Understanding Rapid Shutdown on Residential Solar Installations

The National Electrical Code defines the minimum requirements for safe PV systems, and if you’ve spent any time in residential or C&I solar, you’re definitely familiar with it. Among these requirements, rapid shutdown stands out as a critical safety feature designed primarily to protect firefighters during emergency situations.

In this excerpt from our Residential Grid-Tied Solar Design course, instructor Baker Makarem cuts through the complexity of rapid shutdown requirements with practical explanations. He breaks down the critical definitions of array boundaries and voltage limitations that impact your everyday installations, and also explores the newer PV Hazard Control System (PVHCS) approach – a compliance option that can reduce the amount of electronics on the roof while maintaining code compliance.

To dive deeper into the fundamentals of residential solar design, considering enrolling in Baker’s Residential Grid-Tied Solar Design course.

Transcript below.

First of all, they want us to define an array boundary. The term array boundary is a perimeter that consists of no more than one foot from the array in all directions. Anything that is inside is considered the array boundary. 

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That’s important because for the most common scenarios with the NEC requirement says that everything that is inside that array has to have that rapid shutdown requirement. Once this is initiated, it has to be no more than 80 volts within 30 seconds. It means I need to have an activation method to initiate that rapid shutdown. Once I do it, usually it’s the PV AC disconnects, I’m saying usually in a grid-tied system/no batteries. 

Once you activate that AC disconnect, it will trigger the rapid shutdown. What’s going to happen is that everything that is within that boundary will not exceed 80 volts and everything outside that boundary cannot exceed 30 volts. Those are going to be my requirements, if we want to write it down here. That applies also for microinverters. 

Before we jump to that,  what they mention there is anything inside the array boundary shall I comply with one of the following…

The first one, I’m not going to cover it. This is something practically new, even though it was implemented in the [NEC] cycle of 2020. Many jurisdictions here in the United States are three years behind any code cycles.

Basically what it means is like it allows me to have a voltage greater than 80 volts inside the array, as long as I can comply with certain requirements from them, and it has to be [UL] listed. 

Basically what it means is as long as it’s within that array boundary, or that array boundary defined by the listing, it can be greater than 80 volts, but anything outside cannot. 

This is one way to also mitigate electric hazard, because once the fire department is on the roof, at least they know that the system is a PV hazard control (PVHCS). It means that we don’t deal with anything on the solar panels or anything closer to the solar panels, because we know that that voltage is greater than 80 volt. 

It basically also helps to reduce the amount of electronics that you’re going to need to have on the roof, because once you start installing solar panels on a roof of a house, now you need to comply with rapid shutdown. It means you need to install rapid shut down devices on the roof, so more electronics in this harsh environment. It means that the rate of failure is going to be greater. That’s what the PV hazard control is – it just limits the amount of electronics that can be installed on the roof as long as I can follow what the manufacturer’s requirements are. 

I’m going to have one of those white papers in the document reference for you to review. If you want to know a little bit more, you are always free to reach out to me or talk to Google about it.