Jeremy Harris

Down here they put a restriction into the local planning policy, that temporary accommodation needed to build must have a fixed time limit, not more than three years, I think. Having said that, I've never seen that applied to building an agricultural building, only either building a dwelling or having to be present overnight at an agricultural site for a justifiable reason (like my friend who needs to be there to deal with foxes at night). One question. What are the grounds for granting permission to live on site in a caravan? Surely they wouldn't have granted permission for this to build the stables, would they? If they granted permission for the caravan because of a demonstrated association with an agricultural business (my lady friend and her chickens again) then there would normally be quite stringent limits imposed as conditions. Worth a read of the full planning file, not just the online stuff, perhaps. On the other hand, I'm very inclined to agree with Jamie, do you REALLY want to waste a lot of emotional energy on a planning fight right at this moment? If it's an "easy win", where the planning enforcement officer does all the work then perhaps it's worth just nudging them in that direction, but otherwise I'd just let things go. Often, if someone wants to get around the planning laws they will, eventually, and it's pretty rare for local objections to have any significant impact.

It's a trick that used to always work down here - get PP for an agricultural building, get permission for temporary accommodation, then after the allotted span keep it there and get a lawful development cert. Our local authority stopped it by stipulating a time limit on temporary accommodation, and by applying stringent rules as to whether or not there was a justified requirement to live on site during the works. That's stopped it dead, to the detriment of a friend of mine I've mentioned before who's been trying to get PP to build on her rare breeds chicken farm for over a decade now, and still lives in a caravan on site. In her case they keep granting her 3 year extensions, because she can always demonstrate the need to be on site at night, because of foxes etc.

Not under UK regs, as far as I know (but I've not had a chance to go through amendment 3 yet, but I don't think that's changed things from the copy of the 17th Ed I've got). It's fine to have multiple outlets on the same radial, as long as the cable is sized correctly for the load, taking into account diversity, cables passing through insulation, max allowable voltage drop and all the usual stuff that applies to cable sizing. You can have more than one 13 A outlet, for example, on a single radial, using normal 2.5mm² T&E. The maximum number would depend on the factors already mentioned. One thing to look out for is the size of the CU, and the space it will take up, bearing in mind that you're going to have at least double the number of MCBs or RCBOs in it. Another is cable runs, as you can, in some layouts, have quite a lot of cables going in roughly the same direction. Neither of these are show stoppers, in my view, and I was tempted to spec our build as radial, but I was pushed for space on the wall in the services area, and a bigger CU would have been a bit of a problem, especially when allowing for all the cables that come up on that same wall.

FWIW, I much prefer the idea of going back to radial wiring. It was the standard in the UK for years, I think until the price of copper and post-war belt-tightening, caused the switch to ring circuits. I have a personal view (and please bear in mind this is just my personal view) that radial wiring is more logical and can be safer. It's normal in many other countries to use radial wiring, and I have a feeling that the UK is in the minority in sticking to ring circuits. I remember fixing a problem in a house in the US (well, helping the owner find and fix a fault) and that house was radially wired, but interestingly with aluminium cable. Needless to say using aluminium cable (or, to be correct in this context, "aluminum" cable) causes corrosion problems at connections, so normal practice there with this stuff is to squirt some anti-corrosion stuff on all connections. The fault we located was caused by a corroded connection, which is why I remember it.

Dave, Jack has a Loxone home automation system, with a mass of Loxone modules in there, plus, IIRC, a division to comply with the regs and keep the ELV/SELV stuff clear of the LV stuff, and that takes up room. As I recall, it's a very neat installation, and, either by accident or design, that board allowed the LV/ELV to be separated very easily. Bear in mind that it's a year or so since I saw it last, and my memory may not be 100% on the detail, plus the electrician was there wiring up the Loxone stuff, and tempting as it was, I didn't want to disturb him with a stack of questions about it!

I've seen Jack's board first hand, when his electrician was there wiring it up, and can vouch for it being big. Very big!. I've seen smaller boards in small factories.................

I apologised for the error, which wasn't as you've stated. I wrote TN-C by mistake when I meant to write TT, as well you know, as I've gone into enough detail to make this clear.

OK, half-asleep this morning I made an error, since corrected after it was pointed out.

I didn't state that the IEE/IET as it is now make the regulations at all, neither did I imply that they did, I just mentioned that I used to be a member of the IEE years ago, nothing to do with regulation making. What I actually wrote, and you've quoted, from your quote of my own words, with regard to making regulations was this: I don't disagree with any of the regs you quote, but if you're going to be critical about me, then please make the effort to be accurate about what I have written, rather than misinterpret something.

