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    John Yvon

    Tigo has 2 product families that offer Rapid shutdown RSD:  
    Flex MLPE  (TS4-S and TS4-O) – Radio communication products which must be used with a TAP and CCA for rapid shutdown functionality to be available. 
    TS4-F Fire Safety – Power line communication product which must be paired with a RSS Transmitter.

    Both solutions rely on a keep alive signal.  For the TS4-F class of units the keep alive is propagated from the RSS Transmitter, and for the Flex MLPE/TS4 Optimizers the keep alive is propagated by the GW/TAP wireless antenna.  When AC loss occurs, like when the main breaker is pulled, the RSS Transmitter or the CCA which powers the GW/TAP will power off.  As a result the keepalive signal will cease and a few moments later the units will automatically enter their rapid shutdown state.

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    Jesse Campbell

    The sticker I received with the CCA for Flex MLPE rapid shutdown says to turn off the AC power to both the inverter and the CCA to initiate module level disconnect, and for rapid shutdown also switch off the inverter's DC disconnect immediately after.

    Is all of this required for rapid shutdown? I thought the NEC 2017 and 2020 spec said that it should only require an AC loss as you said, but this seems to indicate the DC must also be manually disconnected?

    In addition, the other stickers mention a Rapid Shutdown Switch. Is that specifically for the AUX shutdown input on the CCA, unrelated to the automatic RSD on power loss?


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    Gary Hethcoat

    Hi Jesse,

    Great question, thank you!

    Rapid shutdown is normally a cooperative thing between the inverter and the Tigo TS4 units.  Each is expected to do its part to bring the voltage below 80V in 30 seconds.  That's why the inverter and CCA/RSS Transmitter should both lose power at the same time, whether by AC grid power failure or manual shut-off.  It is also why it is so important that the inverter and TS4s are tested and UL listed together for rapid shutdown.

    People sometimes ask how to set this up.  One way I know of is to use a small sub-panel with two breakers, one for the inverter, and one for the CCA or RSS Transmitter.  A breaker or disconnect upstream from this can be used as a solar disconnect for manual rapid shutdown.  Here is a conceptual graphic that may help:

    The statement about the DC disconnect should be considered optional, and should only be done once normal rapid shutdown is complete.  If this is done before rapid shutdown completes, it could interfere with the cooperative operation described above.

    You also mentioned the AUX port on the CCA.  We have an article which explains its purpose and use:

    This is more appropriate for off-grid and hybrid systems.  We have an article for that also:

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    Jesse Campbell

    That makes a lot of sense, okay. My inverter is UL listed with the TS4/CCA rapid shutdown system. (It was originally deployed with a non-sunspec PLC-based shutdown system. It appears this may be incompatible with the optimizers, based on some voltage drops with a partial deployment of TS4s, but I will see with some more testing.)

    I will take a look at what will be needed to wire the CCA into the existing AC shutoff.

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    Greg Smith

    Jesse Campbell I have an SMA SB5.0 hanging on my garage wall and 16 Tigo TS4-F's for rapid shutdown. After reading your question, I went out and threw the AC disconnect with the RSD labeling on it and the array voltage hit 0V in under 10 seconds, well below the requirement. I love theory to practice!

    The SMA inverter has the RSS "keep alive" feature built-in. If you use an inverter without an internal RSS then the RSS will need to be connected to grid power and isolated with a disconnect.

    A caveat with my system, though. Since I have an energy storage system I had to tap off the main panel with the RSD shutoff since It would defeat the purpose of RSD to have the shutoff on the backup panel.


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