PV rapid shutdown requirements were added to NEC 2014 (690.12) to improve electrical and fire safety hazards for first responders. System conductors may remain energized even after the electrical service disconnect has been opened. To alleviate this risk, the NFPA has published specific requirements to de-energize conductors extending from a PV array.
PV system circuits installed in or on buildings must include a rapid shutdown function in accordance with NEC 2014, Article 690.12.
Conductors that extend greater than 10 ft from the array (outside) or more than 5 ft inside a building are required to be de-energized upon command of shutdown. These conductors must be de-energized to below 30 and 240 Vac within 10 seconds of initiating rapid shutdown.
Correct stickers or signage should identify the rapid shutdown initiation method, and all PV equipment performing the rapid shutdown shall be listed and identified.
As states and local authorities begin to adopt the 2017 edition of the NEC, it’s important to review the revisions to Section 690.12. While the complete scope of revisions is beyond the scope of this article, a notable revision is that for “array-level” rapid-shutdown compliance, 690.12(B) redefines the term array boundary to be 1 ft from the array in all directions. This is a reduction from the 10-ft boundary of the 2014 edition.
NEC 2017 690.12(B)(2) also introduces requirements for de-energizing controlled conductors inside of the array boundary. This requirement will be not be required until January 1, 2019.
PV equipment location should be carefully considered when installing a rapid-shutdown-compliant system. Below are examples on how compliance can be achieved for systems of various sizes.
Residential PV systems:
For a residential system, rapid shutdown compliance can be achieved by the following means:
- Use of a rapid-shutdown-complaint combiner installed within 10 ft of the array to de-energize conductors extending from the array to the inverter
- Inverter installed indoors with no more than 5 ft of conductors inside the building
- Inverter installed outside within 10 ft of the array
Commercial PV systems (string inverters):
For commercial systems, rapid shutdown compliance can be achieved by the following means:
- Use of a rapid-shutdown-compliant combiner installed within 10 ft of the array to de-energize conductors extending from the array to the inverter
- Three-phase string inverter installed within 10 ft of array (equipment outside) or within 5 ft of array (equipment inside)
When designing a rapid-shutdown-compliant system, consider the DC bus capacitance inherent of PV inverters. The natural discharge time of this circuity may exceed the de-energization requirements of 690.12 for the DC output conductors. Please inquire with your equipment providers for additional information.
Utility PV systems (central inverters):
For utility projects or systems using three-phase central inverters, rapid-shutdown compliance is achieved through rapid-shutdown-compliant combiner boxes installed at the array.
Installation tip was provied by Michael Nieman, applications engineer, Yaskawa – Solectria Solar