Emergency stop switch for study/lab (UK wiring question) - Page 1
Forum section: electronics / projects

author: splin
author_rank: Frequent Contributor
timestamp: December 01, 2019, 06:38:51 pm
content: I've wiring my new lab/study area but not yet plastered the walls. It occurred to me that it would be a good idea to alter the wiring to include a master switch to disconnect all the sockets on the wall behind the bench to allow all the equipment to be turned off at night or when the house is unoccupied to minimize fire risk. Being in the UK these sockets are currently part of a 30A ring main (ring final circuit in modern nomenclature) using 2.5mm^2 twin and earth cable.I'm thinking to use a 45A double pole cooker switch and rewiring these sockets as a spur off the switch connected into the ring circuit. The spur would be wired into the switch as a sub ring. I realise it is not usually recommended to join any part of a ring circuit together anywhere other than at the consumer unit and it can cause confusion later. Worse, standard ring circuit tests would not pick up a break in the sub-ring created by the intermediate connection (think figure of 8 circuit created from the original single ring).In this case however it should be obvious that these 6 sockets are spurred from the main ring as they can be isolated by the new switch, but there is the possibility of a disconnection/break in the new sub-ring. The break wouldn't be obvious but the 6.sockets would now be connected to a 30A breaker with under-rated 2.5mm cable. Is this acceptable? It wouldn't be any different to a break occurring in any ring circuit except that a standard house wiring check should detect that - but such testing happens very rarely, if ever in many/most UK houses until major rewiring is done. I don't want to have to rewire these 6 sockets with 4mm cable if at all possible.Second question: should I use an emergency stop switch instead? If so, can you get them to fit a standard back box as all the ones I can find in a quick search seem to have their own enclosure or are panel mounted?

author: jbb
author_rank: Super Contributor
timestamp: December 01, 2019, 07:05:51 pm
content: I can't comment on UK wiring rules (especially the particularities of ring circuits), but here's my 2 cents:If it's not too hard, I suggest a separate ring circuit for the lab all the way back to your switchboard. That way you won't take out your fridge, WiFi router etc. when you trip something. How does the UK stand on Residual Current Devices (RCDs) (aka Ground Fault Current Interruptors GFCIs)? They can be a bit prone to false tripping.If you want an isolator switch, use a switch. If you want an emergency stop, use an emergency stop (you'll also need a relay).Make sure the lights will still work even if the switch is off

author: andy3055
author_rank: Super Contributor
timestamp: December 01, 2019, 07:35:52 pm
content: By courtesy of this site (https://www.flameport.com/electric/socket_outlet_circuits/ring_spurs_socket.cs4), you cannot wire more than 1 socket as a spur from the ring. So, you may want to run a completely new ring circuit for the room or the work bench sockets and have it on a separate breaker in the panel. If you need an emergency shutoff, make sure it is a 4 pole switch as the ring has to be broken from both ends. If not, it will still be alive from the unbroken branch of the ring. I say a 4 pole switch so that you can break the live and the neutral lines on both sides of the ring for total isolation.If your aim is to simply guard against earth faults, as suggested by jbb, you can use GFCI protected sockets:http://internationalconfig.com/icc6.asp?item=72300-S-10MA

author: max_torque
author_rank: Super Contributor
timestamp: December 01, 2019, 09:36:29 pm
content: I have a lab bench in my electronics room that has "Build in" socket rails, and i simply wire these to a switch and plug them into the ring main, with a suitably fused plug. That way the bench is a "mobile" device. The downside is that there is a total of 13A available to all the sockets on the bench (currently 10) but realistically, do you need more power (@3kW) than that?It also allows me to include a plug-in isolation transfomer to isolate the entire bench if necessary

