andyscotland

Not quite the same, but my garden office is a SIPS build and certainly with those the OSB sheets that are sandwiched either side of the floor insulation run right to the outside edge and the walls sit on top. My uniformed hunch is the expansion gap is important if the board terminates against a wall, to stop it pushing on the wall/bowing when the board expands. But less important if the wall sits on top, as in theory then the whole assembly can grow/slide slightly sideways. As an aside, how will you be insulating your floor?

Glad you've found the cause and got a solution. Assuming it's 2.5mm2 cable a 20A radial is fine unless it's covered by insulation for any significant length? There's a little confusion here. You're right that BS7671 is non-statutory and only represents one way of achieving compliance with the legal requirements for electrical safety. However the requirement to notify Building Control of certain electrical work in England & Wales is statutory - it comes from regulation 12(6A) of the Building Standards Regulations 2010. BS7671 doesn't include any requirements for notifying, or any specific definition of competence. There is however a bit of a grey area in your case : the only notifiable work defined in law is installing a new circuit, replacing a consumer unit, or circuits in a special location (bath/shower room etc). Other repairs, alterations & replacements are outside the scope of that regulation. I'm not sure whether replacing the existing protective devices on the existing circuits without replacing the consumer unit itself would trigger that requirement (though it probably falls at least within the spirit of the law, if not the letter of it). As @Nickfromwales says, if you're the only person there, and you are confident you have the skills to do a good job, then I suspect it's fairly unlikely you'd get caught. Equally there are some things that can go wrong. For starters, you will need a proper torque screwdriver to ensure that the terminations are at the right torque to avoid fire risk from damaging the cable by crimping it too tight, or arching by having it too loose. You'll also need to ensure the new protective devices are suitable for the board (mechanically , heat dissipation between devices , etc) - e.g. from same manufacturer and same generation. Moving from MCBS to RCBOs can also throw up various faults - e.g. from incorrect connections between neutrals from different circuits - that can be time consuming & faffy to trace especially if you don't have proper test equipment. So depending how much the spark wants to charge, you may find there's a benefit to getting a spark to take that all on for you, in which case you will also have the right paperwork if the council ever do get involved.

Historically, in most cases people used 2-core SWA for single phase circuits, using the outer steel armour as the CPC (earth). This is often ok in principle although it does need to be checked/calculated as the resistance of the steel isn't always appropriate for the circuit. Many people (including me) these days prefer to use a copper core for the CPC even if we could theoretically use the armour. The resistance is better from day 1, less to check, and armour and its terminations often corrodes & degrades over time. The sheath still needs to be earthed at at least one end to protect the cable, but is not officially part of the circuit. 3-core SWA was traditionally used for balanced 3-phase loads e.g. motors, as these do not have a neutral. This is why the cores are coloured for the three live phases (brown, black, grey). You can use that cable for a single phase circuit if you sleeve the cores at both ends. However there are manufacturers now making it in the correct colours (brown,blue,green&yellow) and it would be better practice to use this - it's fairly easy to source. This all assumes that it is ok to export the supply earth to your outbuilding. That depends on a number of factors including distance, type of construction of the building, whether any other services are present etc. It may not be safe to use the house earth - if not then you would use a 2-core cable with the armour earthed at one end and then fit an earth spike. Bear in mind for cable sizing, voltage drop needs to be considered to the furthest point of your circuits (e.g. including the wiring within the man cave) and you also need to consider the Earth Fault Loop Impedance for the circuits to suit the type(s) of protective devices. I'd almost always go up a size for something like this: the extra cost is marginal and it buys you a lot of future-proofing. You only want the hassle of running the cable once. To be honest as you can maybe see there are a few site-specific things that need to be checked/calculated to do this safely. Terminating SWA properly also takes a bit of skill/experience. This is therefore quite an involved job to attempt without an electrician to advise - it's beyond the normal realm of DIY (and I think notifiable in England & Wales? Not sure as I'm in Scotland and our rules are different). If you are keen to do it yourself then you'll probably want to do more research on some of the things mentioned above, and you'll definitely want to buy extra cable to have a practice before you attempt to terminate the real thing.

This is a very good point. I'd assumed as this is indoors then the source of the leak has been identified & fixed but you're right OP doesn't specifically say so.

