LCN installation internals

Hi all,
I have question to al LCN users. I hope there are some beside me. I have LCN installation in my house and I suffer from a basic issue caused by electric fuse. My earth leakage circuit breaker is turned off every few hours if I turn on lcn-binding. My electric installation worked just fine before adding LCN. I’ve tried to follow suggestions from designer to disable sections of installation one by one, however it didn’t help. My earth leakage circuit breaker is still turning off.

That’s why I would like to ask someone who have LCN installation and uses Issendorff’s binding - how the “wiring” is made in electrical switchyard. Did your designer/electrician/installer use LCN-IS module? My installation consist 25 modules, bunch of sensors and converters on two floors. At this stage they control lighting and heating.


Dear Luckasz,

Why are you asking help for a solely proprietary protocol, to an open source community?
If there is someone out there in our community that made any reverse engineering and can publish it without any infringement, then that’s a benefit for the whole community, and I shall stand by it!

Best regards,

I am not asking for help on protocol but physical installation details, which as software developer, I don’t know. There is open source extension which allows to interact with LCN via TCP/IP gateway (

Best regards,

Once again I ask: can we disclose(me or yourself) any information publicly without infrenging any proprietary license?
AFAIK about LCN, it is never really clarified in any statement, or document! But… I might be wrong!

None of modules which I have received had “license” attached denying to talk how to wire them. I don’t know any other system than above, but since you mentioned such constraints, can you please tell me do you know any producer and system who is so restrictive?

I can understand that manufacturer of hardware could be unpleasant when construction details of their devices would be exposed, however here we talk “just” about connecting tings and good practices. At least the last one can not be licensed.


So, let’s start debugging:

Well, with LCN, as I understand has sort of 1 wire communication, and you have a differential current circuit breaker (not only earth leakage)! If your LCN device does not isolate well enough, then you will always have this problem, unless you give up the basic safety of a RCCB (residual-current circuit breaker), which I will never recommend!
AFAIK, I think you have an overall conceptual problem. But, don’t despair, we will find ways together. Do you have any electrical installation plans of your setup so I can have a look upon?

Best regards,

You are correct, it is pretty much one wire communication - it uses extra “data” line to transmit telegrams and neutral line as “return”. Since data lane goes in same cable as power supply it must go over differential current circuit breaker.

I have generic schema of module and peripherals connections. It is not as detailed as usual project. It shows where modules should be installed, which rooms they control, where to put monition and temperature sensors. Based on that I got extra wiring over standard one which comes from electricity project (LCN was launched after building was settled).

Kind regards,

This means that you will need “filters”, or some other tricks to keep the RCCB in place!
So, let’s start with the basics:
How many LCN devices do you have?
What is the minimum and the maximum length of cable between the RCCB and a LCN device (“rule of thumb” is enough)?
For now I think this information can get me an idea on your installation!

Best regards,

I don’t plan to remove any fuses, they been working before just fine, issue started to occur once new parts were added to installation. Electrician did measure resistance of all circuits with device dedicated to such task and they look fine. However based on measurements he made, sometimes resistance is shown in mega ohms, but other times it is shown in kilo ohms. It is still above limit of RCCB, but possibly transmissions made over D and N lane cheats fuse and forces it to act. All lanes - data lane included goes over RCCB.

There are 20 modules in single segment. In some places I have two modules connected behind switch (wall mounted) as there was 4 outputs and to little space to put two relays (one module can handle up to 4 outputs via two additional wall mounted relays, but they take a space).
There are 7 DIN mounted modules and relays connected to them control heating, lighting, irrigation and so on. I can’t tell you exact length of cables, but based on basic measurements they are shorter than 40 meters. Of course circuits have variable length depending on how far circuit is from electrical cabinet.
Remaining modules are located on two floors behind switches.

RCCB gets hit on random manner during the day and night - meaning there are no actions executed by any module, no relay state changes. I have just read only integration via OpenHab to collect sensor values from LCN, however RCCB issue shows up even if integration with OH is disabled (meaning with no external communication).

Dear Lukasz,

if RCCB gets hit within an LCN Installation it’s quite often a wiring fault.
This is getting worse, the more communication is on the LCN wire. Some people report this fault, if they read out the LCN network via LCN-PRO.

The Data wire must be wired through the same RCCB as the neutral wire for this Segment and it is not allowed to have this data wire connected to other modules, which are not connected behind this RCCB.

Some People reported, that the direction of the RCCB is important. So be aware of any input/Output recommendations by the manufacturer.

A last point might be a bad connection of the neutral wire…

If you are familiar with the German language, I would recommend the community of LNC at (but you can also ask questions in English) or the Bus-Profi at where this type of question is more common.

Maybe one of the hints are helping you to find the problem…


Thanks for your reply Andreas,
Indeed this seems to be wiring issue. I got contact to local representative here to trace problem. Main trouble is how to find which thing is wired improperly to avoid extra work without pulling out everything. My electrician says that wiring should be just fine, but he is just a human and as every of us, could make an mistake.
There are separate RCCB’s per floor and only one gets affected, which in theory should narrow search scope. In practice it’s still difficult to diagnose this as it might be cross wired with sockets or other floor.

We will, see if there is a resort. :slight_smile:


If it is only one RCCB which hit, then it must be a module behind this RCCB.
The data wire from the modules behind this RCCB should only be connected to modules behind this RCCB and MUST be connected through this RCCB or via LCN-IS.
If you have any connection between the data wire behind this RCCB and a module which is connected in front of this RCCB you get in Trouble…


Some time passed away, we have new year and its final time to close and summarize this topic.

As suggested by @imhofa, issue indeed was caused by basic wiring problem. LCN Polen was very kind and their director come to me to did help my electrican (and me obviously) to trace the cause. Free of charge even if none of us is “authorized installer”. :slight_smile:

Error was fairly easy to find. Mistaken wiring of PKU module (usb bridge) to the BUS before RCCB caused ocasional resistance drops and reaction from safeguard.
After rewiring of PKU module everything works as expected and there are no failures since several weeks.

Cheers & thank you for your time and assistance.

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