---
title: "WDT-4 Modbus watchdog relay with fallback control | GridBit"
description: "WDT-4 is a DIN-rail redundancy controller. When the modules on the Modbus bus or the module itself stop working, it switches over to an external photo sensor."
url: "https://www.gridbit.tech/hardware/wdt-4"
language: "en"
translation: "https://www.gridbit.tech/bg/hardware/wdt-4"
---

# WDT-4

Modbus watchdog relay, fallback to photo sensor or clock

[Request a quote](https://www.gridbit.tech/contact?product=WDT-4)

- **Relay contact**: Normally open
- **Max. relay voltage**: 250 VAC
- **Modbus RTU**: RS485
- **Supply voltage**: 9 to 36 VDC

Overview

## Where it works

WDT-4 is a DIN-rail redundancy controller. When the modules on the Modbus bus or the module itself stop working, it switches over to an external photo sensor or clock. Its built-in relay operates when Modbus communication is lost, and it runs on 9 to 36 VDC.

Mounting: 35 mm DIN rail (IEC 60715)

1. Automatic switching of the relay contacts to the NC (normally closed) position when Modbus communication is lost (emergency mode)
2. Automatic switching of the relay contacts to the NO (normally open) position when Modbus communication is present (normal mode)

WDT-4 watchdog module, three-quarter view

Datasheet

## Technical data

### General

- **Redundancy module**: Modbus module that monitors the operation of a GWU module

### Power supply

- **Supply voltage**: 9 to 36 VDC
- **Consumption**: max. 35 mA

### Relay output

- **Relay type**: Electromagnetic relay
- **Contact type**: Normally open
- **Maximum operating voltage**: 250 VAC
- **Maximum contact current**: 5 A (AC-3), 1 A (AC-1)

### Communication

- **Interface**: RS485
- **Protocol**: Modbus RTU

### Environment

- **Operating temperature**: -20 to 60 °C
- **Storage temperature**: -20 to 80 °C
- **Relative humidity**: below 95 %, non-condensing

### Status LEDs

- Green On External power supply to the controller present

Installation

## Dimensions and connection

Dimensions in mm

On a 35 mm DIN rail

Systems

## Used in

Street lighting

### [Street lighting management](https://www.gridbit.tech/solutions/street-lighting)

Control and monitor street lighting cabinets from one system, with schedules that follow sunrise and sunset, measurements per phase and alarms for every cabinet.

Learn more

[Previous WDT-1 Watchdog relay that restarts devices when Modbus communication stops](https://www.gridbit.tech/hardware/wdt-1)
[Next GWU-5 4G LTE gateway for Modbus devices, with Ethernet and MQTT](https://www.gridbit.tech/hardware/gwu-5)

### Transport, warranty and maintenance

- **Transport and storage**: Protect the module from shocks and avoid extreme conditions. Store it in the original packaging.
- **Warranty**: Two years from the date of manufacture against manufacturing defects. Modifications to the product after the publication date of its documentation release the manufacturer from liability. The manufacturer is not responsible for typographical or other errors in the documentation.
- **Maintenance**: Under normal conditions the module needs no maintenance. Light dirt comes off with a dry or slightly damp cloth; for heavier dirt use non-aggressive cleaning products. Always disconnect the power supply first, keep liquids out of the housing and reconnect the power only when the module is completely dry.

## Ask for a WDT-4 quote

Tell us the quantity and the project. We answer with a price and lead time.

[Request a quote](https://www.gridbit.tech/contact?product=WDT-4) [office@add-bg.com](mailto:office@add-bg.com)