Rapid shutdown device failure

ID: fm:rapid-shutdown-device-failure
IRI: https://solarlattice.org/kb/fm/rapid-shutdown-device-failure
Status: active
Also known as: defective RSD, MLPE stuck in bypass mode, JMS-F device no longer producing reference voltage, failed or bypassed MLPE, RSD not activating, RSD failure, TS4 communicating but not producing, Failed or Bypassed MLPE Devices, stuck in bypass mode, defective device

A rapid shutdown device fails when a module-level unit stops working or gets stuck in bypass. The string then loses its correct shutdown voltage, its operating voltage, or both. Typical signs are devices that do not activate when grid power is cut, low string voltage, string mismatches, or units that communicate but do not produce. To check, switch AC off and measure the string in its shutdown state. Expect about 0.6 V per TS4-F unit or about 1 V per JMS-F unit. Then measure Vmp with the system running, because a device stuck in bypass can show a correct safety voltage but a low Vmp. Before suspecting the hardware, confirm that the inverter rapid shutdown mode is set to SunSpec Shutdown. To find the bad unit, keep splitting the string in half or isolate single panel assemblies. Check connectors and housings for heat damage. Use a swap with a known-good device or thermal imaging to back up the result. Photograph the serial number of the faulty device, open a case with the manufacturer, and replace it under warranty. To prevent this, attach each device to its panel before stringing, and check the voltage of each assembly before connecting it into a string.

<!-- review notes

sentence 3: support check: partial - u1 and u9 give 0.6V per TS4-F and ~1V per JMS-F (u1 says 1V to 2V); the 'about 1 V' is loosely supported and the range is omitted. -->

Claims

`affects`

c1 drafted · lead Module-level rapid shutdown device

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a
Advanced Troubleshooting Steps for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=9f825260fb2d
Tigo TS4-R not Communicating after TS4 Detection or Communicating but not Producing sec=h1 h=93a1d9e35f6f

`presents_as`

c2 drafted · lead Rapid shutdown failure

Devices do not activate when grid power is removed.

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a
Advanced Troubleshooting Steps for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=9f825260fb2d

c3 drafted · lead Low string safety voltage proposed

In the shutdown state, string voltage reads below the expected per-device reference voltage times the number of devices.

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a
Advanced Troubleshooting Steps for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=9f825260fb2d
FAQ for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=bf1044cdf7d2

c4 drafted · lead Low string operating voltage proposed

The safety voltage can be correct while the operating Vmp is low, which points to an RSD stuck in bypass mode or underperforming.

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a

c5 drafted · lead MLPE detection failure proposed

TS4-R devices not communicating after detection, or communicating but not producing.

Tigo TS4-R not Communicating after TS4 Detection or Communicating but not Producing sec=h1 h=93a1d9e35f6f

c6 drafted · lead Hotspot in IR image

Abnormal heat signatures from RSDs; heat alone does not confirm failure.

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a

`caused_by`

c7 drafted · lead Installation error

Connecting the device to a panel that is already wired into a string may permanently damage it.

Tigo TS4-R not Communicating after TS4 Detection or Communicating but not Producing sec=h1 h=93a1d9e35f6f
Installing Tigo "TS4-R-F" Rapid Shutdown Devices onto PV Panels sec=h1 h=32d44e3827b9

c8 drafted · lead Electrical overstress

Overvoltage damage when assemblies are strung before each panel has its device attached.

Installing Tigo "TS4-R-F" Rapid Shutdown Devices onto PV Panels sec=h1 h=32d44e3827b9

c9 drafted · lead Poor connector contact

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a

review note: support check: partial - u1 mentions inspecting for damage or poor contact and overheating from poor connections, but does not clearly state poor connector contact causes RSD failure.

`detected_by`

c10 drafted · lead MLPE string safety voltage check

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a
Advanced Troubleshooting Steps for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=9f825260fb2d
FAQ for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=bf1044cdf7d2
Creating a String with JMS-F Rapid Shutdown Devices sec=h1 h=fbb01e1f0330
Installing Tigo "TS4-R-F" Rapid Shutdown Devices onto PV Panels sec=h1 h=32d44e3827b9

c11 drafted · lead DC voltage measurement

Vmp check across string terminals while the system is running.

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a

c12 verified · fact Fault localization

Halve the string, or isolate single assemblies, until the faulty device is found.

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a
Advanced Troubleshooting Steps for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=9f825260fb2d

verified by: review-workflowverified on: 2026-10-24

c13 drafted · lead Open-circuit voltage measurement

Advanced Troubleshooting Steps for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=9f825260fb2d
Tigo TS4-R not Communicating after TS4 Detection or Communicating but not Producing sec=h1 h=93a1d9e35f6f

c14 drafted · lead Infrared thermography

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a

review note: support check: partial - u1 offers thermal imaging as optional diagnostic helpful for identifying faults, but says heat alone does not confirm failure, so detection is only suggestive.

c15 drafted · lead Visual inspection

Troubleshooting Failed or Bypassed MLPE Devices (TS4-F & JMTHY) sec=h1 h=0f68753f778a
Tigo TS4-R not Communicating after TS4 Detection or Communicating but not Producing sec=h1 h=93a1d9e35f6f

c16 verified · fact Known-good component swap test

Tigo TS4-R not Communicating after TS4 Detection or Communicating but not Producing sec=h1 h=93a1d9e35f6f

verified by: review-workflowverified on: 2026-10-24

`distinguished_from`

c17 drafted · lead Rapid shutdown mode misconfiguration — told apart by Inverter settings review

Before blaming a device, confirm that the inverter rapid shutdown mode is set to SunSpec Shutdown. If the setting is correct and the voltage is still low, suspect the device.

Advanced Troubleshooting Steps for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=9f825260fb2d
FAQ for JMS-F SunSpec Rapid Shutdown Devices sec=h1 h=bf1044cdf7d2

review note: support check: partial - u2 says to confirm SunSpec Shutdown setting first, but the passages don't frame it as a differentiator or give the 'setting correct and voltage still low' logic explicitly.