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September 15, 2020

Rapid shutdown compliance for US rooftop PV systems

What to know and what to look for

At Tigo, we have been getting a lot of questions surrounding the rapid shutdown requirements as part of NEC 2017 and 2020. Below is a compilation of information on the most relevant subjects related to NEC and Rapid Shutdown System requirements.

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With 35 states (and growing) adopting NEC 2017+, these requirements cover the majority of the US. For the latest list of states, visit nfpa.org

Background / basic requirements:

The specific rapid shutdown requirements are listed in NEC 2017 Section 690.12. Essentially, new rooftop systems require module level rapid shutdown devices with the following criteria.

  • The PV array boundary is defined as 1ft (305mm) from the array in all directions
  • Within 30 seconds or rapid shutdown initiation:
  • Outside the PV array boundary - controlled conductors must be limited to not more than 30 volts  
  • Inside array boundary - controlled conductors must be limited to not more than 80 volts
  • An initiation device (or devices) shall be used to initiate the rapid shutdown sequence
  • The system and the components of the system that perform the rapid shutdown function must be UL certified

UL Certification

The deployment of rooftop PV systems that are not tested and certified by UL exposes installers to potential damage to personnel and property and to regulatory and warranty violations. The key is that both the inverter model as well as the rapid shutdown device being used have been tested and certified together as a “system” under UL PVRSS (Photovoltaic Rapid Shutdown Systems). Details:

  • UL system level rapid shutdown certification is mandatory under NEC 2017 and the only certification relevant to rapid shutdown compliance and acceptance from permitting authorities (AHJs).  
  • NEC 690.12 mandates that rapid shutdown systems be UL listed for the purposes of rapid shutdown. As a result, UL 1741 has created the PV Rapid Shutdown Systems (QIJS) certification that is mandatory for string inverter installations.  
  • UL PVRSS system level rapid shutdown certification requires the inverter manufacturer as well as the rapid shutdown device manufacturer, such as Tigo, to submit for compliance, compatibility, and testing that the two devices work together as a system to safely and effectively provide rapid shutdown compliance in accordance with the guidelines designated by NEC.  
  • Per UL: “When multiple pieces of PV rapid shutdown equipment are used in an overall system configuration, to be Certified (Listed) it is required that the combination be evaluated and tested.”
  • Alternate certification standards that claim interoperability for the purposes of rapid shutdown are not valid under NEC 2017 unless the UL PVRSS certification is in place as the primary certification. As UL has the PVRSS standard, competing certifications are redundant and carry little regulatory authority when it comes to permitting, safety, or compatibility. See UL guidance for more information.

Reliability/Dependability

The purpose of the rapid shutdown requirement is safety. Specifically, it is to “reduce shock hazard for emergency responders” (NEC 2017). Hopefully a site never has to use the rapid shutdown feature, but when it is called upon – which may be years after the installation - it had better work. For this reason, the rapid shutdown system must be reliable.

  • Installers evaluating rapid shutdown devices or any MLPE (module level power electronics) should engage in due diligence efforts to ensure the manufacturer they choose is experienced, bankable, and with a significant real-world installation base.  
  • Tigo has been creating products incorporating safe rapid shutdown principles since our inception in 2007 and are the most experienced MLPE manufacturer when it comes to rapid shutdown applications with multiple inverter types.
  • Tigo’s unique system architecture allows for minimal wear to the electronics, no mechanical switching, and an exceedingly simple PLC-based (power line communication) methodology for RSD compliance – this provides a highly safe, simple, and most importantly, a highly reliable MLPE device that benefits from having the lowest failure rate in the MLPE industry

Ease of Installation/Commissioning/Flexibility

While meeting the certification requirements and installing a reliable solution are critical, it’s also important to make sure rapid shutdown doesn’t add unnecessary cost or complexity to your installation. Tigo provides the most cost effective and simplest method of rapid shutdown compliance in the MLPE space. Here’s how we do it.  

  • Tigo’s module level devices can be installed to a module in 30 seconds or less – with no additional grounding or bonding required and no hardware necessary.
  • Tigo’s rapid shutdown products allow plug-n-play functionality with 200+ commercial and residential inverter models  
  • Tigo also provides the most flexible product platform, allowing you to choose your functionality as needed to save time and money. We have options for: Rapid Shutdown (RSD) only, RSD + Monitoring, and RSD + Monitoring + Optimization
  • Tigo provides MC4 connectors as the standard connector offering to satisfy the majority of the market

Partners and Compatibility

When evaluating an RSD device, simply look to the inverter manufacturer – what are they using?

  • Nearly every major string inverter manufacturer operating in the USA and globally has chosen Tigo as their rapid shutdown and MLPE partner. Many have also integrated Tigo devices within their inverters to provide installers with a simple and cost-effective solution that is easy to install and commission.  
  • In addition to UL PVRSS certification validating rapid shutdown functionality, Tigo also ensures that comprehensive testing with the inverters’ other functionalities are not affected through the use of MLPE.  
  • Tigo enjoys the largest list of integrated module partners in the USA and globally. With over 40 manufacturers currently offering Tigo integrated options, customers get the freedom to choose from many options for RSD and MLPE deployment.  
  • Both inverter and module manufacturing partners practice due diligence and engage in significant testing of the Tigo product prior to adopting the Tigo solution and certifying with UL.

If you’re looking for more information on this subject, you can see our full list of solutions and certifications at our downloads.

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