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Solar Wiring: What Cables and Wires Are Used (Overview)

Published June 28, 2026 · By HelioRoofer Editorial

The wiring is the part of a solar install most governed by code - and the part where mistakes are dangerous. This is a general orientation to what’s used, not a how-to: actual wire sizing must follow the NEC and is licensed work. (See solar electrical basics for the big picture.)

The wiring, roughly in order

1. Module leads & connectors (DC, on the roof)

Panels come with short factory leads ending in MC4 connectors - the standard locking, weatherproof plug that links panels together into a “string.” You don’t cut these; you plug panel to panel.

2. PV wire / USE-2 (DC runs in the open)

Exposed DC wiring rated for rooftop conditions uses PV wire or USE-2 - sunlight (UV) resistant, double-insulated, and rated for high temperatures. This is what runs along the array and down toward the inverter.

3. THWN-2 in conduit (DC and AC runs)

Inside conduit (EMT or PVC), conductors are typically THWN-2 copper. This covers the run from the array to the inverter and from the inverter to your main electrical panel.

4. Grounding (EGC)

Everything metallic is bonded to ground for safety - an equipment grounding conductor (bare or green copper, commonly 6-10 AWG) plus grounding hardware on the racking.

What about gauge (thickness)?

Wire gauge is calculated, not guessed. It depends on:

  • Ampacity - the current the wire must carry without overheating.
  • Temperature derating - rooftops get hot, which lowers a wire’s rating.
  • Voltage drop - longer runs need thicker wire to keep losses low (typically kept under ~2-3%).

A typical residential string conductor is often around 10 AWG, going thicker for higher currents or long runs - but the right size for your system comes from an NEC calculation, not a rule of thumb.

Don’t forget the protective gear

Wiring is only part of a compliant install. It connects through breakers, fused/DC disconnects, and rapid shutdown equipment - all required by code and checked at inspection.

Why this is licensed work

Undersized wire, bad connections, or missing grounding cause fires and shock. That’s why most jurisdictions require a licensed electrician/contractor for the electrical portion - see do you need a license. Even confident DIYers often hand the wiring and tie-in to a pro.

Bottom line

Solar wiring uses MC4 connectors between panels, PV wire/USE-2 for exposed DC, THWN-2 in conduit, and proper grounding - all sized by NEC calculation (ampacity, heat, voltage drop), not by guesswork. Treat this overview as orientation; the actual design and tie-in belong to a licensed electrician.

Educational overview only, current as of June 2026. Not a wiring guide - all electrical work must follow the NEC and local code, done or verified by a licensed professional.

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