1-20
practical for large wires because of the expense and because the insulation is readily fractured when large
wires are bent.
Figure 1-13 shows an enamel-coated wire. Enamel is the thinnest insulating coating that can be
applied to wires. Hence, enamel-insulated magnet wire makes smaller coils. Enameled wire is sometimes
covered with one or more layers of cotton to protect the enamel from nicks, cuts, or abrasions.
Figure 1-13.—Enamel Insulation.
Q28.
What is the common name for enamel-insulated wire?
Mineral Insulated
Mineral-insulated (MI) cable was developed to meet the needs of a noncombustible, high heat-
resistant, and water-resistant cable. MI cable has from one to seven electrical conductors. These
conductors are insulated in a highly compressed mineral, normally magnesium oxide, and sealed in a
liquidtight, gastight metallic tube, normally made of seamless copper (figure 1-14).
Figure 1-14.—Two-conductor mineral-insulated (MI) cable.
CONDUCTOR PROTECTION
Wires and cables are generally subject to abuse. The type and amount of abuse depends on how and
where they are installed and the manner in which they are used. Cables buried directly in the ground must
resist moisture, chemical action, and abrasion. Wires installed in buildings must be protected against
mechanical injury and overloading. Wires strung on crossarms on poles must be kept far enough apart so
that the wires do not touch. Snow, ice, and strong winds make it necessary to use conductors having high
tensile strength and substantial frame structures.
