By Edgar Lim, managing director, UGEngineering
As of August 2021, 13 states have already adopted NEC 2020 and eleven states are undergoing the process of adoption. For the solar industry, these updates to the electrical code will impact project engineering, improve safety and ensure that regulations keep up with the pace of technological advancements. There are several key takeaways that every installer should know to minimize safety hazards and avoid 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 be adopting it in the coming months. (For the latest adoption status, please visit NFPA’s website here.) That means changes could already be effective in your state, and if not, they’ll be happening soon.
Conductors, conduits and OCPDs
The first revision to explore is within Article 690.8. It was rearranged for clarity and 690.8(A)(2) was added to introduce language that provides an alternative to the maximum circuit current calculation. Previously, the only method for calculating the maximum current of a string was through the multiplication of the maximum output of the PV module by 1.25 for irradiance correction. Now, we can base it off the rated input current of the conversion equipment, typically an inverter. This alternative method is more permissible and could result in smaller conductor sizes, sometimes by up to two standard sizes. In light of the upward trend for raw material prices, this could result in substantial savings in both copper conductors and conduit costs.
The next notable change is within Article 690.9(A). It now contains clearer language and leaves less room for interpretation regarding overcurrent protection of PV systems. Per 690.9(A)(3), installers now have the option of locating the Overcurrent Protection Device (OCPD) at either the supply end or the load end of the circuit in certain scenarios.
Module-level rapid shutdown updates
There were some modifications related to rapid shutdown within Article 690.12. The requirements for conductors outside the array boundary (1 ft from the array in all directions) hasn’t changed, but the code now allows the use of PV hazard control systems that are certified to the UL 3741 standard for conductors inside the array, such as the upcoming P1101 optimizer from SolarEdge. Installers will still have the option of using solutions that reduce the voltage within the array to 80 volts within 30 seconds or totally isolating the system with no exposed wiring methods.
The labeling requirements for rapid shutdown-equipped systems were modified within Article 690.56(C). The label verbiage for array-level rapid shutdown was removed since all rooftop PV systems complying with NEC 2020 will now require de-energization at the module-level. Regarding the location of the labels, it must be affixed to each piece of service equipment. However, it should be noted that the definition of service equipment is not limited to just service disconnects, so installers might need to affix it to other AC equipment depending on local AHJ interpretation.
There was language added to Article 690.13 requiring accessible disconnects to be equipped with a lock system or other solutions requiring a tool to open the enclosure. This is to mitigate risks associated with unintentional contact of live components by unqualified persons. Section E of the article lists all the types of disconnect switches that this requirement extends to, including remote-controlled switches that are operable locally.
The next notable change is within Article 690.31. It now contains a table for correction factors going up to an ambient temperature of 120°C, up from 80°C previously. This applies to situations where conductors with higher temperature ratings are used, such as 125°C-rated XLPE cables. Revisions were made in section 690.31(B) that now allow for Class 1 circuits to be placed in the same raceways as DC circuits. The section was also modified to include the requirement of a marking scheme for the polarity of PV system conductors. When conductors are not color-coded, they have to 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 required to troubleshoot ground faults during commissioning and O&M of systems. It can also help prevent crossed polarity during installation, which could be hazardous to installers.
The maximum distance between supports for a single-conductor 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 multiconductor jacketed cables (commonly referred to as MC Cables) and proper installation methods for both rooftop and ground mount applications.
Intermateability of cable connectors used for the connection and splicing of PV conductors is now addressed within Article 690.33. Mismatched connectors have been shown to increase the likelihood of electrical arcs, which is one of the top causes of PV thermal events. It is not uncommon to see a pairing between Staubli MC4 (Multi-Contact 4mm) connectors that come pre-installed on many module-level power electronics, and “MC4 Compatible” connectors that come standard with certain PV module manufacturers. Mismatched connectors have also been observed at string wiring and DC homerun splices when installers do not procure connectors of the same make and model that come with the specific PV module. Connectors from different manufacturers might have differing tolerances during the manufacturing process, which could result in water ingress, hot spots and potentially thermal events in worst-case scenarios. This code revision now shines light on this issue and should help to minimize the occurrence of mismatched connectors by requiring a 100% match.
There are notable changes related to the interconnection of PV systems within Article 705, including clearer language around supply-side connections and disconnecting means. Section 705.13 was added to address the use of power control systems (PCS), which could enable larger system sizes where export is limited by the utility.
It is prudent for developers and EPCs to work with engineering firms that are familiar with the latest electrical code and commercially available solutions to ensure their systems are engineered for safety and reliability. In addition, properly engineered systems take both constructability and O&M into consideration.
Edgar Lim spearheads the technical consulting services business unit for UGE International. He is in charge of strategic growth and execution of projects for our portfolio of respectable clients. After spending more than a decade within the industry, Edgar has experience working in various capacities throughout the lifecycle of solar plus storage projects from business development through to asset management on over 200 MW of commercial and utility-scale projects. Edgar is a North American Board of Certified Energy Practitioners (NABCEP) PV Installation Professional and holds a B.S. in Mechanical Engineering from the Georgia Institute of Technology.