New DB (additional)

westward10 · Jul 31, 2019

I wouldn't lose too much sleep over selectivity you can only play with what you have.

TheReturnOfHightower · Aug 9, 2019

Okay, so I think I've made my mind up and wouldn't mind a sanity check. There's a couple lighting circuits that don't pull much so I'm going to join them in to the same breaker, creating a spare way. Then, C63 MCB as a distro circuit, running in SWA to a little 2-way DB in the room where the new circuits are going, running 2 x B32 RCBOs - they won't be anywhere near 32A at full load, but need 2 circuits as it's computer equipment and would likely trip the RCBO if all lumped together.

Should get away with 10mm SWA for CCC, but was going to install 16mm just to keep the Zsdb as low as possible. Run will be around 8m for SWA from the upstream DB, and then the 2 circuits are RFCs ran in 4mm (again, to keep that Zs down).

All sound tickety boo?

Deleted account · Aug 9, 2019

If your using C type breakers I think I would change this to B type then you’d get away with 10 mm SWA. Probably.

That’s if you where going to use C type.

davesparks · Aug 9, 2019

TheReturnOfHightower said:
Should get away with 10mm SWA for CCC, but was going to install 16mm just to keep the Zsdb as low as possible. Run will be around 8m for SWA from the upstream DB, and then the 2 circuits are RFCs ran in 4mm (again, to keep that Zs down).

If there is a problem with the Zs of the existing submain then that needs to be sorted out rather than oversizing new cables to try and achieve compliance.

TheReturnOfHightower · Aug 9, 2019

davesparks said:
If there is a problem with the Zs of the existing submain then that needs to be sorted out rather than oversizing new cables to try and achieve compliance.

If there was a problem with the Zs of the existing submain, I wouldn't be able to get that Zs down no matter what I did. The Zs is fine - I'm just conscious I'm extending on to a long submain anyway. However, it is only a half dozen metres so I'm probably overthinking it with 16mm. I'm going to take some readings this afternoon and then I will do my cable calculations properly to ensure that circuit Zs's will be compliant.