Why do we need rapid shutdown device?

In general, the operation and maintenance time of a photovoltaic power station is 25 years. As the equipment ages, the probability of fire accidents increases exponentially. Problems such as component hot spots, string mismatch, cable damage, tight connections, and dust accumulation in the inverter can easily cause fire in photovoltaic power stations.

When a station is on fire, if only the AC power from the inverter to the grid is turned off, there will still be hundreds or even thousands of high voltages on the DC side in between each panel and to the inverter. In this case, it is too dangerous for firefighters to climb on the roof to extinguish the fire. At the end, you may just have to let the property burn.   

That’s the main reason that rapid shutdown regulation were first implemented in 2014 as a safety precaution by National Electrical Code (NEC), making it necessary for solar power systems to have a solar panel shut-off switch. With the regulation, solar power systems must have a “hazard control system” to make it in controllable state in critical situations. Control conductors shall be limited to not more than 30 volts and 240 volt amperes with in 10 seconds of rapid shutdown initiation.

Rapid shutdown device can cut off the current in between each panel and to the inverter, and create a safe rescue environment for firefighters, reduce fire losses, and ensure the safety of people and property.

<Schematic diagram of rapid shutdown operation >

How to Choose the Right Rapid Shutdown Device?

Today, there are numerous rapid shutdown options on the market. Yet, many of them embedded with AC switches that are far from enough, the arc extinguishing capabilities and rated load cut-off power of these switches aren’t efficient and can easily be distorted or become overheating. In this case, it may bring greater safety risks to the solar power system. Thus, how to find a suitable and reliable rapid shutdown device has become the main concern to installers.    

Choose a well-known brand that obtains international certifications  

Commonly used certifications for rapid shutdown are CE-LVD, CE-EMC, TUV, UL, etc. Embedded DC isolating switches with IEC60947-3 (Europe standard, applicable to Asia-Pacific), GB14048.3 and other certifications. Most of the big brands that specialize in rapid shutdown have these certifications, such as Projoy Electric. 

Choose a brand that offers full-range products with advanced technology and excellent after-sales service 

Well-known brands often have a complete range of power segments. For example, Projoy Electric has launched a series of string-level rapid shutdown (so called Firefighter Safety Switch) and soon became popular in European countries such as Germany and UK, as well as Southeast Asian countries like Thailand and the Philippines. Today, the company is a first-tier brand in Europe and Asia-pacific markets. 

To meet the diverse needs of global customers, Projoy Electric follows the localization market strategy, and develops authorized distributors in different countries and regions, providing quick and effective after-sales services to the clients. 

<Application of Projoy Rapid Shutdown in Various Environments>

Choose a brand with all needed functions  

First of all, the rapid shutdown device should come with functions such as automatic detection of the ambient temperature, it can shutdown automatically when overheating is detected. The key factor to rapid shutdown is timing. Due to the large output voltage and current of the inverter, the circuit has to be cut off in time when a fault occurs, or a serious incident may happen. Therefore, the automatic detection and shutdown function of the rapid shutdown device is a must.

Secondly, the rapid shutdown device should meet the international standards for firefighter work procedures. When a fire breaks out, firefighter can press the emergency stop button manually to cut off the AC power of the rapid shutdown control box, or cut off it remotely via fire alarm system, as the rapid shutdown device will automatically disconnect the DC side to create a safe operating environment for firefighters.   

Finally, the rapid shutdown device should be able to reset and reconnect the circuit automatically when the power is restored, so that you do not need to manually reset every time. 

<Shutdown Mode>

Choose a brand with high on-off capacity and excellent arc extinguishing effect

The on-off capacity and arc extinguishing effect is one of the most important factors for evaluating rapid shutdown device. A fine rapid shutdown should be equipped with a special arc extinguishing with excellent effect. For example, there is no direct connection between the handle and the contacts of the spring energy storage switching device in the string-level rapid shutdown. The contacts are not directly rotated and disconnected when it turns on and off. When the handle rotates or moves to a specific point, the spring triggers all the contacts suddenly disconnect, so a very fast on-off action is generated, which greatly shortens the arcing time. Other factors such as contact pairs, special self-cleaning designs, arc-extinguishing magnets also play important roles in the arc-extinguishing effect. Generally speaking, a good arc of DC switches can be extinguished within a few milliseconds. Such as Projoy's string-level rapid shutdown extinguishes the arc within 5ms, while the arc generally improved from AC lasts for about 100ms. 

Choose a brand with high flame retardant and protection level

While rapid shutdown device is mostly installed outdoors, it has high requirements of flame retardant properties and protection level. Projoy string-level rapid shutdown meets the standards of UL 94V-0 and IP65, more features shown below: 

• 1500V, 63A, 1~10 Strings

• The internal isolator complies with TUV, CE, CB, SAA, UL certification

• Meet V0 flame retardant grade, anti-UV F1 grade

• Applicable to various distributed PV systems

• IP65 design, equipped with waterproof vent to avoid condensation inside the housing

The device can reduce the voltage in the array to the safe level (below 80V) within 30 seconds. In addition, with built-in temperature sensor, the device can immediately take actions when the temperature exceeds 85°C, automatically shut down and cut off the DC power. Thus, it is crucial to have such device installed to solar panels for public places.

Obviously, continuous improvements in the technology will make the rapid shutdown product more intelligent and reliable, hope this simple guide can help you understand rapid shutdown requirements and associated safety features, and choose the product that best meets your power station’s needs.