As the PV industry rapidly expands, safety concerns have become increasingly prominent. Industry associations and government agencies have introduced safety standards to regulate market operations. The National Electrical Code (NEC) in the United States was the first to propose the concept of rapid shutdown for PV system safety protection.
Rapid Shutdown (RSD) is a critical safety feature that can quickly reduce the voltage of a PV system in emergency situations, ensuring the safety of personnel and property.
What is RSD?
Rapid Shutdowns are safety systems that can quickly shut down a solar panel system in an emergency. They are required by law for all new rooftop solar panel installations in the United States and are designed to protect firefighters and homes from fire.
What Does the NEC Require?
The National Electrical Code (NEC) is the primary standard governing PV rapid shutdown devices. Updated every three years, its adoption varies as each state implements the changes at its own pace.
NEC 2014
The NEC 2014 (Section 690.12) introduced clear guidelines for rapid shutdown in solar installations. It required the installation of a rapid shutdown switch for PV systems, ensuring that the system voltage drops below 30V within 10 seconds to enhance overall safety.
NEC 2017
In NEC 2017, the rapid shutdown requirements (Section 690.12) were made more stringent. It established a boundary of 305mm from the PV array, where, within 30 seconds of initiating shutdown, the voltage outside this boundary must drop below 30V, and within the boundary, the voltage should decrease to under 80V. This introduced the need for “Module-Level Rapid Shutdown,” significantly improving safety by reducing voltage to levels safe for human contact, thereby aiding firefighters in rescue situations.
NEC 2020
NEC 2020 introduced the concept of “PV hazard control systems.” The new standard requires PV systems to include this feature, ensuring that the system remains controllable in emergencies. Module-level rapid shutdown must be achieved, with voltage dropping below 80V within the boundary range within 30 seconds of shutdown activation.
NEC 2023
NEC 2023 requirements for rapid shutdown have not changed significantly from the 2020 version. As with NEC 2020, NEC 2023 Section 690.12(B)(2)(2) continues to state that within the boundaries of the PV array, the DC conductor must be controlled so that it does not exceed 80 volts for 30 seconds.
Why Is the “Rapid Shutdown” Function Necessary?
1. Risk of Electric Shock from High Voltage During Fires
With the increasing prevalence of photovoltaic (PV) installations, fire incidents and system faults have become significant concerns:
- According to data from the U.S. Fire Administration, the number of rooftop PV fire incidents has risen by 69% annually.
- Statistics from several reputable PV websites in China indicate that over 80% of PV system fires are attributed to direct current (DC) side faults.
- In the event of a fire, standard PV modules connected in series accumulate voltages reaching several hundred volts, posing substantial risks to firefighters and hindering firefighting efforts.
- Maintenance personnel are also at risk of electric shock due to the high voltage present in series-connected PV modules during routine inspections and repairs.
2. Fire Hazards Associated with High DC Voltage
- PV modules connected in series generate high DC voltages, which can lead to hazardous arc faults.
- Excessive DC voltage and current increase the likelihood of dangerous arc faults, thereby elevating fire risks.
3. Challenges in Firefighting and Maintenance Under High Voltage Conditions
- Multiple PV modules connected in series can produce DC voltages around 1000V, varying with the number of modules.
- In the event of a fire at a PV installation or building, the persistent high DC voltage prevents the use of conventional firefighting methods.
- During regular maintenance and inspections, maintenance personnel are exposed to significant electric shock hazards due to the high DC voltage present in the system.
Do I Need Rapid Shutdown for Solar?
Even if it is not legally required, rapid shutdown can save lives and property. It is an investment in safety.
| Consideration | Importance |
|---|---|
| Local regulations | NEC mandates for rooftop systems |
| Installation type | Required for buildings, optional for ground mounts |
| Personal safety | Adds a layer of protection |
Rapid shutdown is essential for rooftop solar systems and ensures compliance with safety standards. Evaluate your needs carefully.
Conclusion
Rapid shutdown improves solar safety, meets regulatory standards, and provides peace of mind during emergencies. In the future, more countries are expected to make rapid shutdown a mandatory requirement. As global PV safety standards advance, rapid shutdown technology is likely to become a standard feature in regulations worldwide.
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