Power Supply Unit 320 mA

The power supply unit N 125/12 provides the system power necessary for the instabus KNX. The connection to the bus line is established by clicking the device onto the DIN-rail (with a data rail installed) and/or via the bus connection block located on the front side. If the power supply N 125/12 is installed the bus connector module REG 191 is not necessary (also for other DIN-rail devices connected to the same data rail) because the bus voltage is carried inside the device from the bus terminal block to the data rail.

The integrated choke prevents the data telegrams from short-circuiting on the bus line. When the built-in reset switch is operated (operation > 20s), the bus devices are returned to their initial state.

For each bus line, at least one power supply unit N 125/12 is needed. Up to two power supply units may be attached to a single bus line. A second unit is not required unless the supply voltage at a bus device is less than 21 V.

Note: If two power supply units N 125/12 are operated in parallel on one bus line and if the overload LED is lit on one or both power supplies, then the bus configuration has to be changed until the overload display disappears. The cable length between the two power supply units N 125/12 operated in parallel is not prescribed. When more than 30 bus devices are installed in short bus cable distance (e.g. 10 m), e.g. in distribution boards, the power supply unit N 125/12 should be arranged near these bus devices. The distance between power supply unit N 125/12 and any of its bus devices must not exceed 350 m.

The power supply unit N 125/12 has a voltage and current regulation and is therefore short-circuit proof. Short power failures can be bridged with a backup interval of approximately 200 ms.

To ensure an uninterrupted power supply a separate circuit with safety separation should be used for the power supply unit N 125's power supply line. The power supply units N 125/12 can supply DC 24 V power from an additional pair of terminals (yellowwhite). This DC 24 V output voltage can be used to power e.g. an additional line via a separate choke N 120. The power supply units N 125/12 can be powered by AC 120…230V or by DC 220V.