While some view a wire gauge chart as nothing more than a basic engineering concept, we see them as a more in-depth technical topic. For this reason, we are delighted to see people taking the initiative to learn intermediate subject matters.
This article is mainly for you DIY-ers out there who want to build your own solar generator. But, it can also serve as a guide for creating more specific PV system components such as DIY energy storage units/Powerwalls or solar panels wired in series/parallel.
Simply put, a wire gauge refers to an electric wire’s thickness. The size of the wire will determine (1) how much current (expressed in Amperes) it can carry; and (2) its electrical resistance per unit length (expressed in Ohms per feet or meter). Additionally, their accompanying wire gauge charts are either expressed in AWG or SWG (depending on your preferred terminology).
While we understand that some of you may have preferences, we shall use the American Wire Gauge (AWG) format, given that it is more common than Standard Wire Gauge (SWG).
What Is The Gauge Of A Wire?
So, what do we mean when we say wire gauge? Let’s break it down into digestible chunks.
In the context of this article, the word wire in wire gauge refers to the electrical wires that you’d use in various applications such as PV systems.
The word “gauge” refers to the thickness of the wire. As you’ll see later, each gauge size has a corresponding number in the American Wire Gauge (AWG) standard.
So, for example, a smaller AWG number represents thicker wire gauges (e.g., AWG 4 is 0.2043 inches in diameter), while more significant numbers indicate thinner ones (e.g., AWG 40 is .0031 inches in diameter).
Lastly, the American Wire Gauge (AWG) chart is the standard way to determine the thickness of a conductive wire. It’s a standard developed in the United States and helps users decide the appropriate wire size for their specific project.
How To Read The Wire Gauge Chart
Being confident in reading wire gauge charts begins with knowing the relationships between each AWG size and its corresponding variables.
The essential associated variables we’ll discuss today are (1) diameter, (2) ampacity (current carrying capacity of the wire), and (3) resistance per unit length.
Arguably though, it’s essential to discuss each wire gauge’s corresponding weight per unit length, but this is used more on a grid or utility level.
Let’s dissect the wire gauge chart excerpt containing the standard AWG sizes used in a residential setup with that out of the way.
|AWG||Diameter (inches)||Resistance per 1000ft||Ampacity (amperes)|
To help you better appreciate this table, let’s convert it into a line graph (see image below) and observe the relationship between the AWG size and the other variables.
Relationship Between AWG Size And Resistance Per 1000 Ft.
We’ll look at the first relationship between AWG size and resistance per 1000 ft. As you can see in the line graph, as the AWG size increases, the resistance per 1000 ft. (red line) also increases.
Therefore, they have positive covariance, meaning both variables tend to be high or low at the same time.
However, these two variables don’t have a proportional relationship. This means the ratio of each pair of AWG and Resistance per 1000 ft. aren’t the same.
Relationship Between AWG Size, Diameter, And Ampacity
On the other hand, AWG size has a negative covariance relationship with the wire’s diameter (blue line) and ampacity (yellow line).
Not all variables have a proportional relationship with AWG. Size is also vital since you cannot assume the same ratio of each pair of variables to AWG size. This means that you must rely on a wire gauge chart to determine the best wire size for your needs.
When reading wire gauge charts, ensure you don’t mix values from a different row. Although double-checking your figures should be standard practice, many professionals often overlook this minor but fatal error.
Going back to our previous sample table, the resistance per 1000 ft. value of our size 12 AWG wire is wrong. It should be 1.588 instead of 2.003 (for size 13 AWG) ohms per 1000 ft. Trust but verify.
Wire Gauge Chart
There are many variations of wire gauge charts out there, and this table from Solaris-shop.com is our personal favorite since it strikes a balance between information and simplicity.
We love it for the following reasons:
- It has both metric and English systems
- Contains essential wire gauge information (resistance and max ampacity)
If it were up to us, we would remove the odd AWG sizes since even ones are more commonly used. This would make the information more practical, concise, and less prone to human errors.
Removing the last column is also a good idea.
Lastly, it is also important to point out that the Maximum Current Rating of the same AWG wire will vary depending on the application. For example, the table below is the AWG wire gauge chart for POWER TRANSMISSION or GRID applications. Therefore the ratings are lower or more conservative to account for more safety compared to residential applications (see the table after).
|AWG||Diameter (Inches)||Resistance (Ohms/1000ft)||Max Current (Amps)||Max Frequency (100% skin depth)|
|0000 (4/0)||0.46||0.049||302||125 Hz|
|000 (3/0)||0.4096||0.0618||239||160 Hz|
|00 (2/0)||0.3648||0.0779||190||200 Hz|
|0 (1/0)||0.3249||0.0983||150||250 Hz|
What Wire Gauge Do I Need?
We already touched on this earlier. But let’s elaborate further to help you figure out which wire gauge is best for which application.
Since we are certain that most of our readers are after a wire gauge chart for residential applications, we will use NEC Table 310.15(B)(16) (see table above) and take a conservative approach.
A conservative approach means taking the lowest rating of each AWG size. For example, the 14-gauge copper wire according to our NEC table can accommodate 15 to 25 amperes depending on the conductor temperature rating (140ºF, 167ºF, and 194ºF respectively).
To err on the side of caution, we will stick with the lowest load the 14-gauge copper wire can handle which is 15 amperes.
So which wire gauge will you most likely need?
14-gauge and 12-gauge copper wires are commonly used for outlet circuits. It would be best to use AWG 14 wires only in a branch circuit with a 15-ampere capacity or no more than a 1,500-watt demand.
On the other hand, AWG wires with sizes 6, 8, 10 are for larger appliances such as electric stoves, water heaters, AC units, heat pumps, etc.
4-gauge wires and below are more suitable for feeders depending on your load.