author: splin
author_rank: Frequent Contributor
timestamp: December 01, 2019, 10:02:29 pm
content: Quote from: andy3055 on December 01, 2019, 07:35:52 pmThat used to be the rule but it isn't in the current regulations. You should not add a spur to an existing spur because spurs are usually wired with 2.5mm cable which is underrated for a 30A or 32A breaker - with one double socket spur it is considered unlikely that you would overload the 2.5mm cable. It could happen in fault conditions such as a short within the spurred socket (considered unlikely), but not due to faulty appliances as their mains plugs are fused.However, I don't believe there is a problem if the spurs are wired with suitably rated cable. In my case I could use 4mm cable for the 6 sockets or connect them in a ring with 2.5mm cable, joined into the main ring via the isolating switch.QuoteUnfortunately the regulations here mean that I can extend an existing ring but if I change any connections to the CU (consumer unit or breaker panel), such as putting in a separate ring or radial circuit to the study/lab, I would have to pay to have it certified to our 'part P' regulations.QuoteA 4 pole switch wouldn't work as it would break the existing ring - the other sockets would still work but would be connected as two radial circuits using under-rated cable. My intention is to use a 2 pole switch connected to the main ring on side and to the 'sub ring' on the other. This is known as a bridged or figure 8 ring. AFAIK they are permissible and were even recommended in early documents. They are fairly common in UK housing, probably more by accident by design, when wiring is altered such as connecting two spurs but it isn't usually recommended as it can cause confusion later because the circuits are non-standard and can make it very difficult to work out the wiring connections. In my case though it should be very easy to work out as the six sockets are isolated by the switch.QuoteThe consumer unit already has a 30mA RCD (GFCI). It would be better to have a separate one for the lab but that would require rewiring into the CU and much more expense. Gotta love safety regulations which encourage 'bodgineering' - creative engineering solutions which meet the regulations but may be less than ideal or even less safe (but not in my proposal I hasten add!)

author: splin
author_rank: Frequent Contributor
timestamp: December 01, 2019, 10:15:14 pm
content: Quote from: max_torque on December 01, 2019, 09:36:29 pmYes that would probably be a better solution - 13A is plenty. At the time I hadn't thought about the desirability of being able to switch off all the sockets from a single isolating switch and preffered wall mounted outlets for neatness.QuoteNeat, but an isolation transformer feeding a 4 way power strip would be enough should I ever need one.

author: mcovington
author_rank: Regular Contributor
timestamp: December 02, 2019, 01:09:25 am
content: In a lab/workshop it is also a good idea to have a battery-backed-up light of some kind -- need not be very bright -- so that if all the power goes off, you won't be completely in the dark.

author: Monkeh
author_rank: Super Contributor
timestamp: December 02, 2019, 01:36:56 am
content: Quote from: splin on December 01, 2019, 10:02:29 pmConnecting multiple sockets as a spur using larger cable creates a serious concern of imbalanced current in the ring. A figure of eight creates a big problem in inspecting and testing, and may well cause the same imbalanced condition.Connecting this arrangement as a fused spur would be adequate in terms of avoiding notifications - which does not remove the requirement for proper design, installation, inspection and testing, and you may still be able to cause an imbalance.

author: Ian.M
author_rank: Super Contributor
timestamp: December 02, 2019, 10:28:30 am
content: Back in the days before part P, I would have done an electronics workshop supply as a secondary consumer unit (US: sub breaker panel) on an appropriately rated dedicated circuit and breaker in the main consumer unit.That's still a common setup for feeds to large sheds and detached garages, but is no longer within the remit of a DIYer.However with part P in force, probably the best option is to get in a professional electrician to put a cooker circuit into the room in question, which will give you a 32A or 40A rated feed with an isolating switch and a connection unit for heavy flex. Get the isolating switch put somewhere sane - the electrician will want to put it near the connection unit.You then put an appropriately rated industrial trailing socket on that heavy flex to feed a distribution panel (actually a small consumer unit), mounted to the back of the bench, not the wall, for your bench circuits, which MUST NOT be permanent wiring in the walls.If you expect to work on mains powered devices at all often, any RCD (US: GFCI) protection on the workshop/workbench feed should be set up with discrimination in mind i.e. should have a higher trip current and a greater time to trip than the ordinary domestic RCBO breakers you will be using in the bench distribution panel, so the local RCBOs trip first if the D.U.T on your bench has a fault.

author: max_torque
author_rank: Super Contributor
timestamp: December 02, 2019, 08:17:07 pm
content: The other advantage of not having all the sockets behind a single switch is that things like PCs etc can be left on when you turn the "test bench" off.Oh, and BTW, you can NEVER have enough sockets on your bench......My bench has, right at the this moment:ScopePSU 1PSU 2PSU 3DC LoadBench meter 1Bench meter 2Signal GeneratorTimer CounterSoldering IronHot air stationDe-soldering gun,MonitorSpectrum AnalyserLaptop 1Laptop 2All vying for the avaible 240VAC socket outlets

