Sniffing MBUS data for energy integration

Hi,

In my apartment, the heating consumption is being measured by a Kamstrup Multical 302. This is connected via wired MBUS to a master somewhere in the building (haven’t found it yet) and is regularly being read out (once a day).

I already bought an MBUS slave → USB module, which allows me to see the communication from master → slave(s), but obviously (in hindsight) not the replies of those slaves.

My idea now is to buy an MBUS master → USB module and wire it up directly to the meter, disconnecting the connection with the existing, external master. This would allow me to read out the state eg every 15 minutes.

However, that would prevent the external master from reading the meter and thus the energy company from invoicing me based on my usage.

So either I proxy the requests from the external master (by using my existing slave module) to the meter (using the new master module) or I somehow wire these up so that only a single master is able to communicate with the meter at the same time.

The second approach seems more safe (eg I’m unable to debug if the external master is correctly receiving my proxied data, apart from looking at the bill at the end of the month), however I’m unsure as to what the best approach is to tackle this problem.

I don’t have an electrical engineering background, but intuitively it would make sense to have some kind of relay that switches between the 2 masters. It could even be triggered by the MBUS voltage being present when one of the masters would try to communicate.

Does anyone have any experience with this kind of setup and/or is using/doing something similar?

I found Hacky integration for M-Bus which is somewhat related, but did not want to spam that thread, so I created this new one.

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I have exactly the same issue, except I already have a Master on the mBus querying two meters and sending the data via MQTT to Home Assistant. The energy company will soon install its own Master on the mBus.
Did you find a working solution to this problem of having two Masters on one mBus? I figure a double relay could put each of the Masters on the mBus in alternating fashion, if the bus does not support two Masters at the same time. Switching this with 36V from the Master seems to be tricky, because likely the Master puts this voltage on the line continuously.
Please let me know whether you have devised a working solution, many thanks!!!