How Yaskawa - Solectria Solar PV Inverters Meet NEC 2014 Arc-Fault and Rapid Shutdown Requirements
For 33 out of 50 states in the country, the 2014 version of the National Electric Code (NEC) is currently in effect. Several more will adopt this version by the end of the year. The National Electric Manufacturers Association (NEMA) maintains a list and map of which state follows which revision of the NEC available here: https://www.nema.org/Technical/FieldReps/Documents/NEC-Adoption-Map-PDF.pdf.
In April 2016, Yaskawa – Solectria Solar produced a webinar that explored the primary considerations of achieving compliance with NEC 2014 for arc-fault detection and rapid shutdown requirements. Information in this webinar is valuable for those having to comply with NEC 2011 and 2014 arc-fault detection requirements.
Topics discussed included:
- Achieving AFDI and rapid shutdown compliance for central inverters using string combiners
- Achieving AFDI and rapid shutdown compliance for three-phase string inverters
- Arc-fault detection technology basics
- An introduction to Yaskawa – Solectria Solar's arc-fault compliant string combiner (ARCCOM)
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What is Required by NEC 2014 Rapid Shutdown (Article 690.12)?
PV system circuits installed in or on buildings shall include a rapid shutdown function that controls specific conductors in accordance with NEC 2014, Article 690.12 (1) through (5). These requirements include:
- Control the voltage of conductors more than 10 feet array from the array and the voltage of conductors more than 5 foot in length inside a building.
- Shutdown to 30V & 240VA within 10 seconds
- Create an open circuit for both DC poles, do not short circuit
- Correct labels for the solution
- All PV equipment must be listed and identified
How we support Residential PV Inverters:
Requirements: Installer must wire 5VDC control signal from inverter to the Rapid Shutdown Combiner Box on the roof.
Method: This solution attaches right to the rack and integrates with your modules seamlessly with the MC4 connectors. When the AC power is turned off, the inverter turns off, and the contactors in the combiner open. Solectria is one of the only manufacturers to provide a rapid shutdown combiner that includes a bleed- down circuit.
Normally, when the contactors on the roof are opened, the capicitor bank in the inverter can still hold the voltage above 30V for much longer than 10s. By including a bleed down circuit in the combiner, it ensures that the DC circuits meets the shutdown voltage and timing requirements.
How we support commercial & utility-scale string PV Inverters:
Solution: Yaskawa - Solectria Solar PVI 14-36TL three-phase, string inverters
Requirements: Place inverter within 10 feet of array (equipment outside), or use compatible third-party rapid shutdown combiners.
Method: When the inverters sense the loss of AC power, they turn off in about a tenth of a second. All the live DC is within the 10 foot boundary and since all the wires outside the boundary are AC circuits, those are de-energized as soon as the AC disconnect is opened.
How we support commercial & utility-scale central PV Inverters:
Requirements: External Control Power REQUIRED for all ARCCOMs. Each ARCCOM contains an AC-DC power supply. The customer must supply external control power 120-277VAC to the AC-DC power supply. If a customer would like to use an external 24VDC control power instead, the internal control power from the AC-DC power supply to the main electronics board must be disconnected.
Method: When control power to the combiners is turned off, the contactors in the combiners open. To fully meet the voltage and timing requirements, the inverters must also be turned off by removing AC power to the inverters.
For XTM, XT, and SGI 225-500, the loss of AC power triggers the DC contactors to open, effectively isolating the DC output circuits from both ends. For PVI 50-100kW, the loss of AC activates a bleed-down circuit so the DC circuits on the roof meet the voltage and timing requirements.
PVI 50-100KW have DC Bleed Down Circuit SGI 225-500PE, SGI 500XT, SGI 500/750XTM have DC Vacuum Contactors
We’ve made a cheat sheet available online: http://solectria.com/pv-inverters/solutions/rapid-shutdown-solutions/
Our Arc-fault Detection Solution: ARCCOM
Our ARCCOM string combiner not only allows you to comply with rapid shutdown requirements, but it is also pairs with our central inverters for a complete arc-fault detection solution. It comes with 8, 12, 16, or 24 fused inputs and there is a future option for MC4 Pigtails.
The ARCCOM supports string level arc-fault detection, which is key. String level arc fault is a much more accurate and reliable detection technology. It significantly reduces the amount of false positives and required trips to the site. It detects a series arc-fault and interrupts it by opening the output contactor.
Contact us if you would like more detail on the ARCCOM.
Looking Ahead: Proposed Changes in the NEC 2017 Draft
We are going to be seeing big change in the rapid shutdown requirements, especially within the controlled limits. They are proposed to go from 10 feet to 1 foot from the array. And the requirement outside of that barrier will change from 30V in 10 seconds to a relaxed 30V in 30 seconds.
The conductors inside the boundary may be limited to no more than 80V within 30 seconds of rapid shutdown, effective as of January 2019.
There will be new labeling and marking requirements as well as an addition of Article 691 which will speak to large-scale PV electric supply stations.
Questions or comments? Contact:
Sr. Applications Engineer
Yaskawa – Solectria Solar
Head of Marketing
Yaskawa – Solectria Solar
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