Description: The 1746-IH16 is a 16-point 125V DC Current Sinking Input Module manufactured by Allen-Bradley / Rockwell Automation for the SLC 500 modular control platform, with the “/A” suffix identifying the original Series A hardware revision. Purpose-built for high-voltage DC control buses, the 1746-IH16 accepts field signals across a 90–146V DC operating window at its sixteen sinking inputs — one group of sixteen sharing a single common — and consumes only 85 mA at 5V DC from the SLC backplane. Each channel provides optical isolation to 1500V, a maximum 9 ms on/off signal delay, and a 2.15 mA nominal input current at 125V DC, making the module the standard SLC 500 interface for DC control circuits in power generation, substations, mining, and any facility where 125V DC is the installed control voltage.
Application Scenarios: Inside a power-plant or substation environment, the 125V DC control bus is the backbone of the protective-relay scheme, breaker trip circuits, and annunciator panels — a voltage chosen historically because it survives battery-backup conditions, keeps contact resistance low across long cable runs, and remains isolated from the AC distribution system. When a plant retrofits those hardwired schemes onto an SLC 500 processor for supervisory monitoring, the voltage mismatch becomes the central engineering problem: conventional 24V DC input modules cannot directly accept a 125V DC signal, and stepping the bus down through interposing relays multiplies the wiring, the panel space, and the failure points. The 1746-IH16 solves the problem at the module level — the 125V DC field signal lands directly on the removable terminal block, the module’s sinking input architecture receives current from the sourcing field contact, and the SLC processor sees a standard discrete input bit without any interposing hardware. The same pattern repeats across mining operations using DC haulage and hoist control circuits, water and wastewater facilities with legacy 125V DC annunciator systems, and telecom/power facilities where 125V DC battery plants remain the standard for critical control loads.
Parameter
| Main Parameters | Value/Description |
|---|---|
| Product Model | 1746-IH16 (Series A, “/A”) |
| Manufacturer | Allen-Bradley / Rockwell Automation |
| Product Category | SLC 500 Digital DC Input Module — 125V DC, Current Sinking |
| Voltage Category | 125V DC signal input (sinking) |
| Number of Inputs | 16 |
| Points per Common | 16 (one group of 16, internally connected commons) |
| Operating Voltage Range | 90–146V DC |
| Points ON Simultaneously, Max | 6 @ 146V DC and 30 °C; 12 @ 146V DC and 50 °C; 14 @ 132V DC and 55 °C; 16 @ 125V DC and 60 °C |
| Input Current, Nominal | 2.15 mA @ 125V DC; 2.25 mA @ 132V DC |
| Off-State Voltage, Max | 20.0V DC |
| Off-State Current, Max | 0.8 mA |
| Signal Delay, Max | On = 9 ms; Off = 9 ms |
| Backplane Current | 0.085 A @ 5V DC; 0.0 A @ 24V DC |
| Power Dissipation | 0.32 W/point; 0.217 W minimum; 5.17 W total |
| Isolation | Electro-optical, 1500V between input circuits and control logic |
| Noise Immunity | NEMA ICS 2-230 |
| Configuration ID Code | 0507 (programming software / HHT) |
| Removable Terminal Block | RTB; max 2 mm² (14 AWG) wire, 2 wires per terminal, 0.9 N·m (8 lb·in) torque |
| I/O Cabling Options | 1746-HT or 1746-HCA cables, or interface modules (IFMs) |
| Operating / Storage Temperature | 0 to +60 °C / −40 to +85 °C |
| Humidity | 5–95% non-condensing |
| Vibration / Shock (operating) | 2.5 g @ 57–2000 Hz / 30 g |
| Hazardous Location | Class I, Division 2, Groups A, B, C, D |
| Agency Certifications | UL Listed, CSA / C-UL Certified, CE, C-Tick |
| Dimensions / Weight | ~150 × 130 × 40 mm; ~500 g |
| Lifecycle Status | Discontinued as part of the SLC 500 family (Bulletin 1746) — supplied as verified surplus or remanufactured |