Application ScenariosA 380 MW coal-fired unit running Bailey INFI 90 on the balance-of-plant side needed to land 112 new 125 V DC breaker-auxiliary contacts from a switchgear yard retrofit (6 kV feeders to the forced-draft fans, PA fans, and coal feeders). Running 112 point-to-point 125 V DC wires all the way to the MFC baseplate DI cards would have meant three new baseplates, 600+ terminal lugs, and a week of loop-check. Instead, the E&I lead deployed seven ABB NRDI02​ termination units in a satellite termination cabinet halfway between the MCC and the control room, landed all 112 breaker NO/NC contacts on the NRDI02​ screw terminals (125 V DC wetting from the yard’s 125 V DC UPS), and ran seven NKDI ribbons the remaining 40 m to the RDI cards in the MFC rack. The NRDI02‘s 1500 V channel-to-channel isolation shrugged off the induced transients from the 6 kV switchgear bus (common-mode > 800 V during a feeder fault), and the SOE timestamp resolution of 10 ms at 125 V DC caught a cascading trip root-cause two months later: the PA-fan breaker opened 40 ms beforethe coal-feeder undervolt—a sequence the old 100 ms-resolution DI card would have blurred. The plant accepted the retrofit with zero loop-check overruns, and the satellite cabinet’s NRDI02​ spares (one per seven) covered the whole yard.Parameter

Technical Principles and Innovative Values

• Innovation Point 1: Redundant DI Architecture via RDI + NRDI02 Split.​ The NRDI02​ doesn’t process logic—it conditions. The companion RDI (Redundant Digital Input) card in the INFI 90 rack has twoindependent read circuits per field contact (or 1oo2 card-level redundancy depending on configuration). The NRDI02​ feeds the same field wire to both read paths through its screw terminals and NKDI ribbon, so a single-channel weld or open-wire shows up as a “redundancy mismatch” in the MFC before it becomes a missed trip. This is why power-plant ESD and breaker-aux loops standardize on NRDI02​ + RDI instead of plain DI cards.
• Innovation Point 2: 1500 V Ch-Ch Isolation + 600 m Drive Capability.​ Each of the 16 channels on the NRDI02​ is galvanically isolated from its neighbors and from system logic (1500 V AC, 1 min). Combined with the 3–5 mA field current at 125 V DC, the NRDI02​ can drive a 600 m tray-run from a switchgear yard back to the DCS rack without intermediate repeaters—and without cross-talk between the FD-fan contact and the PA-fan contact sharing the same termination unit.
• Innovation Point 3: SOE-Grade Timestamping at 10 ms (125 V DC).​ The NRDI02​ itself doesn’t timestamp—the RDI card does, but the NRDI02‘s clean thresholding (98 V ON / 91.3 V OFF hysteresis at 125 V DC) ensures the RDI sees a crisp edge, not a bouncing one. The resulting SOE lands at 10 ms resolution for 125 V DC inputs (20 ms for 120 V AC). In a cascade-trip forensic, those 10 ms increments are the difference between “breaker A caused B” and “they were simultaneous.”

Application Cases and Industry ValueA petrochemical cracker running Bailey INFI 90 on the ethylene-compressor train used four ABB NRDI02​ units in the MCC satellite cabinet to land 64 ESD pushbutton latches and 48 motor-protective-relay auxiliary contacts (all 125 V DC, wetting from the plant’s 125 V DC UPS). The train’s pain point was “ghost alarms” during lightning-season: a nearby strike would couple 400–600 V common-mode onto the unshielded portions of the MCC tray, and the old plain-DI cards would see phantom transitions, flooding the SOE with garbage. After moving to the NRDI02​ + RDI nodes (the NRDI02‘s 1500 V isolation + the RDI’s dual-read cross-check), the phantom-SOE events dropped from ~20 per storm to zero. The E&I supervisor noted the per-channel LEDs on the NRDI02​ face saved hours during commissioning—”you can stand at the satellite cabinet, push the ESD button, and watch CH-7 LED flip—no need to walk back to the MFC rack with a PG laptop.”Related Product Combination SolutionsBuild or sustain a Bailey INFI 90 redundant-DI node around the ABB NRDI02​ with these ecosystem companions:

• ABB NRDI01​ – DIN-rail mounted sibling of the NRDI02​ (panel/rack mount); choose NRDI01 when the termination needs to DIN-mount inside a local MCC pocket rather than a central termination cabinet.
• ABB DI02 / RDI (Redundant Digital Input) card​ – The smart card that lives in the INFI 90 card rack and pairs with the NRDI02​ over an NKDI ribbon; the RDI does the dual-read, SOE timestamping, and backplane handoff to the MFC/PCU.
• ABB NDSM05​ – Digital Slave Input Module (64 CH, 24 V DC) we covered earlier; differentarchitecture (slave-bus to MFC, 24 V only, no 125 V AC/DC). Use NRDI02+RDI for high-voltage breaker-duty; use NDSM05 for 24 V dry-contact saturation (pull-cords, pushbuttons).
• ABB NKDI cable​ – The ribbon (typically 20–30 conductor) that links the NRDI02‘s header to the RDI card’s header; length-matched to rack-to-termination-cabinet distance—stock 1 m, 2 m, 5 m variants.
• ABB NTAI02​ – Analog Input Termination Unit, the analog sibling to the NRDI02; if your satellite cabinet also lands 4–20 mA or TC, NTAI02 is the one.
• ABB NPBA-80​ – Profibus-DP adapter (drive-side, covered last round); unrelated to DCS, but often shares the same plant-spares bin in mixed Bailey+ABB drive sites.
• ABB 125 V DC UPS / wetting supply​ – The NRDI02‘s field side needs a stable 125 V DC (or 120 V AC) wetting source; most plants steal this from the switchgear DC system, but a local fused distribution block on the termination cabinet is wise.