Why the correct number is crucial
Too few penetrations force multiple cables into a single opening — increasing the risk of insulation damage and making a clean seal impossible. Proper planning saves time, material, and rework.
Basic rule: One cable, one penetration
One roof penetration per PV cable — for string cables (DC+ and DC−), earthing cables, and monitoring and data cables. Most string inverters have 2–4 MPPT inputs, resulting in 4–8 DC cables.
Calculation based on system size
Up to 10 kWp (1 inverter)
Formula: Strings × 2 + 1 earthing cable. For 2 strings = 5 penetrations, possibly plus monitoring.
10–30 kWp (2–3 inverters)
Multiple cable sets. Cables can be bundled — the 150 mm penetration offers space for thicker cross-sections.
From 30 kWp (commercial)
Cable planning as part of the execution plan. Cable ducts and pipe penetrations facilitate later retrofitting.
Checklist for ordering
- Calculate strings × 2 (DC+/DC−)
- Plan for earthing and monitoring cables
- 10–15% buffer for reorders
- Check cable cross-section, choose appropriate size (105/125/150 mm)
Conclusion
Rule of thumb: One penetration per cable, plus buffer. B2B from 20 pieces — staggered prices cover current and next system.
You can find the suitable PV cable roof penetrations as mechanical abrasion protection in the D24-B2B-Shop (volume discounts from 20 pieces) – UV-resistant TPU, Made in Germany.
