Solar Rapid Shutdown Calculator

Select NEC version, inverter type, and mounting — get NEC 690.12 compliance pathway, required equipment, product examples, and inspector checklist.

System configuration

NEC version adopted?

System / inverter type?

Max system voltage (DC)?

V DC

Number of modules?

modules

Array mounting type?

Roof accessibility?

Rapid Shutdown Compliance Analysis

STRING INVERTER — Module-level rapid shutdown REQUIRED for NEC 2020/2023.

NEC 2020/2023 Section 690.12 requires conductors within 1 foot of the array to be de-energized to below 80V within 30 seconds. A plain string inverter cannot achieve this without module-level controls — each module must have an individual shutdown device.

Array boundary1 foot from array edge (NEC 2020/2023)

Voltage limit after shutdown80V within 30 seconds within array boundary

Cost adder for compliance$600 – $800 est.

Required equipment

Module-level rapid shutdown device at every module (optimizer, SolarEdge SafeDC, Tigo TS4-A-O, or dedicated shutdown device)
String inverter compatible with rapid shutdown communication (or separate PVHCS)
Rapid shutdown initiation switch, labeled per NEC 690.56(C)
System placard at service entrance and initiation switch

Compliant product examples

SolarEdge power optimizer + SolarEdge inverter (SafeDC)
Tigo TS4-A-O optimizer + any compatible inverter
Solaria PowerXT with integrated shutdown (select models)
Fronius Primo + Tigo rapid shutdown system

Inspector checklist

☐ Module-level shutdown device at every module
☐ All devices listed UL 1741 SA or equivalent
☐ Initiation switch visible from utility meter, labeled correctly
☐ Placard installed per NEC 690.56(C) — shows system location and shutdown
☐ 80V within 30s verified in system spec documentation
☐ Grounding and bonding complete per NEC 690.43
☐ Ground fault protection per NEC 690.41
☐ Arc fault protection per NEC 690.11

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How to Use This Calculator

Select your NEC version and system type

Start by checking your local jurisdiction's adopted NEC version — most US states lag 1-2 cycles behind the published NEC. Many jurisdictions are still on NEC 2017 or 2020 even though NEC 2023 is published. The adopted version matters because NEC 2020 significantly tightened the rapid shutdown boundary from 10 feet to 1 foot from the array edge, which changed the equipment requirements for string inverter systems dramatically.

Enter mounting type

Ground-mounted systems (panels installed on the ground, not on a building) are completely exempt from NEC 690.12 rapid shutdown requirements. This is one of the least-understood aspects of rapid shutdown — many installers unnecessarily add MLPE equipment to ground-mount systems. Building-mounted (roof) and carport/canopy systems on a building structure must comply.

Read the compliance pathway

The calculator shows whether your system is compliant, what equipment is required, product examples, and an 8-item inspector checklist. Print this for your permit package.

NEC Rapid Shutdown Requirements by Version

NEC 2017 (Section 690.12): — Applies to: PV systems on buildings — Array boundary: 10 feet from array / inside building — Limit: 30V within 30 seconds outside boundary — Compliant: MLPE (microinverter/optimizer) OR PVHCS — Ground mount: EXEMPT NEC 2020 / 2023 (Section 690.12): — Applies to: PV systems on or in buildings — Array boundary: 1 foot from array edge — Limit: 80V within 30 seconds WITHIN boundary — Required: Module-level shutdown at each module — String inverters: MUST add per-module MLPE — Microinverters: Already compliant (DC stays at panel) — Ground mount: EXEMPT

The shift from NEC 2017 to 2020 was dramatic: the array boundary shrunk from 10 feet to 1 foot, which means string inverter wiring inside the array must also be de-energized. This effectively mandated MLPE (module-level power electronics) for any building-mounted string inverter system — a major market shift toward microinverters and power optimizers.

Example

Residential string inverter system — NEC 2020 jurisdiction

A homeowner wants a 6kW system with a central string inverter on a walkable roof. Their jurisdiction has adopted NEC 2020. The contractor quotes a standard string inverter system without MLPE.

NEC versionNEC 2020

System typeString inverter (no MLPE)

MountingBuilding-mounted roof

Array boundary1 foot from array edge

Result

Compliance statusNON-COMPLIANT as designed

RequiredMLPE at every module

OptionsSolarEdge optimizer + compatible inverter; OR switch to microinverters

Cost adder$400-800 for optimizers (15 modules)

The homeowner should either switch to a microinverter-based system (simpler, directly compliant, module-level monitoring) or add power optimizers to the string inverter design. For most residential systems under NEC 2020+, microinverters are often the cleaner solution since they satisfy rapid shutdown, enable module-level monitoring, and eliminate string sizing constraints.

FAQ

What is solar rapid shutdown and why is it required? ▼

Rapid shutdown is an NEC requirement (Section 690.12) that allows emergency responders — firefighters — to quickly de-energize solar PV conductors on or inside a building. Solar panels generate electricity whenever sunlight hits them; they cannot be "turned off" by simply flipping a switch. Without rapid shutdown, a firefighter cutting through a roof could contact live DC conductors at 600-1000V. Rapid shutdown equipment limits conductor voltage to safe levels within 30 seconds of triggering the initiation device, protecting first responders.

Do ground-mounted solar systems need rapid shutdown? ▼

No. NEC 690.12 explicitly applies only to PV systems "on or in buildings." Ground-mounted systems — panels installed on racking in a field, not attached to or above a building — are completely exempt from rapid shutdown requirements. This is a common point of confusion and misquoting. Ground-mount systems still need proper disconnect means (NEC 690.15) and grounding, but no module-level rapid shutdown equipment is required.

Can I use a string inverter on a roof under NEC 2020? ▼

Yes, but you must add module-level power electronics (MLPE) to every module. Under NEC 2020 Section 690.12, the 1-foot array boundary means the wiring between modules must also be de-energized after shutdown — which is only achievable with a device at each module. In practice, this means adding power optimizers (SolarEdge, Tigo) to your string inverter design. The cost adder is typically $15-40 per module for optimizers, or $30-60 per module if you switch to microinverters entirely.

What is the difference between a rapid shutdown system and MLPE? ▼

MLPE (Module-Level Power Electronics) is a category of devices — microinverters, power optimizers, and module-level shutdown devices — that operate at each individual panel. Rapid shutdown is an NEC code requirement. MLPE satisfies rapid shutdown in most cases because module-level devices can cut DC power at the source. However, not all MLPE is listed for rapid shutdown — you must verify the specific device's UL 1741 SA listing or equivalent. Some power optimizers (like older Tigo units) improve power output but may not have rapid shutdown listing.

What placard is required for rapid shutdown per NEC 690.56? ▼

NEC 690.56 requires placards at: (1) the rapid shutdown initiation switch — labeled "SOLAR PV SYSTEM RAPID SHUTDOWN SWITCH"; (2) the utility service entrance — showing the location of the PV system and how to initiate shutdown; (3) for systems with roof-mounted arrays, the placard must show array location and the initiation device location. Some jurisdictions also require placards at the main service panel. The SolarEdge rapid shutdown switch includes a label; for custom installations, generic rapid shutdown labels are available at electrical supply houses.

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