Homematic Wired Bus question

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vlad
Beiträge: 3
Registriert: 22.08.2021, 00:40
System: CCU

Homematic Wired Bus question

Beitrag von vlad » 22.08.2021, 01:02

Hello!

I use an old LK IHC smarthome solution in my house. I have UTP5 cable "star topology" installed in all light switches. Those are used to activate 24V impulse switches.

Can the existing UTP wiring infrastructure be used for the Homematic IP Wired Bus, which also uses 24V?
In other words, can UTP5 cable be used for Homematic Wired BUS?

Hausmeister
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Re: Homematic Wired Bus question

Beitrag von Hausmeister » 29.08.2021, 14:06

Not all of your question is completely clear to me, so i must assume some of my answer.

Your existing cableing is a Cat5 UTP network cable?

You can use 4 wires of this cable for the HMIP Wired, and you can use 4 wires of this cable for HM Wired. Ensure to keep these two systems speperate. and also keep the wiring seperated from the existing system, as long as this is still active.

The longer the cable length between the Bus Units, the more important would be a shielded twisted pair cable type. Your UTP Cable might be unshielded, i guess, so it could possibly run you into problems.
CCU3 für Heizung, Sicherheit, Energiesparen, Anwesenheit und Klingel
Smart-Home sollte nicht "bedient" werden müssen!

vlad
Beiträge: 3
Registriert: 22.08.2021, 00:40
System: CCU

Re: Homematic Wired Bus question

Beitrag von vlad » 29.08.2021, 22:59

Thanks, Hausmeister, for the reply.
Your existing cabling is a Cat5 UTP network cable?
That's true.
You can use 4 wires of this cable for the HMIP Wired, and you can use 4 wires of this cable for HM Wired. Ensure to keep these two systems separate.
I would like to use the only HMIP. No plans for HM usage.
also keep the wiring separated from the existing system, as long as this is still active.
Sure!
Your UTP Cable might be unshielded
True, UTP stands for Unshielded Twisted Pair.
it could possibly run you into problems
That is the core of the question: What could be the safe distance for UTP? For wired UTP Ethernet (5V), a signal lasts as far as 100 m. I suppose the longest segments in my house are 30 m long. However, it is unclear, how reliable will be HMIP 24V signal in such circumstances. (My existing system uses 24 V too). I assume that in some installations there should be some long segments for HMIP bus, e.g., between the different floors or parts of a building.

HMIP wired hardware is quite expensive. Before investing in that would be good to know for sure.

Hausmeister
Beiträge: 349
Registriert: 20.09.2017, 23:08
Hat sich bedankt: 7 Mal
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Re: Homematic Wired Bus question

Beitrag von Hausmeister » 29.08.2021, 23:13

OK. Hey, just try it.

This can work, but as soon as if you run into issues, that will not be explainable right away, then your cabeling might be difficult.

To be honest, if the cabels are installed nicely, with the right distance to high power installation, it might be ok. but the recommendation tells different.

As you have 2 sets of wires, i would recoommend you to use the´4Wire bus on a redundand set of wires. Means that you should have the weiring doubled.
Take the Wire of each color and the each white one together so you increase your cable cross-section / diameter.

To be honest, if your wiring is not very experimental, this could work fine. but there is no warranty for that.

give it a try and let us know if it is working ior not
CCU3 für Heizung, Sicherheit, Energiesparen, Anwesenheit und Klingel
Smart-Home sollte nicht "bedient" werden müssen!

vlad
Beiträge: 3
Registriert: 22.08.2021, 00:40
System: CCU

Re: Homematic Wired Bus question

Beitrag von vlad » 11.09.2021, 21:52

Thanks for the answer, Hausmeister.

Seems, I found the answer. And it correlated somehow wit with you have suggested.
Eventually, I found that Homematic Wired uses just old very well widespread RS-485 standard. That makes my life easy, as using that bus is well described, e.g. Here: https://ctlsys.com/support/rs-485_cable ... nd_modbus/

E.g.:” With a typical capacitance of 15 pF/ft. and a characteristic impedance of 100 ohms, Cat 5 cables almost meets the electrical requirements for RS-485 cables. The capacitance is close to 12.5 pF/foot but there is a small impedance mismatch (100 ohms for Cat 5, 120 ohms for RS-485). In practice, Cat 5 cables have been used successfully in many installations, but there are some concerns.

The most common cable type is Cat 5e-UTP (unshielded twisted pair) which may work over shorter distances in less demanding applications with low EMI noise levels. Be sure to use a wire pair such as the blue and blue/white pair for the data lines and a third wire or pair twisted together for the common connection. Another concern is that the small #24 AWG solid wires, which are typically used in Cat 5 cables, can break easily when connected to a screw terminal block, which does not provide any strain relief.”

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