Stranded vs solid wire

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Awl --
Apropos of the recent thread on wire nutting stranded with solid, are there any inherent advantages of one over the other? #14-#10.
Stranded is more flexible, an advantage if you have to pull long runs in bends in EMT, but I find it a pain when connecting outlets, etc.
Stranded can be dicey-er with nicks, missing strands. But, stranded might give more contact area under screws, in breakers, etc.
At HD, stranded is $5 more on 500 ft coil of 14 and 12: $25 to $30, and $40 to $45.
BX/romex comes which way? Both?
Who uses what and when?
--
EA



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On 11/12/2009 7:07 PM Existential Angst spake thus:

Yes and yes.

Only missing strands if one cuts them off.

Not an issue.

You seem to have pretty well covered all the properties and pros and cons of solid vs. stranded.

Solid only. No need to snake the wires through anything, so no need for stranded wire here.

You pretty well said it yourself:
o Use stranded wire when pulling through conduit. o Use solid wire otherwise.
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On Thu, 12 Nov 2009 20:04:14 -0800, David Nebenzahl

Actually CMPCT-CU conductors in aluminum flex (BX ) cable IS available. CMPCT-CU is otherwize known as compact copper, or stranded wire. as per ASTM b-8

The stranded stuff is used where flexability is required - or where vibration is a problem. You won't find it at the "borg" but I do have some in my garage.

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On Thu, 12 Nov 2009 20:04:14 -0800, David Nebenzahl

Stranded wire "BX" is available from "Northern Cable" in TC90, MC-THHN and AC-THH flavours. Google it.
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wrote:

The contact area of solid wire under the screw will be several times the cross-sectional area of the wire. Nothing to be gained from more contact area than that. Stranded also has a tendency to squeeze out from under the screw and loosen up. Other than that, I think you covered most of it.
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Existential Angst wrote:

I don't recall solid conductors in an automobile. Stranded wire is less subject to metal fatigue from bending or vibration. The smaller a conductor is, the farther it can flex without bending the metal.
Stuff with 7 or 19 strands is usually classified as Rigid Stranded Wire.
Flexible Stranded Wire usually has 49 strands or more. I'd hate to try to connect the flexible stuff with a wire nut. Until recently, the NEC required crimping for it. Now there's an approved screw terminal.
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wrote:

I know most of you are talking for home use, but never use solid where where are a lot of vibrations such as cars, boats and planes. Solid will break, whereas stranded won't.
Hank
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No one mentioned the fact that stranded wire, at the same diameter, can carry more current. And you could tin the ends of stranded for termination.
bob_v
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In residential applications -- nonsense.
First of all, the NEC doesn't make a distinction between solid and stranded in the limits it places on the ampacity of a conductor. The only factor is size.
Second, presumably you're referring to the "skin effect" -- which at 60Hz is completely negligible. The frequency needs to be a *lot* higher than that before there's any noticeable effect.
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wrote:

I was going to bring this up as well.
It depends on how the NEC defines gauge of a wire.
If it accurately sums the cross sectional area of each strand, so that this sum is equal to the CSA of solid, then the ampacity should be very nearly equal. But the diameter of the stranded would be slightly bigger -- because of the inherent inefficient of "packing circles" -- ie, gaps between non-touching parts of a circle.
If the NEC determines gauge based on diameter, then stranded will have less ampacity than solid, for the same circle-packing reason -- less net CSA of copper.
So, how DOES the NEC define "gauge"?
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EA



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Existential Angst wrote:

I believe the NEC uses AWG, which uses total cross section.
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Existential Angst wrote: ...

It references AWG which is wire area for either.
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No one mentioned the fact that stranded wire, at the same diameter, can carry more current. And you could tin the ends of stranded for termination. ============================================= Tinning the ends of stranded is an excellent idea -- proly no one does it, tho.
--
EA


bob_v



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Existential Angst wrote:

No, it defeats the purpose of it being stranded in the first place.
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Just the ends?
When attaching line-cord (ordinary wire for lamps, etc) to those two screws, to keep the strands from coming "loose" and maybe shorting on the other side, I of course twist it tight, but then tin the end, before wrapping the end around the screw and tightening it.
Anything wrong with doing that?
Thanks!
David
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On Fri, 13 Nov 2009 08:23:35 -0500, "Existential Angst"

stops, making the wire more succeptible to fatigue breaking of the strands. NOT ALLOWED in aircraft wiring, for one "solid" example.
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Please say more.
Wiring a lamp socket, tinning just the last 1/4th or 1/8th of an inch, just to keep the strands from sticking out from where screwed down, surely that's ok?
And being screwed down hard, no flexing, I'd hope.
Seems to me that a strand coming loose within airplane wiring would be a lot more dangerous than tinning just a tiny bit at the end to keep a strand from sticking out, with who knows what effects.
Now, I am willing to be educated. Please don't just dictate the correct answer, but try to CONVINCE us via argument, data, metallurgy, whatever.
THANKS!
David
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Worked at wiring broadcast studios, and we were not allowed to tin stranded wires.. It was said that solder is too soft, and after tightening down screws or clamps, the solder would just compress, and would eventually cause a loose connection.
Ray
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David Combs wrote:

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Bob Villa wrote:

I won't get into that.

By doing so you take away flexibility of the stranded wire so right at your connection it is more likely to fail. As much as I hate crimped on wire connectors and always believed soldered was better than connectors, where there is a lot of vibration they do last much longer than soldered on wires. Can someone check with NASA?
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