1734-OB8: Installation, Wiring, Configuration, and Programming Guide
The 1734-OB8 is an 8-channel 24VDC sourcing digital output module for the Allen-Bradley POINT I/O platform. It connects to a controller via a POINT I/O communication adapter (1734-AENT for EtherNet/IP or 1734-ACNR for ControlNet) across the POINTBus backplane. Each output sources a positive voltage of up to 1 A with respect to its DC return. The outputs are not isolated from each other. This guide covers system assembly, field wiring, Studio 5000 configuration including fault and program mode actions, ladder logic examples, and LED diagnostics.
Contents
1. Module Overview
The 1734-OB8 is a fixed 8-point current-limited sourcing digital output module for the POINT I/O platform. It drives 24VDC loads such as solenoid valves, indicator lights, motor starters, and relay coils. Each channel is independently controllable. Per-channel status indicators help with troubleshooting; the standard OB8 has no diagnostic status bits (those are on the 1734-OB8E).
Catalog Number Breakdown
| Code | Meaning | Value |
|---|---|---|
| 1734 | Platform | POINT I/O -- modular distributed I/O |
| O | Module type | Output |
| B | Signal type | DC sourcing (B = DC source output) |
| 8 | Channel count | 8 discrete output points |
Key Specifications
| Parameter | Value |
|---|---|
| Number of Outputs | 8 (1 group of 8), sourcing |
| Diagnostics | No (standard OB8 -- no per-channel diagnostics; see 1734-OB8E for diagnostics) |
| Electronically Protected | Yes (current-limited outputs). Only the 1734-OB8E adds per-channel short-circuit/open-load diagnostic bits (1734-SG001, 1734-UM001). |
| Voltage, On-State (nominal) | 24V DC |
| Voltage, On-State (range) | 10 -- 28.8V DC |
| Voltage, On-State Drop (max) | 0.2V DC |
| Voltage, Off-State (max) | 28.8V DC |
| Current, On-State (min) | 1.0 mA per channel |
| Current, Leakage Off-State (max) | 0.5 mA |
| Output Filter Time (Off-to-On / On-to-Off) | 0.1 ms |
| Output Current Rating | 1.0 A per channel, 3.0 A max per module |
| Surge Current | 2 A for 10 ms, repeatable every 3 s |
| POINTBus Current (max) | 75 mA @ 5V DC |
| Power Dissipation (max) | 2.0 W @ 28.8V DC |
| Thermal Dissipation (max) | 6.8 BTU/hr @ 28.8V DC |
| Isolation Voltage | 50V continuous, reinforced insulation. Type tested at 2500V DC for 60 s, field-side to system. |
| External DC Power Supply (nominal) | 24V DC |
| External DC Power Supply (range) | 10 -- 28.8V DC |
| External DC Power Supply Current | 32 mA |
| Terminal Base | 1734-TB, 1734-TBS, 1734-TOP, or 1734-TOPS (1734-IN018) |
| Wiring Category | 2 -- on signal ports |
| Keyswitch Position | Not stated in 1734-IN018G or 1734-SG001 for the OB8; check the module label before setting the base keyswitch |
| Operating Temperature | -20 to +55°C (-4 to +131°F) |
Source Output -- What It Means
The 1734-OB8 is a sourcing output module. When a channel is turned ON, the module sources (supplies) +24VDC from the field power bus to the output terminal. The load connects between the output terminal and the DC common return. Current flows from the module's output pin, through the load, and returns to 0VDC. This is the standard output configuration for driving solenoid valves, indicator lights, and relay coils in North American industrial controls.
2. Hardware Installation
The POINT I/O system uses a No Tools design. The terminal base mounts to a DIN rail, the I/O module snaps into the base, and the removable terminal block (RTB) clips onto the front for field wiring.
