PV DC cable — EN 50618 and the H1Z2Z2-K designation

Solar panel installations use a cable type on the DC side (between panels and inverter) with its own specification: EN 50618, identifiable by the type designation H1Z2Z2-K. This cable differs fundamentally from regular installation cable, precisely because conditions on a roof — direct sun exposure, temperature swings, prolonged outdoor exposure — are far more demanding than for a cable indoors in conduit.

What the H1Z2Z2-K designation means

H1 — harmonised cable, design type 1.
Z2 (insulation) and Z2 (sheath) — halogen-free, heat-resistant polymer (often XLPO/EVA-based), applied twice: as core insulation and as outer sheath, giving the cable double insulation.
K — flexible conductor (class 5), fine-strand stranded copper, often tinned to limit corrosion under prolonged moisture exposure.

Key specifications

Property	Requirement per EN 50618
Insulation	Double insulation (halogen-free)
UV resistance	Tested to HD 605/A1
Ozone resistance	Tested to EN 50396
Conductor	Class 5, fine-strand (flexible), often tinned copper
Voltage class	AC 1000 V / DC 1500 V
Operating temperature	-40 °C to +90 °C

Why regular installation cable is not sufficient

Regular PVC-insulated installation cable is not designed for prolonged exposure to UV radiation and ozone, and typically has a lower operating temperature range and a lower voltage class than what is required on the DC side of a solar panel installation. A DC string can generate a significantly higher voltage than the nominal system voltage under high irradiance, and the cable often lies unprotected on or just above the roof surface for years, where temperatures can rise considerably above ambient due to solar heating.

Practical relevance

When cabling the DC side of a solar panel installation, H1Z2Z2-K is almost always the specified cable — manufacturers of solar panels and inverters typically require this type explicitly in their installation manuals. Using a non-specified cable on the DC side can lead to premature ageing of the sheath (UV embrittlement), increased risk of short circuit or earth fault, and potentially voids the factory warranty on the installation.

Common mistakes

Using standard installation cable (for example a generic PVC cable) on the DC side because it happens to be on hand — such cables lack the UV, ozone and temperature resistance that EN 50618 requires.
Not checking the cable's voltage class against the maximum string voltage at low ambient temperature — the open-circuit voltage of a PV string rises in cold weather, and can exceed the assumed system voltage.
Damaging the cable sheath during installation (sharp edges of mounting rails, over-tightened cable ties) — a damaged sheath directly undermines the double-insulation property that distinguishes this cable from regular cable.
Not accounting for the higher operating temperature on a roof when calculating current-carrying capacity — the ambient temperature just above a dark roof surface in summer is often well above the standard 30 °C reference used in regular current-carrying-capacity tables.