What Does AWG Mean? Understanding Solar Cable Gauge Sizes
- Vicky
- 9 hours ago
- 18 min read
You're planning a solar installation — whether it's a rooftop home system, an off-grid cabin setup, or a power system for your RV — and suddenly the wire specifications are full of numbers like 10 AWG, 6 AWG, and 4 AWG. The numbers seem to go backwards. The cables labeled with smaller numbers are thicker. Nobody explains why.
AWG is one of those abbreviations that gets used constantly in solar and electrical work, assumed to be universally understood, and almost never properly explained to the people who actually need to understand it. This guide fixes that.
By the end of this article, you will know exactly what AWG means, how the sizing system works, which cable gauge is right for your solar system, and how to avoid the wiring mistakes that compromise performance and safety in solar installations of every scale.
Key Takeaways
AWG stands for American Wire Gauge — a standardized wire sizing system used throughout North America in which a lower AWG number indicates a thicker, higher-capacity wire.
The AWG system is counterintuitive: 10 AWG wire is thicker than 12 AWG, which is thicker than 14 AWG. The numbers decrease as the wire gets larger.
The two factors that determine the correct AWG for a solar cable run are current capacity (ampacity) and voltage drop over the cable length — both must be checked, and the larger resulting wire size wins.
For most residential and off-grid solar systems, the most commonly used AWG sizes are 10 AWG (panel-to-controller runs, small systems), 8 AWG (medium system runs), 6 AWG (larger system runs and battery connections), and 4 AWG or larger for high-current battery bank connections.
In most international markets outside North America, wire is sized in mm² (square millimeters) rather than AWG. A conversion table is provided in this guide.
Always apply a safety factor of 1.25× the calculated current when sizing solar cables — solar panels can produce higher currents than their rated output under certain conditions, and the NEC requires this margin for PV source circuits.
Undersized wire is one of the most common — and most dangerous — mistakes in DIY solar installations. When in doubt, go one size larger.
What Does AWG Stand For?
The Short Answer
AWG stands for American Wire Gauge — a standardized system for specifying the diameter of electrical conductors used throughout North America. In the AWG system, the gauge number and wire diameter have an inverse relationship: the lower the AWG number, the thicker the wire and the higher its current-carrying capacity. A 4 AWG cable is significantly thicker and can carry considerably more current than a 10 AWG cable. The system applies to copper and aluminum conductors and is used across residential wiring, automotive applications, and solar power systems.
Reference Links : AWG stands for American Wire Gauge
Why AWG Matters in Solar Installations
In a solar installation, the wire connecting your panels, charge controller, inverter, and battery bank is not a detail — it is a core safety and performance component. Undersized wire creates resistive losses that reduce your system's energy output. More critically, undersized wire generates heat under load. In a direct current solar circuit, where fault currents can be sustained without the natural interruption that occurs in AC systems, that heat is a fire risk.
Every wire selection in a solar system involves AWG. The cable from your solar panels to your charge controller. The cable from your charge controller to your battery bank. The cable from your battery bank to your inverter. The grounding conductors. Each one has a correct size, and AWG is the language in which that size is specified in North American markets.
How the AWG System Works — and Why It Seems Backwards
The Counterintuitive Rule: Smaller Number = Thicker Wire
The most confusing thing about AWG for anyone encountering it for the first time is that the numbers run backwards relative to intuition. You might expect a higher number to mean a bigger, more capable wire. In AWG, it means the opposite.
The reason is historical. The AWG number originally corresponded to the number of drawing dies a wire was pulled through during manufacture. More draws through progressively smaller dies produced thinner wire — so more draws meant a higher gauge number and a thinner wire. The system was standardized in the mid-nineteenth century and has remained in use in North America ever since.
The practical rule to memorize is simple: every three AWG steps roughly doubles the cross-sectional area of the wire. So 7 AWG wire has approximately twice the cross-sectional area of 10 AWG, which has approximately twice the cross-sectional area of 13 AWG. This relationship gives you a quick mental model for comparing cable sizes without needing to look up the exact dimensions each time.
Where the AWG System Came From
AWG (originally called the Brown & Sharpe gauge, after the company that standardized it) became the dominant wire sizing system in North America through the late nineteenth and early twentieth centuries. It was adopted by the American wire manufacturing industry as a consistent standard and codified into electrical codes and standards that persist today.
