Reliance Electric 57C Series Modules: Reliance 57C421B Input Module —

Technical Dossier

Product Details And Specifications

Reliance Electric 57C Series: Comprehensive Module Range and Technical Overview

The Reliance Electric 57C Series represents a core component family within the Reliance AutoMax Distributed Control System (DCS), one of the most widely deployed process automation platforms in global heavy industry throughout the 1980s and 1990s. Installations of the 57C Series are documented across petrochemical refineries, pulp and paper mills, steel processing facilities, nuclear power auxiliary systems, and offshore oil platforms. The series encompasses discrete I/O modules, analog signal conditioners, communication adapters, and CPU carrier boards — all designed for rack-mounted backplane integration within the AutoMax chassis architecture. Due to the long operational lifecycles typical of heavy industrial assets (15–30 years), the 57C Series remains in active service at thousands of facilities worldwide, making spare parts availability a critical operational concern for maintenance engineers and reliability teams.

The Evolution of 57C Series Architecture

The 57C Series was introduced as part of Reliance Electric's AutoMax platform, which succeeded the earlier Automax Series 1 and competed directly with Honeywell TDC 3000 and Bailey INFI 90 in the distributed control segment. The 57C backplane uses a proprietary parallel bus architecture with deterministic scan timing, optimized for high-speed discrete I/O in process-critical loops. Early revisions (Rev A/B) supported 24VDC and 120VAC field wiring; later revisions introduced enhanced noise immunity and expanded diagnostics LEDs for field troubleshooting without a programming terminal.

Following Rockwell Automation's acquisition of Reliance Electric in 1995, the 57C Series was progressively superseded by the Allen-Bradley ControlLogix and FlexLogix platforms. However, Rockwell did not provide a direct migration path for all 57C I/O types, meaning many end users continue to operate original 57C hardware rather than undertake full system replacement. The series is now classified as End of Life (EOL) by Rockwell Automation, with no new production. All procurement is sourced from surplus inventory, tested refurbished stock, or decommissioned system pulls.

57C Series Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly traded modules within the Reliance Electric 57C Series. Each module is listed with its primary functional classification and a concise technical descriptor.

Discrete Input Modules (DI)

• 57C421B: 16-point 24VDC discrete input module, sink/source compatible, backplane bus interface
• 57C420A: 16-point 120VAC discrete input module, optically isolated field side
• 57C422A: 32-point 24VDC discrete input module, high-density rack format
• 57C423B: 16-point 48VDC discrete input module, extended voltage range

Discrete Output Modules (DO)

• 57C430A: 16-point 120VAC discrete output module, triac output, 0.5A per point
• 57C431B: 16-point 24VDC discrete output module, transistor sourcing output
• 57C432A: 8-point relay output module, Form C contacts, 2A per point
• 57C433A: 32-point 24VDC discrete output module, high-density, short-circuit protected

Analog Input Modules (AI)

• 57C441A: 8-channel analog input module, 4–20mA, 12-bit resolution
• 57C442B: 8-channel analog input module, ±10VDC, differential input configuration
• 57C443A: 4-channel thermocouple input module, J/K/T/E type, cold junction compensated
• 57C444A: 4-channel RTD input module, Pt100/Pt1000, 3-wire configuration

Analog Output Modules (AO)

• 57C451A: 4-channel analog output module, 4–20mA, 12-bit DAC, loop-powered
• 57C452A: 4-channel analog output module, ±10VDC, voltage drive mode

CPU / Controller Modules

• 57C300A: AutoMax CPU module, 80186 processor base, ladder/function block execution
• 57C310B: AutoMax enhanced CPU module, expanded memory, faster scan rate

Communication & Network Adapters

• 57C410A: AutoMax network adapter module, coaxial token-ring bus interface
• 57C411A: Remote I/O adapter module, AutoMax RIO protocol, rack expansion

Power Supply Modules

• 57C100A: AutoMax rack power supply, 120/240VAC input, 5VDC/24VDC output
• 57C101B: Redundant power supply module, hot-swap capable, status relay output

Sourcing Hard-to-Find & Obsolete 57C Series Parts

As the 57C Series has been formally discontinued by Rockwell Automation, procurement through standard distribution channels is no longer possible. DriveKNMS maintains a dedicated surplus inventory of 57C Series modules sourced from decommissioned plant assets, system integrator stock, and controlled warehouse pulls. Our inventory is continuously updated and cross-referenced against active customer demand lists.

For end users operating legacy AutoMax systems, DriveKNMS provides: direct replacement modules for all major 57C I/O types; cross-reference support for identifying functional equivalents where direct replacements are unavailable; emergency same-day shipping for critical plant maintenance scenarios; and long-term consignment agreements for facilities requiring guaranteed spare parts availability over multi-year maintenance contracts.

Quality Control for the 57C Series Range

All 57C Series modules processed by DriveKNMS undergo a structured inspection and functional test protocol prior to dispatch. Given the proprietary backplane bus architecture of the AutoMax chassis, standard bench testing is insufficient — modules must be validated under live backplane conditions.

Our test procedure includes: visual inspection for capacitor degradation, PCB corrosion, and connector pin integrity; powered backplane insertion test using an AutoMax chassis test rig; channel-by-channel I/O verification for all discrete and analog point types; communication handshake validation for network adapter modules; and burn-in cycle (minimum 24 hours) for CPU and power supply modules. Each unit is issued a test report and ships with a 12-month warranty against functional failure under normal operating conditions.