System Assembly Order
| Position | Module | Example |
|---|---|---|
| Slot 0 (leftmost) | Communication Adapter | 1734-AENT (EtherNet/IP) or 1734-ACNR (ControlNet) |
| Slot 1 -- 13 | I/O Modules | 1734-OB8 in any available slot (up to 13 modules on a 1734-AENT, POINTBus current permitting; up to 63 with 1734-EP24DC/EPAC expansion power supplies; 10 A max field power) |
| Optional | Expansion Power Supply | 1734-EPAC or 1734-EP24DC (if field power bus needs extending) |
Installation Steps
- Mount the terminal base on the DIN rail. Position the 1734-TB or 1734-TBS terminal base vertically above the rail. Hook the top rail clip, then press the bottom until the locking mechanism engages. The base interlocking side pieces connect to the adjacent base to form the POINTBus backplane.
- Slide the I/O module into the terminal base. Align the module with the base guides and press down firmly until it seats with an audible click. The module engages the POINTBus connector on the base automatically.
- Install the RTB. Insert the end of the RTB opposite the handle into the base (this end has a curved section that engages the base), rotate the RTB into the base until it locks, then snap the handle onto the module (1734-IN511). The RTB can be pre-wired at a bench before installation.
- Note the slot position. The adapter is slot 0; the first I/O module to its right is slot 1. Record the slot number for Studio 5000 configuration.
- Set the adapter chassis size. Set the chassis size to 1 (the adapter) plus the number of I/O modules. The adapter makes no I/O connections until the chassis size matches the modules present (1734-UM011, Set the Chassis Size).
- Apply power. Connect 24V DC field power to the communication adapter's field power terminals. The POINTBus distributes backplane power to all modules.
Removal and Insertion Under Power (RIUP)
POINT I/O supports Removal and Insertion Under Power (RIUP). Removing one module does not disrupt the other modules; the adapter flashes its POINTBus Status LED red and reports a minor recoverable fault. If you remove more than one adjacent module, none of them reconnect until all are replaced (1734-UM011). When you insert or remove the module or the RTB with power on, an electric arc can occur; in a hazardous location, remove power or verify the area is nonhazardous first (1734-IN018).
Terminal Block Removal
The 1734-OB8 uses an 8-position removable terminal block (RTB) on a 1734-TB (screw-clamp) or 1734-TBS (spring-clamp) terminal base. The RTB separates from the module to allow module replacement without rewiring.
- Pull up on the RTB handle to unlatch it.
- Pull on the handle to remove the RTB.
- To reinstall, hook the curved end opposite the handle into the base, rotate the RTB in until it locks, then snap the handle onto the module (1734-IN511).
3. Wiring
Terminal Assignments
The 1734-TB and 1734-TBS bases with 8 terminals have pins numbered 0 through 7. All 8 RTB terminals are outputs; there is no common terminal on the OB8 RTB, so land load returns on an auxiliary terminal block tied to the field-power common. Common is daisy-chained from the adapter, 1734-FPD, 1734-EP24DC or a user-supplied external terminal block; the 24V DC for the outputs comes from the internal power bus (1734-IN018).
| Pin | Function | Description |
|---|---|---|
| 0 | Output 0 | Channel 0 -- load connection |
| 1 | Output 1 | Channel 1 -- load connection |
| 2 | Output 2 | Channel 2 -- load connection |
| 3 | Output 3 | Channel 3 -- load connection |
| 4 | Output 4 | Channel 4 -- load connection |
| 5 | Output 5 | Channel 5 -- load connection |
| 6 | Output 6 | Channel 6 -- load connection |
| 7 | Output 7 | Channel 7 -- load connection |
Wire Specifications
| Parameter | Value |
|---|---|
| Wire Size | 0.25 -- 2.5 mm² (24 -- 14 AWG) for 1734-RTB; 0.08 -- 2.5 mm² (28 -- 14 AWG) for 1734-RTBS; 1 wire per cavity |
| Wire Size (18 AWG) | 0.75 mm², 2 wires per cavity (stranded only) |
| Strip Length (without ferrule) | 16 ± 1 mm (0.63 ± 0.03 in.); 18 ± 1 mm for two 18 AWG wires |
| Signal Terminal Voltage | 28.8V DC, 120/240V AC max |
| Signal Terminal Current | 2 A max |
| Terminal Base Screw Torque | 0.8 N·m (7 lb·in) |
Source Wiring Configuration
For source wiring (the standard configuration for the 1734-OB8), connect loads as follows:
| From | To | Description |
|---|---|---|
| Module output terminal (pin 0 -- 7) | Load (one side) | Module sources +24VDC to the load when ON |
