The site has two buildings (A&B) each with a 3 phase mains supply and its own earth. One is TN-C-S, one is TN-S.  I wish to run one of the phases from building A into building B.  The supplies come off the DNO road cable approx. 100m apart.  I am interested in what options there are for providing an earth for the phase from building A running into building B.  I can see two options but am looking for advice about whether either of these would be acceptable.  The options are:

1. Connect the two earth's together.

2.  Use earth A up to the building but earth B inside the building.