Handbook of Electrical Engineering

238 HANDBOOK OF ELECTRICAL ENGINEERING

Table 9.30. Cable data for the worked example

Nominal Current 3-core conductor GSWB armouring

conductor

area (mm^2 )

rating

at 40◦C

(amps)

Resistance at

90 ◦C ohms

Rc

Reactance at

50 Hz (ohms)

Xc

resistance

(ohms)

Ra

16 0.2960 0.0268 4.62 70.35

25 0.1872 0.0250 5.62 93.45

35 0.1348 0.0242 2.086 110.3

50 0.0998 0.0236 2.362 141.8

70 0.0688 0.0224 2.722 178.5

Table 9.31. Fuse data for the worked example

Fuse rating

(amps)

Operating current

at 5.0 sec

(amps)

Maximum earth loop

impedance at 240 V/phase

Zloopf(ohms)

100 500 0.4792

125 650 0.3686

160 850 0.2819

200 1100 0.2179

Table 9.32. Cable data for the worked example

Fuse rating

(amps)

Operating current

at 5.0 sec (amps)

Minimum conductor

CSAAmin(mm^2 )

Nearest practical

CSA aboveAmin(mm^2 )

100 500 7.82 10

125 650 10.17 16

160 850 13.29 16

200 1100 17.20 25

WhereK=143 for EPR insulation andAminis the smallest conductor cross-sectional area.

The resultingAminfor the four sizes of fuses are given in Table 9.32:

Hence all the cables 16 mm^2 to 70 mm^2 in c) that suit the motor full-load current will be adequately

protected by the fuses in the range given.

f) Calculate the volt-drops for running and starting the motor.

From (9.3) for ‘running’ conditions,

cos Ø= 0 .85 and sin Ø= 0. 5268

Assume the cable conductor area is 16 mm^2 ,

Therefore,

R= 0 .2960 ohms andX= 0 .0268 ohms