Basic ladder logic question: 1 rung or 2

Is it better to use rung 1 or rungs 2 and 3? I generally don't hesitate to put two outputs in parallel on a single rung if the inputs are all the same but this scenario made me wonder if there is a "best" way, and if so why? Thanks for any input.


I think there are multiple schools of thought here. Paralleling outputs make it easier to see that they are activating at the same time. Additionally if there is a change in the logic that affects both outputs there is only one place to change it. If the logic is repeated in two different rungs, then the change has to be correctly implemented in two different places. My preference is to have the logic set an intermediate bit and then use this bit in separate rungs to set other outputs as required. If there is a change that affects only one output, I change its rung. If the change affects the common logic I change the rung with the intermittent bit.

I have seen ladders programmed in such a way that it makes it easier for the coder to make changes. I have also seen applications which were written to make the logic easier to understand by the guy on a call out at 2 AM.
I would have no problem with putting it in the 1st rung. As long it is not too complex.
When the 1st rung was very complex with many conditions, I would have split it up because of ease of debugging in case of problems and because of serviceability of the code (for future upgrades).
But since this one is so simple I would also have done it in the same rung 1.
(my 5 cents after 30 years of industrial automation incl. worldwide local/remote service)