RSD stands for Rapid Shutdown. It is a safety requirement for photovoltaic (PV) systems, specifically for grid-connected solar installations. Rapid Shutdown is designed to protect firefighters and other emergency personnel from potential electrical hazards during emergency situations.

During a Rapid Shutdown event, the PV system’s DC voltage and current are required to be reduced to a safe level within a specified time frame. This allows emergency responders to safely access the building or area where the solar system is installed without the risk of electric shock or injury.

Rapid Shutdown is typically achieved through the use of specialized devices such as Rapid Shutdown Devices (RSDs) or Rapid Shutdown Systems. These devices are installed in conjunction with the solar inverters and enable the system to quickly shut down or de-energize in response to a signal or command.

The specific requirements for Rapid Shutdown vary depending on the local electrical codes and regulations. In the United States, for example, the National Electrical Code (NEC) has specific guidelines for Rapid Shutdown, which may vary between different editions of the code.