user manual

Appendix C Technical data for the 7951
Page C.16
Earthing requirements for group 2 connections only
The status inputs do not have to be earthed because the circuitry contains only opto-electrical components.
Earthing requirements for group 3 connections only
These depend on what sort of installation you have and the environment in which it operates. You therefore have
to decide what earthing arrangements you need. It is likely that this group has to be earthed at a zener barrier
earth. For further information, refer to the documentation for the external devices which are connected to the
installation.