author: Docara
author_rank: Regular Contributor
timestamp: December 02, 2019, 08:42:52 pm
content: Hi Slin,I'm a UK sparks.Obvious disclaimer - Make sure you get your own independent advice only use what I say as a discussion with you own electrician.I've written, rewritten amended this so many times I hope it stall makes some sense - sorry if it doesn't.First off, any additional circuit or change to an existing circuit and you'll get clobbered by Part 'P'. Basically, in a domestic installation, you are only allowed to change 'like for like' anything else required a minimum of a 'Minor Works Certificate'. Sorry Bud testing is required no matter what you do. I'm a tester I've signed off major installations but I can't install a socket in my own house. I don't do enough private (domestic) work to justify the Part 'P' registration. I do infrequent full house major jobs and just pay £100 to the local council to rubber stamp my certification. Anyway I digress!!!Get a friendly electrician in and have chat on your pre-plastered installation. I'm thinking about cable zoning and verification of your houses earth bonding. Then see if they will be happy for you to do the work under their direction - beers might be needed leading up to certification.First off, ring final circuits terminate at a breaker in the fuseboard - nowhere else apart from rare occasions using contactors, so this answers your question about the cooker switchMy assumptions are you want to isolate your lab at one location on leaving, that you have adedicatedring circuit to your lab and that it is a new/convert build so you don't want it to look like a dogs dinner.When you start doing what you want to do, ring circuitsstartto become a right royal PITA so avoid them unless used conventionally.Right, the easiest way to achieve what you want is to convert your lab ring sockets into 2x radials. So the ring enters your lab at a convenient location then radial 'loads' splits off. SO ring in, 2x radials out. Where the ring and two radials meet install 2x Switched Fused Connection Units (switched spurs) with 13A fuses installed. Keep adding FCU and Radials to your hearts desire - remember on a ring there is no limit to points fed. There would be nothing wrong if you wanted 1 FCU per socket. I would change the 32A main MCB to a 20A (though consider length of run and Earth Fault Loop (Zs) implications). The important part is the 13A fuse in the FCU. You are limiting each 2.5mm2 leg to 13A from a 20-32A supply. I don't like 32A on anything other than a kitchen ring to be honest. If the ring breaks then 32A protecting a 2.5mm leg is too much - 20A protecting a 2.5mm leg is fine. I think 24A capacity for 2.5mm2 T&E.If you REALLY want to keep your lab ring and have remote off I would suggest you go down the small consumer unit route (think garage supply £40 - cheapest DIN rail box with lid) local to you lab, and get a suitably rated contactor (ideally DP). Bear in mind to verify the number of ways needed in the consumer unit/garage supply before purchase - from memory they are 6 ways - 2 main switch, 2 RCD 1x32A MCB 1x6A MCB. The coil circuit could then be controlled by an external switch using a 1 or 3A MCB in series with the contactor coil or connected to an emergency switch (also in local consumer unit/garage supply). As you can appreciate when do you stop adding control circuits and MCB's? Things can get messy/fiddly very quickly.Another option could be installing a contactor in your existing consumer unit if there's room and run a remote switch to you lab or RF switcher etc etcBut on balance I think I would do the first option have two or more conveniently positioned Switched FCU feeding 13A radials from the existing 20-32A ring supply. Remember discrimination of circuits, you are not expecting all sockets to be pulling 13A each.Strictly speaking these radials are not part of the fixed installation but an 'accessory', though it's hard not make that argument when buried in walls with T&E supplying flush sockets in a wall - down to the guy certifying. Remember to protect your cables with capping before plastering. Obviously RCD protection on sockets.Lastly, apart from it possibly looking like shit if youcouldwork out a nice way to have the two radials on a 2.5mm flex on plugs, plugged into switched sockets you are guaranteed not to need certification after the sockets. The 'Point of Isolation' is removable (plug).If your installation would lend itself to perhaps having a couple of surface back boxes mounted about 150-200mm apart, with the lower box having a blanking plate and 2x stuffing glands in the top, flexes coming out with plugs and plugged straight into the sockets. If all white it should look OK. You could always terminate the flex into the back of 2x FCU's instead of plugs and sockets so again it is obvious what is going on.All your electrician would need to do is cert for a double socket/FCU on a ring (cheap) and leave you alone to you installing the sockets in your lab where and when you want them.I don't think I've cocked up with the above let me know if there are any glaring errors

