The Q55B is Mitsubishi Electric’s extended-width 5-slot main base unit for the MELSEC-Q programmable controller series, providing five peripheral module slots in a wider physical housing than the compact Q52B — designed for installations where standard module spacing is required for field wiring access or where the panel layout mandates a larger base unit footprint. Like all MELSEC-Q main base units, the Q55B serves as the structural and electrical foundation of the MELSEC-Q system, distributing 5 VDC power from the installed power supply module and providing the high-speed internal bus for CPU-to-module data exchange. Atlantech Drives holds stock of the Q55B. Contact us for fast worldwide delivery and competitive pricing.
What Is the Q55B?
The Q55B is a main base unit for the MELSEC-Q series with five peripheral module slots and a wider physical form factor compared to the Q52B. While both the Q52B and Q55B accommodate five peripheral modules plus one power supply and one CPU module, the Q55B’s extended width provides greater physical separation between adjacent modules, improving accessibility for field wiring connections on modules with front-panel terminal blocks (such as QX10, QY10, and QX40 I/O modules with removable terminal blocks). The Q55B is a main base unit and cannot function as an extension base — systems requiring more than five peripheral slots must add extension base units (Q6B, Q12B, Q25B) connected via QC extension cables. All MELSEC-Q CPU modules, power supply modules, and peripheral modules are compatible with the Q55B without modification.
Key Technical Specifications
- Model: Q55B
- Type: Main base unit (extended width)
- Number of Module Slots: 5 (peripheral modules only)
- Power Supply Slot: 1 (dedicated, leftmost)
- CPU Slot: 1 (dedicated, slot 0)
- Total Slots Including Power Supply and CPU: 7
- Internal Bus: MELSEC-Q high-speed internal bus
- Compatible Power Supply Modules: Q61P, Q61P-D, Q62P, Q63P, Q64P, Q61SP
- Compatible CPUs: All MELSEC-Q series CPU modules
- Extension Base Connection: Not supported (main base only)
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.45 kg
Series Comparison & Selection Guide
Mitsubishi Electric’s MELSEC-Q main base unit range spans several slot counts and physical configurations: the Q33B (3 slots), Q35B (5 slots compact), Q52B (5 slots compact alternative), Q55B (5 slots extended width), Q63B (3 slots extended), Q65B (5 slots extended alternative), Q68B (8 slots), and Q312B (12 slots). The Q55B occupies the 5-slot extended-width position in this range. When selecting between the Q52B and Q55B for a 5-slot application, the decision is primarily driven by panel layout: if the control panel’s DIN rail pitch and wiring duct positioning align with the Q55B’s wider module spacing, the Q55B’s improved wiring access justifies the slightly larger footprint. For panel designs where horizontal space is the primary constraint, the Q52B’s more compact dimensions are preferable. Both base units support identical CPU, power supply, and peripheral module combinations and deliver identical electrical performance.
Replacement & Upgrade Notes
The Q55B is the recommended replacement for MELSEC-AnS series base units (A1S52B, A1S55B) in retrofit projects migrating from the MELSEC-AnS platform to MELSEC-Q. When performing such a migration, note that MELSEC-AnS I/O modules are not directly compatible with MELSEC-Q base units — the existing AnS modules must be replaced with equivalent MELSEC-Q modules (QX/QY series), or an AnS-to-Q adapter module must be used to retain the original AnS I/O modules. The field wiring terminal blocks from AnS I/O modules can typically be reused with MELSEC-Q QX/QY modules by ordering the appropriate replacement terminal block, minimising rewiring effort during migration. For projects replacing a Q32B (2-slot base) or Q33B (3-slot base) with a Q55B to accommodate additional modules, no CPU or power supply module changes are required — all MELSEC-Q CPUs and power supply modules are physically and electrically compatible across all main base unit types.
Frequently Asked Questions
Q: Can the Q55B support a redundant power supply configuration?
A: Standard MELSEC-Q main base units including the Q55B do not support redundant power supply in a single base. Redundant power supply configurations in MELSEC-Q are achieved using the Q3MDBR redundant base unit, which is a specialised base designed specifically for redundant CPU and power supply operation. For non-redundant systems requiring power supply backup, an external UPS is the standard approach.
Q: What extension cables are compatible with the Q55B for connecting extension base units?
A: The Q55B does not support extension base connection — it is a main base unit only. To expand the system beyond 5 peripheral slots, a separate Q6B, Q12B, or Q25B extension base unit must be connected to a compatible main base (Q6B, Q12B, or Q25B main bases support extension). The Q55B itself cannot be used as the host base for an extension chain.
Q: Is the Q55B compatible with iQ-R series modules?
A: No. The Q55B is a MELSEC-Q series base unit and is not compatible with Mitsubishi Electric’s iQ-R series modules, which use a different internal bus standard and physical connector. iQ-R modules require R-series base units (R33B, R35B, R38B, R312B). The Q55B is compatible exclusively with MELSEC-Q series modules.
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