Cables Sizing tables

It is common practice to prepare cable-sizing tables for low voltage cables that are to be used for a particular project. These tables are usually prepared for,... 

Consider a 55 kW motor to be switched direct on-line and instalied, say, at 75 m from its controlgear. To select the most appropriate cable size refer to Table 12.4, where... 

CABLES, WIRES AND CABLE INSTALLATION PRACTICES 195 Table 9.10. Equivalence between metric and American cable sizes... 

From Table 9.22 a suitable cable size to provide at least a 10% margin is 150 mm, giving a rated current in air of 430 amps. Hence the appropriate choice for the primary is 2 x 3c x 150 mm cables. The margin will allow for short duration overloading of the transformer. 

From Table 9.17 the smallest cable size for a running current of 219 amps is 70 mm which from Table 9.16 has a specific resistance r of 0.342 ohm/km and a specific reactance x at 50 Hz of... 

Table 9.25. Cable-sizing chart for DOL induction motors...

Appendix 4 of the lET Regulations (BS 7671) and Appendix F of the lET On Site Guide contain tables for determining the current carrying capacities of conductors which we looked at in the last section. However, for standard domestic circuits. Table 3.6 gives a guide to cable size. 

Table 3.6 Cable size for standard domestic circuits...

Table 14.4 Cable Size for Standard Domestic Circuits...

All these devices and their likely locations are indicated in Figure 12.39(a). The sizes of control cables to connect these devices are indicated in Table 12,3. 

Table 12.3 Recommended sizes of cables for various sensing and monitoring devices...

Table 12.4 Selection table for switches, fuses, relays and cables for different sizes of LT motors...

The ratings and sizes of main components and cables can be selected from manufacturers catalogues. But cables required for the switchgear internal control and power wirings, being typical of all, are normally identified by their cross-sectional area rather than the current ratings. We have therefore piovided the technical data and current ratings for the most common sizes of such cables for a ready reference in Table 13.15. 

I,// 2 =//f = maximum resistance of the connecting leads from the CT terminals to the relay terminals. For calculating this, for an estimated length and size, refer to cable data in Table 13.15... 

These are common for all types and sizes of cables, except where noted. Derating of cable ratings resulting from site conditions and laying parameters are provided in Tables A16.17-A 16.26. 

The ground conductor can be of aluminium, GI or copper, as discussed earlier. A humid or a chemically contaminated location is corroding in nature. Aluminium has a rapid reaction and is fast corroding. At such locations, use of GI or copper conductor would be more appropriate. Table 22.4 suggests the ground conductor sizes for aluminium conductor power cable.s for small and medium-ratine feeders when aluminium is used for the ground... 

Table 22.4 Size of aluminium ground conductor for different sizes of power cables for a grounding system...

In an attempt to provide as much information on the related subjects as possible and to make the book more complete for a project or a design engineer w e have provided data and tables on cables and described in detail the procedure for the selection of the type and size of control and LT and HT pow er cables. 

The power requirements for heating the crucible are adequately met by a 20-A variable transformer (120-V input, 0-120 V output) feeding a 1.5-kW step-down transformer designed for a 15-V output with a 120-V input. Cables to the reactor electrodes must be of adequate size to handle the large currents, which may range up to 300 A. A rough idea of the voltage and current requirements for specific metals may be obtained from Table I. 

Hence from Tables 9.16 and 9.17 the small size of cable could be 95 mm. Table 9.28 can be prepared for cables of 95 mm and above, routed in air. 

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