solid vs stranded

[deepthreat]

This may sound like a dumb question, but here goes: If electron flow occurs only on the surface area of a wire, is it safe to say that a stranded wire is more preferable to solid due to the fact that each strand has a surface area, does a stranded conductor conduct electricity more efficiently than a solid? I know we use stranded in conduit more for plyablility but is it a better conductor as well? Thanks in advance

 

[dereckbc]

If electron flow occurs only on the surface area

That is only partially true, DC and lower frequencises use all the conductor cross-section. As you move higher in freq is when you get into SKIN EFFECT

 

[dereckbc]

More INFO

More INFO

[edit] Examples
In copper, the skin depth at various frequencies is shown below.

frequency d
60 Hz 8.57 mm
10 kHz 0.66 mm
100 kHz 0.21 mm
1 MHz 66 ?m
10 MHz 21 ?m

In Engineering Electromagnetics, Hayt points out that in a power station a bus bar for alternating current at 60 Hz with a radius larger than 1/3rd of an inch (8 mm) is a waste of copper, and in practice bus bars for heavy AC current are rarely more than 1/2 inch (12 mm) thick except for mechanical reasons. A possible solution to this problem consists of using cables with multiple insulated conductors. A thin film of silver deposited on glass is an excellent conductor at microwave frequencies.

 

[jim dungar]

At 60Hz, skin effect ratios for "wire" are not even calculated except for 300Kcmil and larger which are always stranded conductors.

 

[ryan_618]

I find it interesting that in Table 8 of the NEC (which is DC resistance only, not impedance), it lists stranded condcutors as having a higher resistance than solid. I was always taught the opposite. Again, this is only the physical resistance, not the impedance.