Hi Guys Before we start, NOT qualified, just competent, I think!.... aware of Part P and will have the work tested and signed off by a qualified electrician. New shed in back garden, the distance from House CU to shed CU will be total length 31m SUPPLY TO SHED as follows: 32amp RCBO from House CU up to attic with 4mm TWE, across attic (above insulation) to soffit Connection via Junction Box to 4mm SWA 3 core (using earth) Through soffit down outside wall with SWA cleated, Bury under patio 500mm with warning tape, across patio Into shed, new junction box connection to 4mm TWE terminated at CU. Although using internal earth, thinking of earthing the SWA, haven't used this in years, do i earth both ends of cable? Bear with me, trying not to forget anything, but also trying not to bore you all with details! I want to install CU in shed as follows: Screwfix BG 4674G 6 Way High Integrity Unit 100 amp main switch, 2 x 63A 30MA RCD's. MCB's 6 amp - outside shed canopy and wall lights (led) supplied via DP Isolating switch 6 amp - garden lights (led) supplied via DP Isolating switch 6 amp - internal lights (led) 16 amp - outside socket supplied via DP Isolating switch 32 amp - 5 internal sockets (occasionally use of TV and 3 exercise machines) I'd appreciate knowing where and if i'm going wrong or not (hopefully the latter!)
Of course you have to earth armour. U don't need or want 30 man protection on submain, only in out building. TT supply earth rod . Only need 2 core then
I would suggest you get this sparks your going to get in to instruct what he wants cos he's going to sign it off
Thanks Nigel What is the best way of connecting TWE to SWA, what products are out there today for the job?
There is a time and place for DIY. I'm the same as you - competent DIYer, but I wouldn't do this myself under current regs - find a sparks to do it. Maybe cut down his time on site by cutting all the holes/chases.
a SIX way CU for a bloomin shed!??? WHY? That must be one heck of a shed. That CU is bigger than many houses have got. And PS If you aware of it, you should also know that it is the eletrician who does the design, testing and installation that can notify and certify electrical works. Its not something that's done just before switch-on. Better for you to get a spark on board who will let you do the grunt work, under his direction. DO NOT go buying anything until the design work has been completed by someone who is competent. With respect, that is not you, and you won't get it on a DIY Internet forum either. And PPS 4mm, 31metres, 3 exercise machines (+heating??) I don't think so...
There is 4mm SWA in situ and would save a lot of work. The load in the shed is only 4 x 18 LED Ceiling Panels,possibly a small LED screen and the 3 exercise bikes only suppling 12v transformers for small digital info displays. Outside 8 x 8 watt LED Lights and occasional use of cold water power washer. I could future proof with 10mm main feed and have no worries, but I'm here for another 30 years hopefully and these are the wattage requirements of the 4mm cable. The 6 way CU can seem over the top, but that's in my nature, isolating every circuit as mentioned above. is it needed no, some electricians will put a few circuits on one MCB, just my choice. Admittedly not being an electrician I will need to work out the voltage drop across 30m, something I have never done and will have to wait for my electrician to come back from hols which is three weeks. Thought if i could get some help of you guys, I could have got the main feed in before he comes back. As far as a DIY'er, there are some areas of electrical work that I have not experienced, due to not being in the trade on a regular basis, but I am open to learn and over the years have installed many house rewires and successfully had them signed of by qualified electricians. So, why is there a problem with 4mm over 30m not incased in any insulation and run as a single wire clipped to stud work. Again, I am all for learning, we learn everyday, so can someone explain the how to calculate the voltage drop and why not to use 4mm. Thanks
Sorry, not making myself clear, the TWE from the CU will be clipped to stud work across the attic 20m, this will be clipped above insulation so there is no heat factor to consider if covered by thick insulation. Just before soffit TWE into junction Box connected to SWA before going outside SWA.
TN-C-S Maybe consider TT'ing the shed - I am not saying that you cannot export the PME, but with the use of 4mm it might go borderline. Myself I would TT, but hey ho I am only diy, and whatever you do Paul everything has to be verified and certificated m8. I wish you all the best on your project.
Yes, you are right, i had thought about TTing the shed, i think i'll do that. Was it BT, not sure, that saying......."good to talk". also got the sparky booked in for signing off. Cheers JP
Use a standard SWA gland in a metal box next to the CCU to earth the supply end of the swa, At the shed end cut off the swa flush with the sheath and ignore it. Your earth should be VIA an earth electrode by the shed with a 30mA RCD protecting the whole shed installation. The reason for not using the house earth is due to mixed disconnection times, you could be exporting a 5 second disconnection time fault into an area that can only have a 0.3 sec disconnection. So we use a 'clean' earth. For more on this look at agricultural, equine and horticultural installation practice. Don't forget to properly cover the top of the earth electrode.
