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Stranded Or Solid (and Why)

 
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Old 12-31-2009, 06:12 AM   #21
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Re: Stranded Or Solid (and Why)


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Originally Posted by 480sparky View Post
12 and smaller, solid unless specs or manufacturer dictates otherwise.

10 and larger, stranded if at all possible.
# 8 and larger is required to be stranded if installed in conduit. 310.3
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Old 01-19-2014, 10:20 PM   #22
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Re: Stranded Or Solid (and Why)


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Stranded is certainly easier to pull.

Electrically, there's some theory I learned decades ago--and don't know if it's been disproven or not--that says electrical current tends to travel mostly on the "skin" of a conductor. If that's truly the case, stranded would provide much more surface area for that flow and therefore be significantly more efficient.
I realize that this is an "old and dead" thread, but I came across it while searching and wanted to add some information for others who may stumble across the thread.

The skin effect is in fact real and does matter, but is not a factor for choosing stranded vs solid for 12 gauge wire for low frequency A/C. I am not an expert on this topic, but the summary section on the Wikipedia entry seems good:

http://en.wikipedia.org/wiki/Skin_effect

"Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. The skin effect is due to opposing eddy currents induced by the changing magnetic field resulting from the alternating current. At 60 Hz in copper, the skin depth is about 8.5 mm. At high frequencies the skin depth becomes much smaller. Increased AC resistance due to the skin effect can be mitigated by using specially woven litz wire. Because the interior of a large conductor carries so little of the current, tubular conductors such as pipe can be used to save weight and cost."

(Emphasis added)

Practically speaking you can disregard the skin effect for anything you can get in solid core.
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Old 01-31-2018, 11:56 AM   #23
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Re: Stranded Or Solid (and Why)


Much as i'm loath to contribute to such an old thread.

Skin effect is just about non-existent at 50/60Hz on 2.5mm^2 cross section cable or indeed just about anything you will find in a domestic or light commercial setting.

In addition. The difference in the skin effect between solid and stranded conductors is particularly small. When skin effect is an issue, engineers use litz wire where each strand is insulated from each other. This overcomes the skin effect as the current in the central conductors is unable to travel to the outer conductors.

in stranded cable there is no such insulation and hence skin effect is just as prominent as in solid core cable.

As for the observation about the use of hollow pipes rather than cable for some high current applications. This is normally done for other reasons such as allowing the passage of coolant.

If anything skin effect can be useful as one of many natural means to attenuate high frequency harmonics on the network.

Overhead power lines on the MV and HV networks are normally Aluminium Conductor Steel Reinforced. They are metallic all the way through - albeit with the inferior electrical conductor on the inside but I believe this is for structural and not electrical reasons.

Underground cables too rarely contain any centre hole.
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Old 02-01-2018, 01:38 AM   #24
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Re: Stranded Or Solid (and Why)


FWIW the only thing I can say for stranded, is that alot of sparkys don't realize that when making the connection to a screw terminal, you have to wind the strands counter clockwise when you make to shepherd's bend to screw it home.
That's all I got.
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Old 02-01-2018, 07:06 AM   #25
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Re: Stranded Or Solid (and Why)


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FWIW the only thing I can say for stranded, is that alot of sparkys don't realize that when making the connection to a screw terminal, you have to wind the strands counter clockwise when you make to shepherd's bend to screw it home.
That's all I got.
I wind the wire around the screw clockwise. I leave the insulation on the end also.

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Old 02-01-2018, 07:14 AM   #26
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Re: Stranded Or Solid (and Why)


Was he talking about the direction of wire twist, not wrapping the screw?
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Old 02-01-2018, 07:23 AM   #27
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Re: Stranded Or Solid (and Why)


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Was he talking about the direction of wire twist, not wrapping the screw?
Why are you twisting the wire?

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Old 02-01-2018, 08:29 AM   #28
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Re: Stranded Or Solid (and Why)


Retwisting.

I also learned that trick from a sparky. Leave 1/2" pc of the insulation on the end of the wire so it holds it together until the screw is tightened.
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Old 02-01-2018, 09:41 AM   #29
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Re: Stranded Or Solid (and Why)


All stranded wires that go directly under screws get sta-kons.

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Old 02-01-2018, 10:10 AM   #30
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Re: Stranded Or Solid (and Why)


The skin effect applies to much larger wires. Something like 5/8" diameter per strand.

Carry on.

edit: I didn't see page two of this thread. I'm a little late to the game.

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