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    what's the advantage of using 4 core cable over 3.5 core cable ? And then, what chang

    what's the advantage of using 4 core cable over 3.5 core cable ? And then, what changes do we have to make for the neutral size & earth size cable calculation ?

    thanks

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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    With 4 core cable you can run one phase to its maximum load with out the other phases being used. So if you have a 3 phase supply running into a 3 bay switch board, each bay feeding a different floor in an office block, you could switch off two floors.
    Frank


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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    can you provide any example of this ? what do you mean by maximum load on any one phase ?

    thanks



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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    if your circuit is rated at 100A/phase, then using cable rated for 100A for the neutral allows you to use 100A from one phase and zero amps from the others. If all three phases were loaded to 100A, then there would be zero current in the neutral conductor. Electric motors are made without a "neutral" wire because the currents through all three phases are the same and even if a neutral wire was supplied then no current would flow through it.
    Frank


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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    Some general info (thumb rules)...

    Neutral conductor must be at least 1/2 the size of other conductor.
    It is theoraticaly explained , that algebric sum of all the phases when in balanced condition
    then neutral current will be zero.

    Now suppose one phase fail i.e. total unbalanced condition its neutral conductor will provide
    a return path and its current will be half the load on other phases so by this
    result on neutral conductor for every unbalanced condition its current will not exceed
    the rated value (same as in phase conductors).

    The selection of neutral conductor depends on the nature of loads, such as the load harmonics
    (more than 20% loads are electronic) or the load balancing (most of the loads are 3 phase motor) etc, etc.

    So, there are few general cases to consider here:
    1. If the loads are almost balanced and there is no significant electronic loads, you can select 3.5 (3 + 0.5)

    2. If the loads are not balanced and there is no significant electronic loads, you can select 4 (3 + 1)

    3. If the loads are balanced and there is significant electronic loads, you can also select 4 (3 + 1)

    4. If the loads are not balanced and there is significant electronic loads, you need to select even higher size
    for neutral (3 + 1.5)

    With modern equipment it is getting to be a major problem especially with IT gear.
    Some cable manufacturers can now supply cable with a neutral 1.5 X phase conductor.
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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    1. If the loads are almost balanced and there is no significant electronic loads, you can select 3.5 (3 + 0.5)

    2. If the loads are not balanced and there is no significant electronic loads, you can select 4 (3 + 1)

    3. If the loads are balanced and there is significant electronic loads, you can also select 4 (3 + 1)

    4. If the loads are not balanced and there is significant electronic loads, you need to select even higher size
    for neutral (3 + 1.5)

    Would you give the examples of the circuitry for these given stated 4 cases ?

    thanks



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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    Quote Originally Posted by kak111 View Post
    Some general info (thumb rules)...

    Neutral conductor must be at least 1/2 the size of other conductor.
    It is theoraticaly explained , that algebric sum of all the phases when in balanced condition
    then neutral current will be zero.

    Now suppose one phase fail i.e. total unbalanced condition its neutral conductor will provide
    a return path and its current will be half the load on other phases so by this
    result on neutral conductor for every unbalanced condition its current will not exceed
    the rated value (same as in phase conductors).

    The selection of neutral conductor depends on the nature of loads, such as the load harmonics
    (more than 20% loads are electronic) or the load balancing (most of the loads are 3 phase motor) etc, etc.

    So, there are few general cases to consider here:
    1. If the loads are almost balanced and there is no significant electronic loads, you can select 3.5 (3 + 0.5)

    2. If the loads are not balanced and there is no significant electronic loads, you can select 4 (3 + 1)

    3. If the loads are balanced and there is significant electronic loads, you can also select 4 (3 + 1)

    4. If the loads are not balanced and there is significant electronic loads, you need to select even higher size
    for neutral (3 + 1.5)

    With modern equipment it is getting to be a major problem especially with IT gear.
    Some cable manufacturers can now supply cable with a neutral 1.5 X phase conductor.
    How to check & measure whether the load is balanced without any cabling ?
    What are the examples of significant electronic loads ?

    thanXxX



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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    How to check & measure whether the load is balanced without any cabling ?
    Measuring without cables ??? Impossible.
    We can say that 3-phase load is balanced, when load impedance in each phase has same value.
    ( This means that resistance and reactance in every phase has same value , i.e. currents and cos(phi)´s are equal too.)

