I struggle to get tradesmen here in the highlands and have failed to get an electrician to show interest in rewiring my garage. So I'm going to do it myself if I can educate myself sufficiently.
I already have a modern armoured cable into the detached garage installed by an electrician last year. This is all single phase, no big loads, I recall the spur cable is rated at 40 amps. Scope a consumer unit, three led 'strip' equivalent lights, and a handful of sockets.
Advice please on how to educate myself. I'm close to purchasing a copy of BS7671 but a second hand copy seems to go for £60 - does the BS7671 On site guide at about £25 have the detail I require? Or is there some other resource I can use to do a good job?
Comments from professionals particularly appreciated. Or, if you are an electrician working near postcode PH34 would you like the job to save me the bother?!
To put the minds of any doomsters at rest I am an engineer with an HND in Electrical and Electronic Engineering (but it is a hazy memory) and a degree in Civil Engineering. I have no intention of carrying out any bodgery. I do however have a slightly rebellious streak when it comes to rules and regulations, in this case because the work required is in an outbuilding well removed from my house.
Any advice on educating myself to produce a quality job gratefully accepted.
Google “bs7671 pdf” and you can read it for free. I say go for it, hardly rocket science is it?! 🙂
Hopefully one of the actual electricians on here will comment. As a DIYer I have done a lot of electrics - some more complex than that. ( and had it professionally checked by a really fussy bugger) Its not difficult if you work methodically. Proper tools help ie decent wire strippers and snips.
For the cost of the full guide at £60 is that not a good investment? It will keep you in line with the regs for sure. Or do you want it to be safe but not care about the precise regs? Is the spur cable really 40 amps? That requires a really thick cable / wires. Are you surface mounting or hidden? If surface mounting you obviously need conduit. Think about where to run the cables - there are guides to the safe zones to run them.
There are quite informative guides on the net as well
Be methodical, keep it all neat and tidy, put in more stuff than you think you need.
Edit - if putting in a consumer unit then have more slots than you think you need - makes future additions much easier.
Trouble with the standards is they aren't really how-to guides. It's all in there but in a very user unfriendly format.
If you can get a rough handle on what you want then posting on here or on diynot should give some useful information on whether you have it right. You will also get people telling you to get a pro in so you have to filter out the good from bad.
My set up is an armoured cable. That is on a 40 amp non RCD breaker in the house. That comes into a 5 way metal consumer unit with an RCD. Having a local RCD is better but you do need the supply cable to be wired appropriately, not essential if you the existing cable already has an RCD. I then have 5 mcbs for: 1 16a socket, 2 some metal sockets switched from a cooker switch so I can turn them all on/off easily, 3 some metal sockets on permanently, 4 led lights 5 armoured cable to another shed. I'm very happy with this. I don't feel anything is missing.
It's all easy to fit if you are reasonably competent. You want some test kit, at least a multimeter and a socket tester. There are rules about DIY and sign off, and they are different for Scotland and England.
Happy to talk about it further either here or via DM. I spent a while researching and asking before doing mine. It's close to my day job and I already had some pretty good test kit so was happy to have a go.
BS7671 won't actually tell you how or what to do - on site guide is slightly more practical with diagrams etc, but again more as reference than a how to. Regs despite being from the IET are seemingly written by lawyers and not engineers when you look at wording etc.....
If you can find the 'practical guide to the IET regulations' that's more helpful - although haven't seen a current version of it - mine is a 16th Edition.
As above know what you want, plan it, ask questions and work methodically and you should be ok. Main areas are type of circuit (radial or ring), mechanical protection to cables, correct sized MCB/RCD's to ensure discrimination and earthing to back boxes etc.
Sounds like you most likely have a 4mm2 SWA feeding the garage. 40a being the upper end of its rating! So derate the mcb/rcd rcbo.
lighting circuits are radials, 1mm2 would be adequate, 1.5mm2 on a 6amp you can’t really go wrong with that.
Rule of thumb for sockets is 2.5mm2 ring main backed by 32a device. A 2.5mm2 radial backed by 16amp device would be fine.
Just choose method of installation, surface clipped t&e. Plastic trunking or conduit. Plastic trunking probably the easiest to make a neat job if you buy the bend caps.
The first thing to do is find about the Building Regs (E&W equivalence) situation in Scotland. Your project might be illegal and you're on the radar now 🙂
dirkpitt74 and nickjb +1. The regs aren't an easy read; the on-site guide is better in that respect
...in this case because the work required is in an outbuilding well removed from my house.
You need to look at the distance/cable size/voltage drop and also the earthing arrangement
I’d go the DIY route. Yes, I’m an electrician. It’s simple. You will struggle getting the new SWA gland on properly, watch some youtube clips to see how it is done. Make sure all cable runs are supported correctly, preferably with metal clips every 3 clips.Cables run up/down/across in safe routes. Presumably it is all typical garage loads, battery charger, power washer, vacuum etc, then run a 20 amp radial circuit, typically, 2.5mm twin and earth cable will be fine for that. Lighting, as said above, 1mm twin and earth will be fine. You will need a ‘garage’ consumer unit, which is just a small consumer unit with 2 or 3 outgoing ways. I’d be tempted to go for something a little bigger, so you have the possibility of having 4 or 5 outgoing ways, and, I’d be going for individual RCBOs rather than a single RCD and 2 or 3 circuit breakers. I wouldnt bother with surge protection for a garage, but if you are likley to have expensive electronic equipment in there, fit a surge protector.
