Troubleshooting Rapid Shutdown Device 101

Fire safety is the most important thing to keep in mind when it comes to solar energy. Numerous solar regulations reduce the risk of fire, but they must be regularly updated to reduce hazards for firemen while doing their tasks on or in buildings with PV arrays.

Many countries have put safety precautions in priority to guarantee that solar energy functions safely and permits firemen and other first responders to go to the area of fire safety. The rapid shutdown can be used in this situation. 

Let’s examine the rapid shutdown criteria in more detail and see why it’s crucial for all solar installers and system owners to be aware of them.

How Does It Work? 

The National Electrical Code introduced the requirement for rapid shutdown as an electrical safety requirement in the United States (NEC). 

Solar PV systems must have a method to de-energize or lower the voltage, of the solar modules on the roof in order to meet this criterion. This requires the addition of an “on or off” switch.

Rapid shutdown provides a safe way for solar installers or firefighters to halt or reduce the voltage and current from a photovoltaic array, allowing them to work safely and productively while avoiding electrical hazards.

Inverters have the capacity to shut down in order to interrupt the flow of energy generated by modules through them. However, the solar panels will continue to generate electricity as long as the sun is up, placing voltage and current on the wires that connect the panels to the inverter.

Turning off or decreasing the voltage on your roof at the module level lowers or eliminates the possibility of a fireman getting shocked by an excessive voltage coming from the solar modules.

The inverter and the module-level quick shutdown device must communicate with one another in accordance with the US National Electrical Code, and together they make up a system.

Why Would a Rapid Shutdown Device Stop Work? 

A Rapid Shutdown Device is a kind of microinverter or module-level power electronic (MLPE). They are equipped with tools that can shut down and lower voltage output throughout the solar system in order to adhere to PV Rapid Shutdown regulations.

Finally, a rapid shutdown system requires an inverter. The electricity generated by the solar modules is transformed into useful energy for your home via an inverter (for more information on this process read our previous blog). Inside the inverter are several Rapid Shutdown initiators.

These three components are known as photovoltaic rapid shutdown equipment. These devices enable a rapid shutdown system in bringing the voltage down to a safe level. For the purpose of a rapid shutdown, PVRSE and PVRSS must be UL Listed. The rapid shutdown switch can stop functioning if these parts aren’t functioning properly.

Steps to Identify Common Rapid Shutdown Device Failures 

A deeper change in the world’s energy structure has led to an expansion of the new power system, which uses new energy as its primary fuel, and an increase in the number of structures with rooftop photovoltaic systems. 

Whether it is a home system or an industrial and commercial power plant, it is anticipated that the installed capacity of photovoltaics will expand significantly, and the safety issues associated with it have always caught the attention of the industry.

• Switching off the device in an emergency

Solutions must be trustworthy because firefighter safety necessitates module-level shutdown. The array must be successfully switched off and de-energized when a quick shutdown is enabled by the rapid shutdown devices. 

Firefighters presume that the array is actually de-energized, so if this doesn’t happen, the risk might even be greater than it would be without the shutdown procedure at all.

So how do we ensure safe switching? Mechanical DC disconnects, such as those used on inverters, must pass testing in accordance with UL 98B. In addition to other safety tests, this standard mandates testing under conditions that are similar to those in which the disconnect is intended to operate. 

Today’s solid-state DC switches, in contrast, are only tested to UL1741 and are employed in module-level shutdown compliance. A DC disconnect or safety switch is not covered by UL 1741. 

The working environment for MLPE devices is actually harsher than the working environment for a typical DC disconnect at or on the inverter. Testing the rapid shutdown feature outside of the range of normal operating temperatures is recommended.

• Detecting arc fault and proper shutdown response

Electrical noise can be produced by electronic components. This is usually not a problem on the DC side of a solar system. However, the noise levels can rise dramatically and obstruct accurate arc fault detection when using today’s rapid shutdown equipment. 

Arc Fault Circuit Interrupter (AFCI) algorithms keep track of the solar system’s DC current and voltage and seek specific traits (such as abrupt fluctuations) that resemble arcs. They base their detection on a collection of arc signatures that describe what a typical arc looks like. 

The AFCI is activated to put out an arc or stop a prospective arc before any damage happens if the detected current and voltage patterns resemble an arc signature. The AFCI algorithm has trouble distinguishing a true arc when electrical noise produced by quick shutdown devices (such as from optimizers switching frequencies) provides signals that resemble real arcs. 

Due to the commotion, there is a higher chance of nuisance tripping or, worse yet, of failing to notice an actual arc. Furthermore, it may be ironic that this extra noise interferes with some systems’ shutdown signals, making it difficult to trust that they will shut down when necessary.

• Identifying the number of connections for less arc risk

DC connectors are a major contributor to serial arcs in a PV array, according to research from the Fraunhofer Institute in Germany and the BRE National Solar Centre in the UK. DC connector issues typically have one of two root causes:

1. Installation mistakes: The most frequent installation mistakes are improper on-site crimping and connectors that are not fully installed, both of which result in weak connections that might cause arcing. 

