CABLE SIZE

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  • #12511
    admin
    Keymaster

    Did any one has selection table of cables, I mean for every size what is the current carrying capacity and the derating tables.

    #11315
    Spir Georges GHALI
    Participant

    Dears ;

     

    please find below an exsemple to define the section of a cable supplying a load.

     

    Assume that we have the following load :

    – Power : 450 kW

    – Cos φ : 0.82

    – Supply : 3Ph + N

    – Voltage : 400/231V-50Hz

    – Length from the panel : 125 m

    – There's no Harmonics

    – ku = 100%

     

    So, the nominal current for this load is :

    Ib = 450 x 103 / 1.73 x 400 x 0.82

    Ib = 793 A

     

    The Correction Factors ( or Reduction Factors ) will be defined accordingly to the Method of Installation and the kind of cable, assume that :

    –          Method of installation ” F ” :

    • ” Horizontaly Perforated Cable Tray “
    • ” Touching – Flat “

    –          The kind of Cable : ” Single Core Cable – Copper – PVC “

    –          2  cables per Phase.

    So, the Reduction Factor : 0.91

     

    –          The Ambiant Temperature is ” 45 °C ” in the air

    So, the Reduction Factor : 0.79

    And the total Reduction Factors is : 0.91 x 0.79 = 0.718

    And the nominal current for needed cables is : 793 / 0.718 = 1105 A

     

    We assume that we will use ” Single Core Cable – Cu – PVC – 300 mm2 “, and from table
    ” A.52-10 ” of ” IEC 364-5-52 “, we find that the Current Carrying Capcity for ” 300mm2 ” for ” Touching – Flat / Methode F ” is ” 587 A “, and the number of cable per phase is :
    1105 / 587 = 1.88

    So, we will use :

    – For each Phase        : ” 2 Single Core Cables of 300 mm2

    – For Neutral              : ” 1 Single Core Cable of 300 mm2

     

    Noting that :

    –          for Neutral : the load is ” 3 phases “, and we haven't the 3rd Harmonic.

    –          If ” Ku ” is different, the calculation should be re-done.

     

    After that, you should calculate the ” total Voltage Drop “ from the source till the load to decide if that cables are suitable or not.

     

    To calculate the ” Voltage Drop “, we use the following formula :

    Δ U = 1.73 . I ( R . Cos φ  +  X . Sin φ ) 

    1 – For section : from the panel to the load :

    As the cable is ” Singl core, 300 mm2, Touching-Flate “, So :

    R = ρ . L / S    →   18.51 x 1.23 x 125 / 300 x 2    →    4.74 mΩ

    X = λ . L          →    0.13 x 125 / 2                       →    8.12 mΩ

    Cos φ = 0.82    →    Sin φ = 0.57

     

    Δ U = 1.73 x 793 ( 0.00474 x 0.82  +  0.00812 x 0.57 )    →    11.68 V

    Δ U = 2.92%

    2 – For section : from the source till the load :

    To be able to calculate this section we should have the following information :

    –          The section of cable if the panel is supplying directly from the source, or the sections of cables if there's many sections.

    –          The length of cable  or  lenghts of cables.

    –          The kind of cable  or  cables.

    –          The nominal for this section  or  the nominal currents for these sections.

    –          The Cos φ for this section  or  for these sections.

    –          The Method of installation for each section.

    By using the same formula, we caculate the percentage of Voltage Drop for each section, then we sum these perecentages to have the ” Total Voltage Drop ” that should be compliance with the standard percentage, if not, the section of cable should be oversized.

     

    By the way, if the load is a motor, we should calculate the Total Voltage Drop 2 times that :

    – After running ( nominal current for the motor ) ( as before )

    – During running ( current  &  Cos φ  for the motor during running )

    And the Total Drop Voltage during running shouldn't be exceeded 10-12%

    #12506
    Spir Georges GHALI
    Participant

    Soufi said:

    Did any one has selection table of cables, I mean for every size what is the current carrying capacity and the derating tables.


    Dear Soufi ;

     

    As there's many tables, please send me your e-mail to send them. noting that my e-mail is :

    hagersg@aloola.sy

     

    regards.

    #12520
    ahmadalsayed20
    Participant
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