(Apologies to the group in advance, since I am not sure how much of this rambling is actually a question as such, so much as just an exercise in writing down all the options hence clarifying my thoughts!)
I will shortly get round to replacing my consumer unit. The current one is well behind the times (rewireable fuses, no RCDs etc), and has insufficient free ways to accommodate the new circuits I need to add. The setup is a TT (overhead cable) 60A supply. The meter tails are currently split in a Henley block. One connection goes to current CU via an old ELCB, the other goes to dedicated 30mA RCD then via SWA to outbuildings (which have their own CUs and sub mains). It does not appear that there is any over current protection installed for the feed to the outbuildings at the source end (although there is at the far end).
One difficulty is lack of space for locating a new CU if it is much larger than the current one. So a split load CU will not fit. Hence, given the following alternatives, which would be preferable?
Option 1
Replace CU with 8 way unit (about the widest that will fit). Install
100mA Trip Time delayed RCD in main switch position. Install regular MCBs for lighting and smoke alarm circuits, use single module RCBOs on the 4 final ring circuits.This would seem to be compliant with the regs and give the required fault isolation and discrimination between RCDs. The limitation is high cost and no further expansion available (all 8 ways would be used).
Option 2
as above but but place 100mA Time delay RCD in separate enclosure before CU to allow possibility of adding additional CU later.
Option 3
Install two CUs fed via a main switch in a separate enclosure. Install
100mA standard RCD in one, and 30mA standard RCD in second. Connect all final rings to 30mA RCD CU, and everything else to 100mA RCD CU.This gives lower cost (no expensive time delay RCD or RCBOs) and more expansion potential, but reduces fault separation of final ring circuits (and leakage budget available per final ring circuit) since they are now all sharing one RCD. Having said that, this setup would seem to be a functional equivalent to having a single split load CU. If there were a problem with nuisance tripping then there is also the possibility of moving high leakage circuits (i.e. the kitchen ring) to the higher trip current CU on its own RCBO.
Option 4
As option 3, except use RCBOs in place of MCBs and have a standard switch in place of overall RCD. This gets the good fault separation back along with the high price, but also allows for future expansion.
Questions:
Any options I have missed?
Which option would you go for?
How many sets of tails fit into one Henley (only 16mm Sq by the look of them)?
The chances of all the existing circuit wires reaching their new CUs is slim, and hence some will probably need extending. Given that there is not enough wall space for a pile of junction boxes, I would have to resort to crimped or soldered connections. What is an acceptable way to provide overall insulation for said extensions? Heat shrink?