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AWG stands for American Wire Gauge. This is something interesting that I learned today (at least what the abbreviation means).

In terms of networking it represents the wire diameter of an Ethernet cable or probably any cable. Contrary to expectations, the higher the number the thinner the wire is. There are also a bunch of characteristics related to it that I don't understand.

It has a total of 44 possible values (1-40, plus 0, 00, 000 & 0000) and according the TIA 568-C.2 standard Ethernet patch cables should consist of four balanced twisted-pairs of 22 AWG to 26 AWG (0.64516mm to 0.40386mm) solid or stranded conductors.

I'm wondering if smaller or bigger values are better. Is the signal better, or the tension higher, and what's the importance of characteristics such as:

+-----+------------------+-------+-----------------------+-------------+-------------+
|     |     Diameter     |  Area |       Resistance      | Max Current |  Max Freq.  |
| AWG |------------------+-------+-----------------------+-------------|  for 100%   |
|     |  [in.] |  [mm]   | [mm²] | [Ω/1000ft] |  [Ω/km]  |  [Amperes]  | skin depth  |
+-----+--------+---------+-------+------------+----------+-------------+-------------+
|  21 | 0.0285 | 0.7239  | 0.41  |    12.8    |  41.984  |    1.2      |    33 kHz   |
|  22 | 0.0254 | 0.64516 | 0.326 |    16.14   |  52.9392 |    0.92     |    42 kHz   |
|  23 | 0.0226 | 0.57404 | 0.258 |    20.36   |  66.7808 |    0.729    |    53 kHz   |
|  24 | 0.0201 | 0.51054 | 0.205 |    25.67   |  84.1976 |    0.577    |    68 kHz   |
|  25 | 0.0179 | 0.45466 | 0.162 |    32.37   | 106.1736 |    0.457    |    85 kHz   |
|  26 | 0.0159 | 0.40386 | 0.129 |    40.81   | 133.8568 |    0.361    |   107 kHz   |
|  27 | 0.0142 | 0.36068 | 0.102 |    51.47   | 168.8216 |    0.288    |   130 kHz   |
+-----+--------+---------+-------+------------+----------+-------------+-------------+

Where I live, I only see cables rated AWG23, AWG24, AWG26, AWG26/7. Not sure what to pick because I have no idea what the differences are.

Is there a right diameter for a specific situation?

Conduit, signal resistance, ohmic resistance (DC), impedance (AC), Power over Ethernet - how are these things related and how do they influence the network and the devices I am using.

Basically, how do I know which AWG is the best?

  • 2
    To supplement the how-it-works answers below, this is the (highly simplified) practical way to look at it: It's effectively a budget decision. Stranded + maximum AWG gives you the cheapest, most flexible wire. The longer distance, greater bandwidth, more features (PoE) you want to support, the more likely it is you'll need to upgrade to a more expensive cable (smaller AWG number, solid instead of stranded) to meet those requirements. – M-Pixel Jul 21 '18 at 3:38
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    @robinCTS Wow! You deserve an ASCII layout award for that table cleanup. Bravo!!! – JakeGould Jul 22 '18 at 5:28
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    @JakeGould Thanks. I found the original source of the table here and used the Tables Generator site as a starting point. None of the online table generators have all the features I want/need, though. I'm planning on whipping up my own Workbook-based table generator. I might eventually set up an online version of it ;-) – robinCTS Jul 22 '18 at 5:50
18

In general, AWG is used for ampacity (i.e. how much amperage you can force down a conductor for a given wire diameter before it starts to heat). It is also a gauge for resistance (DC) or impedance (AC). When talking about resistance or impedance, it usually has to do with voltage drop. In the case of Ethernet we are talking about signal loss (voltage drop over distance).

Total distance (Signaling)
When referring to distance, a higher AWG rating (smaller diameter) will have a greater signal attenuation for the same distance compared to a lower AWG rating (larger diameter).

Conduit
In situations regarding conduit, when dealing with a conduit that has 80-85% of its total capacity used, you may have to use a smaller diameter cable.

Power over Ethernet

Power over Ethernet (PoE) has become extremely popular. Here is a quote regarding AWG sizing from Belden.

No longer confined solely to VoIP phones and security cameras, more types of powered devices are beginning to call for Power over Ethernet connections. And these devices are requiring higher power levels, too. Wireless Access Points, digital signage, videoconferencing systems and laptops are all increasing the amount of power running through cables. In fact, a new PoE standard, IEEE 802.3bt, supports up to 100W of power per cable.

