Branch placement principles for ladder diagram design that do not include contac
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Branch placement principles for ladder diagram design that do not include contac
In 2024 we published a quick checklist on where to place branches in a ladder diagram
Detail
The six 2024 branch-placement principles still apply, but every IDE now autoflows them , your job is to constrain layout so auto-layout doesn't misread your intent.
New in 2026: branches must be reviewable by code-generation AI (Studio 5000 LogixAI, TIA Portal AI helper, MELSOFT AI) and lint-friendly under IEC 61131-3 4th edition.
New in 2026: each branch should carry a tag, a comment, and a security zone label so the diagram survives an OPC UA over TSN / IEC 62443 handover.
New in 2026: if the program may end up on a soft-PLC or vPLC target, write branches so they import cleanly via PLCOpenXML / PLCopen OPC UA , no implicit rung order.
Will the AI linter, the AI code generator, and the security review all accept it on first pass?
If the same branch both "permits the operation" and "selects the mode", split it. AI code generators in Studio 5000, TIA Portal, and GX Works3 will misread the dual intent and produce an AOI that satisfies only one of the two at runtime.
The branch label should be the same identifier as the boolean tag driving it (e.g. branch
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