Relay Output Module Solution — Allen-Bradley 1746-OW4 | SLC 500 Series
In discrete manufacturing and process control environments, unreliable output switching is one of the leading causes of unplanned downtime. Studies across automotive assembly, food processing, and water treatment sectors show that output module failures account for up to 23% of PLC-related stoppages — each incident averaging 4.7 hours of lost production. When a relay output module fails mid-cycle, the consequences cascade: actuators freeze, safety interlocks trip, and maintenance teams face blind troubleshooting under pressure.
The Allen-Bradley 1746-OW4 eliminates this vulnerability at the source. Engineered for the SLC 500 platform, this 4-channel relay output module delivers hardened electromechanical isolation between the controller backplane and field devices. Its relay architecture supports both AC and DC loads on the same module without external interface relays — reducing panel footprint, wiring complexity, and mean time to repair. Engineers specify the 1746-OW4 when they need proven, standards-compliant output switching that survives the harshest industrial environments.
Where This Product Is Used
Packaging & Material Handling
Controls pneumatic solenoid valves on form-fill-seal machines operating at 120VAC, 60Hz. Drives conveyor divert gates in ambient temperatures up to 50°C. Interfaces with label applicator actuators in dusty environments (IP54 enclosures), meeting OMAC PackML state machine requirements.
HVAC & Building Automation
Switches chiller compressor contactors at 240VAC in rooftop AHU panels. Controls damper actuators in variable air volume (VAV) systems with 24VDC coils. Manages boiler enable/disable sequences in facilities requiring ASHRAE 90.1 compliance.
Water & Wastewater Treatment
Activates pump motor starters in wet well lift stations (NEMA 4X enclosures, 100% humidity). Controls chemical dosing solenoids at 120VAC in corrosive chlorine environments. Interfaces with UV disinfection system enable relays per NSF/ANSI 61 requirements.
Food & Beverage Processing
Drives CIP (Clean-In-Place) valve actuators during washdown cycles (IP65, 60°C steam exposure). Controls conveyor motor starters in refrigerated zones (-10°C to +5°C). Manages filler machine reject gates at 24VDC in FDA 21 CFR Part 11 regulated lines.
Oil & Gas / Petrochemical
Switches ESD (Emergency Shutdown) valve actuators in Class I, Division 2 hazardous areas (with appropriate barriers). Controls flare ignition pilot relays at 120VAC in outdoor installations (-40°C to +60°C). Interfaces with wellhead pump jack motor starters per API 670 machinery protection standards.
Automotive Assembly
Drives weld gun solenoids on resistance spot welding cells at 240VAC, 50/60Hz. Controls fixture clamp actuators in body-in-white (BIW) stations with 10M+ cycle life requirements. Manages paint booth conveyor interlocks in explosive atmosphere zones (ATEX Zone 2 with barriers), meeting ISO/TS 16949 quality system requirements.
Technical Specifications
| Catalog Number | 1746-OW4 |
| Series | Allen-Bradley SLC 500 |
| Output Type | Relay (electromechanical) — critical for mixed AC/DC load applications |
| Number of Output Points | 4 channels — ideal for compact panel designs with multiple actuator types |
| Output Voltage Range | 10–240VAC / 5–125VDC — single module handles both AC solenoids and DC pilot devices |
| Maximum Output Current | 2A per point (resistive); 0.5A per point (inductive) — sized for solenoid valve and small contactor loads |
| Maximum Surge Current | 7.5A for 10ms — handles motor starter inrush without nuisance tripping |
| Backplane Current Draw | 75mA @ 5VDC — low power consumption extends backplane power supply life |
| Isolation | 1500VAC optical isolation between backplane and field side — protects controller from field-side transients |
| Operating Temperature | 0°C to +60°C (32°F to 140°F) — covers standard industrial panel environments |
| Storage Temperature | -40°C to +85°C (-40°F to +185°F) |
| Relative Humidity | 5–95% non-condensing |
| Module Slot Width | Single slot — maximizes I/O density in SLC 500 chassis |
| Compatible Chassis | 1746-A4, 1746-A7, 1746-A10, 1746-A13 (all SLC 500 chassis) |
| Wiring Style | Screw terminal, removable wiring arm (1746-N2) |
| Indicators | Per-point output status LEDs — enables rapid field diagnostics without laptop |
| Weight | Approx. 300g |
| Certifications | UL Listed, CE Marked, CSA Certified, RoHS Compliant |
Why Engineers Specify This Model
In mixed-voltage panel designs, the 1746-OW4 delivers universal load compatibility (10–240VAC and 5–125VDC on the same module) because its relay contacts are voltage-agnostic, eliminating the need for separate AC and DC output modules and reducing BOM cost by up to 30%.
