This study employs a benchmark that couples 21 prompting techniques with 25 real-world PLC use cases, yielding 525 prompt–task evaluations across simple, medium, and complex scenarios. The prompting suite spans foundational methods (zero-/few-shot), reasoning-focused prompts (CoT, PoT, CoC, SCoT), utility and optimization prompts (documentation, OP, RaR, APE), verification and role prompts (CoVe, CoN, ReAct, AP, RBP), and vendor-/symbol-aware variants (RAG, ITP, CoS, CoTP, CCoT, MTPR). The industrial cases range from conveyor and tank-level control to CNC tool change, AGV docking, and robot pick–place, providing broad coverage of sequencing, safety interlocks, and multi-axis coordination. Each instance includes a problem description, an expected IEC~61131-3 output (ST/IL), and a human-verified ground truth, enabling consistent application of fixed prompts and fair comparison across vendors. This design supports reproducible ablations on prompting strategy, facilitates cross-task generalization studies, and allows researchers to select subsets aligned with their evaluation goals.