On Tuesday, 26 March 2019 19:46:41 UTC, ARW wrote:
On 25/03/2019 20:09, tony sayer wrote:
(perhaps with a little caution introduced if it sounds like the poster
is about to qualify for a Darwin award!)


+1


Although I have one more tip

It's probably worth having a practice run of removing the main fuse
before you start. I have very occasionally found that they will not
move. Not very likely to happen in the OP's case as it is a newish house
but still worth checking.

The Main Switch of the CU must be in the OFF position when fitting and
removing the main fuse.



Adam..


What's the latest on getting the distribution company putting a 100 amp
isolator switch in these days, do you still have to pay for it?..


Yes in my area if it is a request and not a new supply.

It's probably easier and cheaper just to fit your own.

--
Adam

Just following up on all the useful help and advice that was given in relation to swapping my CU.

I completed this task yesterday. Some notes and feedback which I hope may be useful for others considering doing this themselves.

In summary (to avoid reading back through the old posts), I am planning to fit an induction hob as part of a kitchen re-fit. This requires a 32A connection and there is no suitable connection available in the kitchen (I didn't want to extend/share the cooker connection which is on the other side of the kitchen). The CU is 25 years old, has no spare positions so a new CU was the way to go. Advice was (cost permitting) to go for RCBOs which I have done.

I bought a BG 10 way CU (just 100A isolator provided) and a set of RCBOs to match the current MCBs, plus some spare MCBs as advised (see later) to help with problem circuits. These were bought from TLC direct who delivered everything next working day (nearest store 20 miles away, and it was free delivery anyway). Total cost £205.

First observation (on receipt of the CU) - it is much smaller than it looks in the photos, and smaller than the current CU. Lesson #1: Check the measurements.

As advised, I marked up each cable with sharpie pen and backed this up with tape with the same information on each cable. The 3 ring circuits were individually paired. Took photos of the existing wiring. I have 3 separate lighting circuits and a mains smoke detector circuit. As part of previously turning off each circuit in turn, I have two lighting circuits on the ground floor which I planned to combine, and the upstairs lights would be combined with the smoke detector to both create 2 spare circuits in the CU (one being needed for the hob) and to make it obvious if there is a fault in the smoke detector circuit by having the lights not work.

I prepped the CU the day before - cutting slots in the top for some of the cables (and gluing in gromet strips) and fitting the RCBOs.

Saurday morning. Checked my meter was working by measuring the voltage in the CU. Then turned off each MCB before turning off at the outside isolator switch (no need to cut the seal and pull the fuse). Went back and checked that there was no voltage coming into the CU and then off it came. One thing I was surprised with (perhaps I shouldn't have been) was how loose some of the neutral and earth connections were. I've never checked the tightness of these connections in the 20 years we've been in this house. Perhaps that needs to be an annual check?

As part of the re-fit I checked there was continuity between the the two halves of the ring mains.

Given the smaller than expected size of the CU the cabling didn't go in as neatly as I was hoping. I could have shortended the length of some of the cables but decided at this stage the main job was to get power back on the house. A tidy up could wait for another day.

After a few issues with fitting the cables (see below) I had everything re-instated. Final check of tightness of every screw and a tug test on each cable then powered back up. All circuits came up apart from one of the combined lighting circuits which kept tripping. By trying each circuit in turn isolated the circuit with the fault and for now connected it to a 6A MCB to allow time for fault investigation. The lighting circuits were not on the RCB protected side of the old CU so this fault must have been present for some time. Will need to go around each of the lights to see if I can see where the problem is.

In total, with the fault investigation, it took 90 mins with a brief pause for a cold drink. I still need to fill any gaps with intumescent sealant which I'll do when I finally connect up the hob (cable has been run from the kitchen to the CU - what a chore that was - cutting holes in the ceiling at every joist which of course were perpendicular to the direction the cable needed to go). When I fit the cable next month I'll re-tighten all screws.

The CU has now been in for 24h. No nusance trips so far...

Some observations
1. The cable receptacles on the BG MCBs/RCBOs/Isolator switch are pretty shallow. I had to trim back every cable inc the tails down to 10mm
2. It is too easy to insert the cable behind the cable receptacle which meant the cable wasn't clamped. I had to remove 3 or 4 RCBOs to push back the clamp.
3. The CU case has a number of round "punch outs". These were recessed but there was no way (for me) that these were going to come out in any way other than by being cut out. Perhaps I needed a larger hammer and a more suitable drift?
4. Why are the neutral tails on the RCBOs so long? I didn't want to cut them (read somewhere that it was wasn't recommended to cut them). Perhaps if I had the appropriate crimps they could have been shortened but it was just a load of cable to tuck away behind the rail and which would make it much harder to replace a RCBO by having to unpick the neural wire.

Thanks again for the feedback and suggestions. My only regret is the cabling isn't neater. The only additional tools I purchased was a quality long nosed pilers and heavy duty cutters.