Why Cable Cross-Section is Crucial for Roof Penetrations
When planning a photovoltaic system, the cable cross-section plays a central role – not only for electrical safety but also for selecting the appropriate roof penetration. Incorrect planning here risks either too tight a penetration or unnecessarily large openings in the roof.
Common Cable Cross-Sections in PV Systems
Most solar modules come with pre-assembled cables. An overview of the most common cross-sections:
| Cross-Section | Outer Diameter (approx.) | Typical Application |
| 4 mm² | 5.5–6.5 mm | Module cables, string cabling up to 30 m |
| 6 mm² | 6.5–7.5 mm | Longer strings, DC main line |
| 10 mm² | 8.0–9.5 mm | Large systems, long DC lines |
| 16 mm² | 10.0–11.5 mm | Grounding cables, equipotential bonding |
The outer diameter varies depending on the manufacturer and insulation thickness. The actual diameter should be measured before ordering a roof penetration.
How many cables need to pass through the roof?
The number of cables depends on the system configuration. Typical scenarios:
- Small single-family house (5–10 kWp): 1 string with 2 DC cables (positive and negative)
- Medium single-family house (10–15 kWp): 2 strings with 4 DC cables
- Larger system (15+ kWp): 3 strings with 6 DC cables
Additionally, a grounding cable (PE) may be required for equipotential bonding.
Choosing the Right NEXCAPE Roof Penetration
NEXCAPE offers roof penetrations made of TPU (Thermoplastic Polyurethane) in six variants:
- 2 PV and 2 PV+PE – for single-string systems
- 4 PV and 4 PV+PE – for two-string systems
- 6 PV and 6 PV+PE – for three-string systems
The PE variants include an additional conduit for the grounding cable. Each variant is available in lengths of 105 mm, 125 mm, and 150 mm to accommodate different tile sizes.
Routing Cables without MC4 Disassembly
A significant advantage of NEXCAPE penetrations: MC4 connectors do not need to be disassembled. The cables, including connectors, are routed through the flexible TPU penetration. This saves time and eliminates a common source of error during installation.
Practical Tip: Always Plan for Some Reserve
Experienced solar installers recommend choosing a slightly larger dimension. If cables are too tight, this can lead to stress due to temperature fluctuations. The flexible TPU construction of NEXCAPE penetrations compensates for small tolerances, but the diameter should still be correct.
Find the right roof penetration for your cable cross-sections: View PV Roof Penetrations
