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The Schmersal SRB301MC-24V is a high-performance safety relay module. Its core advantages include 3 safety contacts plus 1 signal output, STOP 0 stop category, Performance Level e (PL e) and diagnostic coverage ≥99%. It is widely deployed in safety protection systems for various industrial automation equipment. Featuring a dedicated design for magnetic safety switches and cross-wire detection function, it delivers outstanding performance in safety gate monitoring applications. Please check compatibility with safety input devices during model selection, and strictly follow wiring specifications during installation to ensure safe and reliable system operation.
- Model Code Explanation
The SRB301MC-24V is a safety relay module of the PROTECT SRB series manufactured by Schmersal, Germany. The breakdown of the model code is as follows:
| Code Segment | Definition |
| SRB | Series code: Safety Relay Block |
| 301 | Function code: 3 safety contacts and 1 signal output, compatible with single/dual-channel safety inputs |
| MC | Characteristic code: Designed for signals from BNS series magnetic safety switches, supports cross-wire detection |
| 24V | Rated operating voltage: 24V AC/DC, compatible with AC and DC power supply |
Order Numbers: 101190684 (Standard Version), 161190684 (International Version), 151190684 (China Version)
- Main Technical Specifications
| Category | Technical Data | Remarks |
| General Specifications | ||
| Type | Safety monitoring module, emergency stop safety relay | STOP 0 stop category |
| Operating Voltage | 24V AC (-15%/+10%) / 24V DC (-15%/+40%) | Maximum ripple voltage: 10% |
| Power Consumption | 2W | Low power consumption design |
| Ingress Protection | IP20 (Terminals) / IP40 (Housing) | Suitable for control cabinet installation |
| Input Characteristics | ||
| Monitoring Channels | Switchable single/dual channel | Cross-wire detection supported |
| Input Type | Passive contacts / Active signals (AOPDs) | Compatible with safety light curtains, emergency stop buttons, etc. |
| Input Current | >500mA | Reset time of monitoring circuit: approx. 1 second |
| Output Characteristics | ||
| Safety Contacts | 3 contacts (2NC + 1NO) | DC13: 24V/6A; AC15: 230V/6A |
| Signal Output | 1 auxiliary contact | For status indication or alarm |
| Performance Level | PL e (Highest level) | Compliant with EN ISO 13849-1 |
| Safety Category | Category 4 | Compliant with EN IEC 61508 |
| Diagnostic Coverage | ≥99% | High reliability design |
| Physical Characteristics | ||
| Dimensions | 22.5mm × 100mm × 121mm | DIN rail mounting, space-saving |
| Mounting | 35mm standard DIN rail | Standard industrial mounting |
| Operating Temperature | -25°C ~ 60°C | Wide temperature range for industrial environments |
| Terminals | Screw terminals | Cable cross-section: 0.25mm² ~ 2.5mm² |
| Certifications | BG, UL, CSA, CE | Compliant with international safety standards |
- Cross-Brand Compatibility List
| Brand | Replacement Model | Compatibility Description |
| Schmersal | SRB E 301MC-24V (103014374) | Enhanced replacement, fully compatible with improved performance |
| Siemens | 3SK1111-1AB30 | Equivalent safety relay, 3 safety contacts, 24V DC |
| Schneider | XPSAC5121 | 24V AC/DC, 3 safety contacts and 1 signal output |
| Omron | G9SA-321-T075 | 24V DC, 3 safety contacts, STOP 0 stop category |
| ABB | MSR132TP | 24V AC/DC, 3 safety contacts, single/dual channel |
Selection Guideline: Match voltage and contact quantity; do not downgrade safety performance level; keep identical mounting dimensions.
