KM2604 by Beckhoff

The KM2604 is a relay output terminal manufactured by Beckhoff for the KM Bus Terminals series. Installed on a DIN rail beside a bus coupler, it places four electromechanical changeover contacts under PLC control so that line voltage can be switched through the low-power K-bus system. This arrangement lets distributed automation panels control motors, solenoid valves, or lighting circuits without routing the switched voltage back to the central controller, reducing wiring and cabinet space.

The relays have a breaking-current rating of up to 16 A and can withstand a maximum switching voltage of 400 VAC, enabling direct control of compatible single-phase loads. Electrical contact endurance is rated for 1 × 10⁶ cycles, while the electronics draw only 15 mA from the K-bus so that large terminal groups do not overload the backplane. The IP20 housing is intended for closed control enclosures where protection against finger contact is sufficient. Each relay coil is energized from a 24 VDC supply, separating actuation power from the switched circuit and simplifying common power distribution. Continuous current through a closed contact can remain at 16 A, providing the required capacity during steady operation.

The terminal tolerates a cold inrush current of 30 A, helping it switch capacitive or incandescent loads when they are first energized. The module contains 4 changeover contacts, and its process image provides four outputs so that the PLC program can address each contact individually. To avoid contact oxidation, the relay requires a minimum switching load of 5 mA at 10 VDC when handling low-level signals. Each active relay coil draws 50 mA, which must be considered when sizing the 24 V field supply. Mechanical endurance reaches 5 × 10⁶ cycles, and the lack of manual operation prevents accidental overrides of automated sequences. Rated working limits of 250 VAC or 30 VDC accommodate common control and signaling duties in industrial panels.