Two solutions, one goal: Safely routing cables through the roof
When installing a photovoltaic system, the DC cables must be routed from the roof into the interior of the building. There are essentially two approaches for this: the classic sealing grommet and the roof penetration specifically developed for PV cables. Both have their justification – but the practical differences are significant.
The classic sealing grommet
Sealing grommets made of EPDM or silicone have been used for pipe penetrations for decades. For PV cables, they are often used for other purposes:
- Universally applicable for various diameters
- Available in hardware stores and from wholesalers
- Relatively inexpensive to purchase
However, sealing grommets also have disadvantages for PV installation:
- MC4 connectors must be disassembled before and reassembled after routing
- Only one cable per grommet – multiple cables require multiple penetrations
- Additional tile often needs to be drilled or modified
- No specific adaptation to tile shapes
The PV-specific roof penetration
Modern roof penetrations like those from NEXCAPE are specifically designed for photovoltaic installation. They are made of TPU (Thermoplastic Polyurethane) and are manufactured using 3D printing in Germany.
- Multiple cables in one penetration (2, 4 or 6 PV cables)
- No MC4 removal necessary – connectors remain assembled
- Tool-free installation directly on the tile
- UV-resistant and permanently flexible
- Optional PE variant for potential equalization
Direct comparison in practice
| Criterion | Sealing Grommet | NEXCAPE Roof Penetration |
| Installation time per penetration | 15–25 minutes | 2–5 minutes |
| MC4 disassembly necessary | Yes | No |
| Tools required | Yes (drill, cutter) | No |
| Cables per penetration | 1 | 2, 4 or 6 |
| Earthing cable (PE) | Separate solution required | Integrated (PE variant) |
| Material | EPDM/Silicone | TPU |
| UV resistance | Medium | High |
Cost comparison: Purchase vs. working time
At first glance, the sealing grommet appears cheaper. However, if you include the working time for MC4 disassembly, tile modification, and installation, the picture changes significantly. Especially for systems with multiple strings, the PV-specific penetration saves considerable time – and thus money.
Conclusion: For PV professionals, there's no way around the specialized solution
Sealing grommets have their place in the plumbing sector. However, for professional PV installation, specialized roof penetrations made of TPU offer clear advantages in speed, safety, and durability.
See for yourself: find the right PV roof penetration
