BECKHOFF BC7300 - Manual (Page 13)

Basic Principles
BC7300 13
Plugging together the power contacts creates a supply rail. Note the circuit
diagrams for the Bus Terminals, since some Bus Terminals do not loop
these power contacts through, or only do so partially (e.g. analog Bus
Terminals or 4 channel digital Bus Terminals). The potential feed terminals
interrupt the power contacts, and represent the start of a new supply rail.
The Bus Coupler can also be made use of to feed the power contacts.
Insulation testing
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. Note that, for reasons of
electromagnetic compatibility, the PE contacts are capacitatively coupled to
the mounting rail. This can both lead to misleading results and to damaging
the terminal during insulation testing. (e.g.: breakdown of the insulation
from a 230 V power user to the PE conductor.) The PE conductor to the
Bus Coupler must be disconnected for the insulation testing. In order to
uncouple further feed locations for the purposes of testing, the feed
terminals can be pulled at least 10 mm out from the connected group of
other terminals. In that case, the PE conductors do not have to be
disconnected.
The “PE” power contact must not be used for other potentials.