Do electrons flow through or around a copper wire?

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Ed_Flecko

Ed_Flecko

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I'm shopping for some new, high-quality, jumper cables. I read a statement by one manufacturer that says "The fine strand construction and soft flexible jacket offer excellent flexibility – far superior to standard battery cable and better than the best welding cable!" - http://www.ceautoelectricsupply.com/batterycable.html

If I understand it correctly...

1.) The more strands of copper a cable has, the more flexible it is, AND

2.) The more electricity the cable is capable of carrying because electrons flow around a copper wire and not through the core of a copper wire. Is this correct?

From what I've read, this explains why a cable made up of lots of fine, individual copper wires will flow more electricity than a solid copper wire, i.e., more electrons can flow around the exterior of multiple wires rather than a single large wire of the same gauge. Correct? Incorrect?

smile.gif


Ed
 
For DC, it uses the entire wire. With AC, you get some skin effect.

The reason to make stranded cable for DC is the ease of bending it. It makes no difference electrically in jumper cables, a DC application.
 
I remember hearing in my circuits course in engineering school that current flows mostly on surface of a conductor. Don't ask me why, or how they determined that, because it's been more than 30 years since I took that course.
 
No. I'm just asking "in theory" I guess you'd say.

smile.gif


Do electron flow around or through copper wire.

Ed
 
Through. The flow rate is kind of slow and measurable. Sometimes the actual electrons only move like inches per hour, yes, that slow. Don't confuse this with voltage and the onset of flow, which is near instantaneous.
 
Originally Posted By: javacontour
For DC, it uses the entire wire. With AC, you get some skin effect.



Oh, so it's an AC thing.
 
What you're thinking of is "skin effect," the tendency of current density in a circular wire to be higher at the outer edge. But that effect is a function of frequency, and doesn't apply at all to constant DC current. In a steady DC environment, the current density is the same at the center of the wire as at the edge. Skin depth is not even a huge issue at 60Hz, its more of a problem at 400Hz (aircraft), and a much bigger factor at radio frequencies- that's where you have to start actually accounting for it... either there or in high-current short-pulse DC applications like pulsed laser power supplies.

Furthermore, stranded wire doesn't change skin depth unless *each* strand of the wire is insulated from all the others, and connected individually at both the load and source end. Believe it or not, such wire exists, is called "Litz wire," and is used in pulsed-power applications (lasers, experimental fusion reactors, rail-guns, etc.). Its excruciatingly difficult to work with because you have to individually solder *every* strand.

So for jumper cables- strand size doesn't affect a darn thing except flexibility. Finer is better, and yes you can get more total cross-section of copper in a given diameter the finer the strands are... but there's no effect on conductivity over a solid wire of the same diameter.
 
Copper and other conductors are already loaded with electrons throughout their cross section, and those actually jump from atom to atom, so the answer is "through". Google "speed of electricity".
 
Originally Posted By: javacontour
For DC, it uses the entire wire. With AC, you get some skin effect.

The reason to make stranded cable for DC is the ease of bending it. It makes no difference electrically in jumper cables, a DC application.


So, assuming the wire gauges were identical, you're saying that a cable made of a single, solid copper wire should flow just as much electricity as a cable made up of multiple copper wires?

So the only advantage the cable made of multiple strands has is that it's more flexible?

Ed
 
Originally Posted By: Ed_Flecko
I'm shopping for some new, high-quality, jumper cables. I read a statement by one manufacturer that says "The fine strand construction and soft flexible jacket offer excellent flexibility – far superior to standard battery cable and better than the best welding cable!" - http://www.ceautoelectricsupply.com/batterycable.html

If I understand it correctly...

1.) The more strands of copper a cable has, the more flexible it is, AND

2.) The more electricity the cable is capable of carrying because electrons flow around a copper wire and not through the core of a copper wire. Is this correct?

