Rapid Shutdown- A Wonderful Electrical Safety Requirement

If you’ve just installed a solar panel system, or are looking at pictures of it, you may notice a box with an on/off switch that says “Rapid Shutdown.” But what does a rapid shutdown mean? Why is it important for solar panel systems?

As we all know, photovoltaic (PV) technology is evolving rapidly and we are seeing more and more rooftop solar PV arrays being installed on residential and commercial properties. While PV array equipment must be certified for safety against impact and fire risks, these certifications do not take into account all of the specific interactions with firefighters working around the arrays during fire suppression.

Many countries have realized the importance of safety measures to guarantee safe solar operation and allow firefighters and other emergency personnel safe access to roof areas. That’s where rapid shutdown comes into play.

An Introduction to Rapid Shutdown

It is an electrical safety requirement set by the National Electrical Code (NEC) for solar panel systems. Simply put, it provides a quick way to shut down a rooftop solar panel system.

The National Fire Protection Association (NFPA) wrote the rapid shutdown requirement into the NEC in an effort to keep first responders safe. Hopefully, your home never catches fire and you don’t even have to worry about the rapid shutdown feature – but if that happens, firefighters can use the rapid shutdown solution to shut down your solar panel system in case they need to get on your roof. Surprisingly, this is not always the case with simply turning off a solar inverter: with some solar inverter settings, wires and circuits can retain energy even when the solar inverter is turned off, increasing the risk of electric shock for firefighters working on rooftops or attics. A rapid shutdown switch allows firefighters to physically pull the switch in less than a minute, reducing the voltage of the solar panel system to a safe level.

The rapid shutdown requirement most familiar to installers today was first introduced in 2014; Among other things, the regulation sets a standard for rapidly reducing the voltage of any conductor (i.e., material in a wire or cable flowing through) if those conductors are located more than 10 feet outside the array, or at least 5 feet long within a building. The latest regulations, NEC 2017, take these standards a step further: The new regulations reduce closing boundary requirements to include any conductor located within 1 foot of your solar array, or more than 3 feet long in your home.

In fact, the NEC 2017 changes stipulate that a rapid shutdown needs to occur on a single solar module, not on an entire solar array. Importantly, NEC is not a federal law — individual states can choose to adopt and comply with it, as can individual cities or municipalities. This means that your state’s rapid shutdown requirements may differ from adjacent states (we’ll talk more about this later).

What Are The Legal Requirements of a Rapid Shutdown?

It is a requirement of the National Electrical Code (NEC). Every three years, the NEC issues an updated set of requirements for safe electrical systems. The NEC is not federally mandated and each state adopts the code at its own time and judgment. Some states choose a separate statewide electrical code.

If you live in a state that utilizes NEC 2014 or higher, your solar system will need to follow the NEC Rapid Shutdown Requirements in order to pass the final inspection of your system and connect it to utilities and power.

Below is an overview of the various editions of the National Electrical Code for quick shutdown:

NEC 2014

In 2014, when the first set of regulations was enacted, requiring any conductor (i.e., material in a wire or cable flowing through) to be more than 10 feet outside the array, or at least 5 feet inside a building, there was a rapid shutdown switch that required a rapid voltage reduction in an emergency.

NEC 2017

The regulation was revised in 2017 and expanded to include closures at the individual solar module level, rather than at the entire solar array level. This regulation change means it requires you to power down any conductor 1 foot away from the array to 80 volts in 30 seconds with a rapid shutdown switch, instead of the 10-foot area of NEC 2014.

NEC 2020

Not much has changed with the recent regulatory upgrades. The most notable change is the array-wide guidelines. Instead of a UL Listed or Field Marked Rapid Shutdown System, they now require a UL Listed or Field Marked Photovoltaic Hazard Control System (PVHCS).

Three Ways to Meet The NEC Requirements For 2017

Install a “listed” or field-marked rapid shutdown system

The word “listed” comes from the original name of the UL certification program a century ago. The National Electrical Code uses the word “listed” but does not specifically state that products and systems must be UL certified – but instead talks about the main characteristics of organizations that provide certification services. Obviously, UL believes that manufacturers should be UL certified that their products can be shut down quickly, but so can other nationally recognized test laboratories.

UL has been very active in working with the industry and other stakeholders, such as the emergency response community, to develop these requirements, trying to give the same confidence to emergency responders who interact with these systems as they perform their vital duty to protect society, people and property, and UL wants to make them as safe as possible.

At Solar Energy International 2019, many solar inverter and rapid shutdown equipment manufacturers demonstrated their SunSpec certification. SunSpec has developed important protocols for communication between different devices during rapid shutdowns, but is not a public body like UL. Simply seeing the SunSpec label does not tell the installer that the product is NEC 2017 Rapid shutdown certified.

Another part of the first compliance option, site marking, refers to a limited engineering assessment that is performed after installation at a specific site. If the installation meets NEC 2017 requirements, it can be marked as a rapid shutdown system if allowed by AHJ.

Install a system that can reduce the voltage to 80V in 30 seconds

Microinverters are often considered inherently suited to rapid shutdown because they convert a high-voltage DC power supply into a lower voltage, safer AC power source that can drop to 80V in 30 seconds. However, according to Boyce, the 2017 NEC did not specifically discuss microinverters as a way to meet rapid shutdown requirements.

