Contactor,circuit breaker,solar inverter,electric meter,solar batteries
Allen‑Bradley Guardmaster MSR125HP (440R‑D23171) Two-Hand Control Safety Relay
This unit is a dedicated two-hand control safety relay under the Guardmaster series of Rockwell Automation. It features dual-channel input, 2 NO safety contacts, Category 4 / Performance Level e (PL e) safety rating and removable terminals. Designed specifically for high-risk machinery requiring synchronized two-hand operation, it keeps operators’ hands within safe zones and prevents personal injuries.
- Model Code Explanation
MSR125HP‑440R‑D23171 is a two-hand control safety relay of the Guardmaster series manufactured by Allen‑Bradley / Rockwell Automation, USA. The model breakdown and corresponding order number are specified below:
| Code Segment | Description |
| MSR | Series code: Minotaur Safety Relay |
| 125 | Function code: Two-hand control unit, compliant with Type III safety requirements of ISO 13851 |
| HP | Feature code: High Performance, equipped with removable terminals (differentiated from MSR125H with fixed terminals) |
| 440R‑D23171 | Order number: Exclusive Rockwell identification code, for 24V DC power supply and two-hand control function |
Key Ordering Information
Main Order Number: 440R‑D23171 (Standard version with removable terminals)
Alternative Model: 440R‑D23168 (MSR125H, fixed terminals)
Compatible Model: 440R‑D23172 (with 0.5-second time delay function)
- Core Technical Specifications
| Category | Technical Data | Remarks |
| General Specifications | ||
| Type | Two-hand control monitoring safety relay | Compliant with Type III requirements of ISO 13851 |
| Operating Voltage | 24V DC (-15%/+20%) / 24V AC (-15%/+10%) | Max. ripple voltage: 10% |
| Power Consumption | Max. 3W | Low power consumption design |
| Ingress Protection | IP40 (Housing) / IP20 (Terminals) | Suitable for control cabinet installation |
| Input Characteristics | ||
| Monitoring Channels | Dual channel (1NC + 1NO input) | Dedicated for two-hand control, synchronized triggering required |
| Input Type | Dry contact signal | Compatible with two-hand control buttons and foot switches |
| Synchronization Time Window | ≤ 0.5 second | Operation beyond this window is deemed unsafe |
| Output Characteristics | ||
| Safety Contacts | 2 Normally Open (NO) contacts | AC15: 230V/6A; DC13: 24V/6A |
| Auxiliary Output | None | Optimized for safety control |
| Performance Level | PL e (Highest level) | Compliant with EN ISO 13849‑1 |
| Safety Category | Category 4 | Compliant with EN IEC 61508 |
| Safety Integrity Level | SIL 3 | Meets requirements for high-risk applications |
| Physical Characteristics | ||
| Dimensions | 22.5mm × 99mm × 121mm | DIN rail mounting, space-saving |
| Mounting | 35mm standard DIN rail | Standard industrial installation |
| Operating Temperature | -25°C ~ 60°C | Wide temperature range for industrial environments |
| Terminals | Removable screw terminals | Cable cross-section: 0.25mm² ~ 2.5mm² |
| Certifications | UL, CSA, CE, TÜV | Compliant with international safety standards |
- Cross-Brand Compatibility List
| Brand | Replacement Model | Compatibility Description |
| Allen‑Bradley | MSR125H (440R‑D23168) | Identical functions, only differs in terminal type (fixed terminals) |
| Schmersal | SRB301‑24V (101190686) | General-purpose safety relay with 3 safety contacts; two-hand control logic needs reconfiguration |
| Siemens | 3SK1122‑1AB30 | Dedicated two-hand control relay, 2 safety contacts, 24V DC |
| Schneider Electric | XPSAC5121 | 24V AC/DC, 3 safety contacts; two-hand control requires additional programming |
| Omron | G9SA‑501 | Two-hand control unit, 2 safety contacts, STOP 0 stop category |
Selection Tip: Choose dedicated two-hand control relays; match synchronization window and contact quantity; do not downgrade safety ratings; select terminals according to on-site demands.
