Product Core Brief

• Model: RXDS 4, Full OEM part number: 1MRK000344-A
• Brand: ABB Hitachi Energy
• Series: COMBIFLEX modular secondary relay & measurement system accessory
• Core Function: 4-pole sequential test disconnect switch dedicated for CT, VT and trip control secondary circuits in power substation relay panels. It provides safe, step-by-step isolation of measurement and tripping loops without live wiring disconnection, enabling offline secondary injection testing of protection IEDs (REF615, RET670, REG316 etc.). It automatically short-circuits CT windings before breaking CT loops to eliminate lethal open-circuit CT high voltage hazards, while isolating VT voltage circuits and blocking breaker trip signals during field commissioning and maintenance.
• Product Type: COMBIFLEX modular secondary circuit test disconnect switch
• Key Specs: 4 independent circuit poles; CT auto-short mechanical interlock; rated secondary CT 1A/5A; rated VT 100V; rated control circuit 250V DC/AC; DIN rail COMBIFLEX standard mounting; mechanical interlock anti-misoperation structure
• Note: Mature legacy COMBIFLEX system component, still active production for new utility substation relay panel construction; factory-sealed new modules and fully bench-tested surplus units are widely supplied for thermal power, hydropower, wind farm and industrial MV switchgear maintenance retrofits.

Key Technical Specifications

Product Introduction

The RXDS 4 (1MRK000344-A) is a 4-circuit safety test disconnect module built exclusively for ABB’s classic COMBIFLEX modular relay panel architecture, designed to solve critical safety risks during secondary protection testing.Its core mechanical interlock design is the key safety feature:

1. CT Circuit Protection Priority: When rotating the switch handle from “Service/Normal” to “Test” position, built-in auxiliary shorting contacts fully bridge the CT secondary terminals first, then the main measurement contacts open. This sequence completely avoids open-circuit CT high voltage, which would otherwise cause insulation breakdown and fatal electric shock hazards.
2. VT & Trip Circuit Isolation: The remaining poles safely isolate VT voltage measurement loops and breaker trip control circuits, blocking live grid voltage and trip pulse signals from reaching the connected protection IED during injection testing.
3. Sequential Circuit Restoration: When switching back to normal operating mode, the test isolation contacts close first, then the CT shorting contacts automatically open to restore full measurement function.

Each RXDS 4 module handles up to four independent secondary loops, commonly allocated as: 3-phase CT measurement + residual neutral CT circuit, or mixed CT/VT/trip signal combinations for single bay protection schemes. It eliminates temporary wiring jumpers and manual CT shorting operations during maintenance, drastically shortening commissioning time and reducing human error risks.It is universally matched with all ABB protection relays and IEDs including REF610/REF615 feeder relays, RET670 transformer relays, REG series generator protection relays and REM615 motor IEDs, serving as standard auxiliary hardware in every medium/high voltage substation relay bay panel.

QA & Testing SOP (Transparency Building)

1. Incoming Visual Inspection: Cross-check full part number RXDS 4 1MRK000344-A and serial number against ABB power system spare parts database to reject counterfeit mismatched modules; inspect front operating handle, silver-plated switch contacts, mechanical interlock cam structure and terminal screw blocks for wear, corrosion or deformation; record serial numbers and production batches for full traceability.
2. Mechanical & Electrical Safety Linkage Test: Mount RXDS4 on standard COMBIFLEX DIN rail test bench, simulate 5A CT secondary load circuits; perform 24-hour cyclic switching testing to verify strict interlock sequence (CT short before disconnect), check contact continuity, insulation resistance and absence of contact arcing during operation. Simulate full secondary injection test workflow to validate complete circuit isolation performance.
3. Insulation Resistance Test: Use insulation tester to confirm isolation resistance ≥ 10 MΩ between each pole circuit and module ground base; test chassis ground continuity resistance below 0.5 Ω.
4. Hardware Record Backup: Photograph terminal pin assignment diagrams, switch position mechanical marking definitions and DIN rail mounting dimensions for field wiring reference.
5. Final QC Packaging: Wipe module housing with anti-static microfiber cloth, cover all terminal screw blocks with insulating protective caps, place the unit into independent ESD shielding bag, attach unified printed QC test tag with technician ID and full 24-hour cyclic test runtime timestamp, then pack into foam shockproof carton for long-distance substation transportation.

