NABCEP PVSI key terms

A code-required function that reduces conductor voltage at the array to a safe level, typically 30 volts or less within 30 seconds, for firefighters and first responders. It applies to roof-mounted PV systems on buildings.

The National Electrical Code section governing rapid shutdown of PV systems, defining controlled conductors, the 1-foot boundary, and voltage and time limits for array shutdown initiation.

Devices such as microinverters or DC optimizers mounted at or near each module that provide per-module conversion or control, often enabling rapid shutdown compliance and module-level monitoring.

A DC-to-DC converter installed per module that performs maximum power point tracking and can reduce array voltage on command, commonly used to satisfy rapid shutdown requirements.

A central inverter that converts DC power from one or more series-connected module strings into grid-compatible AC power, typically with integrated disconnects, monitoring, and protective functions.

An inverter control algorithm that continuously adjusts operating voltage and current to extract the greatest available power from a PV array as irradiance and temperature change.

The instantaneous power density of solar radiation falling on a surface, usually expressed in watts per square meter. It drives array output and is measured with a pyranometer or reference cell.

The reference conditions used to rate PV modules: 1,000 watts per square meter irradiance, 25 degrees Celsius cell temperature, and a specified air mass spectrum. Ratings appear on module nameplates.

The rate at which a module's power, voltage, or current changes per degree Celsius of cell temperature, usually negative for power. It predicts output loss on hot roofs.

The manufacturer's labeled electrical values for a component, such as module maximum power or inverter AC output, used as the basis for code calculations and system sizing.

The ratio of array DC nameplate capacity to inverter AC rated output. A ratio above one indicates intentional oversizing to improve production during low-irradiance periods and reduce clipping losses.

The loss of harvestable energy that occurs when array DC output exceeds the inverter's maximum AC capacity, causing the inverter to limit power during high-irradiance periods.

The ratio of actual energy produced to the theoretical energy expected from measured irradiance and nameplate capacity, expressed as a percentage. It normalizes for weather and location.

The primary National Electrical Code article covering solar photovoltaic systems, including circuit sizing, disconnects, grounding, marking, and interconnection requirements for PV power systems.

The code section governing interconnection of power production sources to premises wiring, including busbar and feeder load-side connection rules and the 120 percent busbar allowance.

A PV interconnection made on the line side of the main service disconnect, typically requiring a dedicated disconnect and utility coordination rather than relying on busbar capacity rules.

A PV interconnection made on the load side of the service disconnect, commonly a backfed breaker, subject to busbar and feeder ampacity limits in the code.

The ampere capacity of a panelboard's internal bus, used with breaker ratings to verify that a backfed PV breaker does not overload the panel under the applicable code allowance.

The primary overcurrent device protecting a service panel, whose rating is a key input when calculating allowable PV backfeed capacity on a load-side interconnection.

A fuse or circuit breaker that interrupts excessive current to protect conductors and equipment. In PV circuits it must be rated for DC and for the array's fault-current characteristics.

The maximum overcurrent protection value specified by a module manufacturer for a single string, used to size string fuses and verify reverse-current protection adequacy.

An enclosure where multiple PV source circuits are paralleled, often containing string fuses, a DC disconnect, and busbars, providing a single output to the inverter or charge controller.

The calculation of modules per series string so that cold-temperature open-circuit voltage stays below equipment limits and hot-temperature operating voltage stays within inverter tracking range.

The voltage measured across a PV source with no load connected. It rises as cell temperature falls and is used to verify maximum system voltage compliance.

The highest voltage a module or system component is rated to withstand, such as 600 or 1,500 volts. String voltage at record low temperature must not exceed it.

A switch or breaker that isolates the PV array from the rest of the system, required to be readily accessible and clearly labeled for service and emergency use.

Code-mandated placards and markings identifying PV disconnects, maximum voltages, rapid shutdown equipment, and power sources, ensuring responders and service personnel can operate safely.

The conductor that connects the system's grounding point to the grounding electrode, providing a path for fault current and stabilizing voltage reference for the electrical system.

The conductor that bonds non-current-carrying metal parts of equipment, such as module frames and racking, to the grounding system to clear faults safely.

A conductor that ensures electrical continuity between metal parts, such as module frames and rails, so they remain at the same potential and can carry fault current.

A system that detects unintended current flow to ground in PV circuits and interrupts or isolates the fault, required for many grounded and ungrounded array configurations.

A measurement of resistance between energized conductors and ground, performed during commissioning or troubleshooting to detect damaged cable, moisture intrusion, or degraded insulation.

An instrument that applies a high test voltage to measure insulation resistance in megohms, used to verify conductor and equipment insulation integrity before energizing a PV system.

A diagnostic instrument that sweeps a PV string's current-voltage characteristic to compare actual performance against expected values and identify shading, soiling, or module faults.

The documented process of verifying that an installed PV system meets design intent and code requirements through inspection, testing, and functional performance checks before handover.

A written record of deficiencies found during inspection that must be corrected before project acceptance, tracked to closure and referenced in the final inspection report.

A structured on-site review of installed work against approved plans and code, covering structural attachment, clearances, labeling, wiring methods, and safety access.

Construction documents revised to reflect actual installed conditions, including equipment locations, routing, and ratings, used for inspection, maintenance, and future service.

The pre-construction examination of permit drawings for code compliance, checking structural loads, electrical calculations, clearances, and labeling before work begins.

A schematic showing the electrical topology of a PV system with one line per circuit, including disconnects, overcurrent devices, grounding, and interconnection points.

A scaled drawing showing the property, building footprint, array layout, equipment locations, setbacks, and access paths, used for permitting and inspection planning.

The required distance between PV equipment and roof edges, ridges, or access pathways, set by fire or building code to preserve firefighter access and ventilation.

A clear, code-specified path on a roof allowing firefighters to move safely around and above PV arrays, affecting array layout and module placement.

An engineering assessment of dead, live, wind, and snow loads imposed by PV racking on a building, confirming the roof structure can safely carry the added weight.

The method and hardware connecting PV racking to the building structure, such as lag screws, adhesives, or ballast, verified during inspection for correct type and spacing.

A weatherproofing detail around roof penetrations that directs water away from fasteners and mounts, preventing leaks at structural attachment points.

A web or app platform that collects inverter and sensor data to display production, alarms, and historical trends, supporting performance verification and warranty claims.

The switch or breaker that disconnects the building's service conductors from the utility, serving as the reference point for supply-side and load-side PV interconnections.