Page 239 - Handbook of Electrical Engineering

CABLES, WIRES AND CABLE INSTALLATION PRACTICES 223

Table 9.25. Cable-sizing chart for DOL induction motors

Cable information
EPR cable size in mm 2
Motor 2.5 4 5 10 16 25 35 50 70 95 120 150 185 240
information
Motor Motor Motor Motor
rating FLC FLC I s /I n Derated cable current in amps
(kW) current power ratio
(A) factor
11 19 0.86 6.5 19 26 33 46 62 83 99 124 159 193 223 253 288 343
15 25 0.87 7.2 Maximum route length in metres (in this case limited by starting current)
18.5 30 0.89 7.0 105 156 254 389
22 36 0.88 7.0 99 162 249 375
30 51 0.86 7.0 123 190 287 377
37 63 0.85 7.0 106 164 249 328
45 76 0.85 7.0 110 166 219 278
55 94 0.84 7.0 187 241 299 379
75 124 0.86 7.0 155 200 248 314
90 146 0.87 7.0 Note: 164 204 257 307
110 178 0.88 7.0 a) Volt-drop on starting 15%. 154 195 233 276
132 214 0.88 7.0 b) Volt-drop at full-load 5%. 165 198 234 256
◦
150 243 0.88 7.0 c) Ambient temperature 30 C. 162 192 210 230
185 297 0.88 7.0 d) System voltage 440 V at 60 Hz. 163 178 194 210
200 317 0.89 7.0 e) Cable derating factor for ambient 156 171 185
temperature and grouping in air is 0.93. 152 158
148

Let

θ 2 + 234.5
2
2
K = k log
e
θ 1 + 234.5
For copper conductors
k = 226
160 + 234.5

2
2
K for PVC = 226 log e
70 + 234.5
2
= 226 × 0.25589
Therefore
K = 226 × 0.5088 = 115

Similarly for XLPE and EPR, K = 143.
◦
◦
For bare copper in air with a final temperature of 150 C and an initial temperature of 70 C
◦
the value of K is 109. If the initial current is zero and the initial temperature is 30 Cthen K is 138.
◦
See Table 54 B of IEC60364 Part 5, Chapter 54. If the final temperature is allowed to be 250 Cthen
the value of K will be in the order of 170 to 180.
In the calculation of short-circuit current it is usually assumed that this current is much larger
than the normal load current even if it is its full-load value. Hence I fl in (9.6) can be ignored, thereby