Crosstalk within TS4 Fire Safety Systems (cause and prevention)

This article defines Crosstalk and provides design criteria to mitigate it when using Tigo's TS4-F (fire safety) products.

Contents:

• What is Crosstalk?
• Which Tigo Products Are Affected By Crosstalk?
• How to Prevent Crosstalk
• Installation Case Studies

What is Crosstalk?

Crosstalk is an Electro Magnetic Interference (EMI) phenomenon that happens when cables carrying a signal transmission are in close proximity to another signal source. This type of interference can cause an attenuation in signal strength, line noise, or phasing. Crosstalk is not specific to Tigo technology and is used by many other manufacturers, but it can cause issues in any PV system that uses Power Line Communication (PLC), i.e home automation networks, home entertainment systems, Smart buildings, etc.

Which Tigo Products Could Be Affected By Crosstalk?

The Tigo Flex MLPE solution has two families of products that use different communication methods: 

Crosstalk is not an issue with the TS4 Monitoring Solution as it uses wireless (radio) communication to deliver its Rapid Shut Down (RSD) response.

However, the Tigo Fire Safety Solution uses Power Line Communication (PLC) to transmit a "keep alive" signal on the string conductor. This signal feeds to each MLPE and maintains voltage activity. If there are 2 separate transmitter signals in close proximity on the same system, the Crosstalk (or bleed-over) from one transmitter can affect the signal path of the other one, resulting in unexpected shutdowns.

How to Prevent Crosstalk

Any system designer or installer will want to prevent or reduce the potential for crosstalk, especially when designing larger commercial/utility-scale systems that require multiple inverters and signal transmission sources.

The easiest way to mitigate Crosstalk is to purchase Tigo's new Pure Signal RSS Transmitter(s) and connect them with the Synchronization cable(s). This setup allows the system to have several transmitters connected together to sync the signal output. 

For systems using the original Tigo RSS Transmitter, each unit has its own signal. The mitigation process starts by identifying how many Tigo RSS Transmitters (RSSx) are on site and making sure that their individual DC signal paths (PV lines) are separated to prevent interference. The physical separation of conductor paths will ensure a quality signal. 

Note: The minimum distance suggested for PV conductor separation is 8 inches between the individual conductor paths (both on the roof and in the cable tray). 

Below is an informative chart to illustrate the various methods of crosstalk reduction. This is also provided in the Installation Manual TS4-F, TS4-A-F, TS4-A-2F, and RSS Transmitter.

Path	Recommended	Avoid
Conduit	DO: Run string conductors associated with different transmitters in their own separate conduits.   DO: Keep the + and - conductors from each transmitter together in the same conduit. DO: Twist the + and - of each string or homerun lead.	DO NOT: Separate the + and - conductors of a string into their own separate conduits.
	DO: Separate conduits associated with different transmitters, as far apart as possible, with a minimum of 8 inches of separation.	DO NOT: Run the conduits associated with different transmitters close together. Conduit alone does not significantly mitigate Crosstalk.
Cable Trays	DO: Run conductors from the same transmitters in their own separate cable trays.	DO NOT: Intermix or run conductors for different transmitters in the same cable tray.
	DO: Keep positive and negative conductors close together in the cable tray and twist them.	DO NOT: Keep the positive and negative conductors of a string apart inside a cable tray.

Installation Case Studies

Note: The white side of the RSS Transmitter Core should always be oriented toward the inverter.

Single Core RSS Transmitter:

1x Inverter 1x RSS Transmitter - Single Core
Probability of Crosstalk: 0% - Most small residential systems will not experience Crosstalk Note: Do not exceed standard design limitations - Refer to Installation Manual

Dual Core RSS Transmitter:

1x Inverter 1x RSS Transmitter - Dual Core

Keep the positive and negative conductors of the same string in the same conduit. Twist the positive and negative conductors of the same string(s)  Okay to route all conductors in the same cable tray  RSS Transmitters cores are color-coded by polarity to make installation easy when using a Dual Core setup. Recommendation: The Negative cables coming from the array should enter the black side of the core and leave (to the Inverter), via the white side.

1x Inverter 1x RSS Transmitter - Dual Core
A Dual Core RSS Transmitter can be used to increase the signal strength if the cable run exceeds a distance of 1000 ft (300 m), but no more than 1640 ft (500 m). Both transducer cores can be deployed on the same source circuit. Make sure to face the cores in the same direction (to avoid reverse-polarity issues):    Correct                                                     Incorrect

Multiple RSS Transmitters: 

Bottom Line: Run strings associated with different transmitters in their own conduit.

For more information and education on this topic, Tigo highly encourages our partners and customers to take the Tigo Academy TS4 Installation Certification Course. 100% of the installers and designers who take and follow the course criteria are successful 100% of the time with their Tigo installations. The installs go faster, smoother, and more robust in the long run.

If you have system design questions or would like your design reviewed, email our sales engineers at se@tigoenergy.com. If you need technical support help, Contact Support.