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Urgent: cable calculations

  1. Jul 18, 2012 #1
    Good afternonn,
    these are the motor and circuit data:

    Motor power: 0.37kW,
    Nominal current: I= 0.8 A
    voltage: 415 V,
    cable length = 80m
    ambiant temperature: 50°C
    Maximum voltage drop percentage =415*4% =16.6V

    According to the Bahraini Regulations:
    - temprature factor= 0.89
    - core factor (3core cable)= 0.7

    This is the calculation I did:
    - target current=I/(0.89*0.7)=1,29A ==> 1,5A
    when I check the current rated table, the suitable cable section will be 1.5mm but our contractor us a 2.5mm cable (I must verify his choice and prove that it's correct and submit the calculation to our consultant at least tomorrow morning!!!!)

    According to the current rated table, we get:
    for the cable section: 2.5mm ==> current rating= 33A and Voltage drop /amp/m= 16

    but when I calculate the Voltage drop /amp/m for my circuit, I find:
    mV= dV*1000/(target current *L)= 16.6V*1000/(1,5A*80m) = 138,33mV >16 (from the table)

    Now, what I have to do?
    I don,t know how to proceed and finalize the calculation!!

    I have to make the verification for 20 different equipments with power variying between 0.37 and 48A!
    Would you please help me and show me how to continue with the remainder calculation?

    Your help is extreamly needed, I'am really blocked.
    Thank you

    Walid ABID
  2. jcsd
  3. Jul 18, 2012 #2
    Walid ... your persistance is impressive how many more forums have you posted on?

    Like ive mentioned before key to starting a cable calc for an inductive load is knowing what device you are going to protect the cable with as it will have to be able to cope with the inrush of the motor, having said that this is a very small motor and reduces that concern.
    Secondly, regulations vary and unless one is knowledgable of the bahraini electrical Reg's its thus a hard question to answer, we would need a copy of the regions electrical regs to attain the values to be applied.

    Third and final you haven't stated what your cable type is nor its installation method, you have just given us values that you provide, we cannot confirm these without knowing you haven't made a mistake.

    I assume you must be qualified to be requested to do this, if so you will have done this in your training and i recommend you review your notes or college books.

    I can only re-iterate what i said before in that you need to discuss this with a local electrician who has knowledge of local rules and regulation, your tolerances in calcs may be tighter or more liberal than our (UK)... Hope you can appreciate how arkward trying to answer you question is, had you been UK base or even EU then it would have been a quick reply and full explaination.
  4. Jul 18, 2012 #3


    User Avatar

    Staff: Mentor

    If this calculation needs to be done to local codes, then we cannot help you here. Thread is closed.
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