1734-TB Terminal Bases: Selection, Wiring, and Power Distribution
Every POINT I/O module requires a terminal base — it’s the foundation that mounts to the DIN rail, carries the POINTBus backplane, distributes field power, and provides all the wiring terminals for your I/O connections. Choosing the wrong terminal base means incorrect wiring, incompatible pin counts, or missed thermocouple CJC support. This guide walks you through every 1734 terminal base option, shows you exactly which base works with which module, and covers the wiring specifications straight from the Rockwell Automation selection guide.
Contents
- The POINT I/O System: How It Fits Together
- Two-Piece vs. One-Piece Terminal Bases
- Terminal Base Selection Table
- Catalog Number Breakdown
- Technical Specifications
- Wiring Specifications & Strip Lengths
- Screw-Clamp vs. Spring-Clamp
- Power Distribution & Expansion Supplies
- Installation & Mounting
- Which Base for Which Module
- Troubleshooting
- Related Guides & Resources
1. The POINT I/O System: How It Fits Together
A POINT I/O system has four major components that snap together without tools:
| Component | What It Does | Example |
|---|---|---|
| Communication Adapter | Connects the POINT I/O rack to your network (EtherNet/IP, DeviceNet, ControlNet, PROFIBUS) | 1734-AENT, 1734-AENTR |
| I/O Module | Provides the field interface — digital inputs/outputs, analog channels, temperature inputs, specialty functions | 1734-IB8, 1734-OB8, 1734-IE2C |
| Terminal Base (A) | Mounts to DIN rail, carries the POINTBus backplane, distributes field power | 1734-TB, 1734-TB3 |
| Removable Terminal Block (B) | Snaps into the terminal base, provides the screw or spring terminals for field wiring | 1734-RTB (included with TB), 1734-RTB3 (included with TB3) |
The I/O module snaps into the terminal base from the top. The removable terminal block (RTB) snaps into the front of the base. Once wired, you can remove and replace the I/O module without disturbing field wiring. On two-piece bases the RTB also unplugs from the mounting base, so the base itself can be replaced without rewiring (1734-IN511).
Terminal bases are NOT included with I/O modules. You must order terminal bases separately. Each I/O module needs one terminal base. The terminal base assemblies (e.g., 1734-TB) ship with the matching RTB included — you don’t need to order the RTB separately unless you need spares.
2. Two-Piece vs. One-Piece Terminal Bases
Allen-Bradley offers two terminal base designs for POINT I/O:
Two-Piece (TB Series) — Base + Removable RTB
| Model | Description | RTB Included | Terminals |
|---|---|---|---|
| 1734-TB | Mounting base with 8-terminal screw-clamp RTB | 1734-RTB | 8 terminals |
| 1734-TBS | Mounting base with 8-terminal spring-clamp RTB | 1734-RTBS | 8 terminals |
| 1734-TB3 | Mounting base with 12-terminal screw-clamp RTB (taller; for 3-wire devices) | 1734-RTB3 | 12 terminals |
| 1734-TB3S | Mounting base with 12-terminal spring-clamp RTB (taller; for 3-wire devices) | 1734-RTB3S | 12 terminals |
| 1734-TBCJC | Mounting base with cold junction compensation RTB (1734-IT2I only) | 1734-RTBCJC | 8 terminals + CJC sensor |
Key advantage: The RTB unplugs from the mounting base, so the base itself can be replaced without rewiring (1734-IN511). This is the standard choice for most applications.
8-terminal and 12-terminal bases are the same width. The TB, TBS, TB3, TB3S, TOP and TOP3 are all 13.8 mm wide (1734-SG001). The 12-terminal TB3/TB3S/TOP3/TOP3S are taller and add terminals 8–11; terminals 4, 5, 8 and 9 are shorted together internally, as are 6, 7, 10 and 11, giving extra common (C) and supply (V) points for 3-wire devices.
