I have a fairly large layout run by a CS3+. Recently I had to replace my main bus under the table as the CS3 was giving me that a short existing somewhere on the main line. I reconnected the first feed and everything worked fine. When I connected the second feed no matter where it was, my CS3 reset itself. When I removed the second feed all was fine again. Has anyone else encountered this problem?

Get a multi-meter and start checking dc voltage from the closest to the CS3 and out. If the voltage changes polarity you have reversed the wires. I am assuming you have three rail.

Hi Boris
You know by now that your CS3 has NO problems and that you have a short circuit on the second feed

Here is the process to locate where the problem is:

1. remove all rolling stock from your layout and check if the short is still there
   
2. break the faulty zone into smaller zones tryng to detect when the short appear while adding a new set of tracks
   
3. investigate the small zone causing the short on continue until the one track level
   
4. the result may be obvious or very unconspicuous. E.g. in M track a switch point spring burnt by a short and extended to the stud line. Another example is the result of using a dremel disk producing fine and invisible metal dust making the short, a forgotten tool on a track
   

Cheers
Jean

He indicates that wherever he connects the second feed he shorts out. So, if he is doing it correctly the problem can't be on a section of track but in the second feed. But I wonder if he has isolated the sections of the layout that he is feeding with the busses. If not that might be a solution. Or at least a means of working towards a solution.

The CS3 was set for a 60101 but I can't set it for the actual one that I use a 60 watt 60065 (that is what the manual calls for). The pull down menu only has 60042, 60043 and 60045. The voltage indicator reads 19.4v.

Hi Boris
The CS3 power settings are there to adjust the current limit on the CS3 so that, when a short is detected, the CS3 cuts off the power before the current surge is transmitted to the power supply (60101 for 5 A, 60045 for 3 A). Failure for the CS3 to switch off in good time, the power supply feeding the CS3 switchs off, causing the CS3 to cold-start after the thermal protection is waived off.
Märklin has produced so many power supplies that listing the references was a mistake (too many of them) but rather a power value (100 W, 60 W or the current value 5A, 3 A)
So, long speech to say you should select the 60045 if you have a 60 W PSU.
Cheers
Jean

I have tried all the posts to date. My CS3+ still registers a short but it does not short out automatically. Is there a way to tell if the CS3 is defective or needs a factory reset?

Ho Boris
On my CS3 in the Track Format processor section there is a screen to select the power source model and you must be set to use the first line (60041, 60061) if as I understand you have a 60 W Märklin power supply.

Before you do a CS3 reset
The current-sensing is made by a small-value resistor and a voltage drop measure and you have two of these: the main track and the programming track. Chances that this device is failing are rather small.
Disconnect the track connectors on the CS3 and check the current measure, both measures should read zero. If not your CS3 has a hardware problem (likely not to be solved by a software reset or a program change
If you have (or can get) a power resistor (e.g.: 10 W 100Ω) you should be able to measure a current 100Ω gives you a reading of 0.18A

The CS3 reset procedure
Because it will erase all your records (track plans, devices,settings) it is best to make a back-up on an external memory (USB memory stick, plug-in sim card (I use 32 GByte one)
Once this is done, you select CS3/ restore and, among the files to be restored, one is called LEER.ZIP (Meaning empty in German). If you select this one, it will clear all previous setting BUT it will not erase all your previous recording (have to do this one by one manually.
Cheers
Jean

Edited by user 06 September 2025 18:40:02(UTC)  | Reason: Not specified

I'm a little late to the discussion here but I'll add in something that might have been overlooked. I had my CS3 hooked up working great, then I added a power center for extra outlets. that is where I started having issues. Turns out the power center was flaky. I in turn bought a new one and all the errors disappeared. So that being said how is your CS3 plugged in?

I bought a new CS3 thinking it was defective. It wasn't, i got the same message- short on the main line.
I rewired the entire layout and it checks out fine with a volt meter.
When I connect any feeder to the tracks, it automatically shuts down.
I checked all the track for loose objects such as metal on the tracks and there are no problems.
Any ideas?

Does each of the feeds to the track need to be isolated from the other feeds?

"Does each of the feeds to the track need to be isolated from the other feeds?"
Not if you have wired it correctly but doing so might make it easier to find a short.

Find some other way of powering the layout like a 9 volt battery and then using a multimeter set on dc voltage check the polarity of each of the feeds. If you have one wired incorrectly the polarity should be reversed. Might also show up on the track itself but not sure.

Does this mean that everything works well with the new loop attached and that you can run trains on it without problems - as long as no new feeder wires are attached?

Edited by user 18 December 2025 17:08:15(UTC)  | Reason: Spelling