The rest of the world moved toward the metric IEC system — expressing wire cross-section in square millimeters (mm²) — which is more directly intuitive: larger number always means larger wire. If you are buying cables from European or Asian manufacturers, or working on a project that specifies wire in mm², you will need to convert. The conversion table later in this guide covers the most common solar cable sizes.
AWG vs. Metric Wire Sizing (mm²) — Which System Are You Working In?
If you are in the United States or Canada, your electrical code (NEC or CEC) references AWG. Your charge controller, inverter, and solar panel documentation from North American brands will specify wire sizes in AWG. The cables sold at hardware stores and electrical supply houses will be labeled in AWG.
If you are working with European-manufactured equipment — many quality solar charge controllers, inverters, and panels originate in Europe or are designed to European standards — the documentation may specify wire in mm². If you are sourcing cables internationally, they may be labeled in mm².
The two systems are not directly interchangeable by a round number, but the common solar cable sizes have well-established equivalents. When a European solar panel datasheet specifies 4mm² cable for the panel wiring, the closest AWG equivalent is 12 AWG. When a European inverter specifies 35mm² battery cables, the closest AWG equivalent is approximately 2 AWG.
Solar Cable Gauge Sizes — The Most Common AWG Ratings
14 AWG Solar Wire
Diameter: approximately 1.63mm | Typical ampacity (copper, 60°C): 15A
14 AWG is the smallest gauge commonly used in solar installations. It is appropriate for very low-current applications — small panel strings in a residential grid-tied system where the individual branch circuit currents are low, or signal wiring for monitoring and communication. It should not be used for battery connections or high-current DC runs in any system of meaningful size.
12 AWG Solar Wire
Diameter: approximately 2.05mm | Typical ampacity (copper, 60°C): 20A
12 AWG is widely used for solar panel source circuits in residential grid-tied installations — it is the standard gauge for the wiring between individual solar panels and the combiner box in many residential arrays. For small off-grid systems with modest panel arrays and short cable runs, 12 AWG may be appropriate for panel-to-controller wiring. It is often the gauge used for pre-made MC4 extension cables.
10 AWG Solar Wire
Diameter: approximately 2.59mm | Typical ampacity (copper, 60°C): 30A
10 AWG is one of the most commonly used gauges in small-to-medium off-grid solar systems. It is appropriate for panel-to-charge-controller runs in systems producing up to approximately 20–25A of array current, and for short charge controller-to-battery runs in lower-current systems. Many entry-level MPPT charge controllers (20A–30A rated) specify 10 AWG for their battery connections.
8 AWG Solar Wire
Diameter: approximately 3.26mm | Typical ampacity (copper, 60°C): 40–50A
8 AWG is a versatile mid-range solar cable size, appropriate for charge controller-to-battery connections in 30A–40A controllers and for battery-to-inverter connections in small inverters (up to approximately 500W at 12V, or 1000W at 24V). It is also a common choice for longer panel-to-controller runs where voltage drop on a 10 AWG run would be excessive.
6 AWG Solar Wire
Diameter: approximately 4.11mm | Typical ampacity (copper, 60°C): 55–65A
6 AWG is the workhorse of medium-to-large off-grid solar systems. It is appropriate for 40A–60A charge controller connections, for battery interconnects in medium-capacity battery banks, and for battery-to-inverter runs in mid-size inverters (1000–2000W at 12V; 2000–4000W at 24V; or larger at 48V). For many serious off-grid installations, 6 AWG is the minimum gauge for battery-side DC wiring.
4 AWG Solar Wire
Diameter: approximately 5.19mm | Typical ampacity (copper, 60°C): 70–85A
4 AWG is used for higher-current battery connections, large inverter battery cables in mid-to-large systems, and for runs where a combination of high current and meaningful cable length would create unacceptable voltage drop at 6 AWG. It is a common battery interconnect size for larger lithium and AGM battery banks.
2 AWG and Larger
2 AWG diameter: approximately 6.54mm | Typical ampacity (copper, 60°C): 95–115A
For large inverters (3000W and above at 12V or 24V; 5000W+ at 48V), high-capacity battery banks, and bus bar connections in large off-grid systems, 2 AWG and larger (1 AWG, 1/0, 2/0, 3/0, 4/0) becomes necessary. The 1/0, 2/0, 3/0, and 4/0 designations (pronounced "one-aught," "two-aught," etc.) are the AWG system's way of specifying wire sizes larger than 1 AWG — each step represents a further increase in cross-sectional area.
