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If stranded wire can carry more power for a given wire gauge, why are homes typically wired using solid?

If solid wire is less expensive to make, that provides a compelling reason why solid is used, but if an electrician or homeowner wanted to use stranded, is there any reason not to?

For this question I am mainly referring to legs of U.S. home wiring for 15 and 20 amp breakers carrying 120 volts on a single phase.

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A few reasons:

  • Stranded wire is more expensive to make.
  • At a given wire gauge, stranded is going to be larger than solid wire (it's the cross-sectional area of conductor that counts and there are going to be some air gaps between conductors with stranded). This could make a big difference if you have several cables in a limited space like an electrical box.
  • The main advantage of stranded is that it's more flexible. You generally don't need this in home wiring because it's all put in place once and hidden behind walls/floors/ceilings.
  • When you screw a solid wire into a switch or receptacle, you can tell if it's secure. I could see individual strands coming loose as you fold wires back into an electrical box.

More information in Wikipedia: http://en.wikipedia.org/wiki/Wire#Solid_versus_stranded

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  • 2
    Somehow, I started with your Wikipedia link and ended up here. Randall Munroe was right! – Doresoom Apr 26 '11 at 21:30
  • Once you get upto 6mm, then you do need stranded to get enough flex, but I agree with you list for lower rated cables – Walker Nov 16 '11 at 14:21
  • In addition to this, solid is just nicer to splice together with a wire-nut: it's easier to line the two wires up, they don't tear if you pull on them too hard when checking the connection, and they don't get all frizzy and break apart if you have to undo the wire-nut. – BlueRaja - Danny Pflughoeft Sep 7 '13 at 7:02
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    Interesting read because in Honduras and central America in general, stranded wire is used for all electrical wiring of homes and businesses. – marciokoko Sep 14 '17 at 21:19
  • @BlueRaja-DannyPflughoeft "they don't tear if you pull on them too hard when checking the connection" <- This is the only reason of all the reasons around here that I can see as a compelling reason to use solid. If it weren't for this, I'd switch to stranded in a heartbeat because it's just so much easier to work with for anything 12 gauge or below. – horta Oct 5 '17 at 3:30
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The skin depth for copper wires is roughly 1/3" for 60 Hz. So unless your wire is more than 2/3" in diameter (YIKES!), it won't come into play.

Therefore, solid copper wire CAN carry more power than stranded wire at 60 Hz, due to packing inefficiencies (empty space) that is inevitably between the individual strands.

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  • Per the same Wikipedia article, skin effect is not an on-off thing. Skin depth is set somewhat arbitrarily at 1/e (~37%) current density. So, there's less current at skin depth level than closer to the surface, and there's still significant current below skin depth level. But the overall idea is correct, at 60Hz and typical home wire gauges skin effect does not matter. – Kibber Mar 1 '18 at 3:42
  • Stranded wire also does not help with skin effect, as the current will jump between strands to stay on the outside. You need Litz wire for that. – SomeoneSomewhereSupportsMonica Nov 18 '18 at 4:17
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Stranded is more susceptible to corrosion due to more surface area.

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For AC - electrons run through entire cross-section the of wire

For DC - electrons like to run on the outside of the wire so stranded will have more surface area for a given gauge

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