Product Overview of the Allen-Bradley 1794-OW8

The Allen-Bradley 1794-OW8 is a relay output module from Flex I/O. Specifically, it belongs to the trusted 1794 Flex I/O product family. This module features eight (8) isolated electromechanical relays. Each relay is Form A or Normally Open (N.O.) configuration. Therefore, the 1794-OW8 switches AC and DC loads reliably. Furthermore, all eight channels are fully isolated from each other. Consequently, this module suits mixed voltage applications perfectly.

Relay Contact Ratings for AC Loads

The 1794-OW8 handles various AC load conditions effectively. For resistive loads, the rating is 250V AC, 2A at 50/60Hz. For inductive or pilot duty loads, the rating is different. The make rating is 1800 VA at 120/240V AC, 50/60Hz. Similarly, the break rating is 180 VA under the same conditions. Therefore, this module controls small motors, solenoids, and contactors. The off-state leakage current is 1.0 mA through a snubber circuit.

Relay Contact Ratings for DC Loads

For DC resistive loads, the 1794-OW8 is rated at 2A from 5 to 30V DC. The pilot duty rating is R150 for 5-30V DC applications. Additionally, the rating is 28 VA not exceeding 1A below 28V DC. Therefore, this module switches DC solenoids and indicator lights easily. The minimum contact load is 100 μA at 100 mV DC. Consequently, the relays work with very low-level signals as well.

Relay Performance Characteristics

Each relay on the 1794-OW8 has specific performance specifications. The initial contact resistance is 30 mΩ maximum. The contact bounce time is 1.2 milliseconds typically. Therefore, switching is clean and reliable. The maximum switching frequency is 1 operation per 3 seconds. This equals 0.3 Hz at rated load. Consequently, avoid high-speed switching applications with this module. The maximum signal delay is 10 ms for both ON and OFF transitions.

Contact Life Expectations

The 1794-OW8 offers excellent contact durability. The expected contact life is 100,000 operations minimum at rated loads. The mechanical life may be longer for lighter loads. Therefore, this module suits applications with moderate switching frequencies. For very high cycle applications, consider solid-state output modules instead.

Power Consumption and Current Draw

The 1794-OW8 draws a Flexbus current of 35 mA at 5V DC. The supply voltage requirement is 24V DC nominal. The supply current draw is 125 mA typically. The external DC supply range is 19.2 to 31.2V DC. This range includes 5% AC ripple allowance. Therefore, standard industrial power supplies work perfectly. Maximum power dissipation is 5.5 Watts. Maximum thermal dissipation is 18.8 BTU/hour. Consequently, ensure proper ventilation in your control cabinet.

Isolation Specifications

The 1794-OW8 provides excellent isolation between channels. Continuous isolation voltage between relays is 250V. Similarly, isolation from relay to backplane is 250V. Isolation from relay to power is also 250V. Isolation between power and backplane is 50V. Therefore, you can mix different voltage types safely. This feature is unique to relay output modules.

Status Indicators and Diagnostics

The 1794-OW8 features eight yellow status indicators. Each output channel has its own dedicated LED. Therefore, you can see the state of every relay at a glance. A lit LED means the relay coil is energized. Consequently, troubleshooting becomes quick and intuitive. The module has an open-type enclosure. Therefore, install the entire Flex I/O assembly inside a protective cabinet.

Compatible Terminal Base Units

The 1794-OW8 works with several terminal base units. Specifically, compatible bases include 1794-TB2, 1794-TB3, 1794-TB3S, 1794-TBN, and 1794-TBNF. The required keyswitch position is 9. Therefore, verify your base configuration before installation. If using 1794-TBNF, install a 3.0 Ampere, 250V AC slow-blow fuse. The recommended fuse is Littelfuse part number 239003. The terminal base determines your wire size. Always follow local electrical codes for wiring practices.

Compatible Communication Adapters

The 1794-OW8 works with any Flex I/O communication adapter. Therefore, it integrates into various network architectures. Common adapters include 1794-AENT for EtherNet/IP. Similarly, 1794-ACN15 supports ControlNet networks. DeviceNet applications use the 1794-AND adapter. Consequently, the 1794-OW8 fits almost any existing Flex I/O system.

Environmental Specifications

You can operate the 1794-OW8 between 0 to 55 °C (32 to 131 °F) . The storage temperature range is -40 to 85 °C (-40 to 185 °F) . Relative humidity can range from 5 to 95% non-condensing. Operating shock rating is 30g. Vibration tolerance is 5g at 10 to 500 Hz. Therefore, this module suits most industrial environments.

Physical Dimensions

The 1794-OW8 measures 1.8 x 3.7 x 2.1 inches. Therefore, it occupies minimal panel space. The compact design suits dense control cabinets. The module mounts on a standard DIN rail.

Important Power Considerations

Use only +24 Volts DC power for the 1794-OW8 power terminals. Variations in relay switching time may cause issues. Specifically, one relay might momentarily switch the total load current. Therefore, size your power supply appropriately. Always include proper snubbing for inductive loads. This practice extends relay contact life significantly.

Typical Applications for the 1794-OW8

The 1794-OW8 controls various industrial loads effectively. For example, it starts and stops small motors directly. Similarly, it energizes solenoid valves and contactors. The module also switches indicator lights and alarms. Furthermore, it interfaces with PLCs and other controllers. Therefore, the 1794-OW8 suits many discrete output applications. Common industries include packaging, material handling, and automotive.

Installation Guidelines for the 1794-OW8

First, mount the compatible terminal base on a DIN rail. Second, set the keyswitch to position 9. Third, snap the 1794-OW8 onto the terminal base. You can install or remove this module under power. However, always exercise caution during hot insertion. Fourth, connect your field loads to the appropriate terminals. For AC loads, ensure proper phase wiring. For DC loads, observe correct polarity. Fifth, install snubber circuits across inductive loads. Finally, verify all connections before applying power.

Package Contents

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

• One product information sheet with wiring diagrams

• One label sheet for channel identification

• No terminal base unit included (sold separately)

Frequently Asked Questions (FAQ)

Q1: What terminal base units work with the 1794-OW8?
A: The 1794-OW8 works with 1794-TB2, 1794-TB3, 1794-TB3S, 1794-TBN, and 1794-TBNF. The keyswitch must be set to position 9.

Q2: What is the maximum switching frequency of the 1794-OW8?
A: The 1794-OW8 has a maximum switching frequency of 1 operation per 3 seconds. Therefore, do not use it for high-speed pulse applications.

Q3: Are the output channels on the 1794-OW8 isolated from each other?
A: Yes, the 1794-OW8 provides 250V continuous isolation between relays. Consequently, you can mix different voltage types on one module.

Q4: What fuse should I use with the 1794-OW8 and 1794-TBNF base?
A: When using 1794-OW8 with 1794-TBNF, install a 3.0 Ampere, 250V AC slow-blow fuse. The recommended part is Littelfuse 239003.

Q5: How long will the relays last on the 1794-OW8?
A: The 1794-OW8 relays have an expected life of 100,000 operations minimum at rated loads. Therefore, they provide long-term reliable service.