By Edgar Lim, Director, UGE engineering
As of August 2021, 13 states have already adopted NEC 2020 and 11 states are undergoing the adoption process. For the solar industry, these electrical code updates will impact project engineering, improve safety and ensure that regulations keep pace with technological advances. There are several important things every installer should know to minimize security risks and prevent code violations.
States that have already adopted NEC 2020 include Colorado, Minnesota, Massachusetts, and Maine. California, Connecticut, North Carolina, Rhode Island and a few others have started the process and should take over in the coming months. (For the latest adoption status, visit the NFPA website) here.) That means changes in your state may already be effective, and if not, they will happen soon.
Conductors, conduits and OCPDs
The first revision to be examined falls within Article 690.8. It was rearranged for clarity and 690.8(A)(2) was added to introduce language that provides an alternative for calculating maximum circuit current. Previously, the only method to calculate the maximum current of a string was to multiply the PV module’s maximum power by 1.25 for irradiance correction. Now we can base it on the rated input current of the conversion equipment, usually an inverter. This alternative method is more acceptable and can lead to smaller conductor sizes, sometimes up to two standard sizes. In light of the upward trend in commodity prices, this could lead to substantial savings in both copper conductors and piping costs.
The next notable change is in Section 690.9(A). It now contains clearer language and leaves less room for interpretation regarding overcurrent protection of PV systems. According to 690.9(A)(3), installers now have the option to locate the overcurrent protection device (OCPD) on the supply side or the load side of the circuit in certain scenarios.
Module-level rapid shutdown updates
There were some changes related to quick shutdown in Article 690.12. The requirements for conductors outside the array boundary (1 ft from the array in all directions) have not changed, but the code now allows the use of PV hazard control systems certified to the UL 3741 standard for conductors within the array, such as SolarEdge’s upcoming P1101 optimizer. Installers still have the option of using solutions that reduce the voltage within the array to 80 volts within 30 seconds or completely isolate the system with no exposed wiring methods.
The labeling requirements for systems equipped with quick shutdown have been changed in Article 690.56(C). The rapid shutdown verbiage at the array level has been removed as all NEC 2020 compliant rooftop PV systems must now be shut down at the module level. As for the location of the labels, they should be affixed to any service device. However, it should be noted that the definition of service equipment is not limited to service interruptions only, so installers may need to apply it to other AC equipment depending on the local AHJ interpretation.
Text has been added to Article 690.13 requiring accessible disconnects to be fitted with a lock system or other solutions requiring a tool to open the housing. This is intended to reduce the risks associated with accidental contact of live components by unqualified persons. Section E of the article lists all types of isolating switches subject to this requirement, including remotely operated switches that can be operated locally.
The next notable change is in Article 690.31. It now contains a table for correction factors that go up to an ambient temperature of 120°C, previously 80°C. This applies to situations where conductors with higher temperature ratings are used, such as XLPE cables with a rating of 125°C. Revisions have been made to Section 690.31(B) to allow Class 1 circuits to be placed in the same raceways as DC circuits. The section has also been amended to include the requirement of a marking scheme for the polarity of PV system conductors. If conductors are not color coded, they should be labeled “+”, “POSITIVE” or “POS” for the positive conductor and “-“, “NEGATIVE” or “NEG” for the negative conductor. Properly labeled and color coded conductors can help reduce the time it takes to resolve ground faults during system commissioning and O&M. It can also help prevent crossed polarity during installation, which can be dangerous for installers.
The maximum distance between supports for a single guide is now 24” instead of 12”, which was the previous requirement. This will help increase labor efficiency when performing O&M on PV systems, as the previous maximum support distance made it challenging to remove PV modules. 690.31(C) now covers the use of multi-conductor cables (commonly referred to as MC cables) and proper installation methods for rooftop and ground applications.
The interconnectivity of cable connectors used for the connection and splicing of PV conductors is now dealt with in Article 690.33. Connector mismatches have been shown to increase the likelihood of electric arcs, which is one of the major causes of PV thermal events. It is not uncommon to see a link between Staubli MC4 connectors (Multi-Contact 4mm) that come pre-installed on many module-level power electronics, and “MC4-compatible” connectors that come standard with certain PV manufacturers. modules. Connector mismatches have also been observed in string wiring and DC homerun connections when installers do not purchase the same brand and model connectors that come with the specific PV module. Connectors from different manufacturers can have different tolerances during the manufacturing process, which in the worst case can lead to water ingress, hot spots and possibly thermal events. This code revision now sheds light on this issue and should help minimize the occurrence of connector mismatches by requiring a 100% match.
There are notable changes regarding the interconnection of PV systems in Article 705, including clearer language around supply-side connections and means of decoupling. Section 705.13 has been added to address the use of power management systems (PCS), which could allow for larger system sizes where exports are restricted by the utility.
It makes sense for developers and EPCs to work with engineering firms familiar with the latest electrical code and commercially available solutions to ensure their systems are designed for safety and reliability. In addition, well-designed systems consider both buildability and O&M.
Edgar Lim leads the technical advisory services business unit for UGE International. He is responsible for strategic growth and project execution for our portfolio of respectable clients. Having worked in the industry for over a decade, Edgar has experience working in a variety of capacities throughout the life cycle of solar plus storage projects from business development to asset management on over 200 MW of commercial and utility projects. Edgar is a North American Board of Certified Energy Practitioners (NABCEP) PV Installation Professional and holds a BS in Mechanical Engineering from the Georgia Institute of Technology.