TT System with Upgraded DB/CU

[cliffed]

Thanks for all comments….seems like an interesting outcome… especially in the factory assembled DB/CU where no Mcb required for the SPD.
Looks like the outcome …here it’s ok to leave the Mcb in situ

 

[davesparks]

What’s the correct SPD for the TT system

One where the manufacturers state it is suitable for TT systems, you just have to check the specs on it.

 

[pc1966]

Just to add that on looking for something else, I found the connection types (1+1 vs 2+0 sort of idea) in the 18th AM2 under 534.4.3 and the related table to determine suitability with TT under Table 534.5 where the 2+0 is only suitable down-stream of a RCD, while the 1+1 style is acceptable.