Design Essentials for Rapid Shutdown using TS4-F MLPE – Tigo Help Center

Contents

Rapid Shutdown - How it Works
Required Equipment
Design Background
Design Criteria
Plan Set Submissions
Tigo Academy Rapid Shutdown Courses
Additional Resources

Rapid Shutdown - How it Works

Rapid Shutdown (RSD) is a National Electrical Code (NEC) requirement for any structure-mounted system (ground-mount systems are not subject to RSD compliance).

Tigo's TS4-F MLPE must be used with an RSS Transmitter. When the Transmitter is powered on, the RSS core will transduce a PLC signal onto the string wiring. The PLC is called a "keep-alive signal," as the TS4-F units will only allow full module voltage to pass if the signal is active.

When the PLC transmitter is powered off, this keep-alive signal is no longer present, and the entire DC side of the system goes into rapid shutdown mode: The Tigo TS4-F MLPEs disconnect their PV modules from the string, and the accumulated string voltage is reduced to under 80V within 30 seconds (as per NEC requirements).

Rapid Shutdown Equipment

Designing a system to meet rapid shutdown with the TS4-F products is simple. Each TS4-F must be connected to a PV module, and the RSS Transmitter must supply a keep-alive signal. The F products provide a simple and cost-effective solution for rapid shutdown. If you require module-level monitoring or optimization, you must use the monitored products.

The TS4 Rapid Shutdown Only Equipment:

RSS Transmitter

Uses powerline communication (PLC) to send a keep-alive signal to the TS4s.

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The keep-alive signal for the MLPEs can be supplied by either Tigo's original RSS Transmitter, the Pure Signal RSS Transmitter, or a Tigo UL PVRSS Certified Inverter (factory equipped with an internal RSSx Transmitter).

Rapid Shutdown Design Background

ATTENTION!
The most important thing to remember when designing a rapid shutdown system using the RSS Transmitter is to ensure strong signal strength of the PLC.

A major contributor to PLC attenuation is the effects of crosstalk in the system. Crosstalk is caused by outside interference from other sources of energy, typically AC or DC conductors that are too close to the conductors carrying the PLC signal, or different transmitter group wiring that are too close to each other.

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A bad design leads to a bad installation, which leads to abnormal behavior in the rapid shutdown system. These design criteria will ensure strong signal strengths and years of worry-free operation.

Rapid Shutdown Design Criteria

General System Requirements

Use RSS Transmitter (RSSx) with Pure Signal Technology to prevent signal interference and crosstalk.
Ensure compliance with NEC 690.12 rapid shutdown requirements for rooftop PV installations.
TS4-F systems do not provide module-level monitoring—they are strictly for rapid shutdown compliance.

Crosstalk Prevention & Signal Integrity

Use Pure Signal RSSx technology, which syncs up to 10 transmitters in a single group to mitigate interference. Each group has one Leader and up to 9 Followers.
Multiple RSSx Groups must be separated by at least 8 inches to avoid crosstalk between different inverter groups.

This array layout meets the separation requirements. Each color represents an array segment belonging to the respective inverters using their own RSS Transmitter.

This array does not meet the separation requirements. Different inverter arrays and conductors are crossing under other groups, which would cause this system to experience abnormal behavior.
Do not coil DC conductors, as it increases inductance and weakens the PLC signal.

RSS Transmitter Installation Guidelines

RSS Transmitters must be powered by a single 20A breaker for synchronized power-up, preventing leader-follower confusion.
Use correct power supply: Each RSSx requires 12V/1A power supply (120V or 277V options available).
Daisy-chain RSSx transmitters properly using Rx IN and Tx OUT terminals (CAT5/6 wires are too small—avoid them).
Ensure proper LED behavior:
- Leader RSSx: Solid red LED + Blinking green LED.
- Follower RSSx: Blinking green LED (synchronized with the leader).
- Abnormal operation: Both LEDs red or green LED out of sync.
The maximum distance of RSS Transmitter signal wiring is 100 feet (33m).
The maximum DC homerun roundtrip distance for a single Core RSS Transmitter is 300 meters.
The maximum DC homerun roundtrip distance for a dual Core RSS Transmitter is 500 meters.

DC Conductor Separation

Keep DC conductors from different RSSx groups at least 8 inches apart.
Keep PV inverter DC conductors at least 8 inches away from AC conductors to prevent interference.

This site was experiencing crosstalk issues since the AC conduit ran in the middle of the DC homeruns. This simple fix on the right corrected the issue.
Run only negative DC conductors through the Core and ensure the black side of the Core faces the PV array.
Limit the number of conductors through the Core to 10 to prevent signal loss of the innermost conductors.
Do not separate the positive and negative conductors from an inverter in a separate conduit.

String Sizing & Module Compatibility

TS4 devices do not affect string sizing—follow standard calculations.
Ensure temperature-corrected Voc and Imp values match TS4 specifications.
Improper installation practices (spacing, coiling, over-torqued connectors) can cause electrical faults.

TS4-F Installation Order (Mandatory)

Mount the TS4 to the solar module.
Connect the TS4 to the module’s output.
Connect all TS4s before energizing the system.
Ensure at least ½ inch clearance between TS4 and module backsheet for airflow and heat dissipation. This image shows a violation.

Common Installation Mistakes to Avoid

Mixing incompatible connectors (causes connection failures and overheating).
Routing DC and AC conductors too close together (creates crosstalk). The flex conduit contains AC conductors lying on top of the DC homerun conduit.

Following these design criteria, installers can ensure safe, compliant, and bullet-proof system installations using Tigo’s TS4-F rapid shutdown technology.

Plan Set Submissions

Tigo highly recommends that you submit your plan sets to our sales engineering team for review, especially for commercial applications. We can point out any trouble spots that may introduce crosstalk into the design and, subsequently, the installation.

If you have additional questions or design concerns, please contact our Sales Engineering Team, at: se@tigoenergy.com

Tigo Academy Rapid Shutdown Courses

These Tigo Academy courses cover rapid shutdown and proper installation practices for the TS4 product lines. We highly recommend taking them!
Click on the link and register for the Tigo Academy. Then click on the Catalog button at the top right corner to browse the courses.

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