TT earthing question

[loplug]

I'm working on a Job where the earth is TT there is a sub main fed by 16mm twin and earth if I put a earth rod in at the submain position should I connect the cpc of the submain to the earth rod at the sub dB or just use it as a cpc and earth the sub board separately ?

 

[Welchyboy1]

Link all the tt earthing together, this will eliminate potential difference between points and also hopefully lower your total ra reading