author: Monkeh
author_rank: Super Contributor
timestamp: December 02, 2019, 10:05:20 pm
content: Quote from: Docara on December 02, 2019, 08:42:52 pmI'm not entirely sure you're correct - the regulations, I believe, still contain regulation 12(6A), which requires notification only for new circuits, replacement of the consumer unit, or addition or alteration to circuitsin a special location. Outside that, no notification is required.Yes, a minor works certificate is required, but thisis notnotification and has nothing to do with Part P, but BS7671:QuoteNow, I'm not a sparky by trade and I don't know the various regulations backwards, and it's entirely possible I've missed something (keeping track of amendments to legislation is nigh impossible as the government is incapable of presenting them correctly), but assuming you perform the appropriate testing and do the paperwork, it seems perfectly permissable for work to be performed without invoking any expensive processes. Of course, there is 644.5 requiring a 'competent person', ie. one who's forked out a great deal of money for some paper, and probably been taught a lot of bad habits and nonsense in the process. Not at all attempting to put down properly competent electricians, but there's a lot of 'competent' cowboys and a lot of not 'competent' DIYers who know what they're doing.Obviously, filling out that certificate correctly requires a range of tests most people, even here, simply do not have the equipment to carry out - but in practical terms nothing is going to be made worse by the provision of a few additional sockets, if the workmanship is adequate.All the annoying legal bollocks aside, assuming there's no intention to supply more than 3kW, I see no problem with a single FCU supplying as many sockets as desired.QuoteThis is a fixed installation, no matter how unpluggable it may be, and all the requirements of BS7671 and the building regs apply.

author: artag
author_rank: Super Contributor
timestamp: December 02, 2019, 10:16:36 pm
content: Doesn't it only require certification when you sell the house ?You could collect the changes (and 'repairs' .. I think you're allowed those) and do them all at once.

author: Monkeh
author_rank: Super Contributor
timestamp: December 02, 2019, 10:20:00 pm
content: Quote from: artag on December 02, 2019, 10:16:36 pmCertification is from the wiring regulations (not law) and is required for any substantial work.QuoteThis is not the same as notification, which is to do with the building regulations (law).

author: Docara
author_rank: Regular Contributor
timestamp: December 04, 2019, 07:15:32 pm
content: Ha! Ha! Aren't our regs great !!!!!!So many good points, right not in any particular orderSlightly picky answer and a play on the English language - You do not 'require' a certification 'when' you sell your house, you shouldalready beliving in a certified and tested house and have either an Electrical Installation Certificate (EIC) or Periodic Inspection Report (PIR) in place to cover the installation. If this is under 10 years old you're covered, however it 'looks' better if your house has just passed a Periodic because it gives the buyer the impression the electrics are safe. A domestic dwelling should be tested every 10 years (max), 5 years if commercial or even less if the installation is in a harsh environment or liable to change or abuse (farm yards is the classic example - those farmer boys love nails for fusesand have never seen a rodent eating a cable.You are correct for rental properties a new full Periodic testisneeded when vacated and before new people move in.Competent Person - horrific term - in the electrical sense this does not mean someone 'who is competent'. It means someone who can prove their competency (with qualifications eg City and Guild 2391). How could you stand up in court and show that you knew what you were doing, you would have no defence.As an aside - when I did my 2391, I was told that I would be considered guilty in a court of law unless I could prove myself innocent by issuing a test certificate for any work I did or I was the last electrician to touch an installation and someone was hurt - even if it had nothing to do with me. e.g I change a downstairs socket for a drink for my mate down the pub and his daughter was electrocuted using the upstairs shower some months later, I could be on a manslaughter charge with no defence because I couldn't prove what I did or didn't do.Wiring Regulations and the Law, I don't fully understand this, but basically it goes something like this. The wiring regs are not law but they are incorporated into the building regulations and I think the Health and Safety legislation which ARE law therefore they are a legal requirement. - Something like that.QuoteYes you are correct with this one however it is a difficult one in this context and is ultimately down to the person doing the test. Effectively it is a new circuit - but it's not. In context to the OP I do not know the background of the installation he was talking about. For his house insurance, selling his house in the future and local authority purposes notification from a Part 'P' registered spark would only pay what £1.50 online to ensure his customer (and himself) was covered from all angles. The circuit sounded like it was massively f**ked around with adding many more points on it than it originally had and the functionality had changed. Earth leakage implications, tripping characteristic would need to be addressed which would be fundamentally different to what was there before. The only original part of it was two legs back to the CU. To be fair you are probably correct with a minor works but I am not standing in a guys house with a coffee having a chat but on a pubic forum not knowing who might read this in the future and takes things literally.I would still prefer to tick all boxes inthisapplication. Label up the CU with Lab Supply and notify. If the guys house burned down from an unrelated fault the new lab's electrics 'would' be blamed - no cert - no insurance pay out.I'm not 18th Edition, but I believe there is now a provision for a spark to 'sign off' other peoples installation which was what I was getting at in the post. To me it's a no brainer.QuoteI agree, but again were not chatting personally in his house, its some things to for him to consider and discount as necessary with his sparks.QuoteI disagree - though there's no way in hell I would install this in walls on a professional level, it would allow a DIYer to do his own install and comply with regs. If this was an extension lead screwed to the wall what's the difference? If this was in flex feeding sockets via a stuffing in the end of some dado trunking or any trunking come to that, what's the difference? I don't have my (17th Ed Amend 3) regs to hand but I can't think of anywhere where it states you can't. You don't test extensions cables do you. They rely on the protection offered by upstream devices RCD's, MCB, Fuses as applicable. What if you have a flush FCU, back feeding a boiler with a cable buried in a wall is the boiler part of the fixed installation - No, it' is an accessory. You would disconnect it when carrying out out an Installation Resistance Test! How about a 240V thermostat with cables buried in the wall - again we don't test. There are many instances like these which are not part of the fixed installation.If you know of aspecificsection dealing with buried cablesin this contextI would be very grateful if you would let me know.Remember the regs are not written to be verbatim they are a written as a guide to professional electricians enabling them to use their judgement to comply with the law on their installation given certain criteria. And for the record I am uncomfortable and REALLY squirming writing all of this bitQuoteish!!! Other than replacing like for like, Every piece of electrical work needs or should have had certification of some sort when installed. The killer is the change in colour codes to 'harmonise' with F**cking Europe so this dates your installation. Any new Brown and Blue core cable with Grey outer sheath cables is post requirement for certification and notification. The government has done an absolutely piss poor legislation job with no notification to the public - unlike Gas Safe and Corgi before them.You ask the average man in the street about Part 'P'. If you do get a positive response they think it is a qualification not a £750 odd/year club with the government tracking how much work you notify online to estimate your tax returns.