Installation Pitfalls & 4-Step Replacement Guide

Common Installation Hazards

❗ CT Open-Circuit Safety Risk: Never manually bypass or disable the internal mechanical interlock cam; tampering will break the CT short-first sequence and create lethal high voltage during switch operation.❗ Incorrect Secondary Circuit Allocation: Do not connect VT or DC trip control circuits to dedicated CT poles; mixed wiring may bypass the CT shorting safety function and cause protection misoperation.❗ Terminal Torque Defect: Under-tightened wire terminals create high contact resistance, leading to overheating during long-term CT load current operation; follow ABB specified torque values for all screw terminals.❗ ESD Contact Damage Risk: Wear certified anti-static wrist strap during disassembly and installation; bare hand contact with internal silver contacts causes oxidation and poor measurement signal continuity.❗ Live Circuit Switching Prohibition: Avoid rotating the RXDS4 handle under full energized secondary circuit conditions if unnecessary; frequent live switching accelerates contact wear and reduces service life.

4-Step Module Replacement Guide

1. Pre-install Preparation: Lock out and tag out all CT/VT secondary circuit power sources for the relay bay, wear ESD wrist strap, photograph full wiring sequences of 4 circuit poles connected to CT, VT and trip control terminals of the RXDS4 module.
2. Removal Operation: Loosen all secondary wire terminal screws on the RXDS4 module, release the DIN rail mounting clip, detach the old test disconnect switch from the COMBIFLEX rail.
3. Installation & Wiring: Clip the new RXDS 4 (1MRK000344-A) module onto the original DIN rail, re-terminate all CT/VT/trip secondary wires strictly following photographed wiring allocation, tighten all terminal screws to standard torque values, confirm mechanical switch handle rotates smoothly without jamming.
4. Commissioning Safety Test: Restore secondary circuit supply, slowly rotate the switch handle to “Test” position and verify CT shorting contacts engage before measurement circuits open; switch back to “Normal” position and confirm full measurement signal recovery on the matched protection IED, check no persistent CT/VT measurement fault alarms appear on SCADA/DCS.

FAQ

Q: What is the difference between RXDS 4 and smaller RXDS 2 test switches?A: RXDS 2 only supports 2 secondary circuits for simple single-loop measurement bays. RXDS 4 provides 4 independent poles, suitable for complete 3-phase + residual CT loop allocation, meeting standard full feeder/transformer bay secondary circuit testing requirements in most utility substations.Q: Can be used for primary high voltage main circuit isolation?A: Strictly not allowed. is exclusively designed for low-voltage CT/VT secondary measurement and control circuits (max 250V), it has no arc extinction capacity for primary high-power circuits.Q: What warranty applies to stocked RXDS 4 1MRK000344-A modules?A: Factory-new original COMBIFLEX modules carry 12-month official ABB manufacturer warranty covering mechanical interlock structure, silver switching contacts and terminal base insulation. Bench-tested surplus modules provide 6-month functional warranty; damage caused by interlock tampering, loose terminal overheating or ungrounded ESD handling voids all warranty terms.Q: Has ABB discontinued RXDS 4 production?A: No formal EOL notice issued; remains standard supply for new COMBIFLEX relay panel projects. For modern digital substation cabinet layouts, ABB also provides compatible Flexitest FT series test switches as alternative options.Q: Will protection IED measurement data be permanently lost after replacing ?A: All CT/VT measurement values and protection setting groups are stored inside the connected protection IED flash memory, independent of the test switch. No parameter backup or recalibration work is required after module replacement, only a short secondary signal verification test is necessary.Q: What faults indicate a defective RXDS 4 module?A: Typical failure symptoms: Mechanical handle jamming unable to switch between Test/Normal positions, persistent CT unbalance measurement alarms due to poor contact continuity, failure to auto-short CT loops when switching to Test mode, visible contact arcing or discoloration inside the module housing, incomplete isolation of VT/trip circuits leading to unexpected protection misoperation.