I'm just trying to put some balance into what is a debate about appropriate levels of safety, from my personal perspective. There can never be absolute safety, and that's the point I'm making here. Risk appetite and safety are very variable, and no two people will perceive things in the same way, which is a pretty good thing, otherwise we'd all be pretty dull. Risk must be be assessed by the individual, with the benefit of information from as many reliable sources as possible, if they are making their own choice about something that offers better, or just different, protection than the minimum required by regulation. All I've ever done here is say what my personal view is. It's not wrong, it's not against any regulation, and in my view it's a small improvement on a split board. You have a different personal view, that's fine by me, I've never once stated that you are wrong, either. We are all entitled to an opinion, and holding a different one is not an offence. Do the current electrical regulations state that you have to fit an all DP RCBO board? Do they state that fitting an all SP RCBO board is hazardous? No, the current recommended minimum acceptable standard is a CU with two DP RCDs controlling two separate sections with MCBs for each circuit within each section. The "clever" people say that's good enough for all of us, not me, I'm not one of the clever people, and I ceased to be an IEE member over a decade ago, just before the merger that formed the IET. When it comes to setting safety standards that have to be enforced, then that's done by a committee of clever people, who sit down, weigh up the facts, look at the accident and incident statistics over the last few decades, balance those with cost and consumer impact and produce a set of balanced regulations. It seems you don't agree with all of those regulations, and as it happens I don't either, but in a different way. That doesn't make me right and you wrong, or vice versa, it just means we have a different view as to where the balance lies between risk, safety, the probability of an incident happening, the types of incidents that are common, the types that are less common, convenience, cost etc. There's nothing at all wrong with that. I'm not saying, and have never, ever, said, or implied that, "my way is the only safe way" of doing anything. It's up to people reading and researching to form their own views and make their own decisions.

These choices all come down to being informed, working out your own personal risk tolerance and weighing these up with cost and convenience, together with the potential gotchas in some installations. For example, I have a 10 way CU, filled with SP RCBOs. Despite it being a big box (in terms of depth), there is not a lot of free space in there. If it had DP single width RCBOs then I think it would be pretty stuffed, just because of the volume of wire, the SP ones are bad enough. Yes, it's very convenient to isolate a single circuit to work on it using a DP RCBO. Yes there is a tiny degree of additional protection from a couple of pretty rare fault events from using DP RCBOs. However, is it a major safety enhancement over using all SP RCBOs, with a higher rated DP RCD as a main switch? Not in my view. It's certainly better, but it's not the sort of step-change in safety we got when we first introduced RCDs. And, just as benchmark, our existing house, built around 1982/83, has no RCD, no MCBs, but wired fuses and a single DP isolator. In the 16 years we've lived here we've never had a fuse blow, or a wiring problem, and the house passes the periodic safety checks and tests I do with no problems ever showing. In terms of safety, a standard split box, with two RCDs and bunch of MCBs is actually pretty good, and a massive enhancement over the system I have in our old house. Is an all SP RCBO CU any better? Not in terms of safety, but yes in terms of user convenience. Is an all DP RCBO CU an enhancement in safety? By minuscule amount, realistically. It's big advantage is the convenience of DP isolation of each circuit for maintenance, and that's probably a good enough reason to do it. It's a bit like other risks we accept. Every planning decision I've ever seen has included a comment from a fire officer about the effectiveness of sprinkler systems and that fitting them should be a planning recommendation. However, very few people seem to take heed of that, and in my view, fire is a far greater risk to life now in a domestic situation than an electrical fault.

Funny old thing but I've been looking at SPDs recently, as we've had a spate of nasty spikes on the supply, ever since there was a major cable replacement programme a year or so ago, following a lot of damage by high winds bringing some major cables down.. In our case the situation is exacerbated because our supply voltage never drops below 240V, even in winter, and is often right on the 253V limit on a sunny day. It restricts my PV export a fair bit of the time, as the inverter throttles back to maintain no more than 253V. Several of us on the same supply have had stuff fail due to surges (I lost one of my Makita battery chargers a couple of months ago by leaving it on during a storm) and our PV inverter has shut down around three times now, with the diagnostics showing it was due to an over-voltage spike. The problem is that I really need to do some more investigation to find out how big the spikes are, first, to see if it's always lightning (I think it is, as it seems to coincide with stormy weather) or whether it's just over-voltage events (like an inductive load turning off when the local grid is already at peak voltage). Trying to get the DNO to drop a tapping on the sub-station seems to fall on deaf ears, even though a few of us on the same feed can see that the voltage is always at the high end of the allowable tolerance band, of +10%, -6% around 230 VRMS.

