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covering is woven into fabric during the application to the cable. When tape covering is used, it is
wrapped helically around the cable with each turn overlapping the previous turn.
The most common types of fibrous tape are rubber-filled cloth tape and a combination of cotton
cloth and rubber. Except for duct tape, tape covering is never used as the outer covering on a cable. Tape
coverings are used directly over the insulation of individual conductors and for the inner covering over
the assembled conductors of a multiconductor cable. Frequently, tape coverings are used under the sheath
of a lead-sheathed cable. Duct tape, which is made of heavy canvas webbing saturated with an asphalt
compound, is often used over a lead-sheathed cable for protection against corrosion and mechanical
injury.
Q30.
How many categories of nonmetallic protective coverings are there?
Q31.
What is the most common type of nonmetallic material used to protect wires and cables?
Q32.
What are the most common types of fibrous tape?
Woven Covers
Woven covers, commonly called loom, are used when exceptional abrasion-resistant qualities are
required. These covers are composed of thick, heavy, long-fibered cotton yarns woven around the cable in
a circular loom, much like that used on a fire hose. They are not braids, although braid covering are also
woven; they are designated differently.
Rubber and Synthetic Coverings
Rubber and synthetic coverings are not standardized. Different manufactures have their own special
compounds designated by individual trade names. These compounds are different from the rubber
compounds used to insulate cable. These compounds have been perfected not for insulation qualities but
for resistance to abrasion, moisture, oil, gasoline, acids, earth solutions, and alkalies. None of these
coverings will provide protection against all types of exposure. Each covering has its own particular
limitations and qualifications.
Jute and Asphalt Coverings
Jute and asphalt coverings are commonly used as a cushion between cable insulation and metallic
armor. Frequently, they are also used as a corrosive-resistant covering over a lead sheath or metallic
armor. Jute and asphalt coverings consist of asphalt-impregnated jute yarn heli-wrapped around the cable
or of alternate layers of asphalt-impregnated jute yarn. These coverings serve as a weatherproofing.
Unspun Felted Cotton
Unspun felted cotton is commonly used only in special classes of service. It is made as a solid felted
covering for a cable.
Q33.
What materials are commonly used as cushions between cable insulation and metallic armor?
METALLIC PROTECTION
Metallic protection is of two types: sheath or armor. As with all wires and cables, the type of
protection needed will depend on the environment where the wire or cable will be used.
Metallic Sheath
Cables or wires that are continually subjected to water must be protected by a watertight cover. This
watertight cover is either a continuous metal jacket or a rubber sheath molded around the cable.
