Specifications

2
Thus the insulating materials are grouped into different classes Y, A, B, and C with
temperature limits of 90
0
C, 105
0
C and 130
0
C for the first three classes and no specific limit
fixed for class C. Class Y and A cover the various organic materials without and with impregnation
respectively, while classes B and C cover inorganic materials, respectively with and without a
binder. With the existence of newer insulating materials, namely, the plastics and silicones,
during the middle of this century, a need was felt to reorganize the classification of the insulating
materials. This calssification is shown in fig.1.2. This led IEC (International Electro technical
Commission) to come up with the new categories:
Class Y : 90
0
C: Paper, cotton, silk, natural rubber, polyvinyl chloride, etc. without impregnation.
(formerly O)
Class A : 105
0
C: Same as class Y but impregnated, plus nylon.
Class E : 120
0
C: Polyethylene terephthalate (terylene fibre, melinex film), cellulose triacetate,
polyvinyl acetate enamel.
Class B : 130
0
C: Mica, fiberglass (alkali free alumino borosilicate), bituminized asbestos,
bakelite, polyester enamel.
Class F : 155
0
C: As class B but with alkyd and epoxy based resins, polyurethane.
Class H : 180
0
C: As class B with silicone resin binder, silicone rubber, aromatic polyamide
(nomex paper and fiber), polyamide film (enamel, varnish and film) and estermide
enamel.
Class C : Above 180
0
C: As class B but with suitable non-organic binders; (Teflon, Mica,
Micanite, Glass, Ceramics, Polytetrafluoroethylene).
Fig.1.1