- Full Model List of SRB Series
| Model | Voltage | Contact Configuration | Special Functions | Order Number |
| SRB301MC-24V | 24V AC/DC | 3 Safety (2NC+1NO) + 1 Signal | For magnetic switches, cross-wire detection | 101190684 |
| SRB301MC-24V-STSS | 24V AC/DC | 3 Safety (2NC+1NO) + 1 Signal | Short-circuit protection, for magnetic switches | 101190685 |
| SRB301-24V | 24V AC/DC | 3 Safety (2NC+1NO) + 1 Signal | General type, no optimization for magnetic switches | 101190686 |
| SRB302MC-24V | 24V AC/DC | 4 Safety (3NC+1NO) + 1 Signal | Dual-gate monitoring, for magnetic switches | 101190687 |
| SRB301MC-110V | 110V AC | 3 Safety (2NC+1NO) + 1 Signal | For magnetic switches, high voltage version | 101190688 |
| SRB301MC-230V | 230V AC | 3 Safety (2NC+1NO) + 1 Signal | For magnetic switches, high voltage version | 101190689 |
- 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) |
| 2. Internal fuse blown | 2. Replace 2A internal fuse | |
| Safety contacts fail to operate | 1. Abnormal input signal | 1. Inspect safety input devices (E-stop, light curtains, etc.) |
| 2. Incorrect cross-wire detection setting | 2. Adjust QS switch (Top: cross-wire protection off; Bottom: cross-wire protection on) | |
| 3. Damaged contacts | 3. Replace the safety relay module | |
| No signal output | 1. Safety circuit not reset | 1. Check reset conditions (manual/automatic reset) |
| 2. Damaged signal output contacts | 2. Test continuity of signal contacts | |
| Frequent false tripping | 1. Electromagnetic interference | 1. Add shielding and keep away from interference sources |
| 2. Poor cable connection | 2. Recheck cable connections | |
| 3. Ambient temperature out of range | 3. Ensure temperature within -25°C ~ 60°C |
Check power first, then inputs; wrong settings are common causes; watch out for interference and reset requirements.
- Application Environments & Industry Cases
6.1 Applicable Scenarios
Machinery Safety Protection: Emergency stop systems for injection molding machines, punch presses, press brakes and other stamping equipment
Automation Production Lines: Signal processing for safety light curtains to prevent personnel from entering hazardous areas
Logistics & Warehousing: Safety gate monitoring for stackers and conveyors with BNS magnetic safety switches
Packaging Machinery: Safety interlock for filling and labeling machines to ensure operational safety
Automotive Manufacturing: Safety zone monitoring for welding robots and coating lines
6.2 Not Recommended Scenarios
Harsh outdoor environments: IP20 protection rating is not suitable for outdoor installation
Highly corrosive environments: No anti-corrosion coating, incompatible with acid, alkali and corrosive media
High vibration environments: Vibration over 5g may shorten relay service life
High temperature over 60°C: Will degrade performance and service life
6.3 Application Cases
Case 1: Stamping Production Line for Automotive Parts
Application: Emergency stop system and signal processing of safety light curtains for 3 punch presses
Configuration: One SRB301MC-24V installed on each press, connected with emergency stop buttons and safety light curtains
Effect: Realizes instant STOP 0 shutdown with diagnostic coverage ≥99%, reducing safety risks
Case 2: Safety System for Food Packaging Machinery
Application: Safety gate monitoring for filling and capping machines with Schmersal BNS magnetic safety switches
Configuration: SRB301MC-24V monitors 2 safety gates; cross-wire detection prevents cable failures
Effect: Complies with food industry safety standards and improves equipment reliability
Case 3: Stackers in Automated Warehouse
Application: Safety gate monitoring and emergency stop system for stacker aisles
Configuration: SRB301MC-24V connected to magnetic safety switches and E-stop buttons; signal output linked to PLC
Effect: Stacker is locked when safety gates are open, upgrading warehouse safety level
Detailed Application Cases of Schmersal SRB301MC-24V Safety Relay
This model is optimized for magnetic safety switches, dual-channel monitoring and cross-wire detection, compliant with PL e / Category 4. It is widely used for safety gates, emergency stops and safety light curtains. Below are practical industry cases including wiring schemes, operation methods and application values.
