Connecting to M-Bus, where there is a Master device already

[nilvanis]

> Moving conversiation from #4 started by @xus-droid.

I just need to find a cheap hardware solution for the mbus. I need a solution to sniff the mbus, I disconnected the existing master..

My understanding is that you cannot have two M-Bus Masters on the same rail.
Master is powering the bus: +36V for 1 and +24V for 0.
Source: https://m-bus.com/documentation-wired/04-physical-layer
Two power sources might result in an unreliable communication, but also can damage connected masters.

For a cheap solution I'd say go with ESPHome with two relays.
You get something like this and wire it up like on the diagram below:

Crucial is to switch the relays at the same time.
This way you switch masters :)

------UPDATE-------
ESP32 module from the link can also be powered from a DC7-60V power supply via VCC.
So you can use 12V or 24V PSU for example.

Also, I'd recommend to check the polarity via multimeter and align it on the relays.
And last, but not least: It's just an idea and you do this on your own risk.
There is always a scenario, when for some reason just one relay work (hardware/software failure).
I don't know what happens in such situation.