Copper vs. Aluminum AWG Sizing: How to Upsize Aluminum Cables for 1500V PV Systems Without Losing Ampacity
- Vicky
- Jul 23
- 13 min read
Introduction
If you have ever looked closely at a massive solar farm stretching across hundreds of acres, you might wonder how all that clean energy travels from thousands of solar panels back to the power grid. Behind the scenes, miles of heavy-duty electrical cables act as the energy highway of the installation. For decades, copper has been the king of those highways because of its exceptional ability to carry electricity. However, as large-scale solar projects upgrade to powerful 1500V DC (volts of direct current) systems, engineers and project planners are making a major shift: replacing traditional copper cables with lightweight, cost-effective aluminum.
At first glance, making the switch seems like a simple way to save money, but electricity behaves according to strict physical rules. Aluminum is naturally less conductive than copper—carrying roughly 61% of the electrical current that copper can handle through the exact same wire size. If you simply swapped a copper cable for an aluminum one of the same thickness, the wire would overheat, waste valuable solar energy as heat, and potentially burn out under heavy sunlight.
So how do solar farms reap the massive cost savings of aluminum without risking electrical fires or energy loss? The secret lies in a concept called "upsizing"—selecting a larger American Wire Gauge (AWG) size for the aluminum wire. In this article, we will break down the basic physics of copper versus aluminum, explain how wire gauge upsizing works in plain language, and explore how modern engineering makes aluminum a safe, smart, and efficient choice for giant 1500V solar power systems.
The CAPEX Incentive: Why 1500V PV Systems Are Shifting to Aluminum Conductors
Managing Raw Material Volatility in Utility-Scale Solar Projects
For a utility-scale solar project, cable procurement is not a minor purchasing decision. A large PV installation may require miles of DC cabling to connect solar modules, combiner boxes, inverter stations, and other parts of the electrical infrastructure.
When the total cable requirement reaches this scale, the conductor material becomes a significant part of the project's capital expenditure. A change in the price of the raw material can therefore have a direct effect on the overall cable budget.
Copper has traditionally been the preferred conductor because of its excellent electrical conductivity and established use across electrical infrastructure. However, copper also has a high material value. For a project requiring extensive cable runs, the cost of the conductor itself can become a major consideration during procurement.
Aluminum offers a different economic proposition. Although it has lower electrical conductivity than copper, aluminum is generally less expensive as a raw material and significantly less dense. This creates the possibility of reducing cable material costs while also simplifying transportation and field handling.
The basic comparison looks like this:
Factor | Copper Conductor | Aluminum Conductor |
Electrical conductivity | Higher | Lower |
Relative conductivity | Reference value | Approximately 61% of copper |
Material density | Higher | Much lower |
Cable weight | Heavier | Significantly lighter |
Conductor size for comparable electrical performance | Generally smaller | Generally larger |
Main advantage in large PV projects | Compact conductor size | Lower weight and material-cost potential |
The important point is that aluminum is not a direct, one-to-one replacement for copper.
An aluminum conductor may need a larger cross-sectional area to provide comparable electrical performance. Even so, the lower density and lower material cost of aluminum can make it economically attractive for large-scale solar projects, particularly when the total quantity of cable is substantial.
In other words, the economic advantage does not come from using the same amount of aluminum as copper. It comes from using a properly upsized aluminum conductor while still benefiting from the material's lower weight and cost characteristics.
The Engineering Trade-Off: Lower Conductivity vs. Weight Savings
The decision to use aluminum is ultimately an engineering trade-off.
Copper has higher electrical conductivity. For a conductor of the same length and cross-sectional area, copper generally has lower electrical resistance than aluminum. This allows copper to carry a required current through a relatively compact conductor.
Aluminum has lower conductivity, so a larger conductor is often required to achieve comparable electrical performance.
However, the conductor's physical size is only one part of the weight calculation.
Aluminum has a much lower density than copper. As a result, an appropriately upsized aluminum conductor can still be substantially lighter than a copper conductor designed for comparable electrical performance.
This distinction is important when evaluating large solar installations.
A larger aluminum conductor does not automatically mean a heavier cable system.
The engineering comparison is more accurately expressed by looking at the relationship between conductivity, conductor size, and material density. Copper's higher conductivity allows engineers to use a smaller conductor to achieve the required electrical performance. Aluminum, with lower conductivity, generally requires a larger conductor to provide comparable performance. However, because aluminum has a much lower density than copper, the resulting conductor can still offer a significant reduction in overall cable weight.