But higher power levels running through a cable can cause performance issues – namely by making the cable hotter. And when the cable gets hotter, insertion loss increases. This escalates your chances of your business experiencing a productivity killer – downtime – and may also damage the cable itself.

As you can see it has to do not only with signal loss, but also power drop vs distance when dealing with PoE. And if you try to force too many amps (i.e. the power draw of the device connected to the cable) down it, it may also heat up or damage the cable if the AWG size is not rated for the amperage. For a given situation, you may be able to squeeze that last little bit out of your conduit with a higher AWG size. (With help from a lubricant.)

Do you need PoE over the cabling? If the answer is yes, and this is permanent cable (not patch cords), then you would want solid not stranded cabling, with the lowest number AWG you can purchase.

References:

https://www.belden.com/blog/digital-building/3-reasons-why-power-over-ethernet-demands-cat-6a-cable

https://blog.tripplite.com/whats-the-difference-between-24-awg-26-awg-and-28-awg-network-cables/

  • 1
    This also helps: powerstream.com/Wire_Size.htm – Biswapriyo Jul 20 '18 at 16:04
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    You should also check that your connectors handle the chosen gauge. It seems vendors don't bother to mention this in their patch panel specs these days, but those I've found don't handle 28 AWG. – grahamj42 Jul 21 '18 at 7:52
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    Keep in mind that there is such a thing as skin effect which reduces the gain in conductance to surface rather than volume, especially in the GHz range that is necessary here – PlasmaHH Jul 21 '18 at 16:23
  • While the skin effect is important in most (if not all) electrical engineering and rf design. there isnt really a need to cover it here. As long as it's tia/iso certified cabling, this aspect can be neglected as it was already accounted for in the standard itself. (If there is no deviation from the standard it is of no concern) – Tim_Stewart Jul 21 '18 at 22:59
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In terms of networking it represents the wire diameter of an Ethernet cable or probably any cable.

AWG is as the name suggest an American system for measuring the size of wires. If you are in America you will probably find nearly all wires are measured in this manner. If you are not in America you will likely find other systems are also in use for many types of cable.

Larger numbers mean smaller wires, I belive this system comes from the way wires are made. Each die reduces the size of the wire slightly, so a smaller wire is made by pulling the wire through more dies.

For stranded cables the quoted AWG number is normally not an actual diameter but an "equivilent" diameter of solid core wire that would give the same cross-sectional area.

In general a larger wire (lower AWG number) will have lower losses and will heat up less if power is transmitted through it, on the downside it is likely to cost more and be less flexible. If the wire gets too large or small there may be problems with termination compatibilities hence why the specification for "CAT" cables sets both an upper and a lower limit.

There can also be problems if the wire size gets too big compared to the wavelength of the signals but I don't think this is a problem at anywhere close to the wire sizes and frequencies used for Ethernet.

  • 4
    re: multiple dies, that's true about the "logic" for the numbering direction, but the AWG number isn't the number of die passes. Each successive gauge number changes cross sectional area by a constant multiple. For the mathematically curious, see en.wikipedia.org/wiki/American_wire_gauge. :-) – fixer1234 Jul 20 '18 at 20:33
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Ethernet's signal on the wire is 10MHz to 833MHz wide. These are radio frequencies, and radio frequencies travel on the outer skin of the conductors. The greater the surface area of the wire, the better it conducts radio frequency energy, and therefore lower gauge numbers are better for higher network speed.

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    That has some merit, but you should explain how it relates to question about AWG, otherwise it's not an answer. – Agent_L Jul 21 '18 at 17:05
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    Can you provide a reference for these figures? CAT-6A = 500mhz, and CAT-8 is 2000mhz. I'm unaware of any twisted pair cabling that can support 10ghz frequency bandwidth. TIA. – Tim_Stewart Jul 21 '18 at 23:13
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The wider the conductor, the lower the resistance. Higher resistance results in higher voltage drop with higher current (Ohm's law) and distance. Low-current or low-distance signals are suitable for smaller-gauge (higher numbers) wire, but power should be on the largest gauge (lower numbers) feasible.

  • 4
    resistivity is a material property - it's resistance that depends on the conductor geometry (proportional to length; inversely proportional to cross sectional area) – steeldriver Jul 20 '18 at 20:34

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