| Load (other side) | 0V common on an auxiliary terminal block (daisy-chained from the adapter, 1734-FPD or 1734-EP24DC C terminal) | Return to field supply common |
| +24VDC field supply | Communication adapter V DC terminals | Field power distributed on the internal field power bus |
Typical Field Device Wiring Examples
| Field Device | Load Type | Wiring | Notes |
|---|---|---|---|
| Indicator Light (24VDC LED) | Load | Output pin → Light (+) → Light (-) → DC COM | Light ON when output energized |
| Solenoid Valve (24VDC coil) | Inductive Load | Output pin → Coil (+) → Coil (-) → DC COM | Add suppression diode across coil for inductive loads |
| Contactor Coil (24VDC) | Inductive Load | Output pin → Coil A1 → Coil A2 → DC COM | Add suppression diode; confirm coil current < 1 A |
| Relay Coil (24VDC) | Inductive Load | Output pin → Coil (+) → Coil (-) → DC COM | Interposing relay for loads exceeding 1 A per channel |
Inductive Load Suppression
When driving inductive loads (solenoid valves, relay coils, contactor coils), always install a suppression diode across the load to reduce the effects of high-voltage transients. Connect the diode cathode to the positive (output) side and the anode to the negative (DC COM) side. Without suppression, voltage spikes from inductive kickback can damage the output circuitry and reduce module life.
Field Power Distribution
The 1734-OB8 receives field-side power through the POINTBus backplane from the communication adapter's 24V DC field power terminals. When an output is turned ON, the module switches field power to the output terminal. Only load wires connect to the 8-pin RTB; load returns go to a common terminal block tied to the field-power common.
Output Current Budget
Each output channel is rated for 1.0 A maximum, with a total module limit of 3.0 A across all 8 channels. If all 8 outputs are simultaneously energized, the average per-channel current must not exceed 375 mA. Plan your load distribution accordingly and use interposing relays for loads exceeding 1 A.
4. Studio 5000 Configuration
POINT I/O output modules are configured through the communication adapter in Studio 5000, similar to input modules but with additional Fault/Program Action settings.
Adding the Module to the I/O Tree
- In Studio 5000 Logix Designer, expand Controller Organizer → I/O Configuration → expand your EtherNet/IP network or ControlNet network → expand the 1734-AENT or 1734-ACNR adapter node.
- Right-click the adapter → New Module.
- In the module search dialog, type
1734-OB8and select it. Click Create. - Set the Name -- use a descriptive name such as
DO_Remote1. - Set the Slot number to match the physical position (the adapter is slot 0; Slot 1 = first module to the right of the adapter).
- Click OK. The module appears under the adapter in the I/O tree.
Connection Settings
| Setting | Options | Recommendation |
|---|---|---|
| RPI (Requested Packet Interval) | Direct Connection = 50 ms; Rack Optimization = not selectable | Default 50 ms for direct connection. For digital outputs where response time matters, keep at 50 ms or adjust based on application needs. |
| Connection Type | Data (default), Listen Only, Listen Only - Rack Optimization, Rack Optimization | Data (default) for most applications. Rack Optimization reduces network traffic by combining multiple modules into one connection. |
| Data Format | Integer | Integer is the only option for digital modules. |
Fault/Program Action
Output modules have a Fault/Program Action tab that controls what happens to each output when the controller enters Program mode or when a communication fault occurs. Open the Fault/Program Action tab in module properties.
| Feature | Description |
|---|---|
| Point | Displays the channel numbers (0 through 7). |
| Program Mode | Determines output behavior when the controller transitions to Program mode. Options per channel: Off (default), On, Hold. In Hard Run only, editing is disabled. |
| Fault Mode | Determines output behavior when communication with the controller fails. Options per channel: Off (default), On, Hold. In Hard Run only, editing is disabled. |
Fault Mode -- Safety Consideration
The default Fault Mode is Off -- all outputs de-energize when communication is lost. This is the safest configuration for most applications. Setting Fault Mode to Hold or On means outputs will remain energized or turn on during a communication failure, which can create hazardous conditions. Only change the default if the application specifically requires it and appropriate safety measures are in place.