One-Piece (TOP Series) — Integrated Terminal Block
| Model | Description | Terminals |
|---|---|---|
| 1734-TOP | 8-terminal screw-clamp (integrated) | 8 terminals |
| 1734-TOPS | 8-terminal spring-clamp (integrated) | 8 terminals |
| 1734-TOP3 | 12-terminal screw-clamp (integrated) | 12 terminals |
| 1734-TOP3S | 12-terminal spring-clamp (integrated) | 12 terminals |
Key advantage: Lower cost per point. The terminal block is permanently attached, so installation is faster. Disadvantage: The wiring terminals are part of the base, so replacing the base means rewiring it. (The I/O module still plugs in and out without touching the wiring.)
The 1734-TBCJC is the specified base for the 1734-IT2I thermocouple module. It carries the cold junction compensation (CJC) sensor in its RTB, and the TBCJC is for use with the 1734-IT2I only. Rockwell calls it the easiest, least expensive and most accurate CJC method; without it you must enter an estimated temperature or use external cold-junction compensators (1734-SG001).
3. Terminal Base Selection Table
Use this table to find the correct terminal base for your I/O module. The base must be one listed for the module (Module location / Terminal base unit in the module’s specifications). 8- and 12-terminal bases are the same width, so a base that is not listed may still physically fit; check the list.
| I/O Module Type | Example Modules | Base Type | Screw-Clamp Base | Spring-Clamp Base | One-Piece Option |
|---|---|---|---|---|---|
| DC digital input | 1734-IB8, 1734-IB4, 1734-IV4, 1734-IV8 | 8-terminal | 1734-TB | 1734-TBS | 1734-TOP / TOPS |
| DC digital output | 1734-OB8, 1734-OB4, 1734-OV4E, 1734-OV8E | 8-terminal | 1734-TB | 1734-TBS | 1734-TOP / TOPS (OB4, OB8 only; 1734-SG001 lists TB/TBS only for OV4E/OV8E) |
| AC digital input | 1734-IA2, 1734-IA4, 1734-IM2, 1734-IM4 | 8-terminal | 1734-TB | 1734-TBS | 1734-TOP / TOPS |
| AC digital output | 1734-OA2, 1734-OA4 | 8-terminal | 1734-TB | 1734-TBS | 1734-TOP / TOPS |
| Relay output | 1734-OW2, 1734-OW4 | 8-terminal | 1734-TB | 1734-TBS | 1734-TOP / TOPS |
| Analog current input | 1734-IE2C | 8-terminal | 1734-TB | 1734-TBS | 1734-TOP / TOPS |
| Analog current input | 1734-IE4C | 12-terminal | 1734-TB3 only | 1734-TB3S only | — (not listed) |
| Analog current input | 1734-IE8C | 8-terminal | 1734-TB | 1734-TBS | — (not listed) |
| Analog current output | 1734-OE2C | 8- or 12-terminal | 1734-TB or 1734-TB3 | 1734-TBS or 1734-TB3S | 1734-TOP / TOPS |
| Analog current output | 1734-OE4C | 8-terminal | 1734-TB | 1734-TBS | — (not listed) |
| RTD input | 1734-IR2, 1734-IR2K | 8-terminal | 1734-TB | 1734-TBS | 1734-TOP / TOPS |
| Thermocouple input | 1734-IT2I, 1734-IT2IK | CJC base | 1734-TBCJC (specified base; carries the CJC sensor) | ||
| Safety digital I/O | 1734-IB8S, 1734-OB8S | Two bases per module | 2 × 1734-TB | 2 × 1734-TBS | 2 × 1734-TOP / TOPS / 1734-TOP3 / TOP3S. Do not use 1734-TB3 or TB3S. |
| Communication | 1734-232ASC | 8-terminal | 1734-TB | 1734-TBS | — (not listed) |
| SSI Encoder | 1734-SSI | 8-terminal | 1734-TB | 1734-TBS | — (not listed) |
Base assignments from 1734-SG001 (pp. 16–18, 22–25, 33) and the module installation instructions 1734-IN051 (IB), 1734-IN052 (IV), 1734-IN018 (OB) and 1734-IN016 (POINT Guard I/O).
