Introduction: Rapid shutdown requirements for PV systems have spurred innovations within the industry since the requirement first appeared in the 2014 National Electrical Code (NEC). The requirements imposed by rapid shutdown often seemed ahead of their time. So much so that the 2017 Code provided an allowance to waive a specific subsection for two years to allow the industry to catch up and create products to meet the Code. One of these delayed provisions in 2017 allowed systems “listed or field labeled as a rapid shutdown PV array” to provide the necessary limits of PV conductors within the ..read more

“Is it possible to add a PV system disconnect as a supply-side interconnection when a service has six main disconnects already installed?” The short answer to this common question regarding system disconnects as supply-side interconnection is that the NEC simply does support this type of installation. In this article we present the specific relevant Code sections and a broader explanation of reasoning. Figure 1. PV system interconnections are permissible to electric services with six existing disconnects. The first step in this analysis is defining the maximum number of service disconnects. 2 ..read more

With a maturing PV industry, more inverters are coming to the end of their life and needing replacement. Inverter failures usually occur on systems that are 10+ years old. At this age, the rest of the system, including the PV array, is typically still in good working order with a lifespan of 25 to 30 years. It is financially advisable to take advantage of the rest of the system's components' longer lifespan. Thus, many PV system owners are requesting a repowering and reconfiguring exercise with upgraded replacement inverters. This replacement could also be a requirement of a PPA or utility co ..read more

In this edition of our Code Corner series, we cover the energy storage fire codes timeline. Looking at the history of the fire codes, which is actually provided as an annex in the NFPA 855 document, we can see that stationary energy storage is not a new topic—it has been covered by the Uniform Fire Code (UFC) since 1997. That's 25 years of actual codes that have been implemented, although it was really only for commercial applications and only for vented (or flooded) lead acid batteries. Back then, systems with a liquid capacity of greater than a hundred gallons of electrolyte had to be regula ..read more

In this edition of Code Corner, we're talking about NFPA 855, Standard for the Installation of Stationary Energy Storage Systems. In particular, spacing requirements and  limitations for energy storage systems (ESS). NFPA 855 sets the rules in residential settings for each energy storage unit—how many kWh you can have per unit and the spacing requirements between those units. First, let's start with the language and then we'll explain what this means. In Section 15.5 of NFPA 855, we learn that individual ESS units shall be separated from each other by a minimum of three feet, unless small ..read more

Welcome back to Code Corner from Mayfield Renewables. I'm Ryan Mayfield and I'm here with Ry Heller, one of our senior design engineers. And we're gonna talk more about 7 05.12(B)(3)(3) and (4). Two weeks ago, we talked about (B)(3)(1-2), available here, so this is just a continuation of this code section and how to apply it. First off, (B)(3)(3) is just another option for one of the calculations that you can do to determine how to size your panel, and if you can put PV on it. For this one, also called the sum of breaker rules, you're just looking at the sum of all the overcurrent device ratin ..read more

Our previous installment of our Microgrids blog series (“Microgrids in Practice”) discussed some of the pros and cons of microgrids, including real-world examples of beneficial (and profitable) microgrids already in place today. Residential buildings, large commercial stores, and even entire university campuses can see increased resiliency and reliability, all at a lower generating cost than traditional grid-tied rates. There are many variables that affect the overall results of the microgrid, starting with site-specific weather data and infrastructure will determine the total output potential ..read more

Welcome back to Code Corner, from Mayfield Renewables. My name is Ryan Mayfield and I have Ry Heller, one of our senior design engineers, with me today, to talk about NEC 705.12(B)(3)(1) and (B)(3)(2). These are interconnection sections, and some of the most commonly-utilized sections that we use when we're interconnecting our PV systems to our utility systems. First, let's talk about what those code sections are and what they say – 705.12(B)(3)(1) is saying is that the sum of 125% of the power source output circuit current and the rating of the overcurrent device protecting the bus bar shall ..read more

In our last installment of our Microgrids Blog Series (“Microgrids Explained”), we defined microgrids and the three distinct features that distinguish them from a normal ‘macrogrid’:  an easily identifiable boundary from the rest of the grid resources within the microgrid are controlled together the microgrid can function whether or not it is connected to the larger grid; and also discussed some higher-level applications of microgrids, including cost-cutting, emergency backup, and extended islanding. Microgrids can be a driver for grid reliability, resiliency, security, and contro ..read more

Welcome back to Code Corner by Mayfield Renewables, today we're gonna talk about some more supply side connections in NEC 2020 section 705.11, specifically (C) and (D). We have another code corner where we talked about the first two sections, available here, so today I want to focus on these rules for (C) and (D), how they get put into play, and how we're going to apply those for our installations. So let's first look at the code language, and (C) is clearly about over current protection. How are we going to protect these conductors when we are making connections on the supply-side of our PV s ..read more