Possibly - for us (or at least this one) slow coaches what take a /lot/ longer - fill a flask and cook the bacon before you start?
I suppose there'd need to be a new category of "only if you are terminally slow" to mention that if you happen to have an isolating switch after the meter, spare tails, a Henley block and space to relocate the old CU with one or two circuits temporarily it's possible to work with the comforts of home - and of course the frisson of managing 2 sets of tails, 2 main switches, ....
Hmmm.. recent fiddling with ceiling roses (electrician fitted during the last 12 months) indicates that twisted earth wires may loosen over time. This version has a large brass post with ample space for three twisted earth wires. Of the 5 sets 3 were very slack. I suppose the driver needed for tightening the other shrouded terminals would be inadequate for the bigger earth screw. Or possibly that twisted solid cores can migrate?
Adam (and everybody else) - thanks for the very helpful comments and suggestions which I will take on board. Good to have some affermitve feedback rather than a list of reasons why this job can't be DIY.
I'll post some feedback on how it goes, but it may not be for a few weeks.
Make sure you have plenty of light, and try and find a way of getting comfortable to work - be it suitable ladder or stool to stand / sit on, and perhaps even some coats / cushions etc to prop against in those horrible understairs cupboard working situations.
(for the latter, taking the cupboard door off its hinges can yield a bit more wriggle room)
Must admit I don't think I have ever timed doing it...
I don't think twisted cores are any more vulnerable to loosening, if anything they're less so, as you're less likely to end up with one weakly gripped. Screw connectors are known for coming loose, especially if not done up well to begin with.
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.
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
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
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.
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?
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.
There was a time a "normal" CU and MCBs could have costed that - so not a bad deal.
Yup I have noticed that on old CUs a number of times. Hence the comments last time to go back in a few weeks and tighten again after the copper has had a chance to "relax".
Yup I said that to myself when I did the main one here ten years ago... :-)
(in reality I did need to do a bit of tidyup some time later as I wanted to move the kitchen onto its own RCBO - and that forced a bit of cable trimming to get it all fitted in there).
Yup its a common issue - especially if the lighting circuits are old. Good move having the 6A MCB to hand.
On many, just undoing the screw on the MCB "all the way" will force the back of the cage to the back of the recess. Even if creating an opening far wider than required for the wires in question, it is a way of ensuring they all go in it, and not behind it.
20mm hole saw is often easier.
Not all CUs are small - so they have to give you enough slack to cope with most situations. Its far less annoying to have to trim them down, than needing to extend them. If trimming it makes sense to keep them long enough that they can still fit in multiple positions in the CU - so cut a bit longer than the "right" length in most cases.
This may add to the expense unless you can borrow one but using a screwdriver with a torque setting ensures you get all the terminal screws correctly tightened. As I was adding the last circuits to my garage CU I checked the ones I had done a couple of weeks before and they were still spot on. If you have to buy one Toolsatan do a Draper for £65 which is probably the cheapest around.
Whilst on the subject, I was tempted by the BG CU with the mini RCBOs until I read a review by an electrician that as he was torquing up the terminal screws the casing on the RCBOs were distorting and tending to split before he achieved the recommended torque even though his driver was recently calibrated.
I did see a couple of electricans on youtube using torque screwdrivers to finish off working on a CU. I did check the prices - around £65 as you say - but decided not to bother as I'm unlikely to need to do this again anytime soon.
I also noticed the body of the RCBOs flexing when I was doing the final tightening. There must be a reason these are nearly half the price of say the Hager RCBOs.
Shurely after the first 20 gallons had gone the temperature of your "hot" water would be literally diluted by replacement incoming mains cold? Bagsy first shower!
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