Selecting and Customizing Solar Photovoltaic Cabling Systems

Common cable types in solar systems

Solar installations use several cable families, each engineered for a specific routing condition. The most common types and their primary applications are summarized below.

PV Wire is intended for exposed connections between panels and from panels to combiner boxes, with insulation rated for sunlight, weather and temperature cycling. USE-2 cable is used from combiner boxes to charge controllers and is suitable for wet locations and direct burial. THHN is typically limited to indoor conduits and inverter-to-main-panel runs. Tray Cable supports multiconductor runs between buildings or along cable trays, while battery cable is built with large conductors for high-current battery and inverter connections.

Why correct cable selection matters

Using a cable outside its rating is a frequent source of solar project failures. Non-UV-rated insulation exposed to sunlight can become brittle and crack, exposing conductors and increasing the risk of short circuits. Cable without a wet-location rating can allow moisture intrusion, leading to leakage current, corrosion and insulation damage. Such errors can also prevent a system from passing electrical inspection, delaying commissioning and adding remediation costs.

Installation and custom-length considerations

Connections that require specific lengths or nonstandard configurations are often better handled with factory-made or professionally customized assemblies than with field splices. Properly executed terminations use listed crimping systems and adhesive-lined heat-shrink tubing, which seals the connection against moisture and helps maintain mechanical strength.

Field installation still requires suitable stripping and crimping tools. Improper tooling can nick conductors, create weak crimps or leave gaps in insulation, any of which may reduce long-term reliability in outdoor and high-current circuits.

Matching ratings to the routing environment

Cable selection should account for current load, voltage drop over distance and the physical route. Direct-burial, wet, exposed and conduit installations each impose different requirements, and local electrical codes set minimum standards for insulation, ampacity and protection. A cable that performs well indoors may be unsuitable for a rooftop array, just as a sunlight-resistant cable may not be appropriate for every enclosed raceway.