2. Common errors include using the wrong crimping tools, installing connectors imprecisely, or just having insufficient installation training.

DC connectors made by different manufacturers are referred to be mismatched connections. Incompatibility causes loose connections, corrosion, water intrusion, and variable thermal expansion behavior.

Any quick shutdown method that substantially raises the number of connection points can make the system more dangerous.

• Discovering the device longevity

Solar energy adoption is driven by cost-effectiveness, thus it’s critical that quick shutdown technologies don’t drive up system costs to levels that are out of reach for consumers. Solar systems are also a 20+ year investment. Systems with fewer parts and ones that don’t subject electronics to harsh rooftop conditions should be more dependable.

Safety should come first when evaluating market-available rapid shutdown technologies, followed by additional cost.

The rapid shutdown was originally included in the 2014 National Electrical Code (NEC) to give firefighters an easy way to de-energize solar system DC conductors during an emergency and maintain a safe environment on a building’s roof. 

This is so that, on a typical string inverter solar system, the DC wire from the solar system remains alive when the sun is shining even after the inverter is turned off.

The 2017 NEC changed the standards for rapid shutdown based on how close the PV system conductors are to the PV array boundary, which is now the region that extends 1 foot (305 mm) in all directions from the array.

Within 30 seconds of rapid shutdown initiation, PV circuits inside buildings that are outside the boundary of more than 3 feet (1 m) from the point of entry must be limited to no more than 30 volts.

With effect from January 1, 2019, one of the following three alternatives must be utilized for PV circuits that are inside the array boundary:

The PV array must be mentioned or field designated as a PV array with the rapid shutdown. Such a PV array must be set up and utilized in accordance with the guidelines listed in the field labeling or listing for rapid shutdown PV arrays.

PV conductors inside the perimeter or less than 3 feet (1 m) from the point where the building’s surface penetrates them must be limited to no more than 80 volts within 30 seconds of the quick shutdown initiating.

PV arrays installed more than 8 feet from exposed grounded conductive elements or the ground and lacking exposed wiring methods and conductive parts are exempt from the regulations.

The expansion of the new power system, which uses new energy as its principal fuel, and an increase in the number of buildings with rooftop photovoltaic systems are the results of a more profound transformation in the global energy structure.

The installed capacity of photovoltaics is expected to increase dramatically, regardless of whether it is a household system or an industrial and commercial power plant, and the safety concerns related to it have always attracted the attention of the industry.

Rapid Shutdown’s interaction with inverters and power optimizers

While other inverter systems need extra components to enable quick shutdown, others are already fundamentally compliant with module-level rapid shutdown (NEC 2017 and later).

The most popular inverter choices for residential solar panel systems in the United States are microinverter and power optimizer systems. Thankfully, power optimizers and microinverters both work at the panel site and have quick shutdown features built in.

‘To be in compliance with NEC 2017 or NEC 2020, you might additionally need to install module-level power electronics (MLPE) if you install a string inverter alone. It should work if you combine power optimizers with a string inverter, as SolarEdge does.

However, when additional states started implementing NEC 2017, many string inverter manufacturers and other solar companies developed new MLPE technologies with rapid shutdown capabilities, so power optimizers weren’t your sole choice for rapid shutdown compliance. These MLPEs designed expressly for quick shutdown are frequently a more economical choice than adding power optimizers or microinverters.

While some inverter systems can trigger the quick shutdown without the need for extra components, others do not. Power optimizers and microinverters both include built-in shutdown features. To be in compliance with the 2017 NEC code, you might need to add module-level devices if you have a string inverter.

Before you make any adjustments to your solar panel system, you should check to see if your system complies with the rapid shutdown criteria because you will be inspected for the same. To find the best rapid shutdown components for your system, you might seek professional assistance.

Power optimizers deliver low voltage DC to a centralized inverter for conversion to grid-compliant AC voltage, and microinverters convert low voltage DC to utility grid-compliant AC voltage. AC power is then exported to the electric service for usage by loads onsite or exported to the grid for use by others when the utility grid is available. 

These MLPEs stop producing AC power and are no longer able to provide AC voltage or current into the inverter output circuits or to the grid, thus meeting the requirements of Article 690.12, when the grid fails or the PV system AC circuits are disconnected from the utility service by an AC circuit breaker, utility meter removal, or other AC disconnect.

When the AC power to the system inverter is cut off, systems with power optimizers achieve rapid shutdown compliance. 

The inverter delivers a signal to the optimizers so that they can automatically reduce their voltage output to one volt upon the loss of an AC signal. In this case, the average 350 volts of a line of 18 panels with optimizers would be decreased to 18 volts.

The 10-foot termination distance for DC wires inside the PV array would be reduced to a 1-foot border as part of the 2017 NEC’s proposed change to article 690.12. Additionally, it would keep the existing 30-volt conductor constraint while needing an in-array 80-volt limitation inside the one-foot border. 

