Sizing Solar Cables Correctly: Cross-Section, Standards, and Installation
Solar cables carry the direct current generated by the modules to inverters, battery storage systems, or the utility grid. Voltage drops along this path—and this is precisely what determines whether a system operates efficiently. A cross-section that is too small reduces performance, causes the cable to heat up during operation, and can result in significant losses—in extreme cases, even leading to a fire.
Why Cable Cross-Section Determines Efficiency and Safety
The voltage drop depends directly on cable length and current: the longer the cable and the higher the current, the greater the loss. To limit this effect, the cross-section must be precisely matched to the operating conditions.
Accurate sizing has a noticeable impact on efficiency, particularly with long cable runs. The selection of the cross-sectional area is therefore a key parameter for planning and installation.
Standard Basis: DIN VDE 0295 and Supplementary Regulations
DIN VDE 0295 classifies copper and aluminum conductors according to their structure (fine-, medium-, or fine-stranded) and assigns typical cross-sections and current-carrying capacities to them. It has since been partially superseded by DIN EN 60228 (VDE 0295), but in practice it continues to serve as the basis for cross-sectional area selection.
In combination with other standards, it provides the practical basis for selecting cross-sections. These include DIN VDE 0100-520 for installation and VDE-AR-N 4105 for generators in low-voltage networks. Planners should consider these standards together rather than applying individual specifications in isolation.
Determining Cable Cross-Sectional Area Step by Step
Correct sizing follows a logical sequence:
- 1. Determine the current: The starting point is the maximum current flowing through the cable. This is calculated based on the power of the modules and the number of strings connected in parallel.
- 2 Determine the cable length: The length directly affects the voltage drop. It is important to add the forward and return paths together.
- 3 Calculate the voltage drop: A good rule of thumb is a maximum voltage drop of two percent.
- 4 Calculate the cross-sectional area: The final determination is made using tables and standards.
In practice, cross-sections of four or six square millimeters are frequently used. The appropriate value depends on the cable length, installation method, and factored-in safety margins.
Other Factors Affecting Cable Selection
The cross-sectional area alone is not sufficient—the technical properties of the cable material are just as important. UV-resistant outer insulation and high temperature resistance are recommended, as the cables are permanently exposed to the elements.
In damp environments or when cables are buried, additional requirements apply. In these cases, the cables must be reliably protected against water and mechanical stress. For underground installation, this protection is a separate planning criterion.
Practical Installation Guidelines
For photovoltaic systems, only approved cable types such as H1Z2Z2-K or PV1-F should be used. They are designed for long-term use under voltage and exposure to the elements. Stranded cables are preferable: they break less often and are easier to install than rigid wires.
Tight bend radii, kinks, and loops should be avoided. Improper fastenings, such as those using non-UV-resistant cable ties, can also lead to problems over time. Suitable mounts are therefore required. Keeping the cable route as short and direct as possible further reduces voltage losses.
Conclusion: Neither too small nor too large
The correct sizing of PV cables is crucial for the efficient operation of the system. A cross-section that is too small risks power losses and safety issues, while one that is too large results in avoidable costs.
The foundation is a thorough calculation based on current, cable length, and permissible voltage drop. Environmental factors, applicable standards, and the installation method must all be considered in every selection decision—to ensure the system operates safely and efficiently throughout its entire service life.
Frequently Asked Questions (FAQ)
What is the standard cable cross-section for solar cables?
In practice, four or six square millimeters are commonly used. The appropriate value is determined by cable length, installation method, and factored-in safety margins.
What is the maximum allowable voltage drop for solar cables?
A good rule of thumb is a maximum voltage drop of two percent. It increases with longer cable lengths and higher current levels.
Which cable types are approved for photovoltaic systems?
Types specifically approved for PV, such as H1Z2Z2-K or PV1-F, are suitable. They are designed for long-term use under voltage and exposure to the elements.
Which standard is relevant for selecting the cable cross-section?
The basis is DIN VDE 0295, which has been partially superseded by DIN EN 60228 (VDE 0295). In addition, DIN VDE 0100-520 (installation) and VDE-AR-N 4105 (low voltage) must be observed.
Why are stranded cables preferable to solid wires?
Stranded cables are less prone to breakage and are easier to install. This increases installation safety and the longevity of the system.
For more in-depth practical guidance, EMC-direct offers the free white paper “Understanding—and Avoiding—Common Causes of Damage to Photovoltaic Systems,” which addresses typical sources of error in assembly and electrical installation.
Download the white paper for freeSource Citation & Further Information:
First published: September 19, 2025
Source: https://www.photovoltaik.eu/wartung/emc-direct-kabel-richtig-dimensionieren
Author: Thaddäus Nagy is the CEO of EMC-direct.