# Cables problem

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#### tsoupl

##### New Member
A problem was published at my university that was refered to wires(Cables).It says:
we have a wire,diameter 10 mili meter from which is passing through current i=imax(current equals maximum current).We want to replace it with two wires which are placed(connected)parallel and can pass through them the same current, i=imax.what there diameter would be for the two wires?

#### crust

##### Member
Ignoring the skin effect that occurs at high frequency, I believe this is a simple geometry problem --- by what technique have you attempted to solve this problem?

#### Sebi

##### Active Member
You need to know the cross-section: diam=10mm, A=r*r*pi=78,5 divide by two, reverse to diameter= 7mm

#### Klaus

##### New Member
Its not quite as simple as the last answer given, two wires in close proximity to each other would also heat each other if the maximum current, rated for each wire, flows. Therefore the maximum current should be less than that of a similar cross section single wire if one does not wish the wires to get hotter.
Any wire and cable guide always shows a derated current carrying capacity for individual wires in a multi core cable.
If the two wires were widely spaced then each could indeed carry half the current of a single wire of double cross section.

#### tsoupl

##### New Member
the problem was publised as it is said apon.It didn't had any parameters of what it was asking.So the solution must be something easy.I thought that if the two wires are conected parallel,with out knowing the lenght of the wire,we can see them as two resistors parallel(R1*R2/R1+R2).from which if the one cable has diameter 10mm (kwowing that R(of wire)=p(type of matirial)*l(lenght)/S(that is 2*pi*r))then the two wires will have the half resistans from the 10mm wire.So i think each wire should be 20mm,so as to have the same current as the 10mm(i=imax).What do u think?

#### Agent 009

##### New Member
You could think of this problem as you did, in a "simple way", because it depends what level is required from your solution. If it's quite easy, so be it. But your instructor needs a precise, real-world solution, you should be aware of the length of the two wires, which affects the resistance of the cables, and thus the thermal dissipation in'em would be less/more considerable. The heat produced by each cable could affect the other; consequently, its resistivity will change. Also, the higher the frequency of the signal carried out, the higher the possibility of the two cables to react as inductors, which is also dependent on the way they are placed (wired around each other, which is..., or just parallel, and what kind of shield or protection each wire has. Because, hey, they could be shielded, no?)... I hope I helped you in your quest :wink: ....

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