EL
BG
DE
ES
FR
ITGlossary · Communication and monitoring
Dry Contact
A passive relay contact used to transmit status signals without applying voltage.
Technical level:Intermediate
A dry contact works like a simple switch that opens or closes without supplying any voltage itself. The voltage comes from the external system that "reads" it, for example an alarm panel or a PLC. This keeps the UPS and the external system electrically isolated, and devices from different manufacturers can be connected without a special protocol.
On UPS units, dry contacts are used as outputs for signals such as on battery, low battery, bypass or fault. There may also be dry-contact inputs, for example for remote shutdown or for the emergency power off (EPO) button.
Before wiring, check the contact's voltage and current limits, as it is usually intended for low-voltage signals, and whether it is normally open (NO) or normally closed (NC). Do not use it to power loads directly.
Related terms
- TransformerAn electrical component that changes voltage levels or isolates circuits.
- Serial PortA communication port on a UPS used to connect and transmit signals to computers or monitoring equipment.
- Alarm ContactA relay output on a UPS that changes state on an alarm, such as battery mode, low battery or a fault, to alert an external system.
- ModbusA communication protocol used for connecting industrial electronic devices, including UPS systems.
- NUT (Network UPS Tools)Open-source software that reads the UPS status and shares it over the network, so that several servers and NAS devices can shut down in a coordinated way.
- SNMPA standard network protocol used to monitor and control devices like UPS systems over a network.