As a result, it would be necessary to remotely turn off each individual panel from a master switch. The string voltages between the panels and the quick shutdown box might still exist up to 600 volts DC, hence the rapid shutdown systems now in use under the 2014 NEC criteria would not comply with this new criterion. 

In essence, this new plan requires some kind of in-array or module-level shutdown device for all rooftop PV systems.

Although it is unclear how a new in-array 80-volt limiting would improve the safety of firefighters and other first responders, the additional rule may actually make installers less safe. 

Where is the concern for the lengthened time installers must spend replacing failing or worn-out module-level devices if the solar industry is forced to implement a more harsh module-level shutdown? 

You must take into account that service people will be more likely to experience falls, which are the leading cause of occupational fatalities in the construction industry.

With little to no performance gain, this proposed 2017 NEC extra rule to article 690.12 will increase PV system complexity, installer and maintenance risk, expense, and reliability difficulties, which will have an impact on the future potential of rooftop PV installations. 

Such modifications must be well thought out. The NEC seems to be trying to solve a problem that might not even exist.

The NEC 2017 criteria mark a development in the safety of PV systems. There are several designs and devices on the market that adhere to the NEC code’s control criteria. Utilize the rapid shutdown system to protect yourself and your PV system safely.

You must make sure that you update your solar system in compliance with the updated requirements of the quick shutdown device of your state if your state has codes for the safety of your PV system.

Electricity is produced using a solar panel array to provide direct current (DC). Alternating current (AC), which your appliances may utilize, is created by inverters. Larger inverters may be placed close to the building’s electric meter or main distribution panel, or a system may include numerous small, individual inverters coupled to individual solar panels.

The majority of the building’s electrical lines are routed through conduits along the exterior. An AC disconnect switch is typically installed close to the main distribution panel of the house or the electric meter. Each disconnect switch needs to have a label indicating which solar array it is linked to.

Only the home’s connection to the solar array will be severed by the disconnect switch. The panels can shock people since they continue to produce DC power. The solar power system will continue to generate electricity if it has a battery backup.

Keep in mind that solar panels will continue to function as long as the sun is out. Solar panels can be dangerous, just like any other electrical source. 

Be mindful of the dangers and maintain a secure distance from any electrical equipment if you have solar panels placed on your roof or in another location on your property. Emergency personnel should be informed of the dangers associated with solar arrays.

Tips for a Healthy Solar Rapid Shutdown Device

Any time the sun is out, the conductors in a solar panel system become electrically charged.

There is no safe method to stop the current flowing through those conductors without a rapid shutdown mechanism.

The power cannot be turned off by just turning the solar inverter off, contrary to what most people believe. The solar panels would still be producing electricity, and the electrical connections connecting the solar panels would still be carrying electricity.

Anyone who comes into contact with the solar panel system is at risk of electrocution due to this live current, including first responders who may be called to an incident on your roof.

Firefighters are particularly vulnerable since they frequently ventilate burning buildings by drilling holes into the walls or roofs, which could put them in direct touch with the conductors or cables of the solar panel system.

This issue is resolved by the rapid shutdown device solar, which instantly de-energizes the solar panel system and eliminates the risk of electrocution for anyone climbing on the roof.

A few tips for a healthy solar rapid shutdown device are: 

• Install a “listed” or field-labeled rapid shutdown system

The word “listed” originates from the first name of the UL certification program, which was created more than a century ago. 

The National Electric Code includes the word “listed,” but it does not state that systems and products must be UL-certified; rather, it discusses the general qualities of the organizations that would provide such certification service. 

Although UL obviously believes that manufacturers should certify their products for speedy shutdown through UL, other nationally renowned testing labs may also be able to help.

• Install a system capable of lowering its voltage to 80 V within 30 seconds

Because they transform high-voltage DC power into lower-voltage, safer AC power that can fall to 80 V in 30 seconds, microinverters are often thought of as being innately compliant with the pv rapid shutdown.

Testing after the inverters have been installed is difficult, but UL has proactively carried out these tests to confirm that specific microinverters can meet the 80-V threshold.

• Install a BIPV system with no metal components, no exposed conductors, and not within 8 ft of grounded metal

The NEC 2017 criteria can be met by solar shingles, tiles, or other building integrated PV (BIPV) systems as long as they don’t have any exposed metal conductors or metal components, or if they aren’t located next to any grounded metal. These systems are kept apart from conductive and grounded components.

Conclusion

This was all that you should know as a solar installing business. Globally, rapid shutdown regulations are being developed to safeguard firemen while they operate near solar PV equipment. 

The rapid shutdown system (PVRSE) required by the NEC uses a number of devices to lower the voltage to a safe level (PVRSS). To meet NEC requirements, components such as inverters, initiators, and rapid shutdown devices like MLPE or microinverters are required.

You can contact the leading Rapid shutdown device manufacturer if you are looking for a supplier for your business.