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Impedance Calculation

myCableEngineering Calculation Method

Calculation of Impedance is reasonably involved.  Other notes give an insight into the individual calculations.  

With myCableEngienering, the calculation will typically follow the following procedure

  1. d.c. resistance - is determined using IEC 60288.  For any cases in which IEC 60228 is not suitable, the resistance is obtained using CENELEC CLC/TR 50480. See also Conductor Resistance.
  2. temperature adjustment - the calculated d.c. is adjusted so that is value is accurate relative to the operating temperature of the conductor. 
  3. a.c. resistance - the a.c. resistance is obtained by applying skin and proximity effect factors as defined in IEC 60287. See also Conductor Resistance.
  4. positive and zero sequence impedance - are calculated using the methods give in IEC 60909 and resistance values calculated above. See also Impedance.

Resistance, Reactance

Positive and zero sequence impedance calculated above, are in complex form.  The real part of the impedance gives the resistance and the imaginary part the reactance.

Capacitive Reactance

Currently we do not calculate capacitive reactance.  This will likely be added as the application grows and develops the need for this calculation.

Impedance Equations

Impedance equations are presented in details in Impedance.  Depending on the type of cable, number of cores and system type the following equations are applied:

IEC 60609 Equations
Cores: 1 2 3 4 5
Unscreened Cables          
None 10/11 10/11 10/11 10/11 10/11
TN-S 10/11 10/11 10/11 10/11 10/11
TN-C-S 10/14 10/14 10/14 10/14 10/14
TT 10/11 10/11 10/11 10/11 10/11
IT 10/inf 10/inf 10/inf 10/inf 10/inf
Screened Cables          
None 15/16 15/32 15/32 15/32 15/32
TN-S 15/32 15/32 15/32 15/32 15/32
TN-C-S 15/28 15/28 15/28 15/28 15/28
TT 15/16 15/32 15/32 15/32 15/32
IT 15/inf 15/inf 15/inf 15/inf 15/inf

Equations Z1/Z0 - for a.c. cables (refer Impedance)

Note: for armoured cables, the armouring and earth are always considered as part of the earth return path.  Excepting TN-C-S, earth return through a spare internal conductor is not considered. 

Note: current return through a spare internal conductor for low voltage cables is on our features list to be added


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