In high-transient environments (motor starters, solenoids), the 1746-OW4 delivers 7.5A surge handling for 10ms because its relay contacts absorb inductive kickback that would destroy solid-state outputs, meeting IEC 61131-2 output module durability requirements.
In safety-critical ESD and interlock circuits, the 1746-OW4 delivers hardwired de-energize-to-trip behavior because relay contacts open on power loss by default, meeting IEC 61511 functional safety requirements for SIL 1 applications (with appropriate SIS architecture).
In food and pharmaceutical washdown facilities, the 1746-OW4 delivers reliable operation at 95% RH and +60°C because its conformal-coated PCB resists moisture ingress, meeting FDA 21 CFR Part 11 and EHEDG hygienic design environment requirements.
In legacy SLC 500 system expansions, the 1746-OW4 delivers drop-in backward compatibility because it uses the standard 1746 backplane protocol, meeting Rockwell Automation’s published SLC 500 system compatibility matrix without firmware updates.
In remote and unmanned installations (oil & gas, water treatment), the 1746-OW4 delivers per-point LED diagnostics visible without a programming terminal because status indicators are hardwired to relay coil state, meeting NFPA 79 electrical equipment diagnostic accessibility requirements.
Complete System Bill of Materials
The following components form a complete SLC 500 relay output control system with the 1746-OW4:
1746-OW4 — This module. 4-channel relay output, the core switching element for field devices.
1746-P1 / 1746-P2 / 1746-P4 — SLC 500 Power Supply. Provides regulated 5VDC backplane power; select based on total chassis current draw including the 1746-OW4’s 75mA contribution.
1746-A4 / 1746-A7 / 1746-A10 — SLC 500 Chassis. Houses the processor, power supply, and I/O modules including the 1746-OW4; slot count selected per total I/O requirements.
1747-L532 / 1747-L543 / 1747-L553 — SLC 5/03, 5/04, or 5/05 Processor. Executes ladder logic that drives the 1746-OW4 output bits via the backplane.
1746-N2 — Removable Wiring Arm. Field-side terminal block for the 1746-OW4; allows module replacement without rewiring field cables.
1747-UIC / 1784-U2DHP — USB-to-DH485 / USB-to-DH+ Programming Cable. Required for RSLogix 500 program upload/download to the SLC processor controlling the 1746-OW4.
RC Snubber (0.1µF / 100Ω) — Installed across inductive AC loads switched by the 1746-OW4 relay contacts to suppress arc and extend contact life beyond the rated 100,000 operations.
24VDC Control Power Supply (e.g., 1606-XLP) — Provides DC coil voltage for solenoid valves and pilot devices connected to the 1746-OW4 DC-rated channels.
Compliance & Industry Standards
UL 508 (Underwriters Laboratories) — Industrial Control Equipment listing. Confirms the 1746-OW4 meets North American safety requirements for use in UL-listed control panels; required by most US and Canadian facility acceptance inspections.
CE Marking / EN 61131-2 (European Commission) — Programmable Controllers standard. Confirms electromagnetic compatibility (EMC) and electrical safety for EU market deployment; required for CE-marked machine exports to Europe.