If you think that wiring is messy, have you ever seen French wiring? A friend owned a big house in the Loire that had originally been the hunting lodge for the nearby château. It needed a lot of doing up, having never been intended for occupation, just day use, and came with a lot of outbuildings, 20 acres of chestnut woodland and half a dozen cottages. He gradually restored the place over about 12 years and converted some of the cottages to holiday lets (I've stayed there many times, and flown around there - he used to runs the flying school at the nearby airfield). What amazed me was seeing French electricians first fix. They chase flexible conduits into the walls, and the concept of a "safe zone" for wiring is completely lost on them. The general rule seemed to be to run the wires by the most direct route, so they would literally run conduits diagonally across walls, with nothing running vertically or horizontally as we would do it. They also seemed to always use single conductor wire for everything, just pulling as many wires through a conduit as needed. TBH, it looked chaotic to me, and I can't imagine what it must be like when you come to do something like hang a picture or fix anything to a wall. It must be essential to ALWAYS use a cable finder, as, judging on what I saw, there could be cables under the plaster absolutely anywhere!

Some confusion has crept in here, and that's in part to me making an error (highlighted earlier) and in part by the change in the earthing system demanded by the DNO, part way through the build. The latter was, in my view, barking mad and illogical. We applied for, and had installed, a permanent domestic supply. I'd already fitted the meter cabinet, put in an isolator fused DP switch, an earth block, Henley block and a feed to an external 4 way IP68 CU. That CU had a 100A DP switch and three DP RCBOs, one of which was (and still is) connected to a 16A Commando socket. All this was tested and signed off by the first electrician, and provided a connection point for the house supply (via an 80A fused, 100A DP isolator), and power for the sewage treatment plant, the borehole water supply pump and the 16A Commando. At no time did we apply for, or pay for, a site supply. I expected that the DNO would just fit the head, ready for the suppliers to fit the meter the next day, but they refused point blank to connect it, because of the lack of a TT earth, saying that their policy was that a "temporary site supply" MUST be TT'd. I tried explaining that this was the permanent house supply, not a temporary site supply, and that they were never coming back to this job again once they'd fitted the head, but they were adamant. I ended up driving a 20 mile round trip to get an earth rod, box and bit of conduit, whacking it in and calling my electrician to come in and test and wire it, before the DNO would make the supply live, ready for the suppliers to come in the next morning to fit the meter. The next day the suppliers turned up to fit the meter, and asked why the tails I'd left included a TT earth, when there was a perfectly good TN-C-S earth available under the cover on the head. I told the the tale and they just shook their head in amazement. When we'd finished wiring the house, my electrician asked the same question, why is the meter box TT'd with a dodgy looking rod banged into the soil next to it? I explained, and even pointed out that the earth impedance on the TN-C-S earth had been measured by the DNO and written in felt pen inside the box! At this point my electrician rang the DNO, who told him he could go ahead and pull the plastic cap out and fit the earth to their connection, removing the "temporary" TT earth. Now, I can fully understand why, when fitting a temporary site supply (for which there are separate charges) it would make a lot of sense to have a TT earth. It's the same logic that caused me to fit one in the workshop, it gets the site earth and electrical connection earth at the same potential. However, I cannot see why the same installation, with no changes at all except a DP fused isolator switch being thrown for the first time, should be OK on TN-C-S, when with that same switch off it wasn't, and could only be run TT'd. If our account was for a temporary site supply, rather than a domestic supply, then I could understand it; I'm sure they have a safety policy that says all temporary supplies have to be TT'd (makes sense, as a temporary supply could include a generator, I guess). I cannot for the life of me understand why they applied this policy to a standard domestic supply, though. All answers welcome, because it's been bugging me for ages.....................

