1746-A4 | Allen Bradley | SLC 500 4 Slots Chassis

Allen‑Bradley 1746‑A4 SLC 500 4‑Slot Chassis

The Allen‑Bradley 1746‑A4, also cataloged as the 1746‑A4 chassis, serves as the primary 4‑slot mechanical and electrical backplane frame used to house SLC 500 PLC and I/O modules across 1746/1747 system platforms. It provides fixed backplane power distribution, module seating alignment, and signal‑bus continuity for installed modules.

Hardware Specifications

Backplane Bus Communication Velocity Licenses

The 1746‑A4 chassis supports deterministic backplane communication used in SLC 500 architectures. Each slot maintains fixed electrical spacing and impedance to ensure predictable scan‑cycle timing for analog, digital, and specialty modules. I/O density scaling is preserved by maintaining uniform bus propagation delay across all four slots. Firmware flash compatibility resides entirely within the installed CPU or I/O modules; the chassis itself contains no programmable logic and provides stable passive connectivity.

Frequently Asked Questions

Q: Can modules be inserted or removed while the chassis is energized? A: No. SLC 500 modules require de‑energized conditions to avoid backplane faults.

Q: Does the chassis impose current limits on installed modules? A: No. Current limits are defined by the connected power supply; the chassis only provides mechanical seating and bus continuity.

Q: Are Series B and Series C modules compatible with the 1746‑A4? A: Yes. The chassis supports standard SLC 500 module families across multiple series revisions.

Field Installation Guidelines

• Mount the chassis securely to reduce vibration and maintain backplane alignment.
• Route high‑energy wiring separately from low‑level signal conductors to reduce noise coupling.
• Ensure modules are fully seated to avoid intermittent backplane contact.
• Maintain adequate ventilation around the chassis to support module thermal dissipation.
• Follow grounding and shielding practices per Allen‑Bradley wiring guidelines.