How to connect Dry Contacts

The SNMPv1/v2c/v3 enabled remote monitoring & control systems and the intelligent PDUs from manufacturer Didactum offer inputs for potential-free contacts / dry contacts. Many devices and important equipment use dry contact outputs / potential-free contacts to signals important notifications and alarms to control panels, automation and building management systems.

Connect these dry contacts to the Didactum SNMP monitoring hardware. The dry contact inputs are user definable (NO = dry contact normally open / NC = dry contact normally closed). In addition you can name each dry contact input e.g. UPS, air conditioning system and so on. Each Didactum Monitoring System can send notifications and alerts such as e-mail or SMS (via 4G LTE modem or 3rd party e-mail to SMS gateway). All events and status changes are stored in the syslog of the remote monitoring and control unit. In addition Didactum offers NMS integration for almost all Network Management Systems (NMS) such as Nagios, HP OpenView, OpenNMS, PRTG, WhatsUp Gold, and Zabbix.

Overview Dry Contact Monitoring Hardware

Remote Monitoring Product: Number of Dry Contact Inputs:Support of Dry Contact Expansion unit*
Didactum Monitoring System 502No
Didactum Monitoring System 100 DC4Yes
Didactum Monitoring System 2004Yes
Didactum Monitoring System 300 PoE4Yes
Didactum Monitoring System 4004Yes
Didactum Monitoring System 500 DC12Yes
Didactum Monitoring System 600 DC32Yes
Didactum Monitoring System 700 DC30/96**Yes
Didactum PDU 7004Yes
Didactum PDU 7504Yes

*Dry Contact expansion unit with 32 or 64 connections (optional equipment)

**optional equipment


Functioning of potential-free contacts / dry contacts

Potential-free contacts, also called dry contacts or floating contacts, are used to signal status and status messages. Switching is usually done via a relay. As the name suggests, the circuit is potential-free (without voltage).

Connection of a Dry Contact to the Remote Monitoring System

Plugs for connection of 2-wire dry contact cables are included in the scope of delivery of all SNMP monitoring hardware from manufacturer Didactum. Connect the wires of the potential-free contacts to the corresponding screw terminals (green plugs). Two dry contacts input cables share a common ground. After you have screwed the two-wire cable to the green plug, insert it into the numbered dry contact terminal on the Didactum SNMP monitoring hardware.

Important note: When connecting potential-free / dry contacts, the Didactum monitoring system must be switched off!


Cable assignment for SNMP monitoring systems

The monitoring hardware from manufacturer Didactum offers 2 different types of inputs for dry contacts / floating contacts:

  • One input contact, each with a dedicated ground connection (lower left graphic).
  • b.) Two input contacts share a common ground connection (lower right graphic).