Typical input data required for cable sizing:

General Information

General reference information to facilitate identification of the cable, not used for calculations:

•  cable designation
•  cable description
•  cable source/starting point

System, Load and Protection Details

Details of the type of system (a.c., d.c. etc.), what the cable is supplying (delivering) and details on protective devices:

•  system voltage
•  a.c. or d.c. and frequency if an a.c. supply
•  phase if an a.c. system (1-ph, 3-ph, 3-ph+neutral
•  earthing arrangement for low voltage a.c. systems (TN-S, TN-C-S, TT, IT)
•  
•  load type and details
  •  load designation
  •  distribution circuit or final equipment supply 
  •  distribution/load current and power factor if a.c. system
•  
•  protective device details (if any)
  •  circuit breaker or relay
  •  frame size, trip rating (o/c, e/f) if a circuit breaker
  •  primary trip current (o/c, e/f) if a relay
•  RCD protected if low voltage cable

Cable Selection

•  type of cable (copper, aluminium, pvc, xlpe, armoured, unarmoured, etc.)
•  single-core or multi-core cable
•  prefered cable cross-sectional-area if applicable (including maximum to be considered)
•  length of cable

Sustained Current Capacity

•  cable standard to size to (agreed with client/owner)
•  installation method (air, buried, detailed arrangements, spacing, etc.)
•  buried cables: depth, free laid or in ducts, soil thermal resistivity
•  number of circuits using the same containment/installation path (grouping)
•  ambient temperature (air or ground as appropriate)
•  cable source/starting point

Voltage Drop

•  required maximum allowable voltage drop (per cable, complete circuit or both)

Fault Withstand

•  cable source short circuit and earth fault levels
  •  fault level (kA or Ze, power factor)
  •  maximum duration of anticipated faults
•  any external CPC consideration if low voltage cable