Description
ABB RXKM 2H 1MRK000142-A Digital Time Relay
Product Introduction
The ABB RXKM 2H 1MRK000142-A is a microprocessor-based digital time relay designed for protection, control, automation and signaling applications. It belongs to the ABB COMBIFLEX relay family and provides programmable timing functions over a very wide range, from 20 milliseconds to 99 hours. The exact ordering number for RXKM 2H is 1MRK 000 142-A, as identified in the manufacturer’s technical documentation.
The ABB RXKM 2H 1MRK000142-A accepts either DC or AC operating power, with a specified supply range of 24–250 VDC and 48–240 VAC. Its timing function is implemented using microprocessor technology with digital setting, while the output stage uses an electromechanical relay. The unit provides an instantaneous indication contact together with two delayed medium-load changeover contacts, making it suitable for applications where timing logic must be implemented directly within a relay/control circuit rather than in a PLC.
The ABB RXKM 2H 1MRK000142-A is particularly relevant in legacy substation protection and control cabinets where COMBIFLEX components are used for hardwired timing, interlocking, signaling or auxiliary control functions. The manufacturer describes the RXKM 2H for protection systems, automation equipment, industrial processes and control/signal systems. Its wide timing range allows one relay to cover applications ranging from short intentional delays to long-duration control sequences.
From a procurement standpoint, this is a relatively small component with potentially significant system consequences. A timer in a protection or control circuit can determine trip sequencing, alarm delays, breaker-control logic or interlocking behavior. Replacing it with a generic timer without reproducing the original contact arrangement and timing behavior can change the control philosophy even when the replacement appears electrically similar.
Technical Specifications
| Specification | Details |
|---|---|
| Product Model | RXKM 2H |
| Ordering Number | 1MRK 000 142-A |
| Manufacturer | ABB |
| Product Family | COMBIFLEX |
| Product Type | Digital time relay |
| Technology | Microprocessor-based |
| DC Operating Voltage | 24–250 VDC |
| AC Operating Voltage | 48–240 VAC |
| Timing Range | 20 ms–99 hours |
| Timing Setting | Digital |
| Output Technology | Electromechanical relay |
| Output Contacts | Instantaneous indication contact plus two delayed changeover contacts |
| Timing Functions | Delay and pulse/interval-related timing functions |
| Application | Protection, control, automation, industrial process and signaling systems |
| Mounting System | COMBIFLEX |
| Manufacturer Document | 1MRK 508 002-BEN |
| Legacy Status | Legacy ABB/Hitachi Energy relay family |
The manufacturer’s RXKM 2H documentation specifically identifies the 1MRK 000 142-A ordering number and the broad AC/DC operating range.
RXKM
Main Features and Engineering Considerations
Wide Timing Range
The RXKM 2H covers an unusually broad timing range of 20 ms to 99 hours. This allows the same relay family to be used for short protection/control delays as well as long-duration sequences.
The actual setting should be copied from the existing installation before replacement. A timer with the correct electrical rating but the wrong time range or setting can introduce a substantial change in protection or control behavior.
AC and DC Operation
The RXKM 2H accepts both AC and DC control power. The specified ranges are 24–250 VDC and 48–240 VAC. This makes it suitable for many substation auxiliary circuits, but the actual cabinet supply should still be measured before installation.
Do not assume that every terminal is interchangeable between AC and DC applications. Follow the original wiring diagram and the manufacturer’s terminal diagram.
Microprocessor-Based Timing
Unlike older purely electromechanical timers, the RXKM 2H uses microprocessor technology and digital setting. This provides more consistent timing behavior and a wide programmable range.
For a replacement, record the existing setting and timing mode before removing the original unit. The relay’s timing behavior is part of the control-system design.
Electromechanical Output
The output stage uses an internal electromechanical relay. The manufacturer’s description identifies an instantaneous indication contact and two delayed medium-load changeover contacts.
This is important when replacing the device with a solid-state timer. A solid-state output may have different leakage current, contact isolation, polarity requirements and failure behavior. It should not automatically be considered functionally equivalent.
COMBIFLEX Integration
The RXKM 2H was designed for the ABB COMBIFLEX modular relay and mounting system. Its physical mounting and connection arrangement therefore need to be considered together with the associated relay rack, socket and wiring components. The manufacturer provides separate documentation for COMBIFLEX connection/installation components and relay mounting systems.
Application Scenarios
- Substation protection control circuits
- Circuit-breaker control and sequencing
- Alarm delay circuits
- Trip and interlocking circuits
- Industrial automation control circuits
- Process control timing
- Auxiliary relay logic
- Protection-system signaling
- COMBIFLEX relay panels
- Legacy ABB substation automation installations
Engineer’s Guide: Field Pitfalls
1. Do not classify RXKM 2H as a protection relay.
It is a time relay. It may be installed inside a protection system, but it does not replace a numerical overcurrent, differential or distance protection relay.
2. Match the complete ordering number.
The correct identification is RXKM 2H / 1MRK 000 142-A. Other ABB RX-series relays have similar physical formats but completely different functions.
3. Record the timing setting.
A replacement should reproduce the original delay and timing mode. Do not assume the factory setting is appropriate for the installed circuit.
4. Verify the contact arrangement.
The RXKM 2H provides an instantaneous indication contact and two delayed changeover contacts. Verify the terminal numbers against the actual wiring diagram before substitution.
5. Check AC versus DC supply.
Although the relay supports both AC and DC, the applicable ranges differ: 24–250 VDC versus 48–240 VAC.
6. Check the COMBIFLEX mounting arrangement.
Electrical compatibility alone is insufficient if the replacement must fit an existing COMBIFLEX relay rack and terminal arrangement.
7. Do not replace it with a PLC timer without reviewing the circuit.
A PLC implementation changes the failure modes, scan-dependent timing, power-up behavior and potentially the independence of the timing function.
8. Test the complete control sequence.
After replacement, test not only the relay itself but also the circuit it controls. For protection applications, verify the actual trip, alarm or interlocking sequence under the applicable commissioning procedure.
Frequently Asked Questions
What is ABB RXKM 2H?
ABB RXKM 2H is a microprocessor-based digital time relay designed for protection, control, automation and signaling applications.
What is the part number?
The exact ABB ordering number is 1MRK 000 142-A.
What is the timing range?
The RXKM 2H has a timing range of 20 ms to 99 hours.
What supply voltage does the RXKM 2H use?
It operates from 24–250 VDC or 48–240 VAC.
Is RXKM 2H suitable for protection systems?
Yes. ABB/Hitachi Energy documentation specifically identifies RXKM 2H applications in protection systems, automation equipment, industrial processes, and control and signaling systems.
Does RXKM 2H use semiconductor outputs?
No. Its output stage uses an electromechanical relay, with an instantaneous indication contact and two delayed changeover contacts.
Is RXKM 2H part of the COMBIFLEX system?
Yes. It is a COMBIFLEX time relay, and its installation should be considered together with the appropriate COMBIFLEX connection and mounting components.
Procurement Note
For ABB RXKM 2H 1MRK000142-A, verify four things before accepting a replacement: ordering number, supply type/range, timing setting/function, and contact arrangement.
Because this relay may sit inside a protection or breaker-control circuit, the part should not be evaluated merely as a generic timer. Preserve the existing terminal wiring and timing settings, confirm the COMBIFLEX mounting arrangement, and perform a functional test of the downstream trip, alarm, interlocking or control circuit after installation.
The exact identification is well supported: RXKM 2H = ABB digital time relay; 1MRK 000 142-A = its ordering number.