AWG Solar Cable Size Chart
AWG Size | Diameter (mm) | Cross-Section (mm²) | Max Ampacity* | Typical Solar Application |
14 AWG | 1.63 | 2.08 | 15A | Small branch circuits, signal wiring |
12 AWG | 2.05 | 3.31 | 20A | Panel source circuits, small system runs |
10 AWG | 2.59 | 5.26 | 30A | Panel-to-controller, small off-grid |
8 AWG | 3.26 | 8.37 | 40–50A | Controller-to-battery, small inverters |
6 AWG | 4.11 | 13.3 | 55–65A | Medium system battery connections |
4 AWG | 5.19 | 21.1 | 70–85A | Large battery connections, mid-size inverters |
2 AWG | 6.54 | 33.6 | 95–115A | Large inverter cables, bus bars |
1/0 AWG | 8.25 | 53.5 | 125–150A | Very large inverters, main battery cables |
2/0 AWG | 9.27 | 67.4 | 145–175A | High-capacity battery banks |
4/0 AWG | 11.68 | 107 | 195–230A | Large system main interconnects |
Ampacity varies with insulation temperature rating, installation method, and ambient temperature. Values shown are approximate for copper conductors with 75°C insulation in free air. Always verify against NEC Table 310.12 or your applicable electrical code for your specific installation conditions.
AWG to mm² Conversion Chart
AWG | Approximate mm² Equivalent | Nearest Standard mm² Cable |
14 AWG | 2.08 mm² | 2.5 mm² |
12 AWG | 3.31 mm² | 4 mm² |
10 AWG | 5.26 mm² | 6 mm² |
8 AWG | 8.37 mm² | 10 mm² |
6 AWG | 13.3 mm² | 16 mm² |
4 AWG | 21.1 mm² | 25 mm² |
2 AWG | 33.6 mm² | 35 mm² |
1/0 AWG | 53.5 mm² | 50 mm² |
2/0 AWG | 67.4 mm² | 70 mm² |
4/0 AWG | 107 mm² | 120 mm² |
Note: AWG and metric (mm²) sizes do not correspond exactly. When substituting metric cable for an AWG specification, always select the metric size that meets or exceeds the AWG conductor's cross-sectional area — never substitute with a smaller metric equivalent.
What Determines the Right AWG for Your Solar System?
Two independent calculations must be performed when sizing any solar cable run. The wire must be large enough to carry the current safely (ampacity check) and large enough to keep voltage drop within acceptable limits over the cable length (voltage drop check). Both calculations must pass — and when they give different results, the larger wire size wins.
Factor 1 — Current (Amperage)
The first question is: how much current will this cable carry? In a solar installation, the answer depends on which part of the circuit you are sizing:
Panel source circuit (panel to combiner box or charge controller): The maximum current is the panel's short-circuit current (Isc) multiplied by the number of panels in parallel. Apply a 1.25× safety factor per NEC Article 690 requirements for PV source circuits.
Charge controller to battery: The maximum current is the charge controller's rated output current. This is stated directly on the controller specification — a 40A MPPT controller outputs a maximum of 40A to the battery.
Battery to inverter: The maximum current is the inverter's rated input current at maximum load. Calculate as: Inverter rated watt output ÷ Battery bank voltage = Maximum DC input current. A 2000W inverter on a 24V battery bank draws a maximum of approximately 2000 ÷ 24 = 83A DC at full load. Size the battery cable for this current.
Factor 2 — Cable Run Length (Voltage Drop)
Resistance increases with cable length. A longer cable run at the same AWG carries more resistance and therefore causes more voltage drop between the source and the load. In a 12V system especially, voltage drop is a serious concern — a 0.5V drop on a 12V system represents over 4% of the total system voltage, which translates directly into reduced charging performance and power delivery.
The practical guideline: Size your cables to keep total voltage drop (positive and negative conductors combined) to 3% or less of the system voltage for power circuits. For critical battery charging circuits, 1–2% is a better target.
The calculation:
Voltage drop (V) = 2 × Cable length (m) × Current (A) × Resistance per meter (Ω/m)
Where resistance per meter is determined by the AWG size and conductor material (copper vs. aluminum). Reference tables for conductor resistance per unit length are available in NEC Chapter 9 tables and from cable manufacturers.
