Table 1. - Limiting temperatures for insulating materials. (Note that these data apply to
INSULATING MATERIALS and not to apparatus in which they are used.)
INSULATING MATERIALS and not to apparatus in which they are used.)
Limiting insulation
Insulation class and description of material
temperature
o
Celsius
By RTD or
Hottest
resistance
spot
Class O - Consisting of cotton, silk, paper, and similar materials when
85
90
neither impregnated nor immersed in an insulating liquid dielectric
Class A- Consisting of (1) cotton, silk, paper, and similar organic
Class A- Consisting of (1) cotton, silk, paper, and similar organic
100
105
materials when either impregnated or immersed in a liquid dielectric;
(2) molded and laminated materials with cellulose filler, phenolic resins,
and other resins of similar properties; (3) films and sheets of cellulose
acetate and other cellulose derivatives of similar properties; and
4 varnishes (enamel as applied to conductors
Class B - Consisting of mica, asbestos, fiberglass, dacron glass, and
(2) molded and laminated materials with cellulose filler, phenolic resins,
and other resins of similar properties; (3) films and sheets of cellulose
acetate and other cellulose derivatives of similar properties; and
4 varnishes (enamel as applied to conductors
Class B - Consisting of mica, asbestos, fiberglass, dacron glass, and
120
130
similar inorganic materials in built-up form with organic or inorganic
binding substances. A small proportion of class A materials may be
used for structural purposes only. Fiberglass or asbestos magnet wire
insulations are included in this temperature class. These may include
supplemental organic materials such as polyvinyl acetyl or polyamide
films.
Class F - Consisting of mica, asbestos, fiberglass, dacron glass, and
binding substances. A small proportion of class A materials may be
used for structural purposes only. Fiberglass or asbestos magnet wire
insulations are included in this temperature class. These may include
supplemental organic materials such as polyvinyl acetyl or polyamide
films.
Class F - Consisting of mica, asbestos, fiberglass, dacron glass, and
140
155
similar inorganic materials, or combinations of these materials, suitably
bonded with organic (varnishes or resins) or synthetic inorganic thermo-
setting resins of two types: epoxy mica and polyester mica. A very small
proportion of cotton, silk, paper, and similar organic materials may be
used for structural purposes only.
Class H - Consisting of (1) mica, asbestos, fiberglass, and similar
bonded with organic (varnishes or resins) or synthetic inorganic thermo-
setting resins of two types: epoxy mica and polyester mica. A very small
proportion of cotton, silk, paper, and similar organic materials may be
used for structural purposes only.
Class H - Consisting of (1) mica, asbestos, fiberglass, and similar
160
180
inorganic materials in built-up form with binding substances composed
of silicone compounds, or materials with equivalent properties;
2 silicone compounds in rubbery or resinous forms, or materials with
equivalent properties. A minute proportion of class A materials may be
used only where essential for structural purposes during manufacture.
Class C - Consisting entirely of mica, porcelain, glass quartz, and similar
of silicone compounds, or materials with equivalent properties;
2 silicone compounds in rubbery or resinous forms, or materials with
equivalent properties. A minute proportion of class A materials may be
used only where essential for structural purposes during manufacture.
Class C - Consisting entirely of mica, porcelain, glass quartz, and similar
Not
inorganic materials,
determined
c. Old machines that have been uprated,
d. New machines (post-1982).
e. Machines under warranty (new, recently
rewound or uprated, etc.),
Unless special instructions for a particular
machine state otherwise, machines in categories
a. and b. above having class B or F insulation
may be operated to 115 percent of the original
machine state otherwise, machines in categories
a. and b. above having class B or F insulation
may be operated to 115 percent of the original
rated load of the machine (or 115 percent of
reduced operational capacity as discussed in
reduced operational capacity as discussed in
temperature rise values in
In no event shall loading exceed 115 percent of
rated load except in unusual cases as discussed
in
rated load except in unusual cases as discussed
in
, or unless the Denver Office has
approved higher loads.
Machines in categories c., d., and e. on page 4
should not be operated above rated capacity
should not be operated above rated capacity
4 (FIST 1-4 3/91)