The Passiv Smart Thermostat uses RS485 Modbus to communicate between the Passiv Hub, the Passiv Programmer and the heat pump. To ensure reliable communication, suitable communication cable must be used.
Twisted pair cable is required and screened cable is recommended.
CAT5e or CAT6 ethernet cable is suitable and widely available. Only one of the four twisted pairs should be used. The three unused cables should be cut back. The colour of the twisted pair comms cable should be consistent across the device connections e.g. White core "A", Brown core "B", where the white and brown cores are from the same twisted pair.
CAT5e Shielded Twisted Pair (STP) Ethernet cable can be purchased from several retailers, including Screwfix, CEF and Amazon. CAT5e Unshielded Twisted Pair (UTP) Ethernet cable can be purchased from similar retailers. Cheaper CCA (Copper Covered Aluminum) cable should be avoided due to its more brittle nature, which can cause reliability issues.
Twisted pair comms cable is required to prevent electrical noise present in many homes. It may be an older TV, washing machine or any electrical device in the home. This electrical noise can be picked up by the low voltage communication wires using RS485. If the noise is too large it can drown out the signals sent between the Passiv Hub and the heat pump.
Screened cable is also recommended. The screening or shielding with a drain wire must be connected to earth. This creates a faraday cage around the wires and helps transmit the noise away, safely to earth. This is much like an earth wire used in mains wiring, creating an easier and safer path to earth in the event of a mains wiring fault.
Typically CAT5e cable is with 24AWG size cores. We recommend using ferrules (boot-laces) for connecting cables to the Passiv Hub and Passiv Programmer to make robust connections.