POINT Guard I/O needs two bases, and never a TB3/TB3S. You need two terminal bases to install each POINT Guard I/O module (1734-IB8S, 1734-OB8S): either 2 × 1734-TB or 1734-TBS assemblies, or 2 × one-piece 1734-TOP, TOPS, TOP3 or TOP3S bases. Do not use the 1734-TB3 or 1734-TB3S terminal base assemblies (1734-IN016).
In stock at PLC Exchange: We carry the 1734-TB, 1734-TB3, and 1734-TB3S with free UPS Ground shipping and a 2.5-year warranty. Need terminal bases for a new build or a retrofit? Request a quote for quantity pricing.
4. Catalog Number Breakdown
| Code | Meaning |
|---|---|
| 1734 | POINT I/O platform (Bulletin 1734) |
| TB | Two-piece terminal base (removable RTB) — 8 terminals, screw-clamp |
| TBS | Two-piece terminal base — 8 terminals, spring-clamp |
| TB3 | Two-piece terminal base — 12 terminals, screw-clamp |
| TB3S | Two-piece terminal base — 12 terminals, spring-clamp |
| TBCJC | Two-piece terminal base with Cold Junction Compensation sensor (1734-IT2I thermocouple module only) |
| TOP | One-piece terminal base (integrated block) — 8 terminals, screw-clamp |
| TOPS | One-piece — 8 terminals, spring-clamp |
| TOP3 | One-piece — 12 terminals, screw-clamp |
| TOP3S | One-piece — 12 terminals, spring-clamp |
| RTB | Replacement removable terminal block for 1734-TB (spare part) |
| RTB3 | Replacement removable terminal block for 1734-TB3 (spare part) |
5. Technical Specifications
| Attribute | 1734-TB / TBS / TB3 / TB3S / TOP / TOPS / TOP3 / TOP3S | 1734-TBCJC |
|---|---|---|
| Field power bus supply voltage, max | 28.8V DC, 120/240V AC | — |
| Field power bus supply current, max | 10 A | — |
| Signal terminal voltage | 28.8V DC, 120V/240V AC | — |
| Signal terminal current | 2 A | — |
| Terminal base screw torque | 0.8 N·m (7 lb·in) — TB, TB3 (screw-clamp); spring-clamp bases (TBS, TB3S, TOPS, TOP3S) have no torque spec | 0.5–0.6 N·m (5–7 lb·in) |
| Terminal base screw torque (TOP, TOP3) | 0.4 N·m (3.5 lb·in) | — |
| Wire size | 0.25–2.5 mm² (24–14 AWG) solid or stranded shielded copper wire rated at 75 °C (167 °F), 1.2 mm (3/64 in.) insulation max | Shielded thermocouple wire, 1.2 mm (3/64 in.) insulation max |
| Temperature, operating | −20 to +55 °C (−4 to +131 °F) | 0 to +55 °C (32 to +131 °F) |
| Temperature, surrounding air max | 55 °C (131 °F) | 55 °C (131 °F) |
| Relative humidity | 5–95% noncondensing | 5–95% noncondensing |
| Vibration | 5 g @ 10–500 Hz | 5 g @ 10–500 Hz |
| Shock | 30 g operating, 50 g nonoperating | 30 g operating, 50 g nonoperating |
| Mounting | DIN rail (EN50022 — 35 × 7.5 mm) | DIN rail |
| Enclosure type | None (open-style) | None (open-style) |
Dimensions & Weight
| Model | Dimensions (H × W × D) | Weight |
|---|---|---|
| 1734-TB | 133.4 × 13.8 × 79.4 mm (5.25 × 0.54 × 3.12 in.) | 83.95 g (2.94 oz) |
| 1734-TBS | 133.4 × 13.8 × 79.4 mm | 72.86 g (2.57 oz) |
| 1734-TB3 | 158.0 × 13.8 × 79.8 mm (6.22 × 0.54 × 3.14 in.) | 97.52 g (3.44 oz) |
| 1734-TB3S | 158.0 × 13.8 × 79.8 mm | 87.03 g (3.07 oz) |
| 1734-TOP | 144.0 × 13.8 × 78.6 mm (5.67 × 0.54 × 3.09 in.) | 63.79 g (2.25 oz) |
| 1734-TOP3 | 167.6 × 13.8 × 79.1 mm (6.60 × 0.54 × 3.11 in.) | 79.10 g (2.79 oz) |
All specifications from Rockwell Automation publication 1734-SG001, pages 37–40 and 49.
