Purchase now: Allen Bradley 1746-OW8 Relay Output Module
Purchase now: Atlantechdrives provides you the 1746-OW8, a highly dependable 8-channel digital relay output module engineered by Allen Bradley for the widely used SLC 500 programmable logic controller system. This module features electromechanical relay contacts (Normally Open), making it an incredibly versatile solution for mixed-voltage control panels. Unlike solid-state modules that are restricted to either AC or DC logic, the 1746-OW8 can seamlessly switch both alternating current (AC) and direct current (DC) loads. This flexibility allows automation engineers to control a diverse array of field devices—such as 120V AC motor contactors, 24V DC pneumatic solenoid valves, and 220V AC alarm sirens—all from a single, robust hardware component, simplifying chassis layout and reducing inventory costs.
Technical Specifications of the 1746-OW8
The 1746-OW8 is designed with two internally connected groups of four outputs (Outputs 0-3 share one common, Outputs 4-7 share another). This allows you to utilize two distinct power sources on the same module, provided they are separated by group. The module provides excellent optical isolation between the relay coils and the 5V DC backplane.
- Part Number: 1746-OW8
- Module Type: Digital Relay Output Module
- Compatible System: Allen Bradley SLC 500 (1746 Chassis)
- Number of Outputs: 8 Relay points (Normally Open)
- Operating Voltage (AC): 5…265V AC
- Operating Voltage (DC): 5…125V DC
- Continuous Current per Point: 2.5 Amps (Resistive load)
- Maximum Module Current: 16.0 Amps total (8.0 Amps per common)
- Backplane Current Draw: 85 mA at 5V DC, 90 mA at 24V DC
Expert Installation Advice: Inductive Kickback and Snubbers
Electromechanical relays are robust, but inductive loads are their natural enemy. Expert Tip: When the 1746-OW8 interrupts power to an inductive device (like a large solenoid or contactor coil), the collapsing magnetic field generates a massive reverse voltage spike. This spike causes a high-temperature arc to jump across the tiny internal relay contacts as they open. Over thousands of cycles, this arcing causes pitting, carbon buildup, and eventually «welds» the contacts shut. To maximize the lifespan of this module, you must install external surge suppressors. Use an RC network (snubber) or MOV in parallel with AC loads, and a freewheeling diode across DC loads. This absorbs the kickback and ensures your module lasts for years without failure.
Maintenance and Group Wiring
During maintenance and panel upgrades, you must respect the module’s shared commons. Because outputs 0-3 share a single electrical common terminal, you cannot mix 120V AC and 24V DC within the same group. Doing so will result in a catastrophic short circuit. Always verify your wiring diagrams to ensure all devices within a single 4-point group operate on the exact same voltage rail. If an output fails, use a multimeter to check for continuity across the contacts when the PLC commands it ON; if there is no continuity, the internal relay has reached the end of its mechanical life.
Frequently Asked Questions (FAQs)
Q: Can the 1746-OW8 be used for high-speed switching?
A: No. Because it relies on physical moving parts, the switching delay is approximately 10 milliseconds. For high-speed applications like PWM or rapid sorting, you should use a solid-state module like the 1746-OB8 or 1746-OA8.
Q: Does this module supply power to the field devices?
A: No, it provides «dry contacts.» You must land an external power supply to the module’s common terminals to route power through the relays to your loads.
Do you need more references from this brand? Explore our full catalog of Allen Bradley here.
This 8-channel relay card is a versatile choice for small automation tasks using the 1746-A4 compact chassis.
