Extending Main LV switch panel busbars with directly connected cables

I feel a bit queasy about this depending how it has been done. The cables need to be protected against short circuit which the upstream protection will probably provide. In addition they need to be protected against overload.. If the upstream protection does this then happy days or the panel board has an MCCB main switch does this then again happy days. If not non compliant with BS 7671. I would want to know if the integrity of the main panel has not been compromised.

You can look at this from two perspectives:


1 - The cables form a part of the original switchboard and would be described in the standards for the switchgear as "unprotected conductors" - so may ned to meet enhanced temperature ratings etc


2 - They are an outgoing circuit and need to be protected  - as John highlighted, they need short circuit protection, earth fault protection and overload protection - The two initials requirements can be met by the 1250A ACB, and the latter if either the downstream 630A board has an active overload protective device or by design the load from that board is always less than the nominal 1000A rating of the tails (and the 630A rating of the board) or the collective rating of the outgoing ways provides overload protection then all is well


What may be less obvious is the short circuit rating of the assembly and any compromise of the form of separation of the original switchboard.


On balance, it sounds like a pretty normal "extension" where a client isn't prepared to swap out the original switchboard just to get a spare way


Regards


OMS