author: Monkeh
author_rank: Super Contributor
timestamp: December 04, 2019, 07:36:25 pm
content: Quote from: Docara on December 04, 2019, 07:15:32 pmI don't know how this is defined in the regulations (I am neither a sparky nor a lawyer, but I know my way around the bits which spark nonetheless), but an extension lead is designed and supplied to operate as a portable, self-contained item - wall fixing is for convenience. A surface mount box, or some trunking, or any other item designed to befixed to a surfacefor its entire operational life, is, well, a fixed item, and if you're assembling the wiring system from scratch I can't see any reason to exempt it from appropriate standards - I admit BS7671 may not be that standard if it's attached to a desk not the wall.QuoteI don't see how a boiler, its thermostat, pump, zone valve, programmer, and all the cabling involved arenotpart of a fixed electrical installation! There may be limitations on the ability to test (but not inspect!) them, but they're absolutely part of the installation. Or are you suggesting all my central heating wiring can ignore BS7671, cable zoning, current rating calculations, and so forth, because it's all an accessory? Of course that wiring should be inspected and tested as any other!Is a socket with a built in USB charger exempt from being part of the fixed installation and compliance with BS1363 by virtue of not being able to take a 500V IR test?As far as extension leads, well, in commercial environments someonedoestest them, as well as appliances, and as an electrician if working domestically you should at least be performing a visual inspection of customers equipment you come into contact with.As far as the term competent person, I agree, dreadful term. There's a huge difference between actual competency (which I can claim in technical knowledge, frankly, and at least some of the practical, I've yet to do SWA, probably never do MI, and so forth) andqualifications, which is what they're actually after. Unfortunately qualifications don't prove competency adequately in practice, and competency does not imply qualification..QuoteNow, again, I may not be up on the law because they make it impractical to be so, but as I understand it the law effectively only requires that installations be designed and installed in a safe manner - BS7671 is simply the accepted way to achieve this, and if you fully and correctly comply with it (and other actual laws - EAWR..) you have an extremely strong defense. You can deviate from BS7671 or even ignore it entirely, but then you have to defend your position - good luck if you've got more than some minor deviations to cover. The courts will crush you even if you did nothing wrong, just because you're an easy target.E: And oh boy, are we well and truly off on a tangent here. For the benefit of the OP I'll repeat my advice along with generally good advice: Use an FCU (either as a spur or inside the ring, I don't mind) to protect a moderate number of additional sockets for your purposes, with no messing around with figure of eights and cooker switches and other insanity, OR eat the cost and have agoodelectrician around to sort things out to his, your, and the law's satisfaction.