Singlecore/Multicore cable, more than 1 cable per phase.

[vagojr]

Hi all,

Having a range of cross-sections for multicore cables (if higher, then singlecore), I am used to calculating the cable cross sections in an iterative way as follows;

• 1 cable per phase and the lowest section (multicore) =>
• if results are not ok, then I go with the next section (multicore) =>
• if the highest multicore section is not ok, then I go with the singlecore lowest section =>
• if the highest singlecore section is not ok, then I go with 2 cables per phase of SINGLECORE, but not MULTICORE. =>
• Until the results are ok by increasing singlecore sections and later number of cables per phase.

I would like to know if I am doing well, and if so, I would like to know the technical reasons (if possible, referred to the standard) of overpassing multicore cables when having more than 1 cables per phase.

Thank you very much in advance
Regards

 

[Julius Right]

An iterative solution is not so practical, in my opinion.
In my opinion, you have to start with the ampacity-if you know the presumable current.
And then to calculate the voltage drop and to increase the conductor cross-section area
accordingly.
The presumable short-circuit current will state if the cable withstand this.
Of course, you have to increase the cross section up to one suitable if it will be necessary.
Using single core cable may improve the ampacity but will rise the reactance and so the
voltage drop.

 

[vagojr]

An iterative solution is not so practical, in my opinion.
In my opinion, you have to start with the ampacity-if you know the presumable current.
And then to calculate the voltage drop and to increase the conductor cross-section area
accordingly.
The presumable short-circuit current will state if the cable withstand this.
Of course, you have to increase the cross section up to one suitable if it will be necessary.
Using single core cable may improve the ampacity but will rise the reactance and so the
voltage drop.

Thank Julius for your quick answer.
So, is it common to use multicore cables with more than 1 cable per phase? or are recommended singlecore cables? Is there any technical reason for this issue?

 

[Julius Right]

There are not multicore power cable of more than one conductor per phase but, you may use more parallel 3 [or 4 core] cables. On three-or 4- core cable the phase conductors are twisted together that means continuously cross-bonded.
The single core cables installed parallel -and not cross-bonded -could pose the problem of currents unbalance.
See-for instance:
http://jmst.ntou.edu.tw/marine/18-2/290-297.pdf
A cross-bonding method could mitigate the phenomenon.

 

[vagojr]

There are not multicore power cable of more than one conductor per phase but, you may use more parallel 3 [or 4 core] cables. On three-or 4- core cable the phase conductors are twisted together that means continuously cross-bonded.
The single core cables installed parallel -and not cross-bonded -could pose the problem of currents unbalance.
See-for instance:
http://jmst.ntou.edu.tw/marine/18-2/290-297.pdf
A cross-bonding method could mitigate the phenomenon.

thank you again for your answers. The link is very interesting as well.
So the conclusion is that is common to use multicore cables in parallel, isn't it?
Which is preferred for parallel runs? to use singlecore (balance system) or multicore?

 

[Julius Right]

In IEC world where the low voltage is high-400-415 V phase_ to_ phase-the cable conductor cross section area is relative small and a 3 or 4 core cable will be more suitable. In North America where the low voltage is low-240/120 the current is higher and the conductor cross section area is larger the three-or four or five-core cable is heavy and hard to run it. Then a single-core cable will be more suitable. Three, four core cable usually it is limited to 3*300 +150 mm^2 [3*600+300 kcirc.mils]. Single-core up to 2000 mcm[1000 mm^2].

 

[vagojr]

In IEC world where the low voltage is high-400-415 V phase_ to_ phase-the cable conductor cross section area is relative small and a 3 or 4 core cable will be more suitable. In North America where the low voltage is low-240/120 the current is higher and the conductor cross section area is larger the three-or four or five-core cable is heavy and hard to run it. Then a single-core cable will be more suitable. Three, four core cable usually it is limited to 3*300 +150 mm^2 [3*600+300 kcirc.mils]. Single-core up to 2000 mcm[1000 mm^2].

Thank you again Julius :thumbsup:
have a nice day