SunSpec rapid shutdown signal

The SunSpec rapid shutdown signal is a power line keep-alive signal that a transmitter sends over the PV string conductors to module-level rapid shutdown receivers. The receivers let module energy reach the string only while they hear the signal. When it stops, they disconnect the modules so that conductor voltage inside the array falls to the NEC 690.12 limit. SMA Sunny Tripower CORE1 and other SMA US inverters have the transmitter built in and send the permission to operate signal on their DC inputs. Solis 4G-US models and the CPS RSD wirebox also support it, the CPS wirebox for use with APsmart RSD-S-PLC and RSD-D units. APsmart Transmitter-PLC units send the heartbeat to APsmart RSD devices. Switching the transmitter off triggers shutdown, and when the inverter has an integrated SunSpec-certified transmitter, no external transmitter is needed. Opening the AC disconnect, or a grid outage, cuts the signal. The inverter starts transmitting again when grid voltage comes back. SMA event 9034 means the inverter measured more than 30 VDC on an input before it started transmitting. This is often cross-talk from inverters that are already running, and SMA recommends firmware 03.12.23.R or later on CORE1 inverters. During installation, the Tigo RSS Signal Detector checks that the TS4-F receivers are getting the keep-alive signal.

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• sentence 2: support check: partial - Receivers pass energy only with signal and disconnect without it, but the limit is stated as 80 V per NEC 690.12(B)(2)(2); fine, though array-voltage limit tied to this is stated only for CORE1 context; core is supported.
• sentence 3: support check: partial - CORE1 integrated transmitter on DC inputs, Solis 4G-US and CPS wirebox for APsmart are supported, but 'other SMA US inverters' and the CPS wirebox being a CPS product are not clearly stated. -->