Factor 3 — Temperature and Installation Environment
Wire ampacity ratings assume a standard ambient temperature (typically 30°C for NEC table values) and a specific installation method (free air vs. conduit, number of bundled cables). In solar installations, cables often run in conduit on rooftops where temperatures can significantly exceed 30°C, or are bundled together in cable management systems.
Both conditions reduce effective ampacity. The NEC provides correction factors for elevated ambient temperatures and conduit fill. In practice, this means the AWG size that meets your ampacity requirement in free air at 30°C ambient may need to be increased by one or two sizes for a rooftop conduit installation in a hot climate.
Factor 4 — NEC Ampacity Requirements and Safety Factor
NEC Article 690 (Solar Photovoltaic Systems) requires that conductors in PV source and output circuits be sized for 125% of the maximum current — the 1.25× safety factor applied to account for the fact that solar panels can produce higher currents than their rated Isc under certain high-irradiance conditions.
In practice: take your calculated maximum current, multiply by 1.25, and then select an AWG size whose ampacity equals or exceeds this figure. Never size to the exact calculated current without the safety margin — it is both a code violation and a genuine safety risk.
How to Size Solar Cables — A Practical Step-by-Step Method
Step 1 — Calculate Your System Current
Identify the circuit you are sizing and calculate the maximum current it will carry:
Panel source circuit: Isc (per panel) × number of parallel strings × 1.25 (NEC safety factor)
Controller to battery: Charge controller rated output current
Battery to inverter: Inverter rated watts ÷ Battery voltage
Example: You have a 24V system with a 60A MPPT charge controller and a 2000W inverter.
Controller-to-battery circuit current: 60A × 1.25 = 75A (apply safety factor to charge current)
Battery-to-inverter circuit current: 2000W ÷ 24V = 83A (full load inverter draw)
Step 2 — Determine Your Cable Run Length
Measure the actual cable run from source to load — and remember to count both the positive and negative conductors. A charge controller 3 meters from the battery bank requires 3m of positive cable and 3m of negative cable — a total circuit length of 6m for voltage drop calculation purposes.
Step 3 — Apply the Voltage Drop Limit
Using your circuit length and target current, calculate the minimum conductor cross-section required to keep voltage drop within 3% (or your target limit) of system voltage.
3% of 24V = 0.72V maximum allowable drop
Using the voltage drop formula and copper conductor resistance values, determine the minimum AWG that keeps the drop within this limit at your cable run length. Voltage drop tables and online calculators are widely available for this calculation — use one specific to your system voltage and cable length.
Step 4 — Check NEC Ampacity and Apply Safety Factor
Look up the NEC ampacity for the AWG sizes under consideration — Table 310.12 for service entrance conductors, or the appropriate table for your installation method. Apply temperature correction factors if your installation environment exceeds 30°C ambient. Confirm that the selected AWG's derated ampacity equals or exceeds your calculated current including the 1.25× safety factor.
Step 5 — Select the Larger of the Two Results
Your ampacity check and your voltage drop check may point to different AWG sizes. Always select the larger wire (lower AWG number) that satisfies both requirements. Never compromise on either criterion — a wire that passes the ampacity check but fails the voltage drop check will deliver less energy than your system is capable of producing.
AWG Cable Sizing for Common Solar System Configurations
Small Off-Grid System (200–400W, 12V)
A typical small 12V off-grid system: two 100W panels in parallel, 20A MPPT charge controller, 200Ah battery bank, 300W inverter.
Panel to charge controller (short run, under 3m): 10 AWG
Charge controller to battery (under 1m): 10 AWG
Battery to inverter: 8 AWG (300W ÷ 12V = 25A; 25 × 1.25 = 31A — 8 AWG adequate for short runs)
Battery interconnects: 4 AWG minimum for any parallel battery connections
Medium Off-Grid System (400–1000W, 24V)
A 24V system: four 200W panels (2S2P), 40A MPPT charge controller, 400Ah battery bank, 1000W inverter.
Panel to charge controller (under 5m): 10 AWG
Charge controller to battery: 8 AWG (40A output × 1.25 = 50A — 8 AWG adequate)
Battery to inverter: 6 AWG (1000W ÷ 24V = 42A; 42A × 1.25 = 52A — 6 AWG adequate for short runs)
Battery interconnects: 4–6 AWG
Large Off-Grid or Hybrid System (1000W+, 48V)
A 48V system: eight 300W panels (4S2P), 60A MPPT charge controller, 48V 200Ah LiFePO4 battery bank, 3000W inverter.
