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Q & A: why use multiple-strand wires?

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Most recent answer: 12/07/2015
Why in consumer electronics, when they connect a circuit to say a speaker, a battery or a motor, they almost all the time use these small wires that have multiple of thin fine copper wires inside each one of them? I understand that each one of these small wires act as a group of many small resistors in parallel, so if it's a matter of reducing current, then why they don't just use a wire of one single copper wire with proper thickness to match the resistance of many small resistors connected in parallel which corresponds to the fine thin copper wires resistance inside a small wire? does it have something to do with the cost of copper? Idmond
- idmond (age 17)
Nasr City, Cairo, Egypt

The big reason for using multiple-strand wires rather than having all the copper in a single strand is that the multiple strands are much more flexible. It's also easier to connect them to various screw-connectors.  For the same amount of copper you get pretty much exactly the same conductance either way.

Mike W.

(published on 11/25/2013)

Follow-Up #1: Why is stranded wire is more flexible than single wire?

Why stranded wire is more flexible than single wire?
- Alice (age 19)

Great question. Think of a wire with 1mm diameter, bending around a curve with a 5cm radius of curvature. The part on the inside of the curve is squashed in by about 1% and the part on the outside is stretched out be about 1%. That's a big distortion of the spacing between the atoms, and it takes a lot of energy. Now take an 0.1mm wire in the same 5cm radius bend. Its squashing/stretching is only about 0.1%, which takes only (0.1/1)2 as much energy per atom, since the energy per atom goes as the square of the distortion. EVen when you have a lot of those little wires in parallel, there's much less energy needed to bend them.

Mike W.

(published on 12/07/2015)

Follow-up on this answer.