This weight advantage can have practical consequences throughout the project. Lighter cable reels may be easier to transport, handle, and position during installation. For extensive field installations, lower cable weight can also reduce the physical effort required during cable routing and trenching operations.
However, these benefits do not eliminate the need for correct electrical sizing. The larger aluminum conductor must still be selected according to the required ampacity, voltage drop, temperature limits, installation conditions, and applicable electrical requirements.
This is where AWG upsizing becomes important.
The Upsizing Logic: How to Match Copper Ampacity with Aluminum AWG
The General Rule of Thumb for Upsizing AWG Gauges
The first thing to understand about aluminum cable upsizing is the way the AWG system works.
AWG stands for American Wire Gauge, a standardized system used to describe conductor sizes. Unlike many numbering systems, AWG operates in reverse:
For example:
AWG Size | Relative Conductor Size |
10 AWG | Smaller |
8 AWG | Larger |
6 AWG | Larger again |
4 AWG | Larger again |
Therefore, moving from 10 AWG to 8 AWG is an increase in conductor size, even though the numerical value becomes smaller.
This is one of the most common sources of confusion when discussing cable sizing.
When an engineer says that an aluminum conductor needs to be "upsized," the practical meaning is usually to select a larger conductor with a lower AWG number or a larger metric cross-sectional area.
Because aluminum has lower electrical conductivity than copper, a common practical starting point is to consider increasing the aluminum conductor by approximately one to two AWG sizes compared with a copper reference conductor.
For example, an engineer evaluating an aluminum alternative to a copper conductor may begin by comparing a larger aluminum AWG size rather than selecting the same AWG designation.
However, this should only be treated as a rule of thumb.
A 1-to-2 AWG step-up is not a universal copper-to-aluminum conversion formula. The final selection must still be verified against the actual ampacity requirement, voltage drop, installation conditions, conductor temperature rating, and applicable electrical code.
The correct process is therefore to begin with the copper conductor as a reference point and then identify a preliminary aluminum conductor size that can provide comparable electrical performance. This initial selection must then be verified against the required ampacity, followed by a voltage-drop check to confirm that electrical losses remain within acceptable limits. Only after these factors have been evaluated should the final aluminum cable size be selected.
NEC Ampacity and the Copper-to-Aluminum Comparison
AWG size alone does not determine whether a cable is suitable for a PV installation.
The conductor must also be capable of carrying the required current under the applicable installation conditions. This is where ampacity becomes essential.
Ampacity is the maximum current that a conductor can safely carry under specified conditions without exceeding its allowable temperature limit.
Because copper and aluminum have different electrical properties, conductors of the same AWG size do not automatically have identical ampacity characteristics.
A simplified comparison can be organized as follows:
Conductor Size | Copper | Aluminum | General Sizing Implication |
10 AWG | Higher conductivity | Lower conductivity | Aluminum may require a larger conductor |
8 AWG | Higher conductivity | Lower conductivity | Compare actual ampacity values |
6 AWG | Higher conductivity | Lower conductivity | Larger aluminum size may be required |
4 AWG | Higher conductivity | Lower conductivity | Verify ampacity and voltage drop |
2 AWG | Higher conductivity | Lower conductivity | Confirm actual installation requirements |
The table illustrates the sizing principle, but it should not be interpreted as a direct replacement chart.
Actual ampacity values depend on the applicable electrical code, conductor temperature rating, installation method, ambient temperature, and other conditions.
For projects designed according to the National Electrical Code, engineers must consult the applicable ampacity requirements and temperature limitations rather than relying solely on the AWG number or a simple conductivity ratio.
The practical question is therefore not: “What aluminum AWG has the same number as the copper cable?” The better question is: “Which aluminum conductor can safely carry the required current under the actual project conditions?”
That distinction is at the heart of proper aluminum cable upsizing.
The 75°C vs. 90°C Temperature Rating Trap
One of the most important details in conductor sizing is the difference between the cable's temperature rating and the temperature rating of the equipment terminals.
A PV cable may be designed with insulation capable of operating at a high conductor temperature. However, this does not automatically mean that the highest available ampacity column can be used for the complete electrical circuit.
For example, a cable may have a 90°C insulation temperature rating, while the terminal on the connected equipment may only be rated for 75°C under the applicable conditions.
The practical logic is: 90°C-Rated Cable Insulation↓75°C-Rated Equipment Terminal↓75°C Limitation May Govern the Final Ampacity
This is a critical distinction.