Create Aliases for Readability
Always create alias tags for your I/O points. Right-click any I/O tag → New Tag → set the Type to Alias and point it to the I/O address. For example, alias
Motor_Run to the output address. This makes your ladder logic self-documenting and simplifies maintenance.
5. Controlling Outputs in Ladder Logic
Digital outputs on the 1734-OB8 are controlled using standard ladder logic instructions. The module consumes 1 byte of output data (8 bits, one per channel) and produces 1 byte of input data (channel status -- always zero for the standard OB8).
Instructions
| Instruction | Name | Function |
|---|---|---|
| OTE | Output Energize | Sets the bit to 1 (output ON) when the rung is TRUE; clears to 0 (output OFF) when FALSE. Standard non-retentive output. |
| OTL | Output Latch | Sets the bit to 1 (output ON) when the rung is TRUE. The bit stays latched ON until cleared by OTU. Use for outputs that must remain on across scan cycles. |
| OTU | Output Unlatch | Clears the bit to 0 (output OFF) when the rung is TRUE. Used to unlatch an OTL instruction. |
Data Map
The 1734-OB8 consumes 1 byte (output commands) and produces 1 byte (channel status).
Produce (scanner Rx) -- Channel Status -- 1 Byte
| Direction | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
|---|---|---|---|---|---|---|---|---|
| Produce (scanner Rx) | Ch7 | Ch6 | Ch5 | Ch4 | Ch3 | Ch2 | Ch1 | Ch0 |
Where: 0 = No error, 1 = Error (for 1734-OB8E and 1734-OB8EK only; always zero for standard OB8).
Consume (scanner Tx) -- Output Commands -- 1 Byte
| Direction | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
|---|---|---|---|---|---|---|---|---|
| Consume (scanner Tx) | Ch7 | Ch6 | Ch5 | Ch4 | Ch3 | Ch2 | Ch1 | Ch0 |
Where: 0 = Off, 1 = On.
Practical Example: Motor Contactor with Run Pilot and Fault Indicator
This example uses a 1734-IB8 (Slot 1) for inputs and 1734-OB8 (Slot 2) for outputs to control a motor contactor with start/stop, E-stop status, and overload feedback.
Not a safety circuit. Turning Motor_Run off in standard logic is not an emergency stop. The E-stop must de-energize the contactor through a hardwired circuit or a rated safety relay / POINT Guard I/O (1734-IB8S/OB8S) system (1734-SG001). EStop_OK only reports the E-stop state to the program.
I/O Assignment Table
| Tag Alias | I/O Address | Module | Field Device | Contact Type |
|---|---|---|---|---|
| PB_Start | Adapter:1:I.Data.0 | 1734-IB8 Slot 1 | Green pushbutton | NO momentary |
| PB_Stop | Adapter:1:I.Data.1 | 1734-IB8 Slot 1 | Red pushbutton | NC momentary (wired NC) |
| EStop_OK | Adapter:1:I.Data.2 | 1734-IB8 Slot 1 | E-Stop auxiliary (status) contact | NC (status only) |
| OL_OK | Adapter:1:I.Data.3 | 1734-IB8 Slot 1 | Overload relay (95-96) | NC (opens on trip) |
| Motor_Run | Adapter:2:O.Data.0 | 1734-OB8 Slot 2 | Motor contactor coil | 24VDC coil (with suppression diode) |
| Pilot_Run | Adapter:2:O.Data.1 | 1734-OB8 Slot 2 | Green pilot light | 24VDC LED |
| Pilot_Fault | Adapter:2:O.Data.2 | 1734-OB8 Slot 2 | Red pilot light | 24VDC LED |
| PB_FaultReset | Adapter:1:I.Data.4 | 1734-IB8 Slot 1 | Blue pushbutton | NO momentary |
| Motor_Fault | Internal tag | (controller) | BOOL, latched overload fault | -- |
Ladder Logic (Structured Text Representation)
// ── Motor_1 Output Control ──────────────────────────────────
// Module: 1734-IB8 in Slot 1 (inputs), 1734-OB8 in Slot 2 (outputs)
// Adapter: 1734-AENT EtherNet/IP adapter
//
// Tag Aliases:
// PB_Start → Adapter:1:I.Data.0 (NO momentary pushbutton)
// PB_Stop → Adapter:1:I.Data.1 (NC momentary -- wired NC, ON = normal)
// EStop_OK → Adapter:1:I.Data.2 (NC E-Stop status contact, ON = normal; status only)
