BECKHOFF BK3xx0 - Manual (Page 22)

Notes on the Documentation
20 Fieldbus Components
BKxx50 and BKxx51
The Bus Coupler / Bus Terminal Controller require a 24 V
DC
supply for their operation. To meet the UL requirements
use 4 A fuse or class 2 power supply!
The connection is made by means of the upper spring-loaded terminals labeled Us and GNDs. This supply voltage
feeds the Bus Coupler / Bus Terminal Controller electronics and, over the K-Bus, the electronics of the Bus
Terminals. It is electrically separated from the potential of the field level.
UL requirements
Danger
For the compliance of the UL requirements Us should only be supplied
•
by a 24 V
DC
supply voltage, supplied by an isolating source and protected by
means of a fuse (in accordance with UL248), rated maximum 4 Amp.
•
by a 24 V
DC
power source, that has to satisfy NEC class 2.
A NEC class 2 power supply shall not be connected in series or parallel with an-
other (class 2) power source!
Danger
To meet the UL requirements, Us must not be connected to unlimited power sources!
Power contacts supply (Up)
The bottom six connections with spring-loaded terminals can be used to feed the supply for the peripherals. The
spring-loaded terminals are joined in pairs to a power contact. The feed for the power contacts has no connection to
the voltage supply for the Bus Coupler / Bus Terminal Controller.
The spring-loaded terminals are designed for wires with cross-sections between 0.08 mm² and 2.5 mm².
The assignment in pairs and the electrical connection between feed terminal contacts allows the connection wires to
be looped through to various terminal points. The current drawn from the power contact must not exceed 10 A for
long periods. The current carrying capacity between two spring-loaded terminals is identical to that of the connecting
wires.
Power contacts
On the right hand face of the Bus Coupler / Bus Terminal Controller there are three spring contacts for the power
contact connections. The spring contacts are hidden in slots so that they can not be accidentally touched. By
attaching a Bus Terminal the blade contacts on the left hand side of the Bus Terminal are connected to the spring
contacts. The tongue and groove guides on the top and bottom of the Bus Coupler / Bus Terminal Controller and of
the Bus Terminals enables that the power contacts mate securely.