What sunlight does to a sheath
Ultraviolet radiation breaks chemical bonds in polymers. Combined with heat, oxygen and ozone, it slowly embrittles the surface of a cable sheath: the colour fades or chalks, fine surface cracks appear, and eventually the sheath splits when the cable moves or is handled. Once the sheath is open, water reaches the insulation and the cable's mechanical and electrical protection is compromised. The process is gradual and depends on location, orientation, temperature and the compound, so no honest datasheet can turn UV resistance into a fixed number of years.
Whether a sheath resists this depends almost entirely on its formulation. The polymer type matters, but so do the stabilisers and pigments in the compound. Two cables with the same sheath material name can behave very differently outdoors.
Common outdoor sheaths compared
| Sheath | Typical cables | UV behaviour | What to check |
|---|---|---|---|
| Cross-linked halogen-free compound (XLPO type) | Solar DC cable to EN 50618 / IEC 62930 (H1Z2Z2-K) | Formulated for UV and ozone exposure in the reference constructions | UV and weathering tests in the type test report per standard |
| Black polyethylene (PE) | Outdoor fibre cable, ADSS, direct-buried power cable | Good when carbon black is properly dispersed | Compound grade and carbon black content per datasheet |
| Tracking-resistant (AT) sheath | ADSS on high-voltage lines | UV-stabilised and resistant to electrical tracking | Required by line field strength, calculated per project |
| PVC (general purpose) | Building wire, cords, indoor power cable | Variable; many grades are not intended for direct sun | Whether an outdoor or UV-resistant grade is declared |
| Coloured sheaths (any polymer) | Phase or project colours | Generally less stable than black; depends on pigments | UV test result for the actual colour |
Solar PV cable
Solar DC cable is the most exposed cable most buyers handle. It runs along module rows, under trackers and across roofs, often in direct sun for its whole service. EN 50618 and IEC 62930 define the H1Z2Z2-K type for this duty: a tinned copper Class 5 conductor, cross-linked halogen-free insulation and a cross-linked halogen-free sheath, rated DC 1.5 kV. The reference construction on our solar PV cables page is a 1x4 mm2 cable with 0.7 mm insulation, a 0.8 mm sheath and an overall diameter of about 5.7 mm, supplied with red or black sheaths. Public datasheets describe the sheath as UV and ozone resistant.
Two practical notes follow. First, the older PV1-F type has been replaced by H1Z2Z2-K in European practice, and the US uses UL 4703 PV Wire instead; see the EN 50618 article. Second, red sheaths are common for polarity marking, so the desk asks for UV test evidence on the colour actually being ordered, not only on black. Temperature figures such as a 120 C maximum conductor temperature are manufacturer typical values, not a standard requirement, and are confirmed per datasheet.
The cable is only one part of the outdoor system. On solar sites, UV damage is often seen first on the accessories rather than on the cable itself: cable ties, clips and conduit that were not UV-stabilised become brittle, break, and leave the cable hanging against sharp module frames or rubbing on the structure. Loose loops that move in the wind wear the sheath at contact points. A project specification that asks for UV-resistant cable should also cover the fixings, and the installer should follow the bending and fixing guidance on the cable datasheet. Brand owners selling solar extension leads or connector cables to installers can add these points to the product documentation, since the end user rarely reads the cable standard.
Outdoor fibre and aerial cable
Outdoor fibre cables such as the GYTS reference on our outdoor fibre cables page use a black PE outer sheath over the armour tape. Carbon black is the most effective common UV stabiliser for polyethylene, provided it is well dispersed, which is one reason outdoor fibre and aerial cables are almost always black. ADSS cable hangs in full sun for its whole life, so its sheath compound is chosen for UV as well as tracking. On high-voltage lines, an AT (anti-tracking) sheath is selected by calculating the space potential at the cable position; the decision belongs to the line designer, as described on the ADSS aerial cables page.
Power and building cable outdoors
Low voltage power cable with a PVC sheath is often installed outdoors on trays, along walls or on poles, and many PVC grades do degrade in strong sun over time. Where cable is exposed, specifications typically require one of three things: a sheath compound declared UV-resistant by the plant, a black sheath with a suitable stabiliser, or protection by conduit, covered trays or burial. Cable that will be buried can use a standard sheath, provided drums are not left uncovered in sun for months before installation; storage is part of the plan. The LV power cables page lists the sheath options.
In the US, cable for outdoor exposure is selected by its listing and markings rather than by a generic description. Check what the listing held by the partner plant for that construction allows, in the certifier's public database, and let the AHJ requirements decide.
How to check a UV claim
- Name the exposure: direct sun, partial shade or covered; roof, tracker, pole or wall; and the climate zone.
- Ask for the test: the UV or weathering test result from the type test report under the standard that applies, for the same compound and colour.
- Check the compound: the sheath grade named on the datasheet should match the compound used in production. A change of compound supplier is a reason to ask again.
- Check the print: outdoor and solar cables usually carry the standard and type in the sheath print; check it at pre-shipment inspection.
- Plan storage: drum covers and shaded storage on site, especially for coloured sheaths.
UV resistance is never shown by a quick look at a new cable, so the documents are the only real evidence at purchase. Send the cable list with the exposure conditions through the quote form; MOQ for solar cable typically starts from 100 m up to 500 to 2,000 m depending on the plant, confirmed in writing for each order.