Siemens Fail-safe Relay Output Electronic Module for the SIMATIC ET 200S 6ES7138-4FR00-0AA0

Siemens 6ES7138-4FR00-0AA0 – Overview

The Siemens 6ES7138-4FR00-0AA0 is a fail-safe relay output electronic module for the SIMATIC ET 200S distributed I/O system used with SIMATIC S7 automation controllers. It provides one safety relay output (F-RO) with two normally-open (NO) contacts, designed to control higher-voltage loads in safety-critical automation systems.

This module is typically used when a fail-safe PLC (F-CPU) must switch external devices such as contactors, solenoids, alarms, or shutdown circuits while maintaining functional safety compliance. 

Description

The 6ES7138-4FR00-0AA0 is a fail-safe relay output module that allows safety controllers to switch loads up to 230 V AC or 24 V DC using relay contacts rather than transistor outputs.

It is installed as a plug-in electronic module in an ET 200S station, where it interfaces with the PLC via a fieldbus such as PROFIBUS or PROFINET through an interface module (e.g., IM151).

Key functional characteristics include:

• 1 safety relay output channel

• 2 normally-open relay contacts

• Capability to switch AC or DC loads

• Integration with PROFIsafe safety communication when controlled by fail-safe output modules (e.g., F-DO modules).

• Designed for high safety integrity applications such as emergency shutdown circuits.

Typical applications include:

• Machine emergency stop circuits

• Motor contactor control

• Safety shutdown systems

• Industrial automation safety loops

Key Technical Specifications

Safety Ratings

When used in a fail-safe configuration, the module supports high functional safety levels:

• Category 4 according to EN 954-1

• SIL 3 according to IEC 61508

• Performance Level e (PL e) according to ISO 13849-1

These ratings allow the module to be used in high-risk industrial safety systems.

Electrical and Relay Characteristics

Relay Output

• Contact type: 2 normally open contacts

• Thermal continuous current: 5 A max

• Suitable for switching AC or DC loads

Load & Installation Limits

• Maximum module current: 8 A

• Max group current:

  • 8 A up to 40 °C

  • 6 A up to 50 °C

  • 5 A up to 60 °C

Isolation

• Isolation between channels

• Isolation from backplane bus and supply voltage.

Diagnostics and Indicators

The module includes basic monitoring and indication features:

• LED status indicator (green) for output status

• Diagnostic capability via the PLC system

• Electrical isolation to improve reliability in industrial environments.

Mechanical & Integration Details

• Module width: 30 mm

• Installed on ET 200S terminal modules

• Operates within a SIMATIC distributed I/O station connected to the PLC network.

Typical use cases

• Safety interlock circuits

• Emergency stop output control

• Switching safety contactors

• Process plant shutdown systems

• Industrial machine protection systems

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