In that case that's an error, as it's TT. Dave and I discussed this, either here or on Ebuild, back when I was doing it, and IIRC we were both of the same mind that exporting an earth down a moderate length of SWA was OK as far as the regs were concerned, but that I still felt happier having equipotential earthing at the workshop end, with the rod making the local earth in the CU the same potential as the slab. Exporting the earth over that distance was fine in term in terms of impedance, it was solely a personal "comfort factor" that made me put an earth rod in. In case anyone is interested, I fitted the earth rod in an unusual way, and it may be an idea someone wants to copy. I found that the standard, copper-coated steel, screw together sections, type earth rod is a nice sliding fit in (I think) 12mm OD plastic pipe. There's a short length of this set into the workshop floor slab that goes right down through the slab, insulation and type 1. Into this I drove a long rod (two screwed together, so well over 2m, I think). It's at least a metre and half into the underlying soil, maybe more, as the termination plastic box is only about a foot of the floor, and screwed to the inside wall. There's a bit of rigid black conduit running from the green box up to the CU, with a 16mm2 earth lead in it. I don't have the paperwork to hand here, but IIRC it was a damned good earth, probably because the sub-soil under the slab is most probably always a bit moister than the surrounding open ground. The rod is also down below the level of a soakaway, that's a few metres away further upslope, and that may well help keep it damp. It's a neat way of keeping an earth rod well protected, I've seen some outside ones that have been hit by stuff, had multiple coats of paint over them when close to outside walls and generally in places that are subject to damage. The only downside is that it is not easy to pull it out, as it's so close to the wall and right in a corner. I have pulled it out, because originally it was only a single length, but when the temporary one was removed from the main incomer, when the house wiring was completed, I pulled it out, screwed the two together, to double the length. It made not one jot of difference to the effectiveness, mind!

And one of the reasons I TT'd my workshop, as it was a separate EZ and I wanted it the earth at the CU to be equipotential to the local earth under my feet.

You implied that our installation was bodged. Specifically you gave my name and said that I had, quote: That's both bloody rude and untrue. The DNO instructed that the TT rod be removed when the main box was switched from TT to TN-C-S, not me. I very specifically added a local earth rod at the workshop, so that CU is TT, because the earth was being exported via fairly long length of SWA, and although all the impedances were within limits, I wanted to ensure that the local earth (the slab) in the workshop was equipotential with the earth at the workshop CU. That's a damned good reason for doing it, in my view. Finally, whether you or I like it or not, only those with the right bit of paper are now deemed competent. It matters not how qualified or experiences anyone os, if you don't have the flavour-of-the-month bit of paper then you are deemed to not competent. That's not just in this area, either. My sideline for years has been as giving expert evidence in court, in civil cases (almost always insurance-related). Those cases hinge entirely on competence, as shown on a bit of paper, rather than on common sense, qualifications, experience etc. It's not right, in my view, but it's the way the world seems to now work.

The correct diagrams are as you gave in your earlier link from the IET, and are definitive.

Nothing bodged about it at all - it was all done by a qualified electrician - not the one that wired our house, but the one that put in the external wiring on the site, before we started building the house. Bodging implies that I'm dangerous, or my work is, and frankly I don't think that's on. As for the earth system, then we initially had TT when the supply (exactly the same box wiring as now) was initially put in, as the DNO wouldn't accept TN-C-S on a "site supply". It wasn't a site supply at all, it was the permanent supply, just fitted inside a box that wasn't built in to the house, but separate from it. When the house wiring was complete, the electrician asked why we were TT and not TN-C-S. I told him it was at the DNO's insistence, and pointed out that the DNO had measured and written Ze (0.26 ohms) in felt pen inside the box, with the words "no PME for site supply" (see, even the DNO use the wrong term!). My electrician rang the DNO on completion and asked whether the PE could now connect to their head, as normal for TN-C-S. They said yes, but please remove and disconnect the TT local earth rod. He measured Ze again to be sure it was still under 0.35 ohms, and then swapped the earth over and we removed the rod. The system is certificated on that basis - no bodging, no unqualified work done by me, everything tested and signed off by a qualified electrician.

To be frank, it's getting a bit pedantic about terminology that changed as a consequence of harmonisation. In general, we had two earthing schemes in common use pre-harmonisation. One was where the earth was "imported", i.e. came in with the incoming supply cable, and one where the earth was supplied only by a local earth rod, near the point of entry to the house. The former was known as PME, Protective Multiple Earth (a term that shouldn't now been used, as it hasn't been in the regs for years) and was normal in urban and built up areas. Local earthing was the norm in rural areas. Come harmonisation and we adopted EU-wide standards, with letter codes, set out in the link in the post above. The snag is 99% of electricians STILL use PME as a term, hence the confusion. Strictly speaking most installations are either TT (seperate earth rod as the only protective earth) or TN-C-S as described in that link Alphonsox gave.

