What rapid shutdown does
Rapid shutdown lets firefighters de-energize the conductors of a rooftop PV system from one switch, so they can work on or near the roof without live DC wiring. NEC 690.12 applies to PV systems installed on or in buildings. Since the 2017 NEC it is defined around the array boundary: 1 ft from the array in all directions.
The limits, inside and outside the array boundary
| Where | Requirement once rapid shutdown starts |
|---|---|
| Outside the array boundary | Controlled conductors at 30 V or less within 30 seconds |
| Inside the array boundary | A listed PV hazard control system (UL 3741), or controlled conductors at 80 V or less within 30 seconds |
In practice, the 80 V inside-the-boundary limit is what drives module-level power electronics: microinverters, DC optimizers or module-level shutdown devices on every module (or every pair, where the listing allows). A UL 3741 PV hazard control system is the alternative, where the racking, modules and inverter are listed together.
How it changed by edition
- 2014 NEC: conductors more than 10 ft from the array or 5 ft inside the building limited to 30 V and 240 VA within 10 seconds. No array boundary yet.
- 2017 NEC: introduced the 1 ft array boundary, 30 V in 30 seconds outside it, and (from January 1, 2019) 80 V in 30 seconds inside it, or a listed array.
- 2020 NEC: replaced the “listed array” option with a PV hazard control system listed for the purpose (UL 3741), and requires the initiation device for one- and two-family dwellings to be at a readily accessible location outside the building.
- 2023 NEC: keeps the same limits and reorganizes the inside-boundary options around PV hazard control equipment and systems.
The initiation device
The rapid-shutdown initiator is the switch that starts it. For one- and two-family dwellings (2020 NEC and later) it has to be readily accessible outside the building. Common arrangements:
- The service disconnect or main breaker, where turning it off removes the signal that keeps the module-level devices on
- The PV system AC disconnect
- A dedicated rapid-shutdown switch, often part of a battery gateway or inverter
Whatever you use, show it on the site plan and the line diagram, and put it where the fire department expects to find it.
Labels
690.56(C) requires a rapid-shutdown label at the service equipment, or where the initiation device is, telling responders the system has rapid shutdown and what it does. The initiation switch itself is labelled as the rapid-shutdown switch. The exact wording, colours and letter heights changed between editions, so print the version your jurisdiction has adopted, and show each label’s location on the label sheet.
What to show on the plan set
- The rapid-shutdown device on every module (or the PV hazard control system listing) on the line diagram
- The initiation device on the site plan and line diagram
- The spec sheet for the module-level devices showing their UL listing, and compatibility with the inverter
- The labels and where they go
See the plan set checklist for the rest of the set.
How Ballast Solar handles it
Ballast Solar checks every PV set for a compliant rapid-shutdown method under the adopted NEC edition and puts the matching labels on the label sheet.
Questions
What is the array boundary for rapid shutdown?
1 foot from the array in all directions, as defined in NEC 690.12 since the 2017 edition.
What voltage does rapid shutdown require?
Outside the array boundary, 30 volts or less within 30 seconds. Inside the boundary, 80 volts or less within 30 seconds, or a listed PV hazard control system (UL 3741).
Where does the rapid shutdown switch go?
For one- and two-family dwellings under the 2020 NEC and later, at a readily accessible location outside the building. It is often the service disconnect or the PV AC disconnect.
Do ground-mounted solar systems need rapid shutdown?
690.12 applies to PV systems on or in buildings. A detached ground mount generally doesn’t, but check how your jurisdiction treats circuits that run into a building.
This guide explains the code for planning purposes. The adopted edition, local amendments and the AHJ’s interpretation govern; the contractor of record is responsible for the design.