The following factors should be taken into account while selection, the correct size and type of cables.

• SYSTEM VOLTAGE : What is the system voltage and the type of system ? Single phase, Three phase, earthed or unearthed or dc ?
• CURRENT CARRYING CAPACITY : The current rating is the main and basic criterion. Tables Nos. 1-22 give the carrying capacity of various type and size of cables, under different condition of laying . These should be considered before the correct size and type of cables is decided upon. Suitable derating/uprating factor should be used depending on the conditions of laying as under :
  2.1 : Depth of laying.
  2.2 : Ambient temperature of ground or Air.
  2.3 : Soil resistivity.
  2.4 : Whether one or more groups of cables are laid together.
  2.5 : Any heating source near cable run.
• MODE OF INSTALLATION : The mode of installation determines the type of cable to be used. Electricity regulators require the use of armoured cables for underground applications. In general, armoured cables are recommeded where there is any chance of mechanical damage. If subsequent mechanical demage after laying cables is not likely, cheaper, unarmoured cables can be used.
• PERMISSIBLE VOLTAGE DROP : For longer length of cable run it is necessary to check that with the cable size selected the voltage drop does not exceed the prescribed regulations limit. A higher size cable may have to be used if the voltage drop limits are not to be exceeded.
• LOAD CHARACTERISTICS : One should take into account the characteristics of load. It is essential to ensure that the cable selected is capable of handing temporary overloads. "Milan Industries" cables permit a conductor temperatures of up to 130°C under temporary overload conditions. ( It possible, the complete load cycle may be furnished ).
• SHORT CIRCUIT RATING : Short circuit rating depend on the expected level and the expected duration of the short circuit . In certain cases, a larger size of cable than be cable required for normal full load current may be needed. The cables with high KVA capacity are expected to carry short circuit current of high magnitude "CAPTION" cables permit a short circuit temperature of 160°C.
• ECONOMIC CONSIDERATIONS : The most economical construction and size of cable persistent with current carrying capacity and laying conditions has to be selected. A detailed study of 3 or 4 approximate sizes is made. Actual running costs are worked out taking into consideration |2R loss and interest, depreciation of the total cable cost. The size which gives minimum running costs is to be preferred.