24 gauge wire, if you double up strands what equivalence gauge?

Discussion in 'General Electronics Chat' started by sdowney717, Mar 21, 2015.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    Ethernet cable is 24 gauge copper. 4 twisted pairs so 8 strands.
    I was thinking of joining the twisted pairs to give 4 strands in a cable.
    So what copper wire gauge will each pair joined become?

    from here says the cable strands are 24 gauge
    http://en.wikipedia.org/wiki/Category_5_cable
     
  2. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,575
    2,552
    Ethernet cable is solid copper table cable. According to this table, cable #24 ga has a diameter of .5106 mm, and an area of .2047 mm². If you join two of them together, then you'll have twice the area, that is .4094 mm²
    The closest gauge value for that area equivalent is #21, with a cross section area of .4105 mm²
     
    Julesbartow likes this.
  3. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,808
    The AWG standard is designed such that, to a close approximation, the cross sectional area of the conductor doubles for every reduction of 3 in gauge number. So using 2 #24 wires would be equivalent, in cross-sectional area, to #21.
     
    cmartinez likes this.
  4. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,808
    What's the reasoning behind this?

    Just from a sanity check viewpoint I have a hard time buying it (but then, not everyone thinks I'm sane). #18 wire is used in a lot of household appliances for power cords and such. I have a hard time believing that it would be reasonable to power those same appliances using doubled-up #24 wire.
     
  5. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    http://www.duxcw.com/faq/network/awg.htm
    I just found this says some ethernet cable is 22 gauge.
    So what will two 22 gauge wires joined be and how do you know which ethernet gauge you have in a cable?

    Would that marking be on the jacket?

    Maybe the gauge is determined by CAT rating?
    Saw someone said cat5 is 24, cat 6 is 23, cat 7 is 22 gauge?
     
  6. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,575
    2,552
    That's a very interesting observation. The gauge standard for carbon steel sheet metal is such way that the number of lb/ft² of each gauge increments by 1/16 or 1/8, 1/4 etc... fraction of a pound per ft²...
    I wonder what the reasoning behind the wire gauge standard was for assigning ga numbers.
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,808
    Look at the original link that you posted. It states that the Cat 5 wire is solid and can be no thicker than #22 and no thinner than #24 (except that #26 is allowed for short runs).
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    :oops: It was an error based on confusing the diameter column with the cross section column in a chart. I'll delete the offending post which you have now preserved forever in quoting it.
     
  9. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,808
    The gauge number, in most cases, referred to the number of times that the wire was drawn through a reducing die. The amount of stress in the wire needed to pull the wire is roughly proportional to the amount by which the area is decreased. So there's a limit to how much reduction you can get in a single pull without breaking the wire. Since manufacturers want to minimize the number of pulls while also minimizing the amount of broken wire, the reduction per pull became roughly consistent and was eventually standardized. Like most things that get standardized long after an industry has matured, a balance has to be struck between the quality of the standard going forward and compatibility with what is already on the market.

    In this case, the decision was made that the ratio between diameters of two successive sizes would be constant. This reflected the physical reality mentioned above.

    <br />
\phi_{A} \; = \; \phi_{B} \( \alpha^{(B-A)} \)<br />

    It also stipulated, to address compatibility with as much of the existing market as possible, that #4/0 wire would have a diameter of 0.46" and #36 to have a diameter of 0.005". This means that we have to go from 0.005" to 0.46" in 39 proportional steps (#4/0 is effectively #-3 gauge).

    <br />
\alpha \; = \; \({\frac{\phi_{4/0}}{\phi_{36}}}\)^{\frac{1}{(36- -3)}} \; = \; \({\frac{0.46"}{0.005"}}\)^{\frac{1}{39}} \; = \; \sqrt[39]{92} \; \approx \; 1.1229<br />

    Thus, the ratio of AREAS of two wires that are three sizes apart is

    <br />
\( \( \sqrt[39]{92} \)^3 \)^2 \; \approx \; 2.005<br />

    I don't know if this is pure coincidence or not -- I suspect it was not. Notice the very convenient tie in to electrical work with decibels in which 3dB doubles the power while 3 wire sizes double the area.
     
    KJ6EAD, RichardO and cmartinez like this.
  10. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,808
    Engineering is both an art and a science -- the art is learning from your own mistakes and the science is learning from the mistakes of others. The error you made is an easy one to make, so by preserving it here we get to let others practice the science from your practice of the art.

    And heaven knows that I have more than a few "artful" posts on this forum! :D
     
    Julesbartow, Gdrumm and KJ6EAD like this.
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,856
    The 22 gauge is normally for longer runs (plenum cable) and 24 is for shorter runs and longer wall to PC cables. The 26 gauge is for patch cables (modem to router) and short runs from wall to PC.
     
  12. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,575
    2,552
    @WBahn and @KJ6EAD , please read a previous post of mine regarding what I think is the right attitude towards mistakes...
     
  13. RichardO

    Well-Known Member

    May 4, 2013
    1,238
    385
    The one wire size I can always remember is 30 ga since it has nice even numbers: 10 mil diameter and 100 ohms per thousand feet. I can easily mentally calculate from there. (Sorry about the English dimensions).

    edit: Added a wire gauge table.
     
    Last edited: Mar 21, 2015
    cmartinez likes this.
  14. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    I went to the linked post and found to my slight surprise that I had already "liked" it. :)
     
    cmartinez likes this.
Loading...