6. Wiring Specifications & Strip Lengths
1734-RTB / 1734-RTBS (8-Position)
| RTB | Wire Size Range | Wires per Cavity | Strip Length (without ferrule) | Strip Length (with ferrule) |
|---|---|---|---|---|
| 1734-RTB (screw) | 0.25–2.5 mm² (24–14 AWG) | 1 | 16 ± 1 mm (0.63 in.) | 12.5 ± 0.4 mm (0.49 in.) |
| 1734-RTBS (spring) | 0.08–2.5 mm² (28–14 AWG) | 1 | 16 ± 1 mm (0.63 in.) | 14.5 ± 0.4 mm (0.57 in.) |
| RTB / RTBS (2 wires) | 0.75 mm² (18 AWG) stranded only | 2 | 18 ± 1 mm (0.71 in.) | — |
1734-RTB3 / 1734-RTB3S (12-Position)
| RTB | Wire Size Range | Wires per Cavity | Strip Length (without ferrule) | Strip Length (with ferrule) |
|---|---|---|---|---|
| 1734-RTB3 (screw) | 0.25–2.5 mm² (24–14 AWG) | 1 | 14 ± 1 mm (0.55 in.) | 12.5 ± 0.4 mm (0.49 in.) |
| 1734-RTB3S (spring) | 0.08–2.5 mm² (28–14 AWG) | 1 | 14 ± 1 mm (0.55 in.) | — |
| RTB3 / RTB3S (2 wires) | 0.75 mm² (18 AWG) stranded only | 2 | 16 ± 1 mm (0.63 in.) | — |
1734-RTBCJC (Thermocouple Terminal Block)
| RTB | Wire Size Range | Wires per Cavity | Strip Length (without ferrule) | Strip Length (with ferrule) |
|---|---|---|---|---|
| 1734-RTBCJC (1 wire) | 0.08–2.5 mm² (28–14 AWG) | 1 | 14 ± 1 mm (0.55 in.) | 12.5 ± 0.4 mm (0.49 in.) |
| 1734-RTBCJC (2 wires) | 0.75 mm² (18 AWG) stranded only | 2 | 16 ± 1 mm (0.63 in.) | — |
All wiring specifications from Rockwell Automation publication 1734-SG001, pages 38–39.
TWIN wire end ferrules are NOT recommended. Use single-wire ferrules only. Recommended: wire end ferrule with insulating collar, per DIN 46228-4 and UL 486F.
7. Screw-Clamp vs. Spring-Clamp
| Factor | Screw-Clamp (TB, TB3) | Spring-Clamp (TBS, TB3S) |
|---|---|---|
| Wire insertion | Loosen screw → insert wire → tighten to 0.8 N·m | Insert a 3 mm bladed screwdriver (1492-N90) into the access hole → insert the wire → withdraw the screwdriver (1734-IN511) |
| Installation speed | Slower (each screw is tightened) | Faster (no screw to tighten) |
| Vibration rating | Same for all bases: 5 g @ 10–500 Hz (1734-SG001) | |
| Wire gauge range | 24–14 AWG (0.25–2.5 mm²) | 28–14 AWG (0.08–2.5 mm²) — accepts finer wire |
| Cost | Lower | Slightly higher |
| Best for | Standard installations | Faster commissioning; finer wire down to 28 AWG |
PLC Exchange recommendation: For new installations, spring-clamp terminal bases are a good choice for most applications: they install faster and accept finer wire. The 1734-TB3S is our top seller for 12-terminal applications. For budget-sensitive projects, the 1734-TB screw-clamp is the most cost-effective option.
8. Power Distribution & Expansion Supplies
The POINT I/O system distributes power through the POINTBus backplane. Understanding power distribution is critical for system sizing.
Power Flow
- The communication adapter (e.g., 1734-AENT) receives 24V DC field power and converts it to 5V DC for the POINTBus backplane.
