Rapid shutdown: How it makes solar systems safer

Rapid shutdown: How it makes solar systems safer

March 7, 2022 Uncategorized 0
Rapid shutdown | Wolf Track Energy

While researching solar panels, you may have come across the term “rapid shutdown.” But what does that mean? 

Rapid shutdown refers to a set of safety requirements meant to protect first responders from live electrical equipment on your roof. In the event of a fire, firefighters want to be sure that they’re not endangered by high voltages coming from your solar panels.  

As the name implies, first responders want to be able to rapidly shut down the solar system before jumping on the roof.  

Let’s get a bit more detail about how this works.  

Shut it down 

Imagine that there’s a house on fire. Firefighters arrive promptly and, to reduce the danger of entering the home, they or the utility disconnect power to the home.  

But in this case, the house has solar panels on the roof. Electricity may still be flowing, not from the power lines that supply the rest of the neighborhood, but instead from the panels on top of the roof. Firefighters may need to cut a hole in the roof, but are worried that high voltages coming from the solar system may be present.  

That’s where rapid shutdown comes into play.  

Over the past decade, the National Electric Code has been updated to require rapid shutdown systems to reduce hazards first responders may face when working on a house with solar panels.  

The NEC is published by the National Fire Protection Association and guides the safe installation of electrical equipment. While the code is not the law itself, most states have adopted its newer rapid shutdown requirements, including Minnesota and Wisconsin.  


So what does rapid shutdown mean? It involves reducing the voltage coming from the solar panels.

For conductors located outside one foot of the solar array and more than three feet from the entry point of the building, voltage must be reduced to 30 volts within 30 seconds.  

There are a couple of options for meeting the NEC requirements outside the array boundary, but in general, the 2017 update to the rules require “module-level rapid shutdown instead of the array-level rapid shutdown.” That means some kind of module-level electronics like microinverters or optimizers are needed, according to Aurora Solar

Over at altE Store, they have an informative history of the NEC requirements.  

If you remember from a previous blog, microinverters convert DC electricity produced by each solar panel into AC electricity. Optimizers “condition” energy coming from each solar panel before they reach the central inverter.  

As EnergySage notes, microinverters and power optimizers made by Enphase and SolarEdge have rapid shutdown systems built in. For example, Enphase boasts that its safety system kicks in when the electricity coming from the power company is disconnected.  

Bottom line 

The NEC requirements are a reminder of how the growing solar industry is evolving and responding to safety concerns as panels become more commonplace.  

This was only a brief overview of the rapid shutdown rules. If you want to read the NEC language yourself, click here.  

A licensed and certified solar installer like Wolf Track Energy will know the ins and outs of the electrical code, so you won’t have to worry about whether your system is compliant with the requirements.  

Read more from Northland’s solar energy experts:

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