture- and
heat-resistant and may be used in wet or dry locations at a maximum conductor temperature of 75C in wet locations and 90C in dry locations. Type TBS is thermoplastic insulation with a flame-retardant fibrous outer braid and is acceptable only for switchboard
wiring. Type THWN is a moisture- and heat-resistant insulation that is approved for both
wet and dry locations at a maximum conductor temperature of 75C. It has an outer nylon
jacket. Just as in the case of Type RHW, this insulation is also available in a form suitable
for 90C in wet locations, and it has the same “-2” suffix. Thus, Type THWN-2 can be used
in wet locations and where exposed to high temperatures. Type THHN is similar to Type
THWN, except that it is not moisture-resistant and may be used only in dry and damp locations at a maximum conductor temperature of 90C. Type MTW is moisture-, heat-, and oilresistant and is restricted to use in machine-tool wiring at a maximum conductor
temperature of 60C in wet locations and 90C in dry locations.
28. Thermosetting insulation. Four high-quality wires are Types XHH, XHHW,
FEP, and FEPB. Type XHHW is a moisture- and heat-resistant, cross-linked, thermosetting polyethylene with an insulating rating of 75C in wet locations and 90C in
dry locations. Here also, Type XHHW-2 is available, which can be used for 90C exposures in wet locations. Type XHH has a thermoset insulation that is rated at 90C in dry
or damp locations. Type FEP has a heat-resistant, fluorinated ethylene propylene insulation and is suitable for use in dry or damp locations at a maximum conductor temperature of 90C, and Type FEPB is suitable for dry locations at 200C for special
applications.
29. Mineral insulation. The objective in developing mineral insulation was to provide a wiring material which would be as noncombustible as possible and thus eliminate
the hazards of fire resulting from faults or overloads. This insulation consists of highly
compressed magnesium oxide and is designated as Type MI cable. The outer metallic
sheath is copper. A complete description of this cable is given in Sec. 54 of this division
and in Div. 9.
2.16
DIVISION TWO
30. Paper insulation. Impregnated-paper insulation provides the highest electrical
breakdown strength, greatest reliability, and longest life of any of the materials employed
for the electrical insulation of conductors. It will safely withstand higher operating temperatures than either rubber or varnished-cambric insulations. On the other hand, it is not
moisture-resistant and must always have a covering which will protect the insulation from
moisture, such as a lead sheath.
Paper-insulated cables are not so flexible and easy to handle as varnished-cambric or
rubber-insulated cables and require greater care and time for the making of splices. They
are available in the following types:
1.
2.
3.
4.
5.
6.
7.
Solid-type insulation
Low-pressure gas-filled
Medium-pressure gas-filled
Low-pressure oil-filled
High-pressure oil-filled (pipe enclosed)
High-pressure gas-filled (pipe enclosed)
High-pressure gas-filled (self-contained)
The solid-type insulation is composed of layers of paper tapes applied helically over the
conductor and impregnated with mineral oil (sometimes mixed with resin when so specified). A tightly fitting lead sheath is extruded over the assembled conductors and impregnated insulation. The oil must be heavy enough to prevent bleeding when the cable is cut
for splicing and terminations but at the same time must remain semifluid at the lowest operating temperatures. For cables installed as vertical risers, on steep grades, or under high
operating temperatures, a heavier oil, designated as a nonmigrating compound, is sometimes employed to prevent the migration of the oil from the high to the low points of the
cable. The ordinary solid-type impregnated-paper insulation will give off flammable and
explosive gases when exposed to extremely high temperatures. It is a common practice to
clear cable failures on low-voltage network cables by leaving the power on and burning the
fault clear. To reduce the possibility of damage to raceways and manhole structures from
consequent explosions, special nonflammable, nonexplosive compounds are sometimes
used to impregnate the paper insulation.
