Page 196 - WCS - Electrical

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Class E – maximum temperature 120°C

Wire enamel, cotton fabric and paper laminates treated with oil, modified asphalt and synthetic resins, varnished
polyethylene, textile treated with suitable varnish.
Class B – Maximum temperature 130°C

Glass fibre, asbestos, varnished glass fibre, textile, varnished asbestos, built up mica treated with synthetic resin
varnishes.
Class F – maximum temperature 155°C
Similar to class B materials but treated with silicone resins.

Class H – maximum temperature 180°C
Same as class F materials but treated with silicone resins of higher thermal stability than class F.
Class C – maximum temperature above 180°C
Mica, porcelain and other ceramics, glass, quartz, asbestos, treated glass fibre textile, treated asbestos, built up
mica treated with silicone resins possessing superior thermal stability (limited stability up to 225°C).
Series Connection
The total resistance is equal to the sum of all the resistances. In a series connection the end of the first load is
connected to the beginning of the second load and all loads are connected end to end. (Fig 3)

Features of series connection:
• The same current flows through all the loads.
• The voltage across each load is proportional to the resistance of the load.
• The sum of the voltages across each load is equal to the applied voltage.
• The Total resistance is equal to the sum of all the resistances.
l = l = l = ...
1
2
V = V + V + ...
1 2
R = R + R + ...
1
2
Example
Three resistances of 3 ohms, 9 ohms and 5 ohms are connected in series. Find their resultant resistance.
Solution
R = R1 + R2 + R3
= 3 Ω + 9 Ω + 5 Ω
Total resistance = 17 Ω

183

CITS : WCS - Electrical - Exercise 18