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Cable Sizing Input Data Checklist

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

 

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