The temperature rating of the cable insulation and the allowable ampacity of the complete electrical connection are not necessarily the same thing.
The final conductor sizing decision must account for the lowest applicable temperature limitation in the electrical path. A 90°C-rated cable does not automatically allow engineers to use the 90°C ampacity value if the connected equipment or terminal is limited to a lower temperature rating.
This is why ampacity calculations must consider the complete system rather than the cable specification alone.
For aluminum conductors, this check is particularly important because the purpose of upsizing is to ensure that the conductor can safely carry the required current. Choosing a larger conductor based on an incorrect temperature assumption does not replace the need to verify the actual equipment limitations.
Before finalizing the aluminum AWG size, engineers should therefore confirm:
The cable conductor temperature rating
The insulation temperature rating
The equipment terminal rating
The applicable ampacity requirements
The actual installation conditions
Only after these factors have been considered can the upsized aluminum conductor be evaluated properly.
Critical Engineering Considerations When Transitioning to Aluminum AWG
Selecting the right aluminum conductor size is only one part of the design process. Once the preliminary AWG size has been determined, the cable still needs to be evaluated in the context of the actual PV installation. For a 1500V DC system, that means looking beyond ampacity and considering voltage drop, connection reliability, cable routing, and the practical requirements of installation.
Voltage Drop Mitigation for Long-Distance 1500V DC Trunk Lines
Ampacity and voltage drop are often discussed together, but they address different aspects of cable performance. Ampacity determines whether a conductor can carry the required current without exceeding its allowable temperature. Voltage drop, on the other hand, describes how much voltage is lost as current travels through the cable.
The basic relationship is:
Voltage Drop = Current × Resistance
Resistance depends on several factors, including conductor material, cable length, temperature, and cross-sectional area. Increasing the conductor cross-sectional area reduces resistance, which is why upsizing is often an important part of designing long-distance cable runs.
This matters particularly in utility-scale solar projects. A ground-mounted PV plant may cover a large area, and the distance between the array and the inverter or other collection equipment can be considerable. Even when a cable has sufficient ampacity, its resistance over a long run can still result in unacceptable voltage drop and additional power losses.
Increasing the size of an aluminum conductor provides more conductive material and helps reduce its resistance. This can improve voltage performance over the cable run and reduce the energy lost as heat.
The 1500V architecture used in many large PV systems can help reduce current for a given power output, which in turn can reduce resistive losses. However, higher system voltage does not eliminate the need to consider cable resistance. The length of the cable run and the selected conductor size still have a direct influence on voltage drop.
For this reason, a cable that passes the ampacity calculation is not necessarily the final answer. Engineers must also determine whether the voltage drop remains within the project's design limit. In long-distance applications, the required conductor size may therefore be influenced by voltage-drop requirements even when the cable already has sufficient current-carrying capacity.
Termination Security: Preventing Galvanic Corrosion and Thermal Creep
The conductor is only as reliable as the connection made at either end of it.
This becomes especially important when aluminum cable is connected to equipment that uses copper terminals or connection points. Aluminum and copper have different electrochemical properties, and their different thermal expansion characteristics can also affect long-term connection stability.
The first concern is galvanic corrosion. When dissimilar metals are connected in the presence of moisture, electrochemical reactions can occur at the interface. In an outdoor solar installation, humidity, condensation, and rain can all create conditions that make this issue relevant.
Over time, corrosion at the connection can increase contact resistance. As resistance rises, the connection may generate more heat under load, creating a localized hotspot. This is why the termination cannot be treated as a minor detail after the conductor size has been selected.
Temperature cycling creates another long-term challenge. Solar cables and electrical equipment are exposed to repeated heating and cooling as the system moves through daily operating cycles. The conductor expands as its temperature rises and contracts again as it cools. Because aluminum and copper do not respond to temperature changes in exactly the same way, a connection between the two materials must be designed to accommodate this movement.
If the mechanical pressure at the connection gradually changes, contact resistance may increase. In a system expected to operate for decades, even a small deterioration at a termination can become a significant reliability concern.
For this reason, aluminum conductors should be connected using components specifically designed and approved for the materials involved. Bimetallic lugs are commonly used where an aluminum conductor must transition to a copper connection point. The aluminum side is designed to accommodate the aluminum conductor, while the copper side provides a suitable interface with copper equipment terminals.
