Potential Groups, Insulation Testing And Pe; Fig. 12 Potential Groups Of A Bus Terminal Block - Beckhoff BK3 0 Series Documentation

Mounting and wiring
3.4.3

Potential groups, insulation testing and PE

Potential groups
A Beckhoff Bus Terminal block usually has three different potential groups:
• The fieldbus interface is electrically isolated (except for individual Low Cost couplers) and forms the
first potential group.
• Bus Coupler / Bus Terminal Controller logic, K-bus and terminal logic form a second electrically
isolated potential group.
• The inputs and outputs are supplied via the power contacts and form further potential groups.
Groups of I/O terminals can be consolidated to further potential groups via potential supply terminals or
separation terminals.
Fig. 12: Potential groups of a Bus Terminal block
Insulation testing
The connection between Bus Coupler / Bus Terminal Controller and Bus Terminals is realized automatically
by latching the components. The transfer of the data and the supply voltage for the intelligent electronics in
the Bus Terminals is performed by the K-bus. The supply of the field electronics is performed through the
power contacts. Plugging together the power contacts creates a supply rail. Since some Bus Terminals (e.g.
analog Bus Terminals or 4-channel digital Bus Terminals) are not looped through these power contacts or
not completely the Bus Terminal contact assignments must be considered.
The potential feed terminals interrupt the power contacts, and represent the start of a new supply rail. The
Bus Coupler / Bus Terminal Controller can also be used for supplying the power contacts.
PE power contacts
The power contact labelled PE can be used as a protective earth. For safety reasons this contact mates first
when plugging together, and can ground short-circuit currents of up to 125 A.
24 Version: 4.3.0 BK3xx0