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Eaton ESR4 & ESR5 Safety Relays: Selection Guide
Machine Safety · Product Selection Guide
A practical guide to matching an Eaton ESR safety relay to the safety function, required stop behaviour, output configuration and control supply of a machine.
A safety relay monitors signals from safety devices and switches its enabling outputs according to the relay’s safety logic. Selecting the right model means looking beyond the family name: the exact part number determines input compatibility, output paths, timing and supply voltage.
Quick answer: define the safety function first, confirm the required performance level through risk assessment, then match the exact relay variant to the input devices, output requirements and supply available in the control panel.
At a glance
- Choose by the safety device being monitored: emergency stop, guard interlock, light curtain/OSSD or another supported input.
- Confirm the required safety performance and stop category at the machine level.
- Check the number and timing of enabling outputs, feedback/reset requirements and the control supply.
- Verify every specification against the current datasheet for the complete catalogue number.
In this guide
ESR4 and ESR5: what to compare
The supplied draft describes ESR4 variants with different output-path counts and timing options, and ESR5 variants for safety monitoring applications. These family names are a useful starting point, but they are not sufficient to establish a relay’s complete capabilities. Input logic, output arrangement, time delay, control voltage and approvals can vary by exact model.
| Family / example | Control supply shown | Enabling paths shown | Timing shown | Signal contacts shown |
|---|---|---|---|---|
| ESR4 | 24 V DC | 2 | Not specified | 1 |
| ESR4 | 24 V DC | 4 | Off-delay | 2 |
| ESR4 | 24 V AC/DC | 4 | Non-delayed | Not specified |
| ESR4 | 24 V DC | 2 | On-delay | 1 |
| ESR4 | 24 V DC | 2 | Off-delay | 1 |
| ESR4 | 230 V AC | 3 | Not specified | 1 |
“Not specified” means the supplied draft did not identify the value; it does not mean that the device has zero contacts or no timing function. Confirm the complete catalogue number before ordering.
Understanding enabling paths
An enabling path is a safety-related output circuit that permits the connected machine function to operate when the monitored conditions are satisfied. It is not a count of input sensors, and it does not automatically tell you how many independent safety functions can be combined in one design.
Before choosing a model, check:
- Inputs: one- or two-channel wiring, supported contact type or OSSD signal, and cross-fault detection requirements.
- Outputs: the number and type of enabling contacts, plus any separate signalling contacts.
- Reset and feedback: manual or automatic start behaviour, reset monitoring and external-device monitoring where required.
- System performance: whether the complete safety function can achieve the required PL/SIL after sensors, logic, actuators and wiring are considered.
Off-delay vs immediate shutdown
| Output behaviour | What it does | Typical design consideration |
|---|---|---|
| Non-delayed | The enabling output is switched off without an intentional time delay once the relay’s shutdown conditions are met. | Useful where the risk assessment and machine stop response require immediate removal of the enabling signal. |
| Off-delay | The selected output remains enabled for a configured interval after the relevant stop signal, then switches off. | May be part of a Category 1 stop sequence when used with suitable machine controls; the relay timer itself does not control deceleration. |
| On-delay | The selected output changes state after a configured delay, as defined by the specific relay. | Confirm the model’s exact timing function and ensure it is appropriate for the safety design. |
Important distinction: an off-delay relay does not, by itself, make a machine decelerate in a controlled way. A drive or machine controller must perform the controlled stopping action; the safety relay’s role is determined by the designed safety circuit. Stop Category 0 or 1 must be assessed for the complete machine system, not inferred from a relay label alone.
Match the relay to the application
| Application | What to verify | Selection note |
|---|---|---|
| Emergency stop | Input channel configuration, reset, feedback loop, required stop behaviour and output rating. | Choose a model that matches the risk assessment and the machine’s stop design. |
| Guard door / interlock | Contact or sensor type, one- or two-channel monitoring, fault detection and reset logic. | Delayed shutdown is only appropriate when the risk assessment and machine sequence permit it. |
| Light curtain / OSSD | Explicit compatibility with the sensor’s output type, plus required diagnostic behaviour. | Do not assume every safety relay accepts every electronic sensor output. |
| Timed stop or contact expansion | Exact delay range, which contacts are delayed, number of enabling paths and any expansion-module requirements. | Confirm the timing and contact arrangement from the exact model’s datasheet. |
| Charging or process interlock | Required safety function, operating environment, supply and interface to the machine controller. | Validate the application-specific safety architecture rather than choosing on the basis of the family name alone. |
A practical selection checklist
- Document the hazard and safety function. Identify the access point or hazardous motion being controlled and complete the required risk assessment.
- Confirm the target performance. Establish the required PL/SIL and stop category for the complete safety-related control system.
- Match the input device. Check channels, contact/OSSD compatibility, diagnostics and reset requirements.
- Count and specify outputs. Identify enabling contacts, signalling contacts, delayed contacts and feedback requirements.
- Match the control supply. Verify AC/DC type and the exact rated voltage range.
- Check the complete part number. Use the latest Eaton technical documentation for timing, wiring, approvals and terminal arrangement.
Frequently asked questions
No. Compare the exact part numbers for input compatibility, output configuration, timing, supply and approvals. A shared application label does not establish electrical or functional equivalence.
No. It delays the switching of the specified output. Controlled deceleration must be performed by suitable drive or machine-control equipment as part of the designed stop sequence.
No. The achieved performance depends on the complete safety function, including sensors, logic, output devices, architecture, diagnostics, wiring and validation. Follow the manufacturer’s safety manual and applicable standards.
Before you order
Have the safety function, input-device type, required output paths, timing, control supply and exact catalogue number ready. If any one of these is unknown, confirm it against the machine design and current Eaton documentation before selecting a replacement.
Manufacturer references
This article is a selection aid, not a substitute for a risk assessment, current manufacturer documentation, or validation of the complete machine safety function.
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TAG: Eaton ESR safety relay ESR4 safety relay ESR5 safety relay safety relay dual channel safety relay emergency stop relay light curtain safety relay contact monitoring relay enabling paths EN IEC 60204 stop category