Some microinverters are designed to have capacitance at the front end of the circuit, so unless the inspector actually makes a voltage measurement, there is no way to know if it is below the 80V limit. UL has proactively performed these tests to verify that some microinverters can meet the 80 V threshold, but testing after the solar inverter is installed is a challenge.

BIPV Installation: Avoid Metal Components and Grounded Metal

When installing the BIPV system, do not install metal components, do not install exposed conductors, and do not install within 8 feet of grounded metal.

Solar shingles, tiles, or other building-integrated photovoltaic (BIPV) systems that do not contain metal parts or bare conductors or are not near any grounded metal can meet the requirements of NEC 2017. These systems are isolated from grounding and conductive components.

What Makes a Rapid Shutdown System?

There are a few critical components involved in a rapid shutdown system:

First is a Rapid Shutdown Device (RSD). Rapid shutdown devices are a type of module-level power electronic (MLPE) or microinverter that are installed on the backs of solar modules. They are equipped with technology that can turn off and reduce voltage output throughout the solar system to adhere to PV Rapid Shutdown regulations. An example product is the Tigo TS4-A-F or 2F which is our MLPE with Rapid Shutdown compliance only, but Tigo offers multiple MLPE options with Rapid Shutdown compliance.

Another component is an initiator. A rapid shutdown initiator does exactly as the name implies. This device is typically in the form of an emergency stop (e-stop) button that is in an inverter. Typically, Rapid Shutdown can be initiated in two ways, either manually (through an e-stop button) or automatically (loss of power from the grid).

Lastly, you will need an solar inverter in a rapid shutdown system. An solar inverter is a device that converts the electricity produced by the solar modules into usable energy for your home (for more information on this process read our previous blog). Many Rapid Shutdown initiators are located inside the solar inverter.

These three components are referred to as Photovoltaic Rapid Shutdown Equipment (PVRSE). These are equipment used in a rapid shutdown system that reduces the voltage to a safe level. The US National Electrical Code mandates that PVRSE and PVRSS are to be UL Listed for the purposes of rapid shutdown.

Do All Inverters Have a Rapid Shutdown Function?

Some solar inverter systems are inherently compliant with module-level rapid shutdown (NEC 2017 and later), while others require additional components for rapid shutdown.

Microinverters and power optimization systems are the most popular solar inverter choices for residential solar panel systems in the United States. Fortunately, both the microinverter and the power optimizer operate in the field on the battery board and have a built-in rapid shutdown feature.

If you install the series drive yourself, you may also need to install module-level power electronics (MLPE) to comply with NEC 2017 or NEC 2020. Pairing the power optimizer with a string solar inverter should do this. However, power optimizers aren’t your only option for rapid shutdown – as more states begin to adopt NEC 2017, many string solar inverter manufacturers or other solar companies have established new MLPE technologies with rapid shutdown capabilities. In many cases, these MLPEs, created specifically for rapid shutdown, may be a more economical option than installing a power optimizer or microinverter.

Why Do You Need Rapid Shutdown Device?

It is essential for solar systems installed on rooftops. Even though the pipes from panel to panel are completely safe, there are individual cases where these pipes can be damaged by the sun. If this happens, anyone close to the system could be exposed to live electricity and could lead to a dangerous situation. But with the help of a rapid shutdown feature, emergency personnel can quickly cut power to these pipes, providing them with safe access to locations around the solar system.

The conductors of the solar panel system are charged any time the sun shines. Without this device, there is no safe way to turn off the current flowing through these conductors.

Most people would think that they can cut off the power just by turning off the solar inverter, but this is not the case. Solar panels will still generate electricity. Solar panels’ cables will still produce electricity.

This charged current poses a risk of electric shock to anyone who comes into contact with a solar panel system, including first responders who may be dealing with emergencies on the roof of your home.

Firefighters are particularly at risk because they often ventilate burning buildings by drilling holes in roofs or walls, which can put them directly in contact with conductors or wires in solar panel systems.

Solar Rapid shutdown solves this problem by shutting down the solar panel system within a minute, eliminating the risk of anyone getting electrocuted on the roof.

Schlussfolgerung

Rapid shutdown requirements are being adopted globally to protect firefighters working around solar PV installations. NEC requires the voltage to be reduced to a safe level by using a series of devices (PVRSE) that make up a quick shut-off system (PVRSS). Inverters, starters and quick-shut-off devices such as MLPEs or microinverters are necessary components for NEC compliance.

It is a safety requirement imposed by the U.S. National Electrical Code (NEC) that requires switches on solar panels that can cut off power flowing through the system. A rapid shutdown reduces the voltage of the conductors in wires and cables, protecting your house from catching fire quickly.

In addition, it protects first responders, such as firefighters, allowing them to quickly cut off power in the conductors, allowing them to safely access areas near the system.

The solar system rapid shutdown is only suitable for solar systems installed on the roof. If you’re interested in installing solar in your home, hopefully this tweet has helped you understand the rapid shutdown and improve the safety of your solar system.