Design Essentials for Rapid Shutdown using TS4-F MLPE

Purpose: 

Provides detailed information on proper TS4-F design criteria to mitigate the effects of crosstalk.

Target audience: Solar Installers, designers

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 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.

This article covers crosstalk mitigation with the RSS Transmitter with Pure Signal Technology. 

Refer to the Additional Resources at the end of this article to learn about crosstalk mitigation using the previous version RSS Transmitter.
 

RSS Transmitter	RSS Transmitter Pure Signal Technology

The TS4 Rapid Shutdown Only Equipment: 

The TS4-F series provides rapid shutdown. They do not provide monitoring or optimization.

The RSS Transmitters use powerline communication (PLC) to send a keep-alive signal to the TS4s.

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 Overview

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

A major contributor to PLC attenuation is crosstalk in the system. Crosstalk is caused by 

• outside interference from other sources of energy
• AC or DC conductors that are too close to the conductors carrying the PLC signal
• different transmitter groups wiring that are too close to each other.

Rapid Shutdown Design Axiom:

A bad design leads to a bad installation, which leads to abnormal behavior in the rapid shutdown system. 

Adherence to the following design criteria will ensure strong signal strengths and years of worry-free operation

Rapid Shutdown Design Criteria

1. RSS Transmitters with Pure Signal Technology

• 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.
  
  

2. Grouping Separation Requirements

• Multiple RSSx Groups must be separated by at least 8 inches to avoid crosstalk between different inverter groups.
  
  
  
  Good Example
  This array layout meets the separation requirements. Each color represents an array segment assigned to the corresponding inverter, using its own RSS Transmitter.
  
  
  Poor Example
  This array does not meet the separation requirements. Different inverter arrays and conductors are crossing under other groups, which could cause the system to exhibit abnormal behavior.
  

  3. DC Conductor Coils 

• Do not coil DC conductors, as it increases inductance and weakens the PLC signal.
  
   

RSS Transmitter Installation Guidelines

1. Power and Breaker Sizing

• 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).

2. Signal Wiring Attention to Detail

• Daisy-chain Transmitters properly using Rx IN and Tx OUT terminals (CAT5/6 wires are too small—avoid them).
  

3. LED Observation

• 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.

4. Signal Wiring Distance Restriction

• The maximum distance of Transmitter signal wiring is 100 feet (33m).
  
  

5. Homerun Roundtrip Distance Limits

Single Core:

• The maximum DC homerun roundtrip distance for a single Core RSS Transmitter is 300 meters.
  
  
   

Dual Core:

• The maximum DC homerun roundtrip distance for a dual Core RSS Transmitter is 500 meters.
  
  

6. 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.
  
  
  Case Study

  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.
  
  

7. Core and Homerun Limitation

• 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.
  
   

8. Positive and Negative Conductor Separation Integrity 

• 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)

1. Mount the TS4 to the solar module.
2. Connect the TS4 to the module’s output.
3. Connect all TS4s before energizing the system.
    

Common Installation Mistakes to Avoid

1. TS4 Clearance Requirement

• Ensure at least ½ inch clearance between TS4 and module backsheet for airflow and heat dissipation. This image shows a violation.

2. Connector Compatibility

• Mixing incompatible connectors (causes connection failures and overheating).
  
   

3. DC Separation from AC Conductors

• 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 submitting your plan sets to our sales engineering team for review, especially for commercial applications. We can identify any trouble spots that may introduce crosstalk into the design and, subsequently, into 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 here and register for the Tigo Academy. 

Additional Resources

Crosstalk within TS4 Fire Safety Systems (cause and prevention)

Design and Installation Requirements when Employing multiple RSS Transmitters with Pure Signal technology

Using Tigo’s Rapid Shutdown Solutions with the Sol-Ark Hybrid Inverters