The IC694MDL632 brings 125 VDC discrete inputs into a single RX3i backplane slot — 8 points organized in two isolated groups of 4, each group with its own common terminal. The 125 VDC rating is specific to industries where DC control power runs at battery-bank voltage: railway signaling systems (110 VDC nominal, 125 VDC float), power generation station battery rooms (125 VDC station service), and traction power substations. The two-group isolation means a ground fault on a field device in the switchyard does not propagate through the input module to the control system — each group floats independently, and the 250 VAC continuous isolation between groups and from the backplane provides the galvanic barrier.

The 125 VDC niche: why this voltage class exists

In a typical 24 VDC industrial control panel, discrete inputs switch at 24 VDC — the same voltage that powers the PLC, the HMI, and the sensors. In a 125 VDC installation, the control voltage comes from a battery bank that floats at 125 VDC, backed by a charger rectifier and sized to keep the station operating through an extended AC power outage. The higher voltage allows smaller-gauge field wiring over longer distances — a limit switch 500 meters from the control room draws 3.1 mA at 125 VDC through 18 AWG conductors with negligible voltage drop. The IC694MDL632 accepts the 125 VDC signal directly, eliminating the interposing relays and separate 24 VDC power supplies that a 24 VDC input module would require in a 125 VDC station. The red warning bands on the module label and the per-point green LEDs make the presence of hazardous DC voltage immediately visible to a technician opening the panel door.