3 phase supply to garage

[Steve dandy]

I am currently installing a 3 phase supply to an outbuilding. I'm currently updating qualifications as have been out of electrical work for 10 years and have decided to return. I have a house with a 3 phase head . I propose to fit a 3 phase meter  cupboard adjacent to existing 3 phase cupboard,  using Henley blocks. The head is tncs. I was going to put a 3 phase switch fuse with swa underground in duct to feed 3 phase distribution board . I propose to make outbuilding tt system and use rcbos on sockets, and  sauna . I was going to connect armouring at switch fuse but not at other end so the outbuilding is in its own earthing system.  Is this correct? Help pls not sure if I need to 4pole rccb time delay 100ma before switch fuse to protect swa supply

 

[Sidney]

Are there any extraneous conductive parts that require bonding in the garage? Water/gas/steel frame etc

If no bonding is required then I would consider maintaining the supplied earth to the garage.

I wouldn't provide RCD protection for SWA unless 30mA RCD is required for additional protection or earth fault disconnection requirements cannot be met.

Also the sauna is a special location, section 703, and will need to be installed accordingly.