You're right, my error, I have TN-C-S at the main incomer - what most still call PME - where the PE is imported with the incoming supply, as the neutral. At the workshop, I reinforced the earth with a rod to get the impedance down and get the slab ground closer to the local incomer ground potential under fast fault conditions. Although it's only around 30m of 6mm² SWA feeding the workshop, that has a bit of inductance that ups the impedance slightly to fast fault events. I've added the additional earth rod out there really for equipotential ground reasons more than anything else. No need for a rod at the incomer, we're very close to the sub-station, with a 90mm² 3 phase feed directly under my meter cabinet (so less that 2m of coaxial company cable from that to the head). Yes, the upfront master RCD leakage is rated above the smaller RCBOs, so I get the right trip sequences, and I accept that the higher leakage current is slightly less safe as a consequence. TBH, given the way the house is wired, it's hard to come up with a way of getting the sort of failure mode where just SP RCBOs wouldn't trip for any feasible leakage fault. I can understand the dropped neutral failure issue, especially on some older lighting circuits, but realistically, how likely is that as a fault condition now? In my view it was all about balancing risk, probability of failure and convenience. Most faults now seem to be earth leakage faults, rather than overloads (I guess that's because overloads get picked up at the domestic equipment end 99% of the time, now) and, provided no one buggers about with the fixed wiring, then the SP RCBO offers practically the same protection as a DP one, and takes up less space (although I see there are single width DP RCBOs about now, at a price).

B curve is fine for an inverter unit, as they are all very slow start, with no current surge at all. If the cable is clipped to a wall it doesn't need to be SWA, NYY-J is OK, but the section going to the heat pump needs to be flexible, as they vibrate slightly, and that rules out NYY-J for the final section, as it's not flexible, it's solid conductor. That's why I used flex in armoured conduit. You can use flex in rigid conduit along the wall, switching to flexible conduit where it goes into the ASHP, as long as it complies with the de-rating conditions. Makes for a neater looking install in my view, having a dead straight run of conduit, rather than cable clipped to the wall.

You can always fix posts with those long steel earth spikes, that take a standard fence post in the socket on top. Not my favourite method, but quick and easy to do and only needs a sledge hammer and block to drive the spikes in (with a level to get them vertical). You then just bolt the new posts in place, into the sockets on the top of the spikes.

The standard split box with two DP RCDs and MCBs for all the rest is what I'd generally refer to as a "standard 17th Ed CU". I have a DP RCD master, plus SP RCBOs on each circuit, so am compliant, as the DP RCD master will pick up any odd ball faults. We're TN-C-S in the house, and TT at the workshop CU, just because I didn't like the idea of exporting the earth out there without a local earth rod in addition to lower the earth impedance a bit there, as there's machine tools in there (or will be). The outdoor CU is all DP RCBOs (for the borehole pump, treatment plant, and car charge point feeds) and the workshop CU is all DP RCBOs too. I fitted RCBOs on every circuit, because 99% of the time they will pick up any common fault and just trip that single circuit, rather than half the box. I couldn't see the advantage in the split box, TBH, losing half the house because of a single fault seemed little better than the old 16th Ed (and earlier) system of losing the whole house. WRG to heat pumps, the the requirements depend very much on the type of heat pump. A non-inverter type has to be treated for what it is, a high power motor starting under load, and so needs both hefty cable, a fairly high rating on the breaker and a slow response time, like a band C, to cope with the starting surge current. On the other hand, if you have an inverter controlled unit like ours, although it's a 7 kW peak output unit, the max current is only around 10 A, and that current is only reached about 30 seconds after turn on, as the unit slowly ramps up from a standstill to full power. I have mine on a 16 A type B RCBO.

To be honest, I could have done the 17th Ed exam, as I've got a copy of the 17th Ed and had a re-read of it before we started, but my understanding was that I'd have to join Elecsa, NAPIT or one of the others in order to be able to sign off the work; just having done the latest exam wouldn't have cut it with building control. There was also the test gear requirement, I'd have had to hire modern gear for a day to test everything to the current requirements (like all the RCBOs, for example - I don't think my home-made box with a 13A plug and three banana plug leads would cut it, even though it tests to the required current imbalance limits!). The sticking point was really my senior BCO. He was adamant that if I did the wiring, then I'd have to find an electrician with the right ticket to sign off third party work by test and inspection, and produce the installation cert. He assured me there were none he knew of locally, so that sort of put the kybosh on a DIY job. All told, I felt pretty good about giving the young electrician the job. He looked like he could do with a confidence boost (he was very neat and competent, just a bit new at things), and I reckon he came away from doing our job with more confidence to take on bigger jobs in future, so that's no bad thing. Finally, I HATE terminating SWA, and always have done. I've learned all the tricks to keep the armour wires as neat as poss, got a really good pair of double-action side cutters to trim the armour, must have terminated hundreds of the damned things by now, but I still HATE it! Even now I'll get everything set to go in the gland just right with the armour trimmed neatly, get it assembled with all the armour wires neatly under the collet ring and find I've forgotten to slip the boot on first, or something similar. It's for that reason I tend to use NYY-J outdoors whenever I can get away with it, as it's a lot nicer to work with.