Low-pressure gas-filled cables, operating under nitrogen gas pressure of 10 to 15 lb/in2
(68,947.6 to 103,421.4 Pa), are manufactured and impregnated in the same manner as solidtype cable, but prior to leading it is drained in a nitrogen atmosphere at a temperature somewhat above the maximum allowable operating temperature. To give the gas free access to
the insulated conductors, longitudinal gas feed channels are placed in the filler interstices
of the three-conductor construction and flutes or another type of channel under the sheath
of the single-conductor construction. In the three-conductor construction, two of the three
gas feed channels are obtained either by omission of filler material from the interstices or
by use of an open helical coil made from steel strip. The third channel is a solid-wall metal
tube filled with dry nitrogen gas and sealed off at each end before treatment of the cable
length. The end of this solid-wall metal channel is opened at each joint location and ensures
positive control of the pressure over the entire cable length by furnishing a bypass path for
the gas at low points or dips in the cable run where “slugs” of surplus compound may gradually collect in service in the open-wall channels.
Cable operating records indicate that most service failures are attributable to damage to
lead sheaths arising from a variety of causes or to leaks in joint wipes, terminals, or other
accessories. An important advantage of low-pressure gas-filled cable, in common with lowpressure oil-filled cable, is that service failures from these causes are practically eliminated
because a positive internal pressure is maintained continuously within the sheath, the
PROPERTIES AND SPLICING OF CONDUCTORS
2.17
entrance of moisture is prevented, and operation can continue until it is convenient to make
repairs.
Medium-pressure gas-filled cables operate under a nitrogen pressure of about 49 lb/in2
(337,843 Pa). They are constructed in a manner similar to the low-pressure gas-filled
cables, except that a reinforced lead sheath is employed to permit the use of the increased
gas pressure.
In low-pressure oil-filled cables, the paper is impregnated with a relatively thin liquid
oil which is fluid at all operating temperatures. The cable is so constructed that channels
are provided for longitudinal flow of the oil, and oil reservoirs are furnished at suitable
points in the cable installation. A positive pressure of moderate magnitude is thus maintained on the oil at all times, which prevents the formation of voids in the insulation due to
changing temperature, stretching, or deformation of the lead sheath. When the cable is
heated by load, the oil expands and flows lengthwise through the channels of the cable into
the joints and out into the reservoirs. When the cable cools and the oil in the cable contracts,
oil is forced back through the channels of the cable from the oil reservoirs. Any damage to
the lead sheath will allow moisture to enter a solid-type insulated cable. With oil-filled
cable, unless the damage is too severe, the positive internal oil pressure will prevent the
entrance of moisture, so that although there will be some loss of oil, operation can continue
until it is convenient to make repairs.
High-pressure oil-filled cables (pipe enclosed) are insulated and impregnated in the
same manner as single-conductor solid-type cables. The necessary number of singleconductor cables are then pulled into a welded steel line pipe which is protected by a highgrade corrosion-protective covering. The enclosing pipe is then filled with oil, which is
maintained under constant high pressure. An oil pressure of approximately 200 lb/in2
(1,378,951 Pa) prevents the formation of voids in the insulation and is maintained by oil
pumps at one or more points on the line.
To provide protection against moisture entrance during shipment, the cable may be
shipped with a temporary lead sheath or on a special weathertight reel without a lead covering. In the former case a thin temporary lead sheath is extruded over the skid wires and
is stripped from the cable during the pulling operation. When the cable is shipped without
a temporary lead sheath, all seams of the weathertight reel are carefully welded. The outer
layer of cable is covered by a “blanket” of material having a very low rate of moisture
absorption and diffusion. The edges of the blanket are tightly sealed to the inside surface of
the reel flange by a moisture-repellent plastic adhesive and sealing compound. Joints
between external mechanical protection, such as lags, sheet-metal layers, etc., and the steel
rim of the reel flange are sealed in a similar manner. Each reel is also equipped with a
pocket containing a desiccant, and prior to shipment the reel interior is flushed carefully
with dry nitrogen gas.
High-pressure gas-filled cable (pipe enclosed) is similar to the high-pressure oil-filled
type in that the insulated conductors comprising the circuit are installed in a metal pipe but
differs from it in that nitrogen gas at a pressure of approximately 200 lb/in2 (1,378,951 Pa)
is employed as a pressure medium in place of oil.
In the mass-impregnated type, the paper tape is applied to the conductor, and the cable
is impregnated in the same manner as the solid type. Shipment is carried out in the same
manner as that for high-pressure oil-filled cables, either with a temporary lead sheath or on
a weathertight reel without a lead covering.