// OL_OK → Adapter:1:I.Data.3 (NC overload relay, ON = normal)
// PB_FaultReset → Adapter:1:I.Data.4 (NO momentary reset pushbutton)
// Motor_Run → Adapter:2:O.Data.0 (Motor contactor coil)
// Pilot_Run → Adapter:2:O.Data.1 (Green run indicator)
// Pilot_Fault→ Adapter:2:O.Data.2 (Red fault indicator)
// Motor_Fault (internal BOOL -- latched overload fault)
// ─────────────────────────────────────────────────────────────
// Rung 1 -- Fault latch on overload trip (evaluated before the seal-in so a trip is captured)
IF NOT OL_OK THEN
Motor_Fault := 1;
END_IF;
// Rung 2 -- Start/Stop seal-in with permissives
// OTE Motor_Run
IF (PB_Start OR Motor_Run) AND PB_Stop AND EStop_OK AND OL_OK AND NOT Motor_Fault THEN
Motor_Run := 1;
ELSE
Motor_Run := 0;
END_IF;
// Rung 3 -- Fault reset
IF PB_FaultReset AND OL_OK AND EStop_OK THEN
Motor_Fault := 0;
END_IF;
// Rung 4 -- Pilot lights
Pilot_Run := Motor_Run;
Pilot_Fault := Motor_Fault;
Inductive Load Timing
When driving inductive loads like contactor coils, the output turns on in approximately 0.1 ms (output filter time). The contactor's own pull-in time (see the contactor data sheet) adds to this before the contacts close. Always use a feedback contact (auxiliary contact wired to an input) to confirm the contactor has physically engaged before enabling dependent logic.
6. Diagnostics & Troubleshooting
LED Indicators
The 1734-OB8 has Module Status, Network Status, and 4 I/O channel status LEDs. The 4 I/O LEDs each represent two channels: LED 0 = Ch 0 & 4, LED 1 = Ch 1 & 5, LED 2 = Ch 2 & 6, LED 3 = Ch 3 & 7.
Module Status LED
| LED | Color | State | Meaning |
|---|---|---|---|
| Module Status | Off | No Power | No power is applied to the device. Apply power. |
| Module Status | Steady green | Normal | The device is operating normally. |
| Module Status | Flashing green | Standby | Configuration missing, incomplete, or incorrect. Configure the device properly. |
| Module Status | Flashing red | Recoverable Fault | A recoverable fault. 1. Cycle power. 2. If condition persists, replace the device. |
| Module Status | Steady red | Unrecoverable Fault | May require device replacement. Replace the device. |
| Module Status | Flashing red/green | Self-Test | The device is in self-test. No action required. |
Network Status LED
| LED | Color | State | Meaning |
|---|---|---|---|
| Network Status | Off | Offline | The device is not online, has not completed Autobaud detection, has not completed dup_MAC_id test, or is not powered. |
| Network Status | Flashing green | No Connections | The device is online but has no connections in the established state. Device is in Idle or Program mode. |
| Network Status | Steady green | Connected | The device is online and has connections in the established state. |
| Network Status | Flashing red | Timed Out | One or more I/O connections are in a timed-out state. Check for I/O module failure. |
| Network Status | Steady red | Communication Failure | Critical link failure or device has detected an error preventing communication. Verify adapter and terminal bases are properly installed. |
| Network Status | Flashing red/green | Communication Faulted | Device has detected a network access error and is in a communication faulted state. |
I/O Channel Status LEDs
| LED | Color | State | Meaning |
|---|---|---|---|
| I/O Status (per pair) | Off | All outputs are inactive | Both paired channels are in the Off state. |
| I/O Status (per pair) | Yellow | One or more outputs are active and under control | One or both of the paired channels is On. |
The 4 I/O LEDs each represent two channels: LED 0 = Ch 0 & 4, LED 1 = Ch 1 & 5, LED 2 = Ch 2 & 6, LED 3 = Ch 3 & 7. A LED lights yellow if either of its paired channels is On.
