The ground floor receives a TN-C-S feed from which a TN-S feed is taken for the upstairs flat, along with a 6mm earth cable from the TN-C-S earth block. Both flats share the same water supply. The upper TN-S cable has a simple earth clamp instead of being properly soldered to the sheath. My feeling is to run a 16mm earth upstairs from the TN-C-S earth block. Am I correct?