Rapid shutdown (690.12)
Firefighters need the roof to be safe to walk on. Inside the array boundary, conductors must drop to 80 V or less within 30 seconds of the initiator being thrown. Outside the boundary — more than 1 ft from the array — 30 V.
- Module-level shutdown — microinverters and optimizers satisfy it inherently.
- String inverters need RSD transmitters plus per-module receivers, or a listed PVRSS.
- The initiator must be at a readily accessible location outside the building, usually at the service disconnect, and labeled.
Grounding, in plain terms
| Conductor | Job | Notes |
|---|---|---|
| EGC | Bonds metal so a fault trips the breaker | Bare or green. Runs with the circuit conductors. |
| GEC | Ties the system to earth | Lightning and voltage stabilization, not fault clearing. |
| Bonding jumper | Ties rails, modules, racking together | WEEB washers or listed lugs. Not a sheet metal screw. |
Do not do thisEarth is not a fault path. A ground rod will never clear a fault. If the EGC is missing, the ground rod does nothing but hold the enclosure at a lethal potential.
Combiners and fuses
One or two strings in parallel need no string fuses — no string can push enough backfeed current to hurt another. Three or more, and each string gets a fuse sized above 1.56 × Isc and below the module's max series fuse rating (usually 15–25 A). That module rating is a hard ceiling.
Arc-fault and ground-fault
- AFCI (690.11) — required on DC circuits over 80 V on or in a building. Nuisance trips almost always trace to a loose or dirty MC4.
- GFCI/GFDI — built into the inverter. A ground fault that trips it means moisture in a junction box or a pinched conductor under a rail. Find it; do not just reset it.
Labels the inspector will look for
- PV system disconnect, rated max voltage and current
- Rapid shutdown placard with the array boundary diagram
- "WARNING: ELECTRIC SHOCK HAZARD — DO NOT TOUCH TERMINALS" on the DC disconnect
- Interconnection label at the service panel, with the busbar calculation
- Directory of all power sources at the service equipment