On Saturday, 23 March 2019 09:23:54 UTC, ARW wrote:
On 22/03/2019 20:18, wrote:
On Thursday, March 21, 2019 at 11:29:13 PM UTC, ARW wrote:

If you go ahead with it I'll post a few more tips than the wiki article
about real life CU swaps.

I'd be interested in that anyway if you have the time? Would it be worth adding to the article?


John or NT usually add anything worthwhile I post to the wiki.

So here are a couple of tips that would apply if I had more than 2 hours
to swap a CU!

1. Charge up your cordless drills.

2. Start early and give yourself plenty of time.

3. Mark off the live cables with a sharpie pen well before you start,
ideally the day before. I use a series of dashes to identify the circuit
numbers. Write down a schedule of what dashes represent which circuit.
Take a photo.

4. Prep up the new CU as early as you can. Forgot the knockouts that
come with metal clad CUs and get out the jigsaw and make your own. Its
much easier to have a slot instead of a series of holes. If possible do
this the day before and superglue on some grommet strip.

5. Have a supply of spare cable and crimps ready to extend the cables.
If you are running out of time use strip connector and finish off with
crimps another day in your own time without rushing. Or use WAGO.

6. After removing the old CU you should, if required and it is possible,
reorganise the layout of the cables and the tails to suit the layout of
your new CU.

So if fitting a split load CU you would put the upstairs sockets next to
the downstairs lights etc. Prepare your preferred layout to match the
markings you have made on the cables the day before so you can write it
down.

This does not apply to an all RCBO setup (other than the two cables of a
ring might need to be placed next to each other).

In particular to the OPs setup I would not be surprised if all the
cables drop down from the ceiling and could not all be freed up and
organised in any layout he wanted.

7. After organising the layout of the cables tape the ends of each
circuit together ie LNE of upstairs lights or if a ring tape them as a
pair. Labelling the tape also helps as the tape will probably be over
the cable markings.

This will help you get get the cables into the new CU and stop neutral
mix ups

8. Think about the exact positioning of the new CU. If the OPs existing
CU was mounted right up to the ceiling then the front cover would not
fit. Hence it is 5mm below the ceiling. The same might apply to your new
CU. BTDTGTT.

9. If going all RCBO take out an insurance policy when buying the CU. ie
buy a 6A and 32A MCB when you buy the CU. Use them instead of RCBOs if
you have a nuisance trip and it will give you time sort out the cause of
the fault in your own time. If fitting a split load CU you have to leave
a non RCD space available to do this (not all split load CUs have a non
RCD side)

10. The wiki covers the second fix of the CU. However I usually put the
tails, earth and bonding earths in first followed by all the circuits
earths.

11. Go back a week later and recheck the tightness on all the terminals.

And test your ciruits beforehand, so you don't end up with a partly nonfunctional system for a while.


NT