    What are the examples of significant electronic loads ?
    This means all the loads that generate harmonic distortion in the power grid.
    for ex. electronic power supplies, motor inverters, thyristor- and triac power controllers, electronic lamp ballasts, etc,etc....
    ---> Hike with wise men , then you will be wise <---


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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    Quote Originally Posted by kak111 View Post
    Measuring without cables ??? Impossible.
    We can say that 3-phase load is balanced, when load impedance in each phase has same value.
    ( This means that resistance and reactance in every phase has same value , i.e. currents and cos(phi)´s are equal too.)



    This means all the loads that generate harmonic distortion in the power grid.
    for ex. electronic power supplies, motor inverters, thyristor- and triac power controllers, electronic lamp ballasts, etc,etc....

    How to measure the load impedance in each phase ? with DMM .....

    How to measure the reactance in every phase ? with DMM ......

    thank You very much


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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    1. If the loads are almost balanced and there is no significant electronic loads, you can select 3.5 (3 + 0.5)

    2. If the loads are not balanced and there is no significant electronic loads, you can select 4 (3 + 1)

    3. If the loads are balanced and there is significant electronic loads, you can also select 4 (3 + 1)

    4. If the loads are not balanced and there is significant electronic loads, you need to select even higher size
    for neutral (3 + 1.5)

    Would you give the examples of the circuitry for these given stated 4 cases ?

    thanks



  11. #11
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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    I think post#8 is sufficient to explain this question

    You should also examine the national regulations for supply cables
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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    How to measure the load impedance in each phase ? with DMM .....

    How to measure the reactance in every phase ? with DMM ......

    thank You very much



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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    Here is one way to find some approximate values.....
    This is useful only for light loads (current = few amperes )

    Click image for larger version. 

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    Last edited by kak111; 14th January 2012 at 00:09.
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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    Quote Originally Posted by kak111 View Post
    Here is one way to find some approximate values.....
    This is useful only for light loads (current = few amperes )

    Click image for larger version. 

Name:	Approx_X_Z_inGrid.jpg 
Views:	14 
Size:	160.7 KB 
ID:	67277
    why this method & formula isn't valid for heavy loads ?
    And, how to to measure load impedance & reactance in each phase for heavy loads ?

    thanxx



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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    what do you mean by warning that you gave in the attachment ?

    without harmonics
    Presume, pure real power input without imaginary (reactive) part


    although you took reactance in your calculations , so what's imaginary (reactive) part are you pointing at ?

    And, what is 2.load ? (measured current per phase with 2. Load) ...... Is it an another load ????

    thanks yo



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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    what do you mean by warning that you gave in the attachment ?
    without harmonics
    Presume, pure real power input without imaginary (reactive) part
    I made a simplified and shortened presentation
    how the distortion and harmonics affect the power factor cos (phi) and
    so to the result of impedance calculation, made by measuring u, i and cos(phi)
    with multimeter (clamp meter)

    Click image for larger version. 

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    Click image for larger version. 

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    Click image for larger version. 

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    All text...
    http://www3.fsa.br/LocalUser/energia...NAL/ARQ_10.pdf
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    Re: what's the advantage of using 4 core cable over 3.5 core cable ? And then, what c

    Presume, pure real power input without imaginary (reactive) part
    Here is the picture that show the problem, when measuring impedance in
    device connected to power grid.
    In point A cos(phi) is not 1 and measured device is not connected to grid.

    Click image for larger version. 

Name:	Sum_Loads_In_Grid.jpg 
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ID:	67385
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