A machine-tool safety quotation is incomplete when it says only “Schmersal relay”: the switch, safety function, wiring architecture and machine stopping method still need to be defined. By the end, you will be able to specify the right relay and switch combination, check its integration with a lathe or CNC machine, and compare suppliers using documented safety and traceability information.
Key takeaways
- Choose the relay by safety function, not the Schmersal model name alone.
- Match switch contacts, relay inputs and reset wiring to the schematic.
- Trace the stop circuit through contactors, drives or servo-drive STO.
- Request model, ratings, standards and delivery details in the quotation.
Choose the safety relay by machine function, not by brand name
Choose the relay from the machine’s safety function: a Schmersal safety relay in Coimbatore is not interchangeable across every machine tool.
| Type | What it monitors or does | Suitable application |
|---|---|---|
| Emergency-stop monitoring | Evaluates the E-stop circuit and opens safety outputs | Lathes, milling machines or tapping machines requiring emergency-stop isolation; it does not provide guard locking or prove spindle stoppage |
| Guard-door monitoring | Evaluates guard-switch contacts, often through dual channels | A simple lathe enclosure or milling-machine door |
| Two-hand control | Requires both operator controls within the defined time window | Cycle-start operation where both hands must stay away from the tooling |
| Time-delay function | Delays output or release for a defined run-down period | A grinder whose wheel remains hazardous after power removal |
| Safety-contact expansion | Adds monitored safety outputs for additional contactors or circuits | A machine needing more safety contacts than the primary relay provides |
| Configurable safety controller | Combines interdependent functions, multiple guards, muting and detailed diagnostics | A CNC machining centre with several access doors and operating modes |
A lathe guard may need dual-channel guard monitoring, while a grinder may require guard locking and timed release before access is permitted. A two-hand relay suits a tapping cycle only when the controls and timing match the risk assessment; it is not a substitute for door monitoring.
The SRB family contains variants for these different functions, but the exact part number remains essential. Confirm the input arrangement, reset method, output type and time-delay specification before comparing offers. A generic “SRB relay” or “24 V relay” does not identify the correct device.
Match the switch, relay inputs and reset circuit to the machine schematic
The relay’s wiring diagram must match the machine schematic terminal by terminal. Connect the switch’s normally closed, positively opening contacts as specified, then confirm whether the circuit requires one or two safety channels.
A guard-position switch detects whether the door is closed; a solenoid interlock also holds it locked until the specified release condition is met.
Ask a machine safety switch dealer in Coimbatore to identify the device under ISO 14119. A non-coded switch uses a conventional actuator, a coded switch accepts a specifically matched actuator, and an RFID-based switch uses electronic identification.
Replacing a coded device with a generic position switch can increase defeat risk and invalidate the machine’s original protection assumptions.
Put these details on the quotation:
- Exact switch and relay part numbers, safety-input count, dual-channel arrangement, supply voltage and wiring terminals.
- Manual or automatic reset, external device monitoring, auxiliary contacts, and semiconductor or positively guided relay outputs.
- Actuator type, permissible alignment, actuator side load, mounting limits and connector or cable option.
- Cable routing, protection from chips and coolant, vibration resistance and washdown suitability.
Check the door alignment with the actuator fully engaged; side loading or a drifting guard can cause nuisance trips or damage. “24 V relay” is insufficient because variants with the same nominal voltage can have different input and output arrangements. Confirm the quoted relay, switch and accessories together before approval.
Verify the stop path: contactor, starter, VFD or servo-drive STO
A safety relay output opens a circuit; it does not automatically stop the spindle. Trace the complete path to the hazard, including the contactor, motor starter, VFD or servo drive, brake, and stored pneumatic or hydraulic energy.
| Option | What it does | What to verify |
|---|---|---|
| Safety relay output | Opens positively guided safety contacts or semiconductor outputs | Response time, reset method and output ratings |
| Contactor or starter | Removes motor power when its coil drops out | Coil voltage, contact rating, drop-out time, feedback contacts and external device monitoring |
| VFD or servo STO | Prevents torque-producing energy at the drive | STO support, one- or two-channel architecture, response time and drive documentation |
| Controlled stop | Decelerates before power removal | Stop Category 0 or 1, spindle run-down time and brake performance |
A motor can coast after a contactor opens, a vertical axis can descend under gravity, and stored pressure can move an actuator. Confirm that the proposed output path removes every relevant hazard rather than only control power.