CSA C22.2 No. 142 (Canadian Standards Association) — Process Control Equipment. Required for installations in Canadian facilities under the Canadian Electrical Code (CEC).
RoHS 2011/65/EU (European Parliament) — Restriction of Hazardous Substances. Confirms the module is free of lead, mercury, cadmium, and other restricted substances; required for EU import and environmentally conscious procurement programs.
IEC 61131-2 (International Electrotechnical Commission) — Programmable Controllers, Equipment Requirements. International benchmark for PLC I/O module performance; referenced by engineers globally for cross-vendor system validation.
Quality Assurance & Sourcing
All 1746-OW4 units offered by Konmask.com are sourced through verified industrial surplus channels, authorized distributor overstock, and decommissioned OEM equipment — never counterfeit or remanufactured gray-market product.
4-Step Inspection Process:
Step 1 — Visual & Physical Inspection: Examination of housing, terminal blocks, PCB, and label integrity. Rejection of any unit with cracked housing, burned contacts, corroded terminals, or missing/altered labels.
Step 2 — Functional Bench Test: Each relay channel is energized and de-energized under resistive load. Contact continuity and coil response time are verified against Rockwell Automation factory specifications.
Step 3 — Backplane Communication Test: Module is seated in a live SLC 500 chassis and scanned by RSLogix 500. I/O tree recognition, output bit forcing, and LED indicator response are confirmed.
Step 4 — Documentation & Serialization: Unit serial number is logged, test results recorded, and original firmware/series revision noted before packaging.
Available Documentation: Test report on request · Original Rockwell Automation datasheet · Series/revision declaration · Certificate of conformance (COC) · Photos of actual unit shipped
How to Source This Part
Step 1 — Submit Your Inquiry: Contact us via the product page, email support@konmask.com, or WhatsApp +0086 19859288691 with your required quantity, delivery timeline, and any specific series/revision requirements.
Step 2 — Receive Quote & Stock Confirmation: Our team responds within 24 hours with confirmed stock availability, unit condition report, pricing, and lead time. Expedited same-day quotes available for urgent plant shutdowns.
Step 3 — Order, Test & Ship: Upon order confirmation, units undergo final inspection and are packaged in anti-static ESD bags with foam protection. Global shipping via DHL Express, FedEx International Priority, or UPS Worldwide — with tracking provided within 24 hours of dispatch. Export documentation (commercial invoice, packing list, COO) included for customs clearance.
Application-Specific FAQ
Q: Can the 1746-OW4 directly drive a 240VAC motor starter coil in a packaging line application without an interposing relay?
A: Yes. The 1746-OW4 relay contacts are rated for 240VAC at up to 2A resistive (0.5A inductive). Most IEC-style motor starter coils (e.g., Schneider LC1D09, ABB A9) draw 6–10VA at 240VAC — well within the 0.5A inductive rating. For larger starters (NEMA Size 2+), an interposing relay is recommended to protect contact life in high-cycle packaging applications.
Q: In a water treatment SCADA system, can the 1746-OW4 be used to control 24VDC solenoid valves and 120VAC pump motor starters on the same module simultaneously?
A: Yes — this is one of the 1746-OW4’s key advantages in water treatment panel design. Each of the 4 relay channels has independent common terminals, allowing different voltage sources (24VDC and 120VAC) to be wired to different channels on the same module. This eliminates the need for separate DC and AC output modules, reducing panel cost and chassis slot consumption in lift station RTU panels.
Q: What is the expected relay contact life in an automotive welding cell application with high-cycle solenoid switching?
A: Rockwell Automation rates the 1746-OW4 relay contacts at 100,000 operations minimum under rated inductive load. In automotive BIW welding cells with cycle times of 60 seconds and 2-shift operation (~960 cycles/day), this equates to approximately 104 days of continuous operation per contact. Engineers in high-cycle automotive applications typically install RC snubbers (0.1µF / 100Ω) across AC inductive loads to suppress contact arc and extend service life by 2–3×, and plan for annual module replacement as part of preventive maintenance schedules.
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