High-pressure gas-filled (self-contained) cables use a lead sheath reinforced with
metallic tapes as the pressure-retaining member in place of the steel pipe. In these cables,
the permanent lead sheath and the associated reinforcement and protective coverings are
applied to the cable prior to shipment from the factory.
A special grade of untreated paper is sometimes employed for insulating magnet wires.
It is applied to the conductor in ribbon form as a helix with approximately one-third to one-half
2.18
DIVISION TWO
lap. This procedure provides a low-cost insulation of constant thickness and slightly higher
dielectric strength than that provided by cotton yarn, but it is less sturdy.
31. Varnished-cambric insulation has characteristics which in almost every respect
are midway between those of rubber and paper. It is more flexible than paper but not so flexible as rubber, except for large insulated cables. It is reasonably moisture-resisting, so that it
need not always be covered with a lead sheath, but it cannot be operated without such protective covering if it is continuously immersed or is in continuously moist surroundings.
With respect to dielectric strength, allowable temperature, and resistance to ionization and
corona, it is better than rubber but not so good as impregnated paper. Varnished cambric is
not affected by ordinary oils and greases and will withstand hard service.
The term varnished cambric is misleading, since the cotton-fabric base of the insulation
is not cambric. The correct designation should be varnished cloth, but because of longestablished custom the material is designated as varnished-cambric insulation. Varnishedcambric-insulated cable consists of conductors helically wrapped with cotton tape which
has been previously filled and coated on both sides with insulating varnish. During the
wrapping process, a heavy nonhardening mineral compound is applied between the tapings
to act as a lubricant when the cable is bent and also to fill all spaces so as to prevent ionization and possible capillary absorption of moisture.
32. Silicone rubber provides a truly heat-resisting insulation suitable for use at temperatures beyond the limits allowable for other standard forms of cable insulation. However,
it is satisfactory only for low-voltage installations (not more than 8000 V), since it cannot be
applied to the conductors so as to give high dielectric strength to the cable insulation.
Type SA. Silicone rubber insulated with outer heavy glass.
33. Cotton yarn is often employed for the insulation of magnet wire. The wire is covered with one or more wraps of helically wrapped unbleached cotton yarn. When more than
one wrap is employed, each wrap is applied in the reverse direction to that of the next inner
wrap. The untreated cotton is neither heat-resisting nor impervious to moisture. It is not
fully considered to be an insulation, and coils wound with it should be treated or impregnated with an insulating compound by an approved process. The cotton yarn acts as a
mechanical separator, holding the conductors apart and providing a medium for the absorption and retention of the impregnating material. Cotton yarn is also used as a protective covering for enamel-insulated magnet wire.
34. Enamel is widely used as an insulation for magnet wire. It has excellent resistance
to moisture, heat, and oil and possesses high dielectric strength. Enamel wire consists of a
comparatively thin, even coating of high-grade organic insulating enamel applied directly
to the bare wire. It is made in various types as given in Sec. 82.
35. Silk yarn is employed in the same manner as cotton yarn (Sec. 33) for the insulation of magnet wire. Silk coverings have better dielectric characteristics, give a neater
appearance, and are mechanically stronger than cotton. Otherwise, all the statements in
Sec. 33 respecting cotton-yarn insulations apply to silk.
Cellulose-acetate (artificial silk) tape or yarn is used in many applications for the insulation of magnet wire as a substitute for or in combination with natural silk. Artificial silk
PROPERTIES AND SPLICING OF CONDUCTORS
2.19
has somewhat better electrical characteristics and gives a more uniform thickness of insulation. Its strength and abrasion resistance are not so good as those of natural silk.
36. Fibrous-glass yarn has been developed for the insulation of conductors. Up to
the present time it has been employed only for the insulation of dynamo windings and magnet wire for classes of service requiring operation at high temperatures. The conductors are
wound with one or more wraps of alkali-free fibrous-glass yarn.
37. Protective coverings. The insulation of most insulated conductors is protected
from wear and deterioration due to surrounding conditions by a covering applied over the
insulation. Protective coverings are also used on some noninsulated cables such as the
weatherproof wire used for distribution purposes (see Secs. 10 and 11). The materials most
commonly used for these protective coverings are listed in Sec. 38. No one covering will
fulfill all the protective functions that are required for all classes of installations. Each has
its particular advantages and limitations and consequently its proper field of application. In
many cases a combination of two or more types of covering is required to provide the necessary protection to the conductor and its insulation.
