# Modbus RTU Communication with an RTAC

**URL:** <https://forum.inductiveautomation.com/t/modbus-rtu-communication-with-an-rtac/82561>\
**Category:** General Discussion\
**Created:** [November 30, 2023, 9:47pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-communication-with-an-rtac/82561 "2023-11-30T21:47:15Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Sukh\_Virk](https://avatars.discourse-cdn.com/v4/letter/s/db5fbb/32.png) [@Sukh\_Virk](https://forum.inductiveautomation.com/u/Sukh_Virk)\
**Post date:** [November 30, 2023, 9:47pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-communication-with-an-rtac/82561/1 "2023-11-30T21:47:15Z")

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Hi, I am trying to integrate a Micom P521 Modbus/RTU relay to an SEL-3555. The P521 talks perfectly to Modscan software. But it doesn't respond to the RTAC. RTAC is configured well and I checked with SEL. I send them the wireshark capture. They said RTAC's settings are correct and it is doing its job. It could be a faulty cable or relay's configurations aren't correct. I tested the same cable with ION 7330 meter. RTAC talks to the ION meter using the same cable. I am using two wire RS485 connection. I also spoke to an Engineer with Schneider about Micom relay. They couldn't resolve this issue. Does someone have any idea, what else I can try?

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**Author:** ![Sukh\_Virk](https://avatars.discourse-cdn.com/v4/letter/s/db5fbb/32.png) [@Sukh\_Virk](https://forum.inductiveautomation.com/u/Sukh_Virk)\
**Post date:** [November 30, 2023, 9:51pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-communication-with-an-rtac/82561/2 "2023-11-30T21:51:12Z")

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![Modscan](https://us1.discourse-cdn.com/inductiveautomation/original/3X/4/7/47c80338b6521ee3ded83821e9448d0ef636145c.jpeg)  
 ![Online Status](https://us1.discourse-cdn.com/inductiveautomation/original/3X/5/b/5b047f5ae8983aa4552ae27a9cfd6c0da85c7dfc.jpeg)  
 ![P521 Comm Settings in the RTAC](https://us1.discourse-cdn.com/inductiveautomation/original/3X/d/4/d4d7797fb90add47aa05c5a8a1998dfd8297a3b7.jpeg)

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**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [November 30, 2023, 10:04pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-communication-with-an-rtac/82561/3 "2023-11-30T22:04:52Z")

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I moved this to the General Discussion category, as you aren't asking an Ignition question.