Common Faults and Resolutions
| Symptom | Likely Cause | Resolution |
|---|---|---|
| Module Status flashing green | Configuration missing or incomplete | Verify the module is added to the I/O tree in Studio 5000 with the correct slot number. Download the project. |
| Output LED yellow but load not energized | Wiring fault, open load, or no field power | Verify field wiring. Check that 24VDC field power is present at the adapter. Measure voltage at the output terminal (should be near 24V when ON). |
| Output stays ON when program commands OFF | Fault Mode set to Hold or On | Check Fault/Program Action tab in module properties. Verify Fault Mode is set to Off for safety-critical outputs. |
| All 8 outputs do not respond | No field power or module not configured | Verify 24VDC at adapter field power terminals. Check module is not inhibited in Studio 5000. |
| Load draws more than 1 A | Load exceeds the 1.0 A per-output rating | Use an interposing relay for loads exceeding 1 A. Total module current must not exceed 3.0 A. |
| Network Status flashing red | Connection timed out | Check module seating. Verify RPI and connection settings. |
Electronic Keying
Studio 5000 supports electronic keying for POINT I/O modules. By default, Compatible Module keying is used -- the physical module must match the configured catalog number but allows minor revision differences. If you replace a module with a different series or revision, check the keying settings in module properties.
7. Related POINT I/O Digital Output Modules
The POINT I/O platform includes several digital output module variants:
| Catalog Number | Channels | Type | Key Difference | Typical Application |
|---|---|---|---|---|
| 1734-OB2 | 2 | 24VDC Source | 2 outputs, 1.0 A/ch, 2.0 A/module | Low-density applications |
| 1734-OB4 | 4 | 24VDC Source | 4 outputs, 1.0 A/ch, 3.0 A/module | Mid-density applications |
| 1734-OB4K | 4 | 24VDC Source (Conformal Coated) | Same as OB4 with conformal coating | Harsh environments |
| 1734-OB8 | 8 | 24VDC Source | Standard 8-point, 1.0 A/ch, 3.0 A/module -- this guide | General purpose distributed I/O |
| 1734-OB8K | 8 | 24VDC Source (Conformal Coated) | Same as OB8 with conformal coating | High humidity, corrosive |
| 1734-OB2E | 2 | 24VDC Source (Electronically Protected) | Short circuit and wire-off diagnostics | Applications needing wire-off and short-circuit reporting (not a safety output; use 1734-OB8S for safety functions) |
| 1734-OB4E | 4 | 24VDC Source (Electronically Protected) | Per-channel diagnostics | Applications requiring fault detection |
| 1734-OB8E | 8 | 24VDC Source (Electronically Protected) | Per-channel short circuit and open load detection | High-density with diagnostics |
| 1734-OB8EK | 8 | 24VDC Source (Protected, Conformal Coated) | OB8E with conformal coating | Harsh environments with diagnostics |
8. Related Guides
| Guide | Description |
|---|---|
| 1734-IB8 POINT I/O Digital Input Guide | Installation, wiring, and programming for the 8-channel POINT I/O digital input module -- the input companion to the OB8. |
| 5069-OB16 Digital Output Module Guide | Wiring, configuration, and ladder logic for the 16-channel Compact 5000 digital output -- the local I/O equivalent of the 1734-OB8. |
| CompactLogix 5069-L306ER Setup Guide | First-time setup for the CompactLogix 5380 controller. |
Reference Documentation
The following Rockwell Automation publications were used as references for this guide. These are the official manufacturer documents for the hardware covered in this article.
| Publication | Description | Download |
|---|---|---|
| 1734-IN018 | POINT I/O Output Modules Installation Instructions | Not yet on plcexchange.net |
| 1734-UM001 | POINT I/O Digital and Analog Modules and POINTBlock I/O Modules User Manual | |
| 1734-SG001 | POINT I/O Modules Selection Guide |
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