38. Protective-covering materials and finishes
I. Nonmetallic
A. According to material of covering
1. Fibrous braids
a. Cotton
(1) Light
(2) Standard
(3) Heavy
(4) Glazed cotton
b. Seine twine or hawser cord
c. Hemp
d. Paper and cotton
e. Jute
f. Asbestos
g. Silk
h. Rayon
i. Fibrous glass
2. Tapes
a. Rubber-filled cloth tape
b. Combination of cotton cloth and
rubber compounds
3. Woven covers (loom)
4. Unspun felted cottom
5. Rubber jackets
6. Synthetic jackets
7 Thermoplastic jackets
8. Jute and asphalt
B. According to saturant
1. Asphalt
2. Paint
3. Varnish
C. According to finish
1. Stearin pitch and mica flake
2. Paint
3. Wax
4. Lacquer
5. Varnish
II. Metallic
A. Pure lead sheath
B. Reinforced lead sheath
C. Alloy-lead sheath
D. Flat-band armor
E. Interlocked armor
F. Wire armor
G. Basket-weave armor
39. Fibrous braids are used extensively for protective coverings of cables. These
braids are woven over the insulation so as to form a continuous covering without joints. The
braid is generally saturated (Sec. 45) with some compound to impart resistance to some
class of exposure such as moisture, flame, or acid. The outside braid is given one of the finishes
described in Sec. 45 in accordance with the application of the cable.
2.20
DIVISION TWO
The most common braid is one woven from light, standard, or heavy cotton yarn. Such
coverings are designated, respectively, as ICEA Classes A, B, and C. (ICEA are the initials
of the Insulated Cable Engineers Association.) The cotton can be furnished in a variety of
colors for identification in accordance with an established color code in the industry.
Glazed-cotton braid is composed of light cotton yarn treated with a sizing material
before fabrication.
Seine-twine or hawser-cord braid is composed of cable-laid, hard-twisted cotton yarn,
braided to form a heavy, durable covering which will withstand more rough usage than a
braid made from common cotton yarn.
Hemp braid is woven from strong, durable, long-fibered hemp yarn which will withstand even rougher usage than seine-twine braid.
Paper-and-cotton braid is composed of paper twine interwoven with cotton threads.
Jute braid is woven from yarn composed of twisted jute fibers.
Silk and rayon braids are manufactured in the same manner as glazed-cotton braid from
real or artificial silk yarn.
Fibrous-glass braid is woven from fine, flexible glass threads and forms a covering
resistant to flame, acids, alkalies, and oils.
40. Fibrous-tape coverings are frequently used as a part of the protective covering
of cables. The material of tape coverings is fabricated into a tape before application to the
cable, while the yarn in braid coverings is woven into a fabric during application to the
cable. In applying tape coverings, the tape is wrapped helically around the cable, generally
with a certain amount of overlapping of adjacent turns. The more common types of fibrous
tapes employed in cable manufacturing are listed in Sec. 38. Except for duck tape, tape coverings are never used for the outer covering of a cable. They are employed for the covering
directly over the insulation of individual conductors and for the inner covering over the
assembled conductors of a multiconductor cable. Frequently they are used under the sheath
of a lead-sheathed cable. Duck tape made of heavy canvas webbing presaturated with
asphalt compound is frequently used over a lead-sheathed cable for protection against corrosion and mechanical injury.
41. Woven covers, commonly called loom, are used for applications requiring
exceptional abrasion-resisting qualities. These covers are composed of thick, heavy, longfibered cotton yarn woven on the cable in a circular loom like that used for fire hose. They
are not braids. Although braid coverings also are woven, they are not designated as such.
42. Unspun felted cotton is manufactured into a solid felted covering for cables for
some special classes of service.
43. Several types of rubber and synthetic jacket coverings are available for
the protection of insulated cables. These types of coverings do not seem to be standardized.
The different manufacturers have their own special compounds designated by individual
trade names. These compounds differ from the rubber compounds used for the insulation
of cable in that they have been perfected not for insulating qualities but for resistance to
abrasion, moisture, oil, gasoline, acids, earth solutions, alkalies, etc. Of course, no one
jacket compound will provide protection against all these exposures, as each has its particular qualifications and limitations.