The physics of wire carrying DC current?

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Phil Barnett:
There was a somewhat heated discussion regarding stranded wire being able to carry more current than the same guage wire in a solid core amongst some of us on the radio today.

I maintain that the current carrying capability of copper  (or any other material) at DC is a matter of the cross section area of the wire and that stranding has little effect on current carrying capabilities given the exact same cross sectional area. In my mind, that means in order to maintain identical copper cross section area that stranded wire would have to have a slightly larger actual diameter due to the gaps between the wires.

Somebody on the frequency challenged us all to come up with reproducable tests that would prove our assertion at our next luncheon meeting. I figure if this effect is measurable at 8 gauge, it should also be identically measurable at 22 gauge, so experiments should be simple to breadboard.

Now, it's clear that stranded wires are more flexible, easier to handle and more resistant to vibration cracking. And, it's also clear that once you leave DC, skin effect begins to change how current travels down a wire, but none of those were part of the basic assertion.

What do the elmers say?

Does stranded wire carry DC current better than solid core wire?

Alex:
Current carrying capacity is a matter of opinion and some assumptions. What you really mean to ask is if the resistance of each is the same.  If cross sectional area total is the same, the resistance should be very close.  Also, there is probably not an exact equivalent between stranded and solid.  Stranded # 20 may not have exactly the same as # 20 solid as far as cross sectional area.

Lee A Crocker:
A reproducible testing device would be to build a Wheatstone bridge and 2 pieces of wire with the same metallurgic make up, one stranded and one solid of the exact same length.  You would probably want some long pieces to get enough resistance to reduce the current flowing through the bridge.  Balance one piece of wire and then plug in the other and see if the meter deflects toward the lower resistance side or the higher resistance side.    

http://www.geocities.com/CapeCanaveral/8341/bridge.htm

73  W9OY

David Crusan:
What they taught US in college was that electricity flow in wire was just the opposite of water flow in pipes - the electricity flows mainly on the outer edge of the wire - not in the center.  If that's true, it would seem that having multiple strands of wire as opposed to one thick wire would give you more surface area, allowing more electron flow.

However, professors aren't always right.  But that's what they taught us at least.

Phil Barnett:
"What they taught US in college was that electricity flow in wire was just the opposite of water flow in pipes - the electricity flows mainly on the outer edge of the wire - not in the center. If that's true, it would seem that having multiple strands of wire as opposed to one thick wire would give you more surface area, allowing more electron flow."

This is called the "Skin Effect", but I believe it only comes into play at higher frequencies.

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