NEC 690.12 Rapid Shutdown of PV Systems on Buildings – Part 2: Charge Controllers

Rapid Shutdown Recap

When last we met, we discussed NEC 690.12 Rapid Shutdown requirements for inverters. For Part 2 of this topic, we are going to discuss options for Rapid Shutdown (RSD) for charge controllers. As there were initially very few options when the code was first released that provide the required shut down at the solar panels’ output, or module level shutdown, with charge controllers, the code was not always enforced. However, more options are available, depending on which charge controller you use. Therefore, more Authorities Having Jurisdiction (AHJs) are requiring it. We are going to go through some of the options to have RSD with a battery based solar system.

NEC 2017 (Jan.1 , 2019) Exhibit 690.8 Controlled Conductors and Limits

NEC 2017 (Jan.1 , 2019) Exhibit 690.8 Controlled Conductors and Limits

OutBack Power FLEXmax 100 Charge Controller

OutBack Power currently has three models of their FLEXmax (FM) charge controller. The OutBack FM100 can be used with the Tigo Energy TS4-A-F devices connected to the solar panels. A Tigo RSS Transmitter is clamped on the solar wire from the Tigo TS4-F devices to the charge controller.

diagram of a system with Tigo TS4-A-F and RSS with OutBack FLEXmax100 Charge Controller

Tigo TS4-A-F and RSS with OutBack FLEXmax100 Charge Controller

The transmitter injects a Power Line Communication (PLC) signal onto the line. This signal is a heartbeat keep-alive signal that tells the TS4-A-F that all is well, and should remain on. A standard AC switch, generally an outdoor rated Normally Closed (NC) locking mushroom button, is installed between the transmitter and an AC source. If AC isn’t available on the system, for example if it is a DC only system, the RSS can be powered with a 12VDC source.

Locking Mushroom Switch

When the switch is hit, it disconnects the power to the transmitter, turning it off. When the transmitter is off, the keep-alive signal is turned off, and so the TS4-A-F devices turn off at the solar panel. This fulfills the module level shutdown requirement. The other two models of the FLEXmax, the FM60 and FM80, must be handled a different way, which we’ll discuss shortly.

MidNite Solar Classic Charge Controllers

MidNite Solar’s Classic charge controllers can also use the Tigo TS4-A-F and RSS solution. There is a setting in the “Tweaks” setup screen of the charge controller required to make the controller “bleed down” to the low voltage in time, a document detailing the setting is available.

MidNite Solar’s Classic will also work with Tigo’s TS4-O solution described later in this blog. Details of versions supported are described on MidNite’s website.

Schneider Charge Controllers

The transmitter with a PLC keep-alive signal does not work for many other battery based solar systems with charge controllers. The PLC signal injected onto the solar wire causes problems with many charge controllers.

system diagram of Tigo TS4 RSD units with Schneider inverter and charge controller

Tigo Energy with Schneider Charge Controllers

Schneider Electric solved this problem by working with Tigo and creating a MPPT Disconnect RS that goes between the Tigo TS4-A-F at the solar panels and the charge controller. When the keep alive signal is shut off at the RS Initiator Switch, it tells the TS4-A-F to turn off the solar panels, as well as telling the MPPT Disconnect RS to send a signal to turn off the charge controller. This solution works with both models of the Schneider charge controller, the MPPT 60 150 and the MPPT 80 600.

Because the Schneider MPPT Disconnect RS is between the TS4-A-F and the charge controller, it isolates the PLC signal and prevents issues.

OutBack Power FLEXmax 60 and 80 Charge Controllers

The Outback Power FLEXmax 60 and FLEXmax 80 charge controllers require using a different solution for RSD that doesn’t use PLC.

One option is to have an external form of communication between the transmitter and the module level device. Companies such as Tigo Energy have a system that sends the keep alive signal through a dedicated RS485 cable between the transmitter by the inverter and receiver near the panels, that then can be sent wirelessly to the module level power electronics (MLPE) at the panels, such as the TS4-O. This allows them to communicate from the transmitter to receiver on a separate line without injecting the keep alive signal on the DC lines from the solar panels.

The added bonus is since there is a dedicated communication line between the TS4 at the solar panel, the Tigo Access Point (TAP) near the panels, and the Tigo Cloud Connect (CCA) connection from the TAP to the internet, additional information can also be sent on, allowing for module level monitoring. This allows you to see the amount of energy each solar panel is making, and be alerted if something goes wrong.

diagram of TS4-O in an off-grid system

Tigo Energy currently has two options for this solution with monitoring, the TS4-A-S (Safety), and TS4-A-O (Optimization). The -S model gives you Rapid Shutdown and remote monitoring, and the -O model adds optimization to the list, harnessing extra energy by maximizing the output of each panel while minimizing the effect shading or mismatches of other panels have on the panel. The TS4-F that we talked about earlier is just Rapid Shutdown, no monitoring or optimization, and is not used with the CCA solution.

An outdoor rated AC switch (#1 in image) initiates turning off the CCA that will turn off the TS4s. Depending on how quickly the voltage bleeds down to within acceptable range, you may need to also add a DC switch (#2 in image), such as the SquareD DC Switchgear Disconnect between TS4s and the charge controller.

…And the Rest

Some of the other brand charge controllers we carry haven’t been officially tested and verified with Tigo Energy’s products. We do know that Morningstar Corp’s controllers may have issues with solutions with PLC on the PV lines, so they recommend a solution from FireRaptor. altE Store doesn’t currently have them online for us to show you, but we are able to sell them if wanted. We believe the Tigo Energy TS4-O/TAP/CCA solution would also work with Morningstar, but it has not been tested as of this writing. Likewise, Victron Energy has not tested any RSD solution. But as they tend to be used more for off-grid solar systems, RSD may not be needed. Check with the Authority Having Jurisdiction (AHJ) in your area to confirm.

Contact altE Store for Help with Rapid Shutdown

If you are designing a solar system, and need help finding a rapid shutdown solution for it, please contact us at 877-878-4060 to find the right solution for your system.

About Author

Amy Beaudet
Amy Beaudet was in the solar industry at the altE Store from 2007 until her untimely passing in 2021. She was a sales rep, instructor, and an all-around solar evangelist, sharing her passion for solar around the world. When whe wasn't at work, she enjoyed sailing and skiing - but odds were good she was still talking about solar on the boat or on the slopes. See more of Amy Beaudet's blog posts.