I wouldn't necessarily expect corrosion/damp within the cable sheath to cause an issue of itself - the sleeving on the phase and neutral cores should in theory be enough to insulate them from the CPC and any contamination around it. However it's possible in practice that the inner insulation is degraded or cracked (especially if the cable has tight bends and/or is old) which has allowed liquid or salts to migrate into the gap and reduce the resistance. It's also possible the hydrochloric acid has damaged it - in theory I think that's compatible with pvc but I think it depends on the exact makeup of the plastic. I'd certainly agree that I'd start by suspecting this cable if I was fault-finding, unless I could prove it was fine. Yeah in that case I'd ignore that, it's a very acceptable result for a complete energised installation. Yep - faults like this will generally require a higher voltage to overcome the initial resistance of the fault. An insulation resistance test needs to be done at 250/500/1000V to give meaningful results (voltage depending on the characteristics of the circuit and whether any sensitive devices are connected).

If it's on the ceiling and relatively sheltered you might be ok, though I'd leave it as short a time as possible. If you don't need access through the front during that time, could you temporarily board up the opening with some OSB or similar? A couple of sheets would be fairly cheap compared to the cost of redoing the ceiling. If you do need access, maybe you could still put some boarding/protection as a "skirt" across the top section of the opening to prevent wind-driven rain etc from getting to the front edge of the plasterboard.

Personally I wouldn't spend too long chasing that - unless you confirm that it's entirely from the suspect circuit and there are no appliances of any kind connected (including sockets with built-in usb chargers etc). That sort of leakage would be quite normal once you have a few electronic circuits connected as they often intentionally leak to earth as part of electromagnetic interference protection circuits etc. It's nowhere near the 30mA that would be required to trip the RCD and well within the 30%-of-tripping-current safe limit whhich would be 9mA.

As @Mattg4321 says you really need to test the resistance between cores. Your continuity tests have proved that the copper is not broken/damaged. However that doesn't tell you anything about whether there's a section of insulation either damaged (e.g. by rodents) or bridged (e.g. by water). If you're only testing continuity of each core separately then the other cores are not connected to the test circuit, so even if there was a dead short somewhere the test current will flow entirely within the core you're testing and give you the continuity result you expect.

My wife has 🤣

Thanks @saveasteading. I wasn't so much concerned about heat loss as condensation risk at the bottom of the timber. But fair to say I've learned quite a lot in the subsequent 6 years! My experiment is going well so far, will just have to keep fingers crossed that it continues to do so...

I went with @PeterW's plan of laying a thinner section of PIR with 400mm rip of 18mm OSB on top to spread the load. I fixed the OSB down into the slab with hammer in fixings, with mastic around where they pass through the DPM. Then laid the VCL continuous across the whole floor (above the PIR, but the PIR is on the warm side of the insulation) and then screwed the sole plates down into the OSB. Can't comment on BC as I am not yet complete 🤣 and they've not been out to do any inspections as it's a "small" project. However I can say that the stud walls have now been there for 5 years 🤦‍♂️ and no sign of movement or issues.

I may be wrong, but I *think* it's essentially the same product, made by staff who originally worked on CT1 and then split off to do their own thing after the company was sold or something like that. I've used it quite a bit and it's worked well.

Absolutely, about all you can do at this point. Was more just noting for anyone that encounters the thread in future if they've not yet had work done.

Yep. Indeed - although, technically, an EICR is not as in-depth as the EIC that should be done for significant works and in particular doesn't involve anyone actually certifying that the work is safe and compliant. Generally speaking, yes - much more so than in the past - but not in every case. There are still faults that can exist and leave the installation in a potentially dangerous condition without immediately tripping a breaker. Well indeed, it's always sensible to assess the install for selfish reasons before you end up being responsible for fixing things you didn't break 🤣

IMO, you need one to know that the work was done properly by someone competent to do it. It should be a fundamental part of a board change to do the inspection & testing required to know it's connected up correctly, protective devices will function as expected, and the resultant installation is within safe parameters. If the installer has done those checks, why wouldn't they document them in the form required by BS7671? If they have not, then what other corners have they cut? Note: this is not about whether you get a NICEIC/ECA/Part P/whatever cert - I have mixed feelings about the value of the various pay-to-play registration schemes, and it's reasonable to avoid them if you are understand what you're getting/not getting/potentially saving by going that route. But the basic form of certificate is available free of charge and can be issued by any electrician and therefore should be.