For service conductors, the wires or conductor should not be smaller than AWG 8 copper wire.
Bottom line: Residential wiring projects all adhere to the National Electric Code of the United States. If you are not sure about the conductor temperature rating of your wire, we recommend using conservative ampacity ratings to avoid potential problems such as overheating and fires.
Avoid Aluminum Wire
While aluminum wiring is not illegal to use in a residential setting, we highly recommend that you steer clear away from it except for specific applications.
Some examples include residential service entrance wiring and single-purpose higher amperage circuits such as 240-volt air conditioning or electric range circuits.
How Do You Determine Wire Gauge?
Knowing how to determine a wire gauge without the help of a wire gauge chart is unnecessary. In all seriousness, wire gauge charts of different formats are highly accessible in our modern age through the internet.
However, in the event that you find yourself in a pickle, here’s how a handyman (or woman) would handle it:
- Use a wire-stripping tool to remove the cable insulation.
- Determine wether your wire is solid or stranded.
- Gauging solid wires.
- Use a wire gauging tool.
- Compare the wire to another wire with a measured gauge.
- Gauging stranded wires.
- Measure the diameter of a single wire strand.
- Use the CMA formula (Diameter2 multiplied by # of strands).
- Find the CMA’s corrseponding AWG size.
Step 1: Use A Wire-Stripping Tool To Remove The Cable Insulation
The first step you need to carry out when determining a wire gauge is stripping the cable.
Maybe it’s just us, but we find wire stripping using a decent wire stripper or crimper to be very satisfying.
Step 2: Determine Whether Your Wire Is Solid Or Stranded
Once you’ve removed the insulation, determine whether your wire is solid or stranded. Then, follow the corresponding steps depending on the type you have.
Step 3.1: Gauging Solid Wires
3.1.1 Use a wire gauging tool
A wire gauging tool is around measuring device used to confirm the diameter of a wire. Using it is pretty straightforward. Just insert the wire in the gaps (not the round holes) to see the AWG size of your wire.
3.1.2 Compare The Wire To Another Wire With A Measured Gauge
You can eyeball it and compare your wire to a marked one as an alternative. You can do this if you have spare labeled cables lying in your garage. Going to your local hardware store is also an option.
However, in our opinion, this method should be considered a last resort. We recommend consulting your seller before considering this alternative.
Step 3.2: Gauging Stranded Wires
3.2.1 Measure The Diameter Of A Single Wire Strand
In the case of stranded wires, you might need to purchase another measuring tool to measure individual strand diameters (see image below) accurately.
3.2.2 Use The CMA Formula (Diameter2 Multiplied By # Of Strands)
Once you have your strand diameter, you’ll use the Circular MIL Area (CMA) formula to determine the Stranded Wire AWG.
The CMA formula can be expressed as (Wire Diameter)2 multiplied by # of wire strands (see image above).
3.2.3 Find The CMA’s Corresponding AWG Size
Once you get the CMA, look for its corresponding AWG size in this Wire Gauge Chart.
Does Wire Gauge Affect Amps?
Yes. As seen in our line chart before, AWG size has a negative covariance relationship with the wire’s diameter (blue line) and ampacity (yellow line).
This means that wires with smaller AWG sizes shall have thicker wire diameters and vice versa. Thicker wires carry more current.
To help you remember this relationship, we can compare this concept to our water pipes. The wire is your pipe, and the current is the amount of water flowing through the pipes.
Water pipes with bigger diameters can carry more water at any given time. This concept applies to the wire and ampacity too.
Bottom line: Wire gauge affects ampacity. Smaller AWG size means larger diameters and more current carrying capacity.
What Happens If I Use A Larger Gauge Than Required?
To be clear, “using a larger wire gauge” means you are oversizing your wire’s ampacity.
Going with more ampacity will not carry severe consequences. It’ll just cost more and will probably require adjustments to the wire’s physical pathways (more ampacity means thicker wires).
But there are perks to using larger gauges. Wires with larger diameters stay cooler due to low resistance. As you all know by now, the overall resistance per unit length decreases as the wire diameter increases. This means less power dissipation across your wire.
The power dissipation formula can be expressed as:
Current2 multiplied by resistance (P= I2 x R).
The power dissipated across the wire causes it to heat up, which means electric energy is lost as heat energy every second.
Lastly, using a larger gauge AWG wire offers you more allowance to draw more current should you need it in the future.
Bottom line: Using thicker wires with higher ampacity costs more and requires bigger pathways. However, they translate to lower resistance, less heat loss, and more electricity savings. Not to mention, you can accommodate more electric demand in the future without overhauling your wiring system.
Does Wire Gauge Affect Your Electricity Bill?
Yes, as seen in our line chart before, AWG size has a positive covariance relationship with resistance per unit length.
Small AWG numbers have smaller resistances and will save you more money due to less power dissipation.
The use of electricity in the home has risen sharply since the 1930s. Therefore it makes sense to regularly check the adequacy of your existing wires to accommodate current.
And while we did touch on the basic stuff on wire gauge charts, there are more factors to consider when handling electricity during home improvements.
We apologize if we made you feel anxious in some parts of this article. We didn’t put them there to scare you. Instead, we brought them up to inform you about electricity’s inherent safety risks and hazards.
That being said, this last section is included to help impart advanced knowledge and keep you safe altogether.
While we touched on the basics of AWG wires in this article, we highly encourage our readers to consult with professionals when dealing with electricity. It’s no secret that electric power poses severe hazards; hence, it shouldn’t be taken lightly.
Therefore, we suggest that you limit your DIY activities to low-power projects. Tinkering with main breaker panels, service conductors, feeders, branch circuits, and similar electrical components (see image below) needs to comply with NEC standards.