Not that I can think of. I take it the DBs are supplied by SWA or conduit or trunking with singles? Either way that DB and all the CPCs in it will still be connected to the main earth via parallel paths so taking the earth out will not make much of a difference and like I said the only test carried out with the main earth disconnected is the Ze test.So basically a Zdb is a Zs reading for an outgoing distribution board. Which clears up the misunderstanding with some of the previous comments.
Is there a reason / requirement why the engineer is telling us to disconnect main incoming supplie earthss for every Sub DB?