Before beginning the cable sizing process in PVcase, it’s essential to understand the core parameters that affect the calculation. Properly defining these inputs from the start helps calculate cable sizing, ensure compliance with standards, and optimize costs. Understanding these settings also minimizes the need for revisions later and leads to a more efficient workflow.

The parameters you’d need to enter depend on the cable type and electrical standard you select for your project. This guide provides an overview of key parameters, their descriptions, their importance, and how to determine them. Use it as a starting point before beginning work on cabling sizing at the PVcase Ground Mount.

Cable types

Before you begin the cable sizing workflow, you’d need to specify the cable type. These are your options depending on the system type you choose for your electrical system: 

• DC String Cabling: connects individual solar panels together in series (forming a "string") and routes that combined high-voltage DC power from the array to a combiner box or directly to the inverter.
• DC Main Cabling: serves as the central backbone of the DC side, carrying accumulated high-current electricity from the combiner boxes over a longer distance to the central inverter.
• AC Cabling: carries the converted electricity from the inverter, transmitting alternating current (AC) power to the project transformer.

How they differ

The primary difference lies in the type of current they carry and their position in the system circuit. DC String and DC Main cables both handle raw direct current generated by the solar panels, with string cables managing lower-current branches and main cables managing bulk power transmission. AC cabling only comes into play after the inverter, handling the synchronized alternating current ready for commercial or utility grid use.

Power and Cable Parameters

Electrical standard

The regional electrical standard, which serves as the basis for all sizing calculations, can be either IEC (International Electrotechnical Commission) or NEC (National Electrical Code).

Why it matters

IEC and NEC differ in their base calculation temperatures, resistivity reference values, and installation method classifications. Selecting the wrong standard will produce non-compliant results. IEC is the default for most global projects; NEC applies to projects in the United States. Other countries often adopt one of these two frameworks, so the appropriate choice depends on the governing standard for the project location.

Conductor material

The metal used for the cable conductors is either copper (Cu) or aluminum (Al).

Why it matters

The two materials have different electrical resistivities: Copper at 23.7 Ω·mm²/km and Aluminum at 37.6 Ω·mm²/km. Aluminum requires a larger cross-section to carry the same current as copper at equivalent losses, but is significantly less expensive and lighter per meter. Choosing aluminum also offers a practical advantage during construction: its lower scrap value makes it less likely to be targeted for material displacement or unauthorized removal on site.

Typical use

Copper is the standard choice for DC string cabling. It is more workable during installation, and the smaller cross-sections involved (4–10 mm²) do not yield sufficient material cost savings with aluminum to justify switching. For larger-section cables — DC main cabling and AC collection cabling — aluminum is the industry standard because the cost and weight savings become substantial at higher cross-sections.

Insulation type

The polymer material surrounding the conductor, which determines the cable's maximum continuous operating temperature.

Options:

• XLPE (Cross-Linked Polyethylene): Maximum conductor temperature of 90°C.
• PVC (Polyvinyl Chloride): Maximum conductor temperature of 70°C.

Why it matters

The insulation temperature limit directly affects the cable's rated ampacity. A higher temperature limit means the cable can carry more current before the insulation degrades. XLPE is the current industry standard. PVC is a legacy material that is no longer commonly specified, as its 70°C limit creates thermal constraints in outdoor and buried applications. XLPE is recommended for all new projects.

Maximum voltage drop (%)

The upper threshold for voltage loss across a cable segment, expressed as a percentage of the nominal voltage.

Why it matters

Voltage drop represents a permanent energy yield loss. Each percentage point of voltage drop corresponds to a proportional reduction in the power delivered to the inverter or grid connection point. The maximum acceptable percentage is a project design target, typically defined by the design standard, utility interconnection requirements, or internal engineering criteria.

Typical values: 1–2% for most utility-scale DC cabling. A tighter threshold (e.g., 1%) increases the minimum required cable cross-section and raises material cost but reduces energy losses. The correct value depends on the specific project economics.

Cable size options

The set of standard cable cross-sections (in mm²) that the sizing algorithm is allowed to select from.

Options: 

• "Any size" (all standard sizes available) 
• "Specific sizes" (a user-defined subset).

Why it matters

Using "Any size" allows the algorithm to select the optimal cable size from the full range. Using "Specific sizes" constrains the selection to cross-sections that are commercially available from your suppliers or preferred in your project's cable schedule.

Generally, manufacturers make cables from 4 mm² and up. For DC stringing, you can stop at 10mm² because three restrictions are generally achieved for this cross-section.

Short-circuit parameters 

Fault level at supply end

The prospective short-circuit current, in kA. This represents the worst-case fault current that may occur on the electrical circuit until the protective device clears the fault. A conservative default is 25 kA for utility-scale AC collection systems. Project-specific values should come from a short-circuit study.

Circuit breaker clearing time

The maximum time (in seconds) for the protective device to interrupt fault current. This directly affects how long the short-circuit event will take.. A typical default is 0.1 seconds (100 ms). Project-specific values should come from a protection coordination study.

