Allen-Bradley 1794-OW8 Flex I/O Relay Output Module

1794-OW8 8-Point Isolated Relay Output Module by Allen-Bradley

Product Introduction

The Allen-Bradley 1794-OW8 is a versatile relay output module from the Flex I/O family. This module provides eight isolated Form A (Normally Open) electromechanical relays. Each output channel is independently isolated from others. This isolation allows switching of different voltage levels on each channel. Users can control various AC and DC loads with confidence. The module integrates seamlessly with any Flex I/O communication adapter. Its rugged design suits demanding industrial automation environments.

Key Technical Specifications

The 1794-OW8 offers eight isolated relay output channels. Each relay contact is rated at 250V AC, 2A for resistive loads at 50/60Hz. For 120/240V AC, the make rating is 1800 VA and break rating is 180 VA. For DC loads from 5 to 30V DC, the rating is 2A resistive. The pilot duty rating is R150 for 5 to 30V DC, not exceeding 1A below 28V DC.

The module draws 35 mA from the 5V DC FlexBus. It requires an external supply voltage of 24V DC at 125 mA. The operating voltage range is 19.2 to 31.2V DC, including 5% AC ripple. The initial contact resistance is 30 mΩ. The contact bounce time is typically 1.2 ms. The switching frequency is one operation every 3 seconds at rated load.

Environmental and Mechanical Ratings

The 1794-OW8 operates reliably in industrial conditions. The operating temperature range is 0 to 55°C (32 to 131°F). The storage temperature range is -40 to 85°C (-40 to 185°F). It withstands vibration of 5G at 10 to 500 Hz. The operating shock rating is 30G. The module is an open-type enclosure. Therefore, it requires installation inside a suitable protective enclosure.

The module measures 1.8 x 3.7 x 2.1 inches. It mounts on a standard DIN rail. The maximum power dissipation is 5.5 Watts. The maximum thermal dissipation is 18.8 BTU/hour at 31.2V DC.

Terminal Base Compatibility

The 1794-OW8 works with several terminal base units. Compatible bases include the 1794-TB2, 1794-TB3, and 1794-TB3S. Additionally, it supports the 1794-TBN and 1794-TBNF terminal bases. When using the 1794-TBNF, install a 3.0 Ampere, 250V AC slow-blow fuse. The recommended fuse is Littelfuse part number 239003. The keyswitch position is 9 when mounting to the terminal base. Always use only +24V DC power for the power terminals. Variations in relay switching time may cause momentary load sharing.

Indicators and Diagnostics

This module features eight yellow status indicators on its front panel. Each indicator corresponds to one output channel. These LEDs show the energization status of each relay. They provide immediate visual feedback for troubleshooting. Operators can quickly identify active outputs. This simplifies system diagnostics and maintenance.

Contact Life and Performance

Each relay contact has an expected mechanical life of 100,000 operations at rated loads. The minimum contact load is 100 µA at 100 mV DC. The off-state leakage current is 1.0 mA through the snubber circuit at 240V AC. The maximum output delay time is 10 ms for both OFF-to-ON and ON-to-OFF transitions. These performance characteristics ensure reliable switching in most industrial applications.

Isolation and Protection

The 1794-OW8 provides excellent isolation between channels. The continuous isolation voltage is 250V from relay to relay. It also provides 250V isolation from relay to backplane and to power. The isolation from power to backplane is 50V. This high level of isolation protects the control system from voltage transients. It also allows mixing of different voltage levels on different channels.

Installation Guidelines

Installing the Allen-Bradley 1794-OW8 is straightforward. First, mount the appropriate terminal base on a DIN rail. Then, set the keyswitch to position 9 on the terminal base. Align the module with the terminal base groove. Press firmly and evenly to seat the module. The latching mechanism locks it in place.

Connect field wiring to the terminal base according to the wiring diagram. Use wire sizes determined by the installed terminal base. Ensure proper polarity for DC power connections. Secure all connections with appropriate torque. The removable terminal block simplifies wiring changes.

Application Scenarios

The 1794-OW8 suits a wide range of applications. It controls solenoid valves and pneumatic actuators in manufacturing. It switches motor contactors and starter coils in conveyor systems. The module operates alarm annunciators and indicator panels. It also interfaces with HVAC dampers and lighting circuits. The isolated channels allow mixing of AC and DC loads on the same module.

Packaging and Shipping

All modules undergo careful packaging before shipment. We use anti-static materials to prevent electrostatic damage. The packaging provides sufficient cushioning against physical impacts. The packaging list does not include certificates or warranties. Each shipment includes the module only. Terminal bases are sold separately. We ship globally using trusted couriers such as FedEx, UPS, and DHL.

Packaging List

• Allen-Bradley 1794-OW8 Relay Output Module (1 unit)

• Installation Instructions (Printed Quick Guide)

Frequently Asked Questions (FAQ)

1. What terminal bases are compatible with the 1794-OW8?
The 1794-OW8 works with the 1794-TB2, 1794-TB3, 1794-TB3S, 1794-TBN, and 1794-TBNF terminal bases.

2. What is the keyswitch position for the 1794-OW8?
The keyswitch position is 9 when mounting this module to the terminal base.

3. Can the 1794-OW8 switch both AC and DC loads?
Yes, each isolated relay channel can switch either AC or DC loads. This allows mixing different voltages across channels.

4. What is the expected contact life of the 1794-OW8 relays?
Each relay has an expected mechanical life of 100,000 operations at rated loads.

5. Does the 1794-OW8 require an external power supply?
Yes, the module requires a 24V DC external supply at 125 mA. It also draws 35 mA from the 5V FlexBus.