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 disconnecting any field wiring — the RTB stays in place.
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 | Single-width screw-clamp terminal base | 1734-RTB | 8 terminals |
| 1734-TBS | Single-width spring-clamp terminal base | 1734-RTBS | 8 terminals |
| 1734-TB3 | Double-width screw-clamp terminal base | 1734-RTB3 | 12 terminals |
| 1734-TB3S | Double-width spring-clamp terminal base | 1734-RTB3S | 12 terminals |
| 1734-TBCJC | Single-width with cold junction compensation | 1734-RTBCJC | 8 terminals + CJC sensor |
Key advantage: The RTB separates from the base, so you can replace the I/O module without disturbing field wiring. This is the standard choice for most applications.
One-Piece (TOP Series) — Integrated Terminal Block
| Model | Description | Terminals |
|---|---|---|
| 1734-TOP | Single-width screw-clamp (integrated) | 8 terminals |
| 1734-TOPS | Single-width spring-clamp (integrated) | 8 terminals |
| 1734-TOP3 | Double-width screw-clamp (integrated) | 12 terminals |
| 1734-TOP3S | Double-width spring-clamp (integrated) | 12 terminals |
Key advantage: Lower cost per point. The terminal block is permanently attached, so installation is faster. Disadvantage: You cannot replace the module without re-wiring.
The 1734-TBCJC is required for thermocouple modules. If you are using a 1734-IT2 or 1734-IT2I thermocouple input module, you must use the 1734-TBCJC terminal base. It contains the cold junction compensation (CJC) sensor needed for accurate thermocouple measurement. Using a standard 1734-TB will result in large temperature errors.
3. Terminal Base Selection Table
Use this table to find the correct terminal base for your I/O module. The base width (single or double) must match the module width.
In stock at PLC Exchange: We carry the 1734-TB ($28), 1734-TB3 ($32), and 1734-TB3S ($36) 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) — single-width, screw-clamp |
| TBS | Two-piece terminal base — single-width, spring-clamp |
| TB3 | Two-piece terminal base — double-width, screw-clamp |
| TB3S | Two-piece terminal base — double-width, spring-clamp |
| TBCJC | Two-piece terminal base with Cold Junction Compensation sensor (thermocouple only) |
| TOP | One-piece terminal base (integrated block) — single-width, screw-clamp |
| TOPS | One-piece — single-width, spring-clamp |
| TOP3 | One-piece — double-width, screw-clamp |
| TOP3S | One-piece — double-width, 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, TBS, TB3, TB3S | 0.5–0.6 N·m (5–7 lb·in) |
| Terminal base screw torque (TOP series) | 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 Single-Width)
| 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 Double-Width)
| 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 | Push button with screwdriver → insert wire → release |
| Installation speed | Slower | Faster — one-hand operation |
| Vibration resistance | Can loosen over time if not properly torqued | Constant spring force — maintains connection in vibration |
| Maintenance | Periodic re-torquing recommended | Maintenance-free |
| 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, lower vibration | High-vibration environments, faster commissioning |
PLC Exchange recommendation: For new installations, spring-clamp terminal bases are the better choice for most applications. They install faster, resist vibration better, and never need re-torquing. The 1734-TB3S is our top seller for double-width modules. For budget-sensitive projects, the 1734-TB screw-clamp is the most cost-effective option at just $28.
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) 1.0 A @ 5V DC (vertical, 10–19.2V) | 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 | Price | Notes |
|---|---|---|---|
| 1734-IB8 — 8-pt DC Input | 1734-TB or 1734-TBS | from $28 | 21 units in stock |
| 1734-OB8 — 8-pt DC Output | 1734-TB or 1734-TBS | from $28 | — |
| 1734-IE2C — 2-ch Analog Current In | 1734-TB or 1734-TBS | from $28 | — |
| 1734-IE4C — 4-ch Analog Current In | 1734-TB or 1734-TBS | from $28 | — |
| 1734-IE8C — 8-ch Analog Current In | 1734-TB or 1734-TBS | from $28 | — |
| 1734-OE2C — 2-ch Analog Current Out | 1734-TB or 1734-TBS | from $28 | — |
| 1734-OE4C — 4-ch Analog Current Out | 1734-TB or 1734-TBS | from $28 | — |
| 1734-IR2 — 2-ch RTD Input | 1734-TB3 or 1734-TB3S | from $32 | Double-width base required |
| 1734-IT2 — 2-ch Thermocouple Input | 1734-TBCJC only | — | CJC sensor required |
| 1734-IB8S — Safety Digital Input | 1734-TB3 or 1734-TB3S | from $32 | Double-width base required |
| 1734-OB8S — Safety Digital Output | 1734-TB3 or 1734-TB3S | from $32 | Double-width base required |
| 1734-SSI — SSI Encoder Input | 1734-TB3 or 1734-TB3S | from $32 | Double-width base required |
| 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 | Wrong base width (single vs. double) or mechanical keying mismatch | Verify the module requires a single-width (TB) or double-width (TB3) base. Check the selection table above. |
| 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 | Thermocouple modules require the TBCJC terminal base with built-in CJC sensor. Replace the base. |
| 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 | Re-torque to 0.8 N·m (7 lb·in). 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 |
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