- The adapter supplies up to 1.0 A at 5V DC through the POINTBus to power I/O modules to its right.
- Each I/O module consumes a specific amount of POINTBus current (50–220 mA depending on type).
- When total module current exceeds the adapter’s capacity, add an expansion power supply (1734-EP24DC) to provide an additional 1.3 A.
POINTBus Current Requirements by Module
| POINTBus Current | Modules |
|---|---|
| 50 mA | 1734-IB4D |
| 75 mA | 1734-IB8, 1734-IB4, 1734-IB2, 1734-OB8, 1734-OB4, 1734-OB2, 1734-IE2C, 1734-IE2V, 1734-OE2C, 1734-OE2V, 1734-232ASC, and more |
| 80 mA | 1734-OW2 |
| 90 mA | 1734-OW4 |
| 100 mA | 1734-4IOL, 1734-8CFG, 1734-OX2 |
| 110 mA | 1734-SSI |
| 160 mA | 1734-IJ2, 1734-IK2 |
| 175 mA | 1734-IT2I |
| 220 mA | 1734-IR2 |
POINTBus current requirements from Rockwell Automation publication 1734-SG001, page 41.
Expansion Power Supply Specifications
| Attribute | 1734-EP24DC | 1734-EPAC |
|---|---|---|
| Input voltage | 24V DC (10–28.8V range) | 120/240V AC (85–264V range) |
| POINTBus output current | 1.3 A @ 5V DC (horizontal, 19.2–28.8V input) 1.0 A @ 5V DC (horizontal, 10–19.2V input) 1.0 A @ 5V DC (vertical, any input 10–28.8V) | 1.3 A @ 5.2V DC |
| I/O module capacity | Up to 17 modules | Up to 17 modules |
| Field power bus current, max | 10 A | 10 A |
| Power consumption | 9.8 W @ 28.8V DC | 15.1 W @ 264V AC |
Sizing rule of thumb: A standard 1734-AENT EtherNet/IP adapter supplies 1.0 A on the POINTBus. At 75 mA per typical digital module, that’s 13 modules maximum before you need an 1734-EP24DC expansion supply. RTD modules (220 mA each) and SSI modules (110 mA) consume significantly more — always calculate your total POINTBus load.
9. Installation & Mounting
- Mount the DIN rail. Use EN50022 standard rail (35 × 7.5 mm). Must be zinc-plated chromate-passivated steel for proper grounding. Secure every 200 mm (7.8 in.) with end anchors.
- Snap terminal bases onto the DIN rail from left to right, starting with the communication adapter. Terminal bases interlock mechanically via the POINTBus connector.
- Insert I/O modules into terminal bases from the top. Mechanical keying prevents installing the wrong module type.
- Snap the RTB into the front of each terminal base. For two-piece bases, the RTB clicks into place. Wire the RTB before or after snapping it in.
- Allow minimum 25.4 mm (1.0 in.) clearance on all sides of the system. For systems with safety modules, allow 50.8 mm (2.0 in.) clearance above.
DIN rail material matters. Do NOT use aluminum or plastic DIN rail. The POINT I/O system is grounded through the DIN rail — using non-conductive or poorly conductive rail material will result in improper grounding, intermittent communication, and potential safety hazards. Use zinc-plated chromate-passivated steel DIN rail only (per 1734-SG001, page 49).
10. Which Base for Which Module — Quick Reference
Every POINT I/O module on the PLC Exchange website is compatible with the terminal bases listed below. Use this as a quick purchasing checklist.