Depending on the specific connector and installation requirements, aluminum-rated terminals, bimetallic lugs, and anti-oxidant compounds may be specified. The correct choice should always follow the connector manufacturer's instructions and the applicable electrical requirements.
The important principle is simple: an aluminum cable should not be evaluated separately from its termination system. A conductor may have the required ampacity and voltage rating, but an unsuitable connection can still become the weakest point in the installation.
4.3 Conduit Sizing and Mechanical Handling Requirements
Upsizing an aluminum conductor also changes the physical dimensions of the cable. This is easy to overlook when the initial sizing discussion focuses mainly on electrical performance.
A larger conductor may result in a larger overall cable diameter. If the original conduit system was designed around a smaller copper cable, the selected aluminum replacement may affect conduit fill and routing requirements.
This should be checked before installation begins. The engineering team may need to review the cable's outside diameter, minimum bending radius, conduit fill, and pulling conditions. Underground installations require particular attention because the available conduit space is often fixed before the cable is delivered to the site.
The change in conductor size can also affect cable handling. A larger aluminum conductor may have a greater overall diameter than the original copper conductor, even though the aluminum cable remains significantly lighter because of aluminum's lower density.
That lower weight can be a practical advantage during large-scale installation. Cable reels are easier to transport, and long cable runs can be handled with less lifting effort. At the same time, the larger cable profile may require more attention during pulling and bending.
For this reason, the electrical sizing process and the mechanical installation plan should be considered together. Once the final aluminum conductor size has been selected, the cable's actual outside diameter and bending requirements should be checked against the planned conduit and routing system.
Frequently Asked Questions
Q: Can I replace a copper PV cable with an aluminum cable of the same AWG size?
A: Not automatically. Copper and aluminum have different electrical conductivity, so conductors with the same AWG designation do not necessarily provide the same electrical performance. The aluminum replacement should be evaluated according to the required ampacity, voltage drop, installation conditions, and applicable temperature limitations.
Q: How many AWG sizes should I upsize when replacing copper with aluminum?
A: A one- to two-AWG-size increase can be used as a practical starting point when comparing aluminum with copper. However, it should not be treated as a universal conversion rule. The final conductor size must be verified using the actual project requirements.
Q: Does a 90°C-rated PV cable always allow the use of the 90°C ampacity value?
A: No. The cable's insulation temperature rating is only one part of the calculation. The rating of the connected equipment terminals and other applicable limitations must also be considered. If a component in the electrical path is limited to 75°C, that limitation may affect the final ampacity calculation.
Q: Why can a larger aluminum conductor help reduce voltage drop?
A: A larger conductor has a greater cross-sectional area and generally lower electrical resistance. This can reduce voltage drop and resistive losses, particularly over the long cable runs commonly found in large PV installations.
Q: Can aluminum conductors be connected directly to copper terminals?
A: The connection must be suitable for the materials involved and comply with the requirements of the equipment and connector manufacturer. Depending on the application, an aluminum-rated terminal or bimetallic transition component may be required.
Q: Does upsizing an aluminum cable affect conduit sizing?
A: It can. A larger conductor may increase the overall cable diameter and affect conduit fill, bending radius, and cable-pulling requirements. These mechanical considerations should be reviewed after the final cable size has been selected.
Conclusion
Aluminum can be an attractive conductor material for large 1500V DC photovoltaic systems, but its advantages depend on proper engineering. The lower conductivity of aluminum means that a direct same-size replacement for copper is not always appropriate. In many applications, a larger conductor is required to achieve the necessary ampacity and control resistance.
The correct approach is to begin with the electrical requirements of the project and then evaluate a suitable aluminum conductor based on actual ampacity, voltage drop, temperature limitations, and installation conditions. A simple AWG conversion rule can provide a starting point, but it cannot replace the final engineering verification.
The transition also requires attention to the parts of the system that are easy to overlook. Aluminum conductors need compatible termination systems, particularly where they connect to copper equipment. Long-term exposure to moisture and repeated temperature cycling makes connection design an important part of overall cable reliability. The larger physical size of an upsized conductor must also be considered when designing conduits and cable routes.
For EPC contractors, project developers, and procurement teams, the most practical way to evaluate an aluminum PV cable is to review the complete application rather than focusing on conductor material alone. The cable size, ampacity, voltage rating, installation method, termination system, and mechanical dimensions all need to work together.
If you are evaluating aluminum PV cables for a 1500V DC solar project, contact the FRCABLE engineering team to request technical datasheets, product samples, or project-specific sizing support.
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