Panel to charge controller: 10 AWG (series string current is relatively low)
Charge controller to battery: 6 AWG (60A × 1.25 = 75A — verify with voltage drop calculation for your run length)
Battery to inverter: 4 AWG (3000W ÷ 48V = 62.5A; 62.5A × 1.25 = 78A — 4 AWG for short runs; 2 AWG for runs over 2m)
Battery interconnects: 2 AWG or larger
RV and Van Solar Systems
RV systems are almost always 12V and typically compact — short cable runs are the norm. However, the lower system voltage means higher currents for the same wattage, making proper cable sizing critical.
For a 400W RV system with a 30A charge controller and 1000W inverter on 12V:
Panel to controller: 10 AWG (keep runs short — route panels as close to controller as practical)
Controller to battery: 8–10 AWG
Battery to inverter: 4 AWG (1000W ÷ 12V = 83A peak; this is a high-current circuit requiring adequate wire)
In RV applications especially, voltage drop is critical — keep DC cable runs as short as physically possible and size generously
Grid-Tied Residential Systems
In grid-tied systems, the cable sizing from panels to inverter is governed by the string current (typically 8–12A per string for most residential panels) and the string run length. Most residential grid-tied string cable runs use 12 AWG or 10 AWG PV wire from the panel array to the inverter. The inverter's AC output wiring follows standard NEC residential wiring sizing rules.
Solar Cable Types — Does AWG Apply to All of Them?
PV Wire (USE-2 / PV Wire)
PV Wire is the standard cable type for solar panel wiring in the United States — specifically designed for outdoor, UV-exposed, direct-burial-capable solar applications. It carries a 90°C wet/dry rating and is listed for use in solar PV systems per NEC Article 690. AWG applies directly — PV wire is sold in AWG sizes from 14 AWG through 2 AWG and larger. This is the correct cable type for the exposed wiring between solar panels and from panels to rooftop combiner boxes.
THHN / THWN Building Wire
Standard building wire (THHN/THWN) is frequently used for solar system wiring inside conduit — from rooftop junction boxes to the inverter location, and for AC wiring on the output side of inverters. AWG applies directly. Note that THHN/THWN is not rated for direct sun exposure without conduit protection — it should not be used for exposed outdoor solar panel wiring.
Battery Interconnect Cables
Battery interconnect cables — the short, heavy cables connecting battery terminals to each other and to the charge controller and inverter — are typically specified in AWG (in North America) or mm² (elsewhere). At the sizes required for high-current battery connections (4 AWG, 2 AWG, 1/0 AWG, 2/0 AWG), these cables are typically sold as pre-made assemblies with lugs crimped at each end, or as bulk cable sold by the foot.
MC4 Connector Pre-Made Cables
MC4 connector cables — the standardized plug-and-socket connection system used between solar panels — are sold in pre-made lengths and are almost always 12 AWG (approximately 4mm² in metric) for residential panel-to-panel connections. Some higher-current commercial applications use 10 AWG MC4 cables. The AWG rating of your MC4 cables must match the current capacity of your panel string — verify this against your panel's Isc specification.
Common AWG Wiring Mistakes in Solar Installations
Using undersized wire to save money. Wire is one of the least expensive components in a solar installation relative to its importance. The cost difference between 10 AWG and 8 AWG for a 5-meter battery cable run is trivial. The cost of a house fire caused by overheated undersized wiring is not. Always size up if you are near the boundary between two AWG sizes.
Ignoring voltage drop on 12V systems. The lower your system voltage, the more current flows for the same wattage, and the more significant voltage drop becomes. A 12V system with long panel-to-controller runs and undersized wire can lose a meaningful percentage of its daily energy harvest to resistive losses. Size 12V system cables generously and keep runs short.
Confusing panel-rated current with actual circuit current. A 10A rated solar panel has an Isc of approximately 10A. Two of those panels wired in parallel produce a source circuit current of 20A. Apply the 1.25× NEC safety factor and the wire must handle 25A minimum. Forgetting to account for parallel panel currents and safety factors is a common and potentially dangerous error.
