Hi,

I am in the process of studying signals, and am considering for my first signal to try the Viessmann 4011 and 5221 combination.
My question relates to the choice of switch tracks, the Viesmann 6840 reed switch and the Marklin 24994 . If I use the 24994 then I must connect the accessory transformer and track power common leads. I understand why, but is this good practice?
I am leaning towards using the 6840 and keeping the two common lines separate.
I have seen comments through search about keeping the grounds separate to avoid problems?

Not strictly true.
Unlike the M-Track equivalent (with metal roadbed) the 24994 has a detachable return wire.
This is connected to the track "0" by default but can be unplugged and isolated.

As to utilising the common ground (rail) anyway then, as already mentioned this may (and is) generally be done without problems.

However, For Sensor controlled (digital) implementations rather than direct (Analogue) wiring to the signal,
this also implies your sensor unit has its ground reference connected to the same circuit.

Should you have multiple booster sections with technology akin to the 60212(CS1), 60173(Booster), 60213(CS2 early hardware) and have adhered to the guidelines not to use a common ground for these items, then you are better off running a separate Sensor (S88) return wire/bus.

As noted above, the 24994 has a discrete wire for the micro-switch return circuit.
Personally I would make use of it, and keep my sensor wires away from the power circuit

Dale,

I have often wondered about this.

In my mind, the voltages would all be added together to get the gross voltage.
So, when you have a positive 18vAC plus 12vDC you get a surge of 30v for that moment in time.
And when the alternating goes negative 18vAC plus 12vDC you get a net of -6v for that moment in time.
But from what I have seen, this is not the result which one observes with the eye.
(I don't have an oscilloscope to measure the result more accurately)

Previously, I had connected a 12vDC circuit for the Circuit Tracks to a Timing Chip which I made, and connected the ground to the 18vAC Brown Track Ground.
So I was running 18vAC in the track and 12vDC in the chip both through the common ground of the rail.
After a while, I disconnected that because I wasn't sure whether it was such a good idea.
(Clapcott's note of course now makes me realize that I could have adjusted the wire under the circuit track - thanks buddy !!)

Regards,
john

Depends on the wiring.
You have a common ground. Nothing adds up when you connect the consumers between a live wire and the common ground.
The adding effect comes when you connect consumers between two live wires if both power supplies have a common ground.
People normally do not use this.

A simple application: connect a consumer between red and yellow of a Märklin transformer if you need voltages in the range 0 through 4 V. But 0 V are in the right position of the dial!