Allen-Bradley 1746-IO4 SLC 500 Digital I/O Module 2 In / 2 Out By wayne No Comments on Allen-Bradley 1746-IO4 SLC 500 Digital I/O Module 2 In / 2 Out 3 Min Read The Allen-Bradley 1746-IO4 is an SLC 500 combination module with 2 AC inputs and 2 relay outputs. It handles 85-132 VAC and provides reliable machine control.