ohmhead
Senior Member
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- ORLANDO FLA
Well question for today ? When is aluminum wire at a lower resistance to copper no thermal or condition just old standard wire same length same cir mils? Take care
Hmmm. Good question.
High frequency AC source on widely separated copper wires
vs.
DC aluminum?![]()
This is a rather in depth explanation of skin effect:
http://en.wikipedia.org/wiki/Skin_effect
Since Al and Cu are nearly identical in skin effect depths, I don't see where Al has an advantage over Cu for equal cross sections.
Where Al is a better conductor than Cu is by weight which has nothing to do with skin effect. Al is the best conductor by weight than any other metal.
Well yes it has everything to do with skin effect.
Its a function of the relative resistance of the conductor material being less for materials of higher resistance for example the skin effect for a given diameter of cable is greater if the material is copper rather than aluminum .
The induced emf magnetic flux internal in the core of conductor can push the current flow to the outer surface of conductor higher dc resistance of alu to copper alu has higher dc resistance less induced current to push. Meaning flux induced is minimal less push current flows in more of a area in the aluminum conductor . more area less resistance to flow
Copper has less resistance it can push current to its outer surface with more of a induced current and with a higher magnetic flux produced by the nature of less dc resistance of conductor . meaning more current to push but less surface area to flow thur . Its all magnetic flux induced current ac freq and its effects and alu is less in ac resistance then copper . Best to ya
the higher resistance in alu wire tends to make the current flow around the surface with less effort
Even Lithium?Al is the best conductor by weight than any other metal.
Can you post some links?
For one thing, skin effect does not apply to DC. A kilogram of Al will be a better conductor than a kilogram of any other type of metal even at DC.
[We never said it did we said it control the induce ac part by dc resistance of conductor .]
As this chart illustrates, skin effect is nearly identical for Al and Cu.
![]()
Please realize that in any AC circuit, the opposition to current flow is impedance with resistance only being one component of impedance. You
[We see the dc resistance as a limit to the induced current of the ac reactance .
In the core of the wire or conductor .]
speak of induced current which creates impedance, not resistance.
For illustration, the skin effect of 60 Hz in Cu is less than 9 mm. That noted, why is there a need for conductors any larger than 9 mm? There is some conjecture about skin effect on stranded conductors. Stranded vs. solid is virtually the same, with the exception of special 'Litz' conductors that have insulated strands.
[Were not using litz wire high freq were talking 500mcm and larger conductors .]
I am not calling you wrong, I just don't understand your explanation. In my mind there is a graph somewhere that shows the crossing line of the phenomena you purport and that interests me.
[Well its ok we like talking electric and getting input on what others think .]
I find statements like this confusing, however.
Al is more immune, slightly, to skin effect than Cu and may provide for more usable conductor at high frequencies, but be aware that in real life thermal conductivity, ambient temperature, type or lack of insulation, power factor and duty cycle also come into play.
[alu is lower in resistance to skin effect but copper is higher in resistance to skin effect on the surface of the conductors .]
Skin depth has nothing to do with power. All you need to know is the relative permittivity and the frequency to calculate skin depth.
[ skin depth to me has lots to do with its effects over long distances .]
In lieu of a graph, I ask at what frequency does Al become a better conductor than Cu for the same given cross sectional area?
Thanks for putting up with my curiosity.
[I enjoy debates but also learn from others ideas and views iam just a electrician with a different way of thinking about things electrical . iam just reading from a book .] TAKE CARE
Even Lithium?
What book? Really, I am curious.
Thanks.
Well its the Standard Handbook For Electrical engineers Fink & Beaty Eleventh edition page 18 -86 Par 228 .
Electrical Characteristics of Cable Skin Effect copy 1977 it maybe a little old and maybe out of date but theres lots of good stuff . I collect electrical books have a few old and new its fun to see the different things that change thur the years meaning electrical theorems today and yesterday . Is that your call letters K8MHZ ? I was a ham operator my first call letters were WN2MQX in 1968 best to ya
No doubt. Even though silver is the most conductive, its weight knocks it down in the ratings. I looked up a few here is the rank (at room temperature):I couldn't tell. Every time I opened up a roll of lithium wire it caught on fire so I couldn't ever check it's resistance. :grin:
But as far as usable metal goes, I am sure Al is the least resistive per pound.
Thanks! I like the old books too. I like looking at code books from two century turns ago.
Yes, I am guilty of being a ham. Guilty of knowing Morse Code and owning and operating a tube type radio, building my own antennas and filling shelves with various forms of electronic gear from throughout the ages. Did you know it was Samuel Morse's birthday just a few days ago and Google's logo was in Morse for a day?
Thanks for the reference, BTW 1977 isn't that old, OM. :grin:
_ _ --- --- _ _ _-- - _-_ _ _ _ -- _ _ ---- _ _--
7 3 d e k 8 m h z
Is that ok its only been 38 plus years but how did i do ? yes we also built our own transmitters and matching halfwave folded dipoles !! Take care nice
Nope, AC resistance. He did not specify DC resistance only so AC resistance is fair game.I guess we are talking about impedance here and not resistance. The OP refered to resistance.
AC impedance can be reactive. We only only talking about the resistive component of the impedance.Isn't AC resistance Reactive since it has a component of inductive and capacitive properties?