Paperwork - you should get an electrical installation certificate, but to get that you will need to test it thoroughly. I presume you havent got a suitable tester, so get one of the plug in testers that can test RCDs, at least that will tell you if you have an earth at the last in line socket/light, and that the RCD works.
I woudlnt bother with 7671, you wont get anything out of it, the On Site Guide will be fine for what you require, in fact its better, as it has the building regs requirements in there, and gives safe zone diagrams etc.
I completely wired our house when we gutted / renovated it, bought the 16/17th edition (can't remember which) and the onsite guide. Had it signed off by building control at first and final fix/tested. The regs book isnt useful in this instance.
*I'm a multi skilled engineer and used to working with industrial control system wiring.
Building Regs (E&W equivalence) situation in Scotland. Your project might be illegal
Only if it's under a building warrant.
Thanks for the responses folks.
I did mine, ran 2 x 2.5mm2 armoured cables (original ran a ring fro the house) from the DB into a garage consumer unit with a 6A and 16A MCB and an RCD. Sockets are on a 2.5mm2 ring and lighting is in a seperate 1.5mm2 circuit. All in conduit.
I'm not a sparky but as long as you take your time and check your work I really can't see an issue doing it yourself.
Hmm, was going to get a supply and consumer unit put into my new shed then do simple circuits myself by clipping twin and earth to the framing with appropriate junction boxes. Sounds like I need to improve my standards and at least get some conduits to protect the cables!
tthew - don't use junction boxes if you can possibly avoid them. Every connection is a failure point. Very basically if you can see the cables they need to be in conduit
mechanical protection is only really needed where a wire might get caught and damaged.
if your wiring a shed ensure you give some slack on the cables as wood moves. It might not look as nice as it could but its better than stuff potentially being pulled loose.
my shed has the socket loop in conduit at chest height above the worktops, lighting is surface clipped as with the position of the switches and the lights its highly unlikely to get damaged.
If you aren't planning on running anything powerful in the garage a simple fused spur would probably do it.
IANAE
Regarding earths, if all the SWA cable conductors are the same size then connecting the earth at the house end should be ok. If the nominated earth is smaller then an earth stake is usally used with no connection at the house end. Especially important if you're on a PME supply with earth provided at the sub-station.
tthew – don’t use junction boxes if you can possibly avoid them. Every connection is a failure point.
Practically what's another option where you need to make a joint in the circuit? And given it's all going to be visible and accessible in the shed, fault finding would be simple anyway.
Why would you need to make a joint in the circuit? I've rewired a house without a single junction box. Spurs off the back of sockets, lighting ;loop in and out even tho they are radial circuits fused spur points on the ring. Its not wrong to use junction boxes but the fewer connections in a circuit the better
I wired-up my shed/workshop - electrician mate connected an armoured cable to the house supply once I’d finished. Installed a 3 way consumer unit with a 16A and 5A circuit breakers. Metal clad switches and sockets with plastic conduit kept it all tidy. As said, decent wire cutters , stripper and the correct size screwdrivers for the terminal screws. Make sure all the earths are installed and correctly insulated if using metal clad fittings.
if you can see the cables they need to be in conduit
Is that a reg - because the big cable that connects my new EV charge point to the meter isn't, and that was done by a proper firm. All clipped to the garage wall, just as all the (properly installed) wiring is.
if you’re wiring a new socket or lighting circuit and have to use a junction box you’re straight up doing it wrong, there’s no need for them whether accessible or not.
Things to consider for wiring to the garage in no particular order that an electrician should check or calculate are type of earthing system at the cut out, volt drop on the cable run, max Zs/short circuit current, protective device selectively, any extraneous conductive parts. You probably will be fine doing none of that and it’ll work how you want it to but there’s a reason it’s done.
Then there’s the problem of how to terminate the SWA cable correctly at both ends, garage end will be fine as the board will be metal but what’s at the house end
You'll probably do a better job than the leccy did on our garage 30 years ago.
New build, moved in, garage had no electric. FIL recommended 'his' electrician, who ran a cable off the kitchen circuit, through plastic pipe, to the garage. Small 13a fuse box, flo lighting and two double sockets. Nothing has blown up, but seeing how FIL's house was wired when we sold it more recently....
@theotherjonv, cables don’t have to be in conduit if they are double insulated,which you’re cable will be, clipped direct is fine.
I always Do the cable drops to sockets etc in a garage in conduit as it’s a neater job and actually quicker to do
actually, since you mentioned it and I went and checked, that's how mine is. The wiring is at garage roof height and is clipped to the wall or rafter; the lighting is at pretty much the same height (fluo strips either side) so only has tiny 'exposed' drops, and the big drops to the sockets and the light switch, and also the drop to the charger box is actually in conduit.
