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Author Topic: Does a multi-stranded wire have lower resistance?  (Read 18371 times)

Offline Karsten

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Hello All:
Ohm's law says that a thinner wire has a higher electrical resistance than a thicker wire of the same material. Does one thick wire have less resistance than a bundle of thin wires of the same diameter? Does a wire with 100 thin wires have the same resistance than 100 individual wires of the same diameter that do not touch? Does a 1 meter wire containing 100 individual wires have the same resistance than 100 meters of the same thin wire? Does bundling them up change anything?
« Last Edit: 28/06/2012 22:43:33 by chris »


 

Offline RD

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Offline Geezer

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Re: Multi-strand wire resistance less?
« Reply #2 on: 28/06/2012 04:57:03 »
Ohm's Law applies when the current is non-alternating, and has no alternating component, i.e., it is "pure" DC. In that situation, the only thing that matters is the total cross-sectional area of the conductor. It makes no difference whether it is composed of a single wire or a bundle of small wires (assuming, of course, the wires are all properly terminated).
 

Offline David Cooper

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Re: Multi-strand wire resistance less?
« Reply #3 on: 28/06/2012 21:09:15 »
I presume that if you provide more paths for the electrons to flow along, they can move more slowly along each path with the same overall current, less energy being lost along the way through the lower-speed collisions that result. That would account for it making no difference whether it's one thick wire or many thin ones.
 

Offline Karsten

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Re: Does a multi-stranded wire have lower resistance?
« Reply #4 on: 29/06/2012 01:20:51 »
Yes, I am talking DC.

Where do the electrons flow in a bundle? I mean, if the sum of the resistance of the individual wires is higher than the resistance of the bundled up wires, there has to be some other path they take.
 

Offline Geezer

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Re: Does a multi-stranded wire have lower resistance?
« Reply #5 on: 29/06/2012 05:24:52 »
Yes, I am talking DC.

Where do the electrons flow in a bundle? I mean, if the sum of the resistance of the individual wires is higher than the resistance of the bundled up wires, there has to be some other path they take.

Ah! You don't sum the resistances; you sum the conductances. Conductance is the inverse of resistance, so the combined conductance is the sum of all the conductances and the total resistance is the inverse of the combined conductance.

With DC, the electrons spread out throughout the entire conductor or conductors so that the current density is the same everywhere. Of course, this only applies if the conductors are all made of the same material.
 

Offline evan_au

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Re: Does a multi-stranded wire have lower resistance?
« Reply #6 on: 01/07/2012 13:11:51 »
The main reason why you would want to make wires multi-stranded for use at DC (or low frequencies) is to make them flexible.
- One thick conductor is harder to bend around corners, and so is harder to install.
- In case of repeated flexing (eg in wires to an elevator), a single conductor will suffer stress, and fail. Many thin conductors do not get as stressed, and even if one strand breaks, the other surrounding strands can conduct current around the break.
 

Offline Geezer

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Re: Does a multi-stranded wire have lower resistance?
« Reply #7 on: 01/07/2012 19:07:32 »

- In case of repeated flexing (eg in wires to an elevator), a single conductor will suffer stress, and fail. Many thin conductors do not get as stressed, and even if one strand breaks, the other surrounding strands can conduct current around the break.


Yes - copper "work hardens" quite rapidly.
 

Offline CZARCAR

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Re: Does a multi-stranded wire have lower resistance?
« Reply #8 on: 01/07/2012 20:35:53 »
does the oxydation of the copper Affect?
 

Offline Geezer

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Re: Does a multi-stranded wire have lower resistance?
« Reply #9 on: 01/07/2012 20:42:31 »
does the oxydation of the copper Affect?

Yes, but probably very slight. In a multi-strand wire the strands are twisted a bit, so if the strands are partially insulated by oxide, the electrons' path lengths will be slightly longer.
 

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Re: Does a multi-stranded wire have lower resistance?
« Reply #9 on: 01/07/2012 20:42:31 »

 

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