Power factor (AC Cabling)

The ratio of real power to apparent power in the AC circuit ranges from 0 to 1 in PV case ground mount. 

Why it matters

A power factor less than 1 means the cable must carry reactive current in addition to real current. This increases the total apparent current and affects calculations of ampacity and voltage drop. 

How to determine

For most utility-scale solar inverters operating close to unity power factor, a value between 0.8 and 1 is commonly suitable, according to how the solar inverter operates. Adjust if your project specifies reactive power delivery obligations. This obligation is set by the grid operator. 

Note: You can review the mathematical background via the Electrical Installation Wiki Formulae Guide. 

Installation parameters

Installation method

Installation method is a standardized classification of how and where cables are physically installed. The installation method determines the thermal correction factors applied to the cable's rated ampacity.

Why it matters

A cable's ability to dissipate heat depends entirely on its surrounding environment. A cable laid in free air cools efficiently; the same cable buried in a duct in the ground retains heat and must be derated. Specifying the wrong installation method will result in incorrect derating and potential undersizing.

IEC Installation Methods

Cable types options:

• Single-core Cable: Contains a single electrical conductor within its own insulation. It offers excellent flexibility and heat dissipation, making it the preferred choice for high-voltage, heavy-duty industrial power distribution.
• Multi-core Cable: Bundles multiple individually insulated conductors inside a single, shared outer jacket. It simplifies installation by allowing multiple lines to be run at once, making it the standard for low-voltage power supplies.

Most common installation methods: 

• D1 (cables in underground ducts). 
• D2 (cables buried directly). D2 represents the worst-case thermal scenario and is typically used for direct-buried trench configurations. 
• F (Conductors in free air) is also commonly used for trunk/harness systems.

Number of circuits (Cable grouping)

The number of cables or cable circuits running together in the same trench, conduit, or bundle.

Why it matters

When multiple cables share a confined space, their combined heat output raises the local temperature. This mutual heating reduces each cable's ability to dissipate heat, requiring a grouping derating factor (Cg) to be applied. Cable grouping is often the most impactful derating factor in utility-scale solar projects.

How to determine

Review your PVcase layout and identify the trench section with the highest number of circuits — this is the worst-case grouping scenario. Count the total circuits in that section of trench and use that number as the input. Sizing all cables to the worst-case grouping is conservative and ensures compliance even in the most constrained section of the design.

Ambient ground temperature

Ambient ground temperature is a baseline temperature of the soil at the depth where cables are buried, in degrees Celsius.

Why it matters

Ground temperature is the reference condition for applying the ambient temperature correction factor (Ca) to derated ampacity. The standard reference temperature is 30°C. Temperatures above 30°C reduce allowable ampacity; temperatures below 30°C increase it.

How to determine

The preferred source is a geotechnical survey for the project site. If no survey data are available, a common approximation is to subtract 5–10°C from the site's maximum recorded ambient air temperature, since soil is consistently cooler than air.

IEC Ambient Ground Temperature Correction Factors (Ca):

Note: You can refer to you can also refer to the International Electrotechnical Commission IEC 60287-3-1  standards for more information and guidance. 

Ambient air temperature

Air temperature is the maximum ambient temperature in degrees Celsius.

Why it matters

Solar arrays operate in direct sunlight where high temperatures affect wiring performance. Air temperature dictates the ambient temperature correction factor used to calculate safe cable ampacity.

• The standard reference temperature in electrical codes is 30°C.
• Above 30°C: Extreme summer heat limits the cable’s heat-shedding capacity, reducing its allowable current capacity.
• Below 30°C: Cooler winter conditions improve heat dissipation, increasing allowable capacity.

How to determine

The preferred source is to use historical weather data or local design standards to find the maximum design ambient temperature for the project site. However, if cables run through dark conduits or enclosures, or are in direct sunlight, you can typically add a small safety margin (around 10°C) to the peak outdoor air temperature.

IEC Ambient Temperature Correction Factors (Ca):

Soil thermal resistivity

Soil thermal resistivity is a measure of how the surrounding soil conducts (dissipates) heat away from a buried cable, expressed in K·m/W.

Why it matters

Applies only to underground installation methods (D1 and D2). Higher soil thermal resistivity means heat builds up around the cable more readily, requiring greater derating. Typical values range from 1.0 (wet sandy soil) to 3.0 or higher (dry, dense, or clayey soils).

How to determine

Soil thermal resistivity should come from geotechnical testing as part of the site investigation. A value of 2.5 K·m/W is commonly used as a conservative default when site data is unavailable. In cases where data is lacking, you can also refer to the International Electrotechnical Commission IEC 60287-3-1  standards or these guidelines. 

Manual derating factor

This is an option to override the automatically calculated derating factor with a user-defined value.

When to use

If you have performed your own derating calculation — for example, using a more detailed analysis tool or following a project-specific thermal study — you can enter the resulting factor directly. When this option is enabled, the installation method, ambient temperature, soil resistivity, and grouping inputs are ignored.

It is very useful when you have DC String Cables and AC Cables, or DC String Cables and DC Main Cables, in the same trench. The override function allows users to consider different factors for different cable types within the same trench.