Cable Sizing is an integrated electrical design feature in PVcase Ground Mount that automatically calculates the correct cross-sectional area (CSA) for your DC and AC low-voltage cables. It goes beyond a simple voltage drop check by also incorporating current-carrying capacity (ampacity) and short-circuit tolerance, all within your existing PVcase workflow. 

Selecting the wrong cable size carries real consequences. Undersized cables can overheat, fail safety standards, and create dangerous site conditions. Oversized cables unnecessarily inflate material costs. The integrated cable sizing engine eliminates the need for manual cross-checking between external tools by performing all calculations automatically from your project data.

How it works

For each cable in the selected cabling type, PVcase runs three checks in parallel using your input parameters and the automatically derived cable lengths from the layout:

1. Voltage drop check — Calculates the voltage loss along the cable and verifies it does not exceed your defined maximum percentage threshold.
2. Current-carrying capacity check (ampacity) — Determines the cable's derated ampacity under real installation conditions and confirms that load current stays within safe limits.
3. Short-circuit check — Confirms the cable can withstand fault current long enough for the protective device (circuit breaker or fuse) to clear the fault.

The tool then selects the smallest standard cable cross-section that passes all three checks simultaneously.

Dominant Constraints by Segment

The binding constraint shifts depending on where in the system a cable segment is located:

Individual DC string cables are universally optimized for voltage drop. All combined or main cables — both AC and DC — are primarily constrained by ampacity due to the elevated thermal risk associated with aggregated current and the grouping of circuits.

Before you begin

Before opening the Cable Sizing settings, ensure the following are in place:

1. Ensure you've completed all steps to generate the cables.
2. Have your module or inverter datasheet available. Depending on the cabling segment, you will need to manually enter electrical parameters from the datasheet:

• For DC string cabling: module Impp, module Vmpp, and module Isc
• For AC cabling: inverter output current, nominal AC voltage, and power factor
• For DC main cabling: module Impp, module Vmpp, module Isc

1. Know your project's environmental conditions. You will need the ambient temperature and soil thermal resistivity for buried cable configurations. 
2. Identify the worst-case trench grouping. Before entering installation parameters, review your layout and locate the trench section with the most cable circuits running together. This value is required for the grouping derating calculation.

Calculating cable sizing

Step 1| Open the Cable Sizing window

1. Go to Electrical Design in the ribbon and click Cabling.
2. From the Cabling type dropdown, select the segment you want to size: DC String Cabling, DC Main Cabling, or AC Cabling.
3. Click on the Cable sizing button within the detail settings. This will open a new window.

Step 2| Power and Cable Parameters

1. In the new window, go to the Power and cable parameters tab if you’re not there already.
2. Check the box for "enable cable sizing settings" and select the electrical standard.

Note: Select IEC for most global projects or NEC for the United States. This controls which calculation temperatures, resistivity values, and installation method classifications are used. Selecting the wrong standard produces non-compliant results.  

3. Insert load Information parameters from your datasheet. Including:

• DC String and DC Main Cabling: Module Impp, Vmpp, and Isc.
• AC Cabling: Inverter output current (A), nominal AC voltage (V), and power factor.

Note: If the inverter datasheet does not specify the output current, you can calculate it manually. Use I = Power ÷ (1.732 × Vnom × Power factor). For example, 120 kW at 400 V equals 173 A. The power factor is 1 for most utility-scale solar inverters. Adjust only if your project has reactive power requirements from the grid operator.

• Maximum voltage drop (%)

Set the upper limit for voltage loss on this cable segment. This is your project design target — PVcase does not set it for you. Typical values are 1–1.5% for DC cabling and 1% for AC and DC main cabling.

• Conductor, insulation, configuration, and cable size

For most utility-scale solar projects, the standard choices are:

• DC String Cabling: Copper, XLPE, single-core, specific sizes 4–10 mm² (IEC) or 10–2 AWG (NEC). Copper is preferred for these small cross-sections because it is easier to handle on-site, and aluminum offers no meaningful cost savings.
• DC Main and AC Cabling: Aluminum, XLPE, single-core, any size. At large cross-sections, aluminum is substantially cheaper and lighter.

For the full rationale on conductor material, insulation type, and cable configuration, see Cable sizing parameters for reference. 

• Short-circuit settings 

PVcase will handle calculations for DC cabling, so no additional information introduction is necessary. Two additional fields appear for AC cabling. If you do not have project-specific values from a protection study, use these defaults: fault level 25 kA, circuit breaker clearing time 0.1 seconds. Adjust if your protection coordination study specifies otherwise.

Step 3| Installation Parameters

1. Head over to the Installation parameters tab. This tab controls the derating factors applied to the cable’s rated ampacity. Getting these wrong leads to undersized cables in the field.
2. Select Installation method. Select how and where the cable is physically routed. The most common options for utility-scale solar:

• D2 / Conductors directly buried in Earth: Direct-buried trench. Most common, and the worst-case thermal scenario.
• D1 / Conductors buried in conduit: Cables in underground ducts.
• F / Conductors in free air: Overhead runs on racking. Used for trunk/harness systems.

3. Enter the Number of cable circuits in the worst-case trench section. When cables share a trench, their combined heat reduces each cable’s ability to dissipate heat — a grouping correction factor is applied as a result. This is often the largest single source of derating in utility-scale solar. 
4. Insert Ambient temperature and soil thermal resistivity. There are two options:

• IEC: Enter ambient ground temperature in °C (from geotechnical data, or max air temperature minus 5–10°C) and soil thermal resistivity in K·m/W (default 2.5 if no data available).
• NEC: Enter ambient air temperature in °F. Use 68°F for buried installations and 86°F for free-air installations. 

Note: If you have a project-specific derating value from a thermal study, you can override and enter it directly. This overrides the installation method, grouping, temperature, and soil resistivity inputs entirely. This applies only for IEC standards. 

Step 4| Review results

1. Go to the Calculation and Results tab. For each cable segment, PVcase shows the recommended CSA, conductor material, insulation material, voltage drop percentage, and cable lengths.
2. Click Show report to review the underlying formulas. Click Export PDF to save a copy.

Note: If you see ‘Not Found’ in the reports, it indicates that no cable size currently available meets all three constraints under the current setup. The most common fixes are reducing the circuit grouping count by splitting circuits across separate trenches.

Step 5| Export to XLSX

1. Close the Cable Sizing window, then go to Layout Information in the ribbon.
2. Open the Bill of Materials tab, click Refresh, then Export to XLSX. Save and name the file.
3. Open the sheet for your segment to view results: Inverter To String (DC string), Transformer To Inverter (AC), or Central Inverter To DC Combiner (DC main).

Each row is one cable. The error column (column U for IEC; column N for NEC AC) is empty when all checks pass. A value in this column means that the segment has no compliant cable size under the current parameters. Most common resolution options:

• Change the section trench configuration to reduce the number of circuits in a single trench.
• Increase the number of parallel trenches.
• Review and adjust the derating factors (e.g., grouping).