- Full Model List of MSR Two-Hand Control Series
Model Order Number Voltage Contact Configuration Terminal Type Special Function MSR125HP 440R‑D23171 24V AC/DC 2 NO safety contacts Removable Two-hand control, instantaneous output MSR125H 440R‑D23168 24V AC/DC 2 NO safety contacts Fixed Two-hand control, instantaneous output MSR125HP‑0.5s 440R‑D23172 24V AC/DC 2 NO safety contacts Removable Two-hand control, 0.5s delayed output MSR125H‑0.5s 440R‑D23169 24V AC/DC 2 NO safety contacts Fixed Two-hand control, 0.5s delayed output MSR125HP‑240V 440R‑D23173 240V AC 2 NO safety contacts Removable Two-hand control, high voltage version Common Faults & Troubleshooting
| Fault Phenomenon | Possible Causes | Solutions |
| Power indicator off | 1. Power disconnected or abnormal voltage | 1. Check power connection and voltage (20.4V~28.8V DC) |
| 2. Internal fuse blown | 2. Replace 2A internal fuse | |
| Safety contacts fail to activate | 1. Two buttons not synchronized (interval over 0.5s) | 1. Standardize operation to ensure synchronized actuation |
| 2. Fault in input channels | 2. Inspect buttons and wiring, replace defective parts | |
| 3. Incorrect reset mode setting | 3. Verify reset mode (automatic / manual) | |
| Frequent false tripping | 1. Electromagnetic interference | 1. Apply shielding and keep away from interference sources |
| 2. Loose cable connections | 2. Retighten cables and ensure reliable connection | |
| 3. Improper synchronization window | 3. Confirm fixed 0.5s synchronization window (non-adjustable) | |
| Failed reset | 1. Safety circuit not fully closed | 1. Inspect all safety input devices |
| 2. Manual reset button not pressed | 2. Press reset button (under manual reset mode) | |
| 3. Internal component failure | 3. Replace the safety relay module |
Quick Troubleshooting Guide: Check power supply first, then synchronization. For inactive contacts, inspect inputs; for false tripping, eliminate interference; for reset failure, verify the whole safety circuit.
- Application Environments & Industry Cases
6.1 Applicable Scenarios
Stamping & Bending Machinery: Presses, press brakes, shears and other metalworking equipment requiring two-hand operation
Injection & Molding Machinery: Mold area protection for injection molding machines and die-casting machines to prevent hand injuries
Assembly & Testing Tooling: Custom automated equipment with mandatory two-hand operation for operational safety
Welding & Cutting Equipment: Start-up control for welding robots and plasma cutters to avoid accidental activation
Packaging Machinery: Sealing and cutting stations with synchronized two-hand operation to protect operators
6.2 Not Recommended Scenarios
Single-button controlled equipment: Two-hand control function cannot be utilized, resulting in unnecessary cost
Outdoor harsh environments: IP40 rating is not suitable for outdoor installation
Highly corrosive environments: No anti-corrosion coating, incompatible with acid, alkali and corrosive substances
High vibration environments: Vibration exceeding 5g will shorten relay service life
6.3 Typical Application Cases
Case 1: Two-Hand Start Safety System for CNC Press
Application: Start control for 160-ton CNC press, preventing operators from reaching into the stamping zone
Configuration: MSR125HP (440R‑D23171) + 2 mushroom-head two-hand buttons (mounted on both sides of machine, spacing ≥ 60cm)
Working Principle: Both buttons must be pressed synchronously within 0.5 second to close safety contacts and start the press. The machine stops immediately once either button is released.
Effect: Complies with Category 4 / PL e standards, eliminating risks of hands entering hazardous areas during operation.
Case 2: Mold Closing Safety Protection for Injection Molding Machine
Application: Mold closing control for 200-ton injection molding machine, preventing pinching injuries during part removal
Configuration: MSR125HP + two-hand buttons (mounted on both sides of control panel) + magnetic safety switch for safety gate
Working Principle: Mold closing can only be initiated when the safety gate is fully closed and both buttons are pressed synchronously. Mold movement stops instantly if the gate is opened or any button is released.
Effect: Dual safety protection implemented, fully compliant with safety standards for rubber and plastics industry.
Case 3: Two-Hand Coordinated Workstation for Automated Assembly Line
Application: Press-fitting station for automotive component assembly line, two-hand operation required to activate the press head
Configuration: MSR125HP + foot switch (auxiliary control) + two-hand buttons (main control)
Working Principle: Activate foot switch to clamp workpieces, then press both buttons synchronously to start the press head, ensuring operators’ hands stay in safe positions.
Effect: Improves production efficiency while guaranteeing operator safety, ideal for mass production lines.
- Operation Guidelines & Installation Specifications
- Two-hand button installation: Maintain a minimum spacing of 60cm between two buttons to prevent actuation with one single hand.
- Wiring rules: Adopt cross wiring for dual input channels to enhance fault detection capability.
- Reset mode selection
Automatic reset: System recovers automatically after fault removal, suitable for continuous production lines.
Manual reset: Reset button must be pressed manually, recommended for high-risk applications.
- Maintenance schedule: Inspect contact status and wiring every 6 months to ensure stable and safe operation.
- Spare parts management: Prepare one identical relay as spare part to minimize downtime caused by equipment failure.