Hi Bob I have completed the whole installation and awaiting the electrician to attend site for signing off. I have run SWA to plastic box next to sub main in Shed, reducing to grey flat 3 core for easier access and earthed SWA through gland to sub main via supply and earth from CU at house . SWA, again reduced to 4mm grey flat 3 core through attic area and earthed at gland back to CU (SWA EARTHED BOTH ENDS) , there have also been concerns on this thread as to using 4mm cable across the 31m length, I am only running about 200 watts of LED Lighting and two exercise bikes, don't see the problem with such a small load, confused!! But .......as you have alerted above, I will mention the earth rod to Sparky, as I would feel more comfortable with an "onsite earth", better by design. Thanks Bob
WTF this is not a shed, this is an functional outhouse with luxury power outlets lol. No offence but this needs a proper design installation. You are not just powering a shed with a light and few sockets for a weekend hobby, this is a full on functional living space in your back garden.
Fire, all noted. For the purpose of clarity, can you please elaborate on your views. Can you define "proper design installation" and why my design is not suitable. Can you define "functional living space".
This is back to front. Which electrician, the council's?? It's the electrician that will sign his life away by certifying that he DESIGNED, INSTALLED and TESTED the installation. Also he will need to self-notify the work to the LABC as his own work. So you'll need to find an electrician who is prepared to lie and falsify documents. As a design aside. There's no point having RCDs in the outbuilding if you already have an RCBO at the origin. Pointless. There's one bit of your design that's a pile of poo.
I quote: 6 amp - outside shed canopy and wall lights (led) supplied via DP Isolating switch 6 amp - garden lights (led) supplied via DP Isolating switch 6 amp - internal lights (led) 16 amp - outside socket supplied via DP Isolating switch 32 amp - 5 internal sockets (occasionally use of TV and 3 exercise machines) This is an entire outbuilding installation and not just extending your circuits, you have 3 lighting radials, an ip68 socket radial and a ring final. There is allot involved in installing all these circuits such as the type of cable, cabling routes, are they to be installed in conduit singles, T&E chased into the wall, behind plaster board clipped direct, RCD protection and all relevant testing just to mention a few. From what you are saying is you are to feed a split load consumer unit from a 4mm2 cable partially via T&E into a junction box then into 4mm2 SWA cable out and under ground into this split load consumer unit and fed from a single 32Amp RCBO in the house consumer unit. Functional living space = 3 exercise machines, multiple lighting circuits and a TV to watch... Again there are other contributing factors such as the distance as in length of cable run, have you determined if the length of cable will cause a voltage drop and note that a standard RCBO is only a single pole isolator. Circuits leaving the home need to use a double pole isolator so that not only disconnects the live but the neutral as well which a standard single pole RCBO will not do. The type of installation you are trying to design should incorporate a Double pole isolator and the SWA cable should be fed directly from that isolator not travel on a 4mm2 T&E to a junction box and then into the SWA. Is there a reason why you want to do it this way? Again the SWA cable can be 3 core where the two Live and Neutral are used and the 3rd core is used as an earth along with the steel armour which doubles up as the earth when terminated correctly in the brass gland. How were you planning on terminating either end of the SWA? What made you choose to use 4mm2 cable for this design? Also what is your current homes electrical installation setup, TN-C-S, TT etc.
Thanks guys for coming back with so much infomation. Bazza, as far as the electrician is prepared to lie, this is the situation: All cable teminations are visible and accessible, all cable routes are still visible, therefore any alterations that are suggested can be done. My cable routing and termination is very clean and SAFE! ( a lot safer than many qualified electricians!) As far as RCD's a "a pile of poo" I can think of a many more mature ways of explaining your views, is there an element of safety where the RCBO is also protecting the live cable from the CU to the Sub Main, therefore protecting a person if the cable is compromised between CU's. Fire I Can see your point to a degree as far as functional living space, but there are "sheds" with weekend hobbists all over the country running allsorts of carpentry, welding and engineering equipment with a single light and a radial socket, or the more often extension cable through the window scenario, demanding a lot greater loads than what I am requiring. SWA terminated at earthed both sides using brass glands and banjo's, earthed via 3 core. All cable routes are within the safety zone requirements and RCD protected as required if less than 50mm within walls. DP Isolating Switches to all outside lighting and sockets although RCD,MCB protected, for the reasons you mention, but will now include the Isolator to main feed, (learn and make changes appropriately!) Home set up TN-C-S 4mm used as this is the existing armoured cable under existing concrete foundation and patio prior to moving in, therefore used 4mm as continuation of circuit. Junction boxes either side of SWA because the existing SWA just reached inside shed and therefore extended with TWE for ease of use internally and same with attic. As previously mentioned, my concern is the distance (voltage drop and viable earth), perhaps rod required, but this will be all assessed, tested and cerified to regs, if ammendments needed, then will be addressed.
Forums
Facebook
Twitter
You Tube
Instagram
Shop