Product Core Brief

• Model: IEMMU21
• Brand: ABB Bailey
• Series: INFI 90 / Symphony / Symphony Plus
• Core Function: Provides the mechanical rack, backplane bus, and DC power distribution for ABB Bailey I/O and processor modules.
• Product Type: Module Mounting Unit (MMU) / Backplane Chassis
• Key Specs: 12-slot capacity | rear-mount cabinet chassis | passive backplane with module bus and DC power rails
• Condition: New Original / New Surplus (depending on stock)

Key Technical Specifications

• Manufacturer: ABB (Bailey INFI 90 / Symphony product line)
• Part Number:
• Product Type: Module Mounting Unit (MMU), rear-mount backplane chassis
• Slot Capacity: 12 module positions
• Backplane Type: Passive PCB backplane with module bus and DC power distribution
• System Compatibility: ABB INFI 90, Symphony, Symphony Plus DCS
• Power Input: Low-voltage DC rails from system power supply (no onboard AC mains)
• Mounting Style: Rear-mount, cabinet/panel installation
• Typical Operating Temperature: 0 to 55 °C cabinet ambient
• Dimensions: 411.48 × 505.46 × 259.08 mm (D × H × W)
• Weight: approx. 4.876 kg (catalog listing)
• HS Code: 853710 (electrical control panels / assemblies)

Product Introduction (No Fluff)

The ABB IEMMU21 is a 12-slot module mounting unit used in Bailey INFI 90, Symphony, and Symphony Plus DCS cabinets. It holds I/O, communication, and processor modules while supplying backplane signaling and DC power distribution.

Its value shows up during maintenance and expansion. Because the chassis is passive and rear-mounted, replacement is mainly a mechanical and backplane-integrity task rather than a firmware migration. That makes it practical for plants keeping legacy Bailey systems running without redesigning the entire I/O bay.

QA & Testing SOP (Dynamic & Transparent)

Since this is a passive chassis, we do not treat it like a CPU or power supply. The inspection focuses on backplane integrity, slot contacts, and cabinet readiness.

1. Incoming visual inspection: Check for bent backplane pins, damaged slot connectors, cracked PCB traces, corrosion, or shipping damage.
2. Backplane continuity check: Verify module-bus and DC power-rail continuity across slots with a Fluke multimeter before any module is seated.
3. Slot mechanical test: Seat and unseat a known-good Bailey module to confirm proper alignment, retention, and edge-connector contact.
4. Grounding verification: Confirm chassis bonding points and cabinet earth references match ABB Bailey grounding practice before energizing the rack.
5. Anti-static handling and packing: Store and ship in ESD-safe packaging; handle the backplane by the frame, not by connector edges.

Installation Pitfalls & Guide (Engineer to Engineer)

❗ Do not force modules into the slots. A misaligned or damaged edge connector can bend backplane pins and create intermittent faults later.

❗ Verify DC power rails before loading all 12 slots. The MMU distributes power; it does not generate it. If the system supply is undersized, adding modules can cause voltage drop or nuisance trips.

❗ Check grounding before energizing. Poor cabinet bonding can introduce noise into analog modules or create ground loops across termination units.

❗ Confirm compatibility with your existing MMU generation. IEMMU21 belongs to the newer Bailey MMU family; mixing it with older IEMMU01/IEMMU02 racks should be verified against the cabinet layout and module list.

Replacement steps:

1. Pre-install: Document slot positions, label cables, and confirm the rack is de-energized.
2. Removal: Disconnect termination cabling, unbolt the old MMU, and remove it without stressing adjacent modules.
3. Install: Mount the new IEMMU21, verify alignment, reconnect flat cables and termination wiring, and confirm grounding.
4. Power-on test: Energize the DC rails, check slot indicators, and validate module communication one slot at a time.

Technical FAQ

1. Is the IEMMU21 still available?
Yes, but availability depends on stock condition. We carry new original and new surplus units. Lead times vary by inventory.

2. Can I use IEMMU21 in an existing INFI 90 cabinet?
Generally yes, if the cabinet supports rear-mount MMUs and the module generation matches. Verify slot count, termination cabling, and power supply capacity before swapping.

3. Does this unit need firmware loading?
No. The IEMMU21 is a passive mounting unit with backplane bus and power distribution. Firmware applies to processor and certain specialty modules, not the chassis itself.

4. What warranty do you offer?
Standard warranty is 12 months unless otherwise stated. For surplus stock, warranty terms are confirmed at quotation.

5. Can you offer better pricing for multiple units?
Yes. Pricing is flexible for multi-unit orders, panel rebuilds, or long-term spares packages. Send the required quantity and condition preference for a direct quote.