What is 3-wire connection?
Sentera -G sensors require a supply voltage of 24 VAC or 24 VDC. They can be connected with a 3-wire electrical cable - that's why this is called a 3-wire connection. The ground connection of the supply voltage (V-) is internally connected with the ground of the analogue output (GND). It is called a 'common ground'. This means that only 3 wires are required to connect the supply voltage and the analogue output.
Sentera -F and -H sensors do not have this internal connection. For that reason, these sensor types require a 4-wire electrical cable to connect. Their ground signals of the supply voltage and analogue output must be connected separately. For this reason, it is recommended not to combine -G with -F or -H type sensors on the same network.
Never connect the common ground of -G type articles to other devices powered by a DC voltage. Doing so might cause permanent damage to the connected devices.