When talking about wire size of micro coaxial cables, AWG (American Wire Gauge) is the lingua franca for people with different backgrounds. AWG is a standardized wire gauge system that defines the diameters of round, solid, electrically conducting wires. As its name implies, it was originally established in North America, but now has been widely used across the world as the supply chain spreads out globally. The general information about AWG can be easily found by a simple search. However, beyond the general knowledge, there are several important facts to be noted for micro coaxial cables. In this post, we will share such facts in the sense of completeness. If you find any confusion about wire sizing, please feel free to contact us. We will be happy to help.
Important Notes on AWG for Micro Coaxial Cables
Conductor Diameter Larger than Equivalent Solid Wire
Because micro coaxial cables are all made of stranded wires, their AWG follows the rule for stranded wires. A stranded wire of specific AWG is designed to have the same cross-sectional area of a solid wire with the same AWG. Since there are always small gaps between the strands, a stranded wire will have slightly larger overall diameter than equivalent solid wire. Comparing the size of a micro coaxial cable with a standard AWG size table, you will find its center conductor diameter is approximately 18% larger than the corresponding value in the table.
Current Capability Higher than Equivalent PVC Wire
The current capability of a cable is principally determined by three factors.
- The heat yield by conductor at specific current
- The delta between maximum allowed temperature and ambient temperature
- The capability to spread heat from conductor to outer world
You may see lists of current capability versus AWG size somewhere, showing surprisingly low current capacity for each AWG. Actually, those lists assume PVC insulator, which is widely used in home electrical wiring, commonly used in home electrical wiring, which does not allow a temperature higher than 75℃. Micro coaxial cables are usually made of PFA insulator, which can work at temperatures up to 260℃. So a micro coaxial cable can carry much higher current than a standard PVC-insulated cable of the same AWG size. However, since micro coaxial cables are so thin, the current limit should be be carefully verified. Determining the exact current capability of a cable involves complex calculations. In Table 1 we list typical current rating of micro coaxial cables in typical conditions. Note that the rating should be reduced if any of the following conditions apply.
- The application has strict constraints on maximum temperature.
- The ambient temperature is higher than room temperature.
- The cable works in an environment that has high thermal resistance to the outer world.
- There exist multiple wires carrying large current in the same bundle.
- The connector has a smaller current rating.
In many applications, #5 turns out to be the limiting factor, so it is crucial to check connector current rating before determining wire size.
No Standard on Outer Diameter
Since AWG only defines the conductor size, can vary based on other factors. Particularly in the case of micro coaxial cable, impedance plays a significant role in determining their outer diameter. A 50 ohm cable is on average 10% thicker than a 45 ohm cable with the same AWG. Additionally, the outer diameter may vary with supplier and voltage rating. Such variations tend to increase with thicker cables, as manufacturers have more flexibility to balance dimensions, voltage ratings, and costs as the size increases. For convenience, we list typical outer diameters for commonly used micro coaxial cables; however, please note that these are approximate values and not standardized. One should look into the cable datasheet if more accurate dimensions are wanted.
| AWG | Center Wire Diameter (mm) | Typical Outer Diameter (mm) | Max. Current (A) | |
| 45Ω | 50Ω | |||
| #32 | 0.24 | 0.82 | 0.90 | 1.2 |
| #34 | 0.19 | 0.67 | 0.73 | 1.0 |
| #36 | 0.15 | 0.49 | 0.55 | 0.8 |
| #38 | 0.12 | 0.39 | 0.46 | 0.5 |
| #40 | 0.09 | 0.33 | 0.37 | 0.4 |
| #42 | 0.075 | 0.29 | 0.32 | 0.3 |
| #44 | 0.060 | 0.24 | 0.27 | 0.2 |
| #46 | 0.048 | 0.20 | 0.22 | 0.15 |
| #48 | 0.038 | 0.16 | 0.18 | 0.10 |
| #50 | 0.030 | 0.14 | 0.16 | 0.08 |
No Odd-numbered Cables on the Market
In theory it is possible to make odd-numbered micro coaxial cables. However, in practice only even-numbered cables exist on the market. Therefore, you can easily find a supply for 40 AWG and 42 AWG, but not likely for 39 AWG or 41 AWG coaxial cables.
More Strictly Describable with Three Numbers
Sometimes you may see a description on coaxial cable size with three numbers like 42 7/50. This is a more precise way to describe the size of stranded cable. Here are the roles of each number.
- The 1st is overall AWG size.
- The 2nd is the number of strands.
- The 3rd is the AWG size of a strand.
That is to say, 42 7/50 means a 42 AWG cable made from 7 strands of 48 AWG wire. The 7-strand configuration is a common practice for micro coaxial cables, thus the AWG of a strand is usually 8-size larger than the overall AWG.
General Knowledge on AWG
Below is some general knowledge on AWG. You can skip this section if you know AWG well.
How is AWG size calculated
AWG is defined as below
- 36 AWG is 0.005 inches in diameter.
- 0000 AWG is 0.46 inches in diameter.
- There are 40 gauge sizes (or 39 steps) from 36 to 0000. The diameters of any two successive gauges have a constant ratio.
Therefore, the diameter ratio of successive gauges is determined as below.
Since 0.005 inch is equal to 0.127 mm, the diameter of an n AWG wire can be calculated as below.
- In engineering practice, instead of doing this calculation, it is much easier to quickly get the size of an AWG wire by looking up in an AWG size table.
How to Properly Denote AWG Sizes
As showed up in this post many times, the proper way to denote wire size with AWG is the form like 40 AWG. There are alternative forms like below. All are commonly used in the electrical industry.
- #40
- № 40
- No. 40
- No. 40 AWG
- 40 ga.
For wires thicker than 1 AWG, there are also forms like below
- 3/0
- 3/0 AWG
- #000
How to Properly Pronounce AWG Sizes
Taking 40 AWG for example, it is pronounced as "40 gauge" or "No. 40" wire.
For wires thicker than 1 AWG, the zeros are referred to as aught.
- 0 AWG is referred to as "one-aught" wire.
- 00 AWG is referred to as "two-aught" wire.
- 000 AWG is referred to as "three-aught" wire.
and so on.
Quick Estimation on Resistance of AWG Wires
Below are some tricks that will help to make a quick estimation on resistance of AWG wires. Note that the error tends to grow for larger AWG numbers (thinner wires).
- The resistance of a 10 cm 40 AWG wire is approximately 0.4 ohm.
- An increase of 2 gauge numbers (e.g. from 30 AWG to 32 AWG) multipliers resistance by approximately 1.6
- An increase of 3 gauge numbers (e.g. from 30 AWG to 33 AWG) multipliers resistance by 2
- An increase of 6 gauge numbers (e.g. from 30 AWG to 36 AWG) multipliers resistance by 4
- An increase of 10 gauge numbers (e.g. from 30 AWG to 40 AWG) multipliers resistance by approximately 10
- An aluminum wire has nearly the same resistance as a copper wire that is two sizes smaller. (e.g. 30 AWG aluminum wire has the same resistance as 42 AWG copper wire)