406 Chapter 14
flexible and high density high molecular weight formu-
lations are very hard. Moisture resistance is rated excel-
lent. Correct brown and black formulations have
excellent sunlight resistance. The dielectric constant is
2.3 for solid insulation and as low as 1.35 for
gas-injected foam cellular designs. Polyethylene is the
most common plastic worldwide.
14.5.3 Teflon®
Invented in 1937 by Roy Plunkett (USA) at DuPont,
Teflon has excellent electrical properties, temperature
range, and chemical resistance. It is not suitable where
subjected to nuclear radiation, and it does not have good
high voltage characteristics. FEP (fluorinated ethylene-
propylene) Teflon is extrudable in a manner similar to
vinyl and polyethylene, therefore, long wire and cable
lengths are available. TFE (tetrafluoroethylene) Teflon is
extrudable in a hydraulic ram-type process and lengths
are limited due to amount of material in the ram, thick-
ness of the insulation, and core size. TFE must be
extruded over silver-coated or nickel-coated wire. The
nickel and silver-coated designs are rated +260°C and
+200°C maximum (500°F and 392°F), respectively,
which is the highest temperature for common plastics.
The cost of Teflon is approximately eight to ten times
more per pound than vinyl insulations. The dielectric
constant for solid Teflon is 2.1, the lowest of all solid
plastics. Foam Teflon (FEP) has a dielectric constant as
low as 1.35. Teflon is produced by and a trademark of
DuPont Corporation.
14.5.4 Polypropylene
Polypropylene is similar in electrical properties to poly-
ethylene and is primarily used as an insulation material.
Typically, it is harder than polyethylene, which makes it
suitable for thin wall insulations. UL maximum temper-
ature rating may be 60°C or 80°C (140°F or 176°F). The
dielectric constant is 2.25 for solid and 1.55 for cellular
designs.
14.6 Thermoset Compounds
As the name implies, thermoset compounds are produced
by heat (thermo) but are set. That is, the process cannot
be reversed as in thermoplastics. They cannot be recy-
cled into new products as thermoplastic materials can.
14.6.1 SiliconeSilicone is a very soft insulation which has a temperature
range from 80°C to +200°C (112°F to +392°F). It has
excellent electrical properties plus ozone resistance, low
moisture absorption, weather resistance, and radiation
resistance. It typically has low mechanical strength and
poor scuff resistance. Silicone is seldom used because it
is very expensive.14.6.2 NeopreneNeoprene has a maximum temperature range from
55°C to +90°C (67°F to +194°F). The actual range
depends on the formulation used. Neoprene is both oil
and sunlight resistant making it ideal for many outdoor
applications. The most stable colors are black, dark
brown, and gray. The electrical properties are not as
good as other insulation material; therefore, thicker insu-
lation must be used for the same insulation.14.6.3 RubberThe description of rubber normally includes natural rub-
ber and styrene-butadiene rubber (SBR) compounds.
Both can be used for insulation and jackets. There are
many formulations of these basic materials and each for-
mulation is for a specific application. Some formulations
are suitable for 55°C (67°F) minimum while others
are suitable for +75°C (+167°F) maximum. Rubber jack-
eting compounds feature exceptional durability for
extended cable life. They withstand high-impact and
abrasive conditions better than PVC and are resistant to
degradation or penetration by water, alkali, or acid. They
have excellent heat resistant properties, and also pro-
vide greater cable flexibility in cold temperatures.14.6.4 EPDMEPDM stands for ethylene-propylene-diene monomer. It
was invented by Dr. Waldo Semon in 1927 (see Section
14.5.1). It is extremely rugged, like natural rubber, but
can be created from petroleum byproducts ethylene and
propylene gas.14.7 Single ConductorSingle conductor wire starts with a single wire, either
solid or stranded. It can be bare, sometimes called buss
bar, or can be jacketed. There is no actual limit to how