UK Installing 50A Hot tub supply

[Janger92]

The earthing arrangement where the hot tub will be installed is formed in the TN-C-S system.
I want to install the sub-main distribution circuit from the main house consumer unit to the outside of the building to have a power source for the final circuits: hot tub, sockets and lights.
The supply cable is SWA going from the house consumer unit to the outside consumer unit, which will be installed in the TT system.
At the outdoor consumer unit, the SWA cable won't be terminated to the earth to provide separation between TNCS and TT.
SWA doesn't need to be protected by RCD, but I am confused about the situation when you transition from TNCS to TT.
- Do I need to install a fault protection delay time 100mA RCD at the installation's origin (house main consumer unit), or could it be only an MCB? The cable will be fixed to the outside walls.
The outside consumer unit will have 63A RCD type A and then some RCBOs for the final circuits.
If you have a different approach to installing this power supply, please let me know below
Thank you,

 

[Janger92]

No, I am not undertaking this installation. I am just collecting design installation and testing information about this project.

 

[James]

Post #1 reads very much like you are doing this installation in real life, not a theoretical case study.

 

[Janger92]

Post #1 reads very much like you are doing this installation in real life, not a theoretical case study.

At some point, I will be installing and testing this installation anyway, but in accordance with someone else design. I want to prepare my own project and confront this with other people from my company.

 

[James]

Great idea, design it how you think it should be done and compare that with the spec that you are given. Then you can ask the designer to discuss the differences between the two designs.