| PLC Exchange Product | Terminal Base Needed | Notes |
|---|---|---|
| 1734-IB8 — 8-pt DC Input | 1734-TB or 1734-TBS | — |
| 1734-OB8 — 8-pt DC Output | 1734-TB or 1734-TBS | — |
| 1734-IE2C — 2-ch Analog Current In | 1734-TB or 1734-TBS | — |
| 1734-IE4C — 4-ch Analog Current In | 1734-TB3 or 1734-TB3S | 12-terminal base only |
| 1734-IE8C — 8-ch Analog Current In | 1734-TB or 1734-TBS | TB/TBS only |
| 1734-OE2C — 2-ch Analog Current Out | 1734-TB, 1734-TBS, 1734-TB3, 1734-TB3S, TOP or TOPS | — |
| 1734-OE4C — 4-ch Analog Current Out | 1734-TB or 1734-TBS | TB/TBS only |
| 1734-IR2 — 2-ch RTD Input | 1734-TB, 1734-TBS, TOP or TOPS | — |
| 1734-IT2I — 2-ch Thermocouple Input | 1734-TBCJC only | Specified base; carries the CJC sensor |
| 1734-IB8S — Safety Digital Input | 2 × 1734-TB or 2 × 1734-TBS (or 2 one-piece TOP/TOPS/TOP3/TOP3S) | Two bases per module; do not use TB3/TB3S |
| 1734-OB8S — Safety Digital Output | 2 × 1734-TB or 2 × 1734-TBS (or 2 one-piece TOP/TOPS/TOP3/TOP3S) | Two bases per module; do not use TB3/TB3S |
| 1734-SSI — SSI Encoder Input | 1734-TB or 1734-TBS | TB/TBS only |
| 1734-AENT — EtherNet/IP Adapter | Built-in terminal base | No separate base needed |
| 1734-AENTR — EtherNet/IP DLR Adapter | Built-in terminal base | No separate base needed |
| 1734-EP24DC — Expansion Power Supply | Built-in terminal base | No separate base needed |
11. Troubleshooting
| Symptom | Possible Cause | Resolution |
|---|---|---|
| Module won’t snap into terminal base | Base not listed for that module, or keyswitch set to the wrong position | Check the selection table above and set the base keyswitch to the number the module requires. |
| Intermittent communication / POINTBus errors | Loose terminal base on DIN rail, or bases not fully interlocked | Press each terminal base firmly until the DIN rail latch clicks. Ensure all bases are in continuous contact. |
| Incorrect thermocouple readings | Using standard 1734-TB instead of 1734-TBCJC | The 1734-IT2I is specified for the TBCJC base, which carries the CJC sensor. Fit a TBCJC, or enter an estimated temperature / use external compensators in the module configuration. |
| Field power not reaching modules | No field power bus connection, or expansion supply needed | Verify 24V DC is connected to the adapter’s field power terminals. If modules are far from the adapter, add a 1734-EP24DC expansion supply. |
| Intermittent signal on one channel | Loose wire in screw terminal, or wire stripped too short | On screw-clamp TB/TB3 bases, tighten to 0.8 N·m (7 lb·in); on TOP/TOP3, 0.4 N·m. Verify strip length matches the tables above. Consider switching to spring-clamp. |
| Grounding / noise issues | Wrong DIN rail material | Use zinc-plated chromate-passivated steel DIN rail only. Secure every 200 mm with end anchors. |
12. Related Guides & Resources
Related PLC Exchange How-To Guides
| Guide | Topic |
|---|---|
| 1734-IB8 Digital Input Guide | Wiring, configuration, and ladder logic for the 8-point POINT I/O DC input module |
| 1734-OB8 Digital Output Guide | Wiring, configuration, and ladder logic for the 8-point POINT I/O DC output module |
| 5069-RTB Terminal Block Guide | Companion guide for the Compact 5000 platform terminal blocks |
| Analog Signal Types Guide | Understanding 4-20mA, 0-10V, RTD, and thermocouple signals |
| RTD vs. Thermocouple Guide | Choosing the right temperature sensor for your application |
Rockwell Automation Reference Documentation
| Publication | Title | Content |
|---|---|---|
| 1734-SG001 | POINT I/O Modules Selection Guide | Complete terminal base specs, module compatibility, wiring tables, power distribution |
| 1734-UM001 | POINT I/O Digital and Analog Modules User Manual | Detailed wiring diagrams, configuration, and programming |
| 1734-IN511 | POINT I/O Wiring Base Assembly Installation Instructions | 1734-TB/TBS RTB removal, wiring, torque |
| 1734-IN016 | POINT Guard I/O Safety Modules Installation Instructions | Two-base requirement; TB3/TB3S not allowed for safety modules |
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