For a VFD or servo drive, use the STO terminals exactly as specified by the manufacturer. A CNC machine may need STO plus a separate holding brake or controlled stop; a grinder may need guard locking until the wheel reaches a safe condition.
Include access-release timing in the validation. The guard must not unlock before the spindle run-down, drive stop and brake times have elapsed.
Ask any safety switch supplier for machine tools to show the relay response time, contactor drop-out time, drive stop category and complete wiring path in the quotation. A relay-only claim is incomplete.
Check PL, SIL and machine-tool standards before approving the part
Approve the combination only after the risk assessment defines each safety function and its required Performance Level (PL) or Safety Integrity Level (SIL). ISO 13849-1 assigns required and achieved PL to the complete safety-related control system, not to a relay alone; IEC 62061 provides the SIL framework for machinery control systems.
Do not infer either value from the Schmersal name.
1. Trace the complete chain: switch or emergency stop, input wiring, relay or controller, contactor or drive output, diagnostics, architecture and common-cause measures. A Schmersal safety relay in Coimbatore is suitable only when the complete circuit achieves the target.
2. Check the named function against ISO 13850 for emergency stop, ISO 14119 for interlocking devices and ISO 14120 for guards. Use IEC 60204-1 to verify machine electrical equipment, protective bonding, control circuits and verification.
- Model-specific data sheet and terminal diagram
- Mounting instructions and response-time data
- Declaration of Conformity or certificate information
- Validation information and replacement instructions
4. Match the evidence to the machine-tool risk assessment, including stop time, access-release timing and contactor or drive feedback. A safety switch supplier for machine tools should provide project-specific Tamil Nadu or India documents when the end customer specifies them.
Replacing the relay, switch or controller triggers a validation review. Update the electrical schematic, terminal references and calculation records before commissioning; an equivalent-looking part does not preserve the original PL or SIL result.
Compare Coimbatore suppliers using an exact, traceable quotation
A Schmersal relay price has meaning only when the quotation identifies the exact manufacturer part number and quotation revision. “24 V relay” is insufficient: variants can share that voltage while differing in contacts, inputs and outputs.
Request these fields on every offer:
- Supply voltage; safety and auxiliary contact count; input-channel arrangement; manual or automatic reset; EDM method; switching capacity; mounting format; connector or cable option; and required accessories.
- Whether the price includes the safety switch, actuator, guard-locking device, relay, terminals, tax, freight, commissioning and replacement support.
| Quotation check | Acceptable evidence | Comparison result |
|---|---|---|
| Part identity | Exact part number and quotation revision | Reject generic “Schmersal relay” listings |
| Technical file | Original data sheet, wiring diagram and mounting instructions | Match terminals to the machine schematic |
| Compliance trail | Declaration or certificate information, invoice chain, batch or serial information where provided | Preserve traceability |
| Supply service | Local stock, lead time, warranty handling and engineering support | Compare more than unit price |
Verify authenticity and the intended sales channel through Schmersal’s India contact or channel information. A marketplace listing is not technically comparable to a model-specific offer.
A schmersal safety switch relay supplier in coimbatore should explain whether the quote covers one complete safety function or isolated components. SSB INDUSTRIAL SOLUTIONS can help when a builder needs the switch, relay, contactor or drive interface checked against the machine schematic. Keep the approved part number and validation documents in the final purchase file.
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Frequently asked questions
How do you choose a Schmersal safety relay for a machine tool?
Choose it by the required safety function, such as guard-door monitoring or emergency-stop monitoring, then match its inputs, outputs and reset method to the machine schematic.
What must you verify in the machine-tool stop path?
Trace the relay output to the final switching device: a contactor, motor starter, VFD input or servo-drive Safe Torque Off circuit.
How do PL and SIL affect safety relay selection?
Check the machine risk assessment and required Performance Level under ISO 13849-1 or Safety Integrity Level under IEC 62061 before approving the relay.
What should a Coimbatore supplier include in a safety relay quotation?
Request the exact Schmersal model, input and output ratings, reset configuration, applicable standards, lead time, warranty and a clear Schmersal relay price.
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