Loss of rapid shutdown keep-alive signal

ID: fm:rapid-shutdown-keepalive-loss
IRI: https://solarlattice.org/kb/fm/rapid-shutdown-keepalive-loss
Status: active
Also known as: permission-to-operate signal not received, heartbeat signal absent, SunSpec signal loss, RSD deactivated, PLC keep-alive loss, AC signal circuit not energized, module switches in standby, unintended rapid shutdown, Transmitter signal is absent, heart-beat signal, keep alive signal, permission to operate signal

Module-level rapid shutdown receivers only stay on while they keep receiving a heartbeat or keep-alive signal from a power line transmitter. When that signal stops, they shut the PV modules down. The transmitter runs on the inverter's AC power. Opening the AC disconnect or breaker, or losing the grid, stops the signal and puts the array into rapid shutdown. The signal can also be overwritten or weakened by crosstalk from another inverter's transmitter when DC lines run in parallel. In the field the strings show only a very low voltage, a fraction of a volt per module, and the array produces nothing. If string voltages are low, check that the AC breaker is on, that the rapid shutdown switch is popped out, and that any external DC switch is closed so the signal can reach the receivers. Also check that the inverter's rapid shutdown mode matches the module switches used, and that the module switches work. IV curves taken with rapid shutdown devices installed can show steps and kinks caused by the devices switching. Interpret them with care.

<!-- review notes

sentence 4: support check: partial - Low voltage under 1 V per module is stated, but array producing nothing is not explicitly stated.
sentence 4: review: partial - Very low string voltage (under 1 V, or 0.6-0.7 V per module) is stated, but no passage says the array produces nothing. -->

Claims

`caused_by`

c1 drafted · lead Power supply interruption proposed

The transmitter is powered from the inverter AC side. Opening the AC disconnect or breaker, or a grid outage, removes its power and the keep-alive stops.

CPS SCA25KTL-DO-US-208 User Manual Rev 1.2 sec=2.11 h=1e0cace0bb9d
CPS SCA100K-T-US-480 SCA50K-T-US-208 User Manual Rev 1.0 sec=h46 h=9ab0be8a47a5
Solis RSD(1-2)L-1G Manual V1.1 sec=h20 h=a4fea290e8bc
Solis_manual_S6-EH2P(9.6-16)K-SV-YD-L-US_V2.7_20260305 sec=h177 h=a2dd61033bf5

c2 drafted · lead Rapid shutdown PLC signal crosstalk

With parallel DC lines, another inverter's SunSpec signal can overwrite this inverter's signal.

PLC Transmitter Crosstalk Application Note_Ginlong Solis US v5.0 sec=h1 h=b48d859b0cfc
SBxx-US-1XP-41-BA-en-12 sec=h435 h=0f9623b7f0ff
STPxx-US-50-BE-en-14 sec=h627 h=0f9623b7f0ff
SBSExx-US-50-BE-en-11 sec=h743 h=0f9623b7f0ff

c3 drafted · lead Multiple PLC signal transmitters proposed

PLC Transmitter Crosstalk Application Note_Ginlong Solis US v5.0 sec=h1 h=b48d859b0cfc

review note: support check: partial - Passage says multiple transmitters create crosstalk reducing receiver functionality, but doesn't explicitly say keep-alive signal is lost.

c4 drafted · lead Close DC conductor proximity proposed

DC lines run in parallel with lines from another inverter.

SBxx-US-1XP-41-BA-en-12 sec=h435 h=0f9623b7f0ff
STPxx-US-50-BE-en-14 sec=h627 h=0f9623b7f0ff
SBSExx-US-50-BE-en-11 sec=h743 h=0f9623b7f0ff

`affects`

c5 drafted · lead Module-level rapid shutdown device

FIMER APsmart RSD Field Install sec=h3 h=c392ffc1e53e
CPS SCA25KTL-DO-US-208 User Manual Rev 1.2 sec=2.11 h=1e0cace0bb9d
CPS SCA100K-T-US-480 SCA50K-T-US-208 User Manual Rev 1.0 sec=h46 h=9ab0be8a47a5
Solis_manual_S6-EH2P(9.6-16)K-SV-YD-L-US_V2.7_20260305 sec=h177 h=a2dd61033bf5

c6 drafted · lead Rapid shutdown signal transmitter

CPS SCA25KTL-DO-US-208 User Manual Rev 1.2 sec=2.11 h=1e0cace0bb9d
CPS SCA100K-T-US-480 SCA50K-T-US-208 User Manual Rev 1.0 sec=h46 h=9ab0be8a47a5
Solis_manual_S6-EH2P(9.6-16)K-SV-YD-L-US_V2.7_20260305 sec=h177 h=a2dd61033bf5

c7 drafted · lead AC disconnection unit

The open or closed position of the AC disconnect shows the rapid shutdown status.

CPS SCA25KTL-DO-US-208 User Manual Rev 1.2 sec=2.11 h=1e0cace0bb9d
stpxxus50-rapid-shutdown-equipment sec=h1 h=46538d48fa94
CPS SCA100K-T-US-480 SCA50K-T-US-208 User Manual Rev 1.0 sec=h46 h=9ab0be8a47a5

review note: support check: partial - Passages tie AC disconnect opening to stopping the signal and say its position indicates rapid shutdown status, but loss of signal affecting the disconnect is not really stated.

c8 drafted · lead PV array disconnect switch

An external DC switch left open stops the PLC signal from reaching the receivers.

stpxxus50-rapid-shutdown-equipment sec=h1 h=46538d48fa94
sbsexx-us-50-rapid-shutdown-equipment sec=h1 h=fbcb8e01281b
Solis_Manual_S6-EH3P(30-60)K-NV-YD-H-US(21A)_V1_0_20260908 sec=h147 h=e0881a339d61

review note: support check: partial - Passage says an external DC switch off prevents receivers getting the PLC signal, but it's the switch causing the loss rather than the loss affecting the switch.

`presents_as`

c9 drafted · lead Rapid shutdown triggered

FIMER APsmart RSD Field Install sec=h3 h=c392ffc1e53e
CPS SCA100K-T-US-480 SCA50K-T-US-208 User Manual Rev 1.0 sec=h46 h=9ab0be8a47a5
Solis_manual_S6-EH2P(9.6-16)K-SV-YD-L-US_V2.7_20260305 sec=h177 h=a2dd61033bf5

c10 drafted · lead Low string safety voltage proposed

With rapid shutdown receivers installed, the PV string voltages should be very low.

Solis_manual_S6-EH2P(9.6-16)K-SV-YD-L-US_V2.7_20260305 sec=h177 h=a2dd61033bf5
Solis_Manual_S6-EH3P(30-60)K-NV-YD-H-US(21A)_V1_0_20260908 sec=h147 h=e0881a339d61

`detected_by`

c11 drafted · lead DC voltage measurement

Per-module string voltage around the receiver standby level shows the receivers are off.

Solis_Manual_S6-EH3P(30-60)K-NV-YD-H-US(21A)_V1_0_20260908 sec=h147 h=e0881a339d61

review note: support check: partial - Passages give low per-module voltage (0.6-0.7 V) as expected with receivers and a check when voltages are low, but don't explicitly frame it as detecting signal loss.

c12 drafted · lead Inverter settings review

SBxx-US-1XP-41-BA-en-12 sec=h436 h=ab549348ae54
STPxx-US-50-BE-en-14 sec=h628 h=ab549348ae54
SBSExx-US-50-BE-en-11 sec=h744 h=ab549348ae54

review note: support check: partial - Passages list checking rapid shutdown settings as a corrective measure, not as detecting loss of keep-alive signal.