- Machine Tool Industry (Main Application)
Case 1: Safety Gate & E-Stop Interlock for CNC Punch Press / Press Brake
- Matching Devices: Schmersal BNS magnetic safety switches (machine protective gates) + Mushroom-head emergency stop buttons
- Operation:
Adopt dual-channel input and cross-wire detection to monitor front and rear protective gates;
Safety contacts open immediately when gates are opened or E-stop is triggered, executing STOP 0 instant shutdown;
Auxiliary signal contacts connect to PLC for gate status and fault alarm upload.
- Value: Prevent personnel from accessing stamping hazardous areas; detect cable breakage and short circuit to avoid safety failure.
Case 2: Rotating Hatch Monitoring for Machining Centers
- Matching Devices: BNS magnetic safety switches (rotating protective gates)
- Operation: Switchable single/dual channel; equipment cannot start if gates are not fully closed; power circuit cuts off immediately if gates are opened during operation.
- Applicable Equipment: Vertical machining centers, drilling & milling machines, grinders.
- Automation Production Lines & Robotics
Case 1: Safety Fence Monitoring for Robot Workcells
- Matching Devices: Magnetic safety switches (fence access gates) + Safety light curtains
- Operation:
Signals from safety gates and light curtains are wired in series to the relay;
Robot stops and locks when personnel intrude or gates are opened; on-site reset is required for restart.
- Typical Scenarios: Automotive component handling, welding robots, loading/unloading robot cells.
Case 2: Centralized Emergency Stop Control for Production Lines
- Operation: Emergency stop buttons at multiple workstations are connected in parallel to the module, cutting off power of motors and conveyors via unified safety circuit.
- Advantages: Fast response and powerful circuit diagnosis, ideal for full-line safety interlock.
- Packaging, Food & Pharmaceutical Machinery
Case 1: Guard Safety Protection for Automatic Filling & Sealing Machines
- Matching Devices: BNS non-contact magnetic safety switches (movable machine guards)
- Operation:
Frequent opening/closing of guards in food equipment leads to no mechanical wear for magnetic switches and longer service life;
Enable cross-wire detection to avoid safety hazards caused by aging and short-circuited cables in humid environments.
- Applicable Equipment: Beverage fillers, daily chemical packaging machines, pharmaceutical blister packaging machines.
Case 2: Access Gate Interlock for Carton Packaging & Palletizing Machines
Magnetic switches are installed on equipment access gates. The palletizing mechanism and conveyors lock completely once gates are opened, protecting maintenance personnel.
- Logistics & Warehousing Equipment
Case 1: Aisle Safety Gate Monitoring for Warehouse Stackers
- Monitoring Points: Protective gates and access gates of stacker travel aisles
- Logic: Stacker is disabled for travelling and lifting when gates are open; immediate shutdown and alarm during operation.
- Feature: Cross-wire detection effectively diagnoses faults of long-distance cables in warehousing systems.
Case 2: Zone Safety Protection for Belt / Roller Conveyors
Access gates on both sides of conveyors and line-mounted E-stop buttons are connected to the module, realizing full-section emergency stop. Widely used in express sorting and material conveying lines.
- Rubber, Plastic & Injection Molding Machinery
Case: Safety Gate & Mold Area Protection for Injection Molding Machines
- Matching Devices: Magnetic safety switches (front & rear safety gates of injection machines)
- Operation: Mold opening and part picking areas are high-risk zones. Mold closing action is locked when gates are opened to prevent pinching accidents. Complies with national safety standards for rubber & plastic machinery.
- General Auxiliary Applications (Small Equipment & Control Cabinets)
Case: Small Automated Tooling & Test Equipment
For various custom assembly and test tooling, this relay builds cost-effective high-level safety circuits (Category 4 / PL e) with single E-stop and simple protective gates, suitable for small and medium-sized custom equipment.
Supplementary Operation Notes
- For optimal performance, use with Schmersal BNS magnetic safety switches (original manufacturer recommended combination).
- Enable cross-wire detection for long-distance wiring, humid or dusty sites.
- All above applications meet EN ISO 13849 PL e and Category 4, acceptable for equipment exported to the EU.
- Not recommended for outdoor, highly corrosive or severe vibration environments. IP40 rating is only for indoor control cabinet installation.