From what I've read, this explains why a cable made up of lots of fine, individual copper wires will flow more electricity than a solid copper wire, i.e., more electrons can flow around the exterior of multiple wires rather than a single large wire of the same gauge. Correct? Incorrect?

smile.gif


Ed


This is like choice of oil........How good does it need to be? Yes, stranded wire is much more flexible. Yes, more strands make it more flexible, up to the point that the wires break in use.

Once you get up to 4 gauge or so, the cables will flow plenty of electrons. At that point, the clamp connection becomes the bottleneck. Are you jump starting a big diesel? Then yes, more money = more quality, and a bit more chance for success. If you are jumping one gasoline car to another, you don't need $200 cables.

Three things I look at in jumper cables......Size (Gauge) vs. length, and quality clamps. Being able to reach is as important as anything. 20' 4 gauge cables, with good quality copper clamps, will get most vehicles started without getting run over.
 
It's been almost 30 years since I got my EE degree so I'm a bit rusty on this. But I'd say essentially yes, no difference worthy of mention.

Buy the cable that best meets your needs at the price point you are willing to pay.

Originally Posted By: Ed_Flecko
Originally Posted By: javacontour
For DC, it uses the entire wire. With AC, you get some skin effect.

The reason to make stranded cable for DC is the ease of bending it. It makes no difference electrically in jumper cables, a DC application.


So, assuming the wire gauges were identical, you're saying that a cable made of a single, solid copper wire should flow just as much electricity as a cable made up of multiple copper wires?

So the only advantage the cable made of multiple strands has is that it's more flexible?

Ed
 
For DC, it's the entire wire (core); for skin-effect is frequency dependent, and it will become obvious when you get yourself up to 100s of thousands of Hz and beyond.

Jumper cables are just jumper cables and there's no magical compositions to it. Simply buy the biggest gauge possible (lower the number gauge, the thicker the copper wire thus the lower the resistance).

also: multiple strands is what makes copper wiring flexible, as opposed to solid core.

Q.
 
Originally Posted By: Ed_Flecko
Originally Posted By: javacontour
For DC, it uses the entire wire. With AC, you get some skin effect.

The reason to make stranded cable for DC is the ease of bending it. It makes no difference electrically in jumper cables, a DC application.


So, assuming the wire gauges were identical, you're saying that a cable made of a single, solid copper wire should flow just as much electricity as a cable made up of multiple copper wires?

So the only advantage the cable made of multiple strands has is that it's more flexible?

Ed


That's it for DC current. But like I said in an earlier post, the TOTAL cross section of copper has to be the same, so making the strands as fine as possible means that the total wire diameter can be closer to that of a single solid wire. Coarse-stranded wire is less of a benefit than fine-stranded wire.
 
CMA= Circular Mill Area. It was the measure used in all the power transmission formulae used in the course I took.
Glad the frequency-to-surface conductance relationship was explained in detail.
My uncle mentioned it, but his tech training straddled the Second World War.
I doubt the door bell circuit we were working on suffered too much from our nicking the wire. Kira
 
As others have mentioned, in DC skin effect doesn't come into play. In very practical terms though, 4 gauge solid wire would be unusable as jumper cables. NO flexibility at all.
 
Originally Posted By: Ed_Flecko
Originally Posted By: javacontour
For DC, it uses the entire wire. With AC, you get some skin effect.

The reason to make stranded cable for DC is the ease of bending it. It makes no difference electrically in jumper cables, a DC application.


So, assuming the wire gauges were identical, you're saying that a cable made of a single, solid copper wire should flow just as much electricity as a cable made up of multiple copper wires?

So the only advantage the cable made of multiple strands has is that it's more flexible?

Ed


javacountour has already summarized it well and answered your question. No need to double check since brevity and simplification is a sign of deep knowledge.

If you double check his/her wisdom everyone else will just repeat or detail the reasons then it'll turn into rocket science. Well actually electricity is far more complex than rocket science. It's far more valuable too in our Information Age since electricity is it's blood.

Well hopefully you learned enough so you can make a wise decision over the price difference in a $20 vs. $40 jumper cable.
smile.gif
 
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