Using automotive wire for solar installations. Automotive wire (often called GPT or primary wire) is not rated for solar PV applications. It lacks the UV resistance, temperature rating, and listing required by NEC Article 690. Always use properly rated PV wire or approved building wire in conduit for solar installations.
Mixing AWG and mm² without proper conversion. If your charge controller specifies 16mm² battery cables and you substitute 6 AWG because it seems close, you are using a cable with approximately 13.3mm² cross-section — meaningfully smaller than specified. Always convert properly and select the AWG size that meets or exceeds the metric specification.
Not accounting for temperature derating in hot environments. Rooftop conduit installations in hot climates can reach ambient temperatures of 50°C or more. At these temperatures, a wire's effective ampacity is significantly lower than its rated value at 30°C. Failure to apply temperature correction factors results in wiring that is technically undersized for its installation environment even if it appears adequate on paper.
Frequently Asked Questions
What does AWG stand for, and what does it mean for solar cables?
AWG stands for American Wire Gauge — a standardized North American system for specifying the diameter of electrical conductors. In the AWG system, a lower number means a thicker wire with higher current-carrying capacity. For solar cables, AWG tells you the cable's size and therefore how much current it can safely carry and how much resistance it will add to your circuit over a given length.
Why do AWG numbers get smaller as the wire gets bigger?
The AWG number historically corresponded to the number of drawing steps in the wire manufacturing process — more steps produced thinner wire with a higher gauge number. The system was established in the nineteenth century and standardized before metric wire sizing became the global norm. The practical rule: every three AWG steps (e.g., from 10 AWG to 7 AWG) approximately doubles the wire's cross-sectional area.
What AWG wire do I need for my solar panels?
The correct AWG depends on your panel array's short-circuit current (Isc), the number of panels wired in parallel, the cable run length, and your system voltage. As a general starting point: for most residential panel source circuits, 12 AWG or 10 AWG PV wire is appropriate for short-to-medium runs. Always calculate the actual current (Isc × parallel strings × 1.25) and check voltage drop over your specific cable length to confirm the correct size.
What is the difference between AWG and mm² wire sizing?
AWG is the American Wire Gauge system used in North America; mm² (square millimeters) is the metric system used in most of the rest of the world. Both describe wire conductor cross-section, but the numbers do not correspond directly. Common conversion equivalents for solar cables: 10 AWG ≈ 6mm², 8 AWG ≈ 10mm², 6 AWG ≈ 16mm², 4 AWG ≈ 25mm². When substituting metric for AWG, always choose the metric size that meets or exceeds the AWG cable's cross-sectional area.
Can I use a smaller AWG wire if my cable run is very short?
Partially. A shorter cable run reduces voltage drop, which may allow a smaller wire to meet the voltage drop requirement. However, the ampacity requirement — the wire's ability to carry the current without overheating — does not change with cable length. A wire must always be large enough to carry the circuit's maximum current safely, regardless of how short the run is. The ampacity floor cannot be reduced by shortening the cable.
What AWG wire is used for the battery-to-inverter connection?
The battery-to-inverter cable carries the highest DC current in most solar systems and must be sized accordingly. Calculate: Inverter rated watts ÷ Battery voltage = Maximum DC current. For a 1000W inverter on a 12V system, that is approximately 83A — requiring 4 AWG or 2 AWG depending on run length. For a 3000W inverter on a 48V system, approximately 62.5A — requiring 4 AWG for short runs. These are high-current, high-consequence connections — never undersize them.
Conclusion
AWG is not a complicated system once you understand the key principle: the number goes down as the wire gets bigger. From there, the rest follows logically — and the practical application to solar cable sizing is a matter of working through two straightforward calculations: current capacity and voltage drop.
What makes AWG genuinely important in solar installations is not the abbreviation itself but what it represents — the discipline of matching the wire to the job. Every cable in a solar system carries a specific current under specific conditions over a specific distance. There is a correct wire size for each of those conditions, and there is a range of incorrect sizes — some too small to be safe, some merely oversized and wasteful.
The guidance in this article gives you the tools to find the correct size every time. Use the charts as a reference, follow the step-by-step sizing method for each circuit, apply the NEC safety factor without exception, and when you are on the boundary between two sizes, choose the larger one. The extra few dollars spent on the next AWG size up is the cheapest insurance in solar system design.
Wire correctly, and your system will perform safely and efficiently for decades. That outcome begins with understanding what AWG means — and applying that understanding every time you make a cable selection.
