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Hi all,
Having had the frustrating experience of getting someone out to estimate for the job who then obviously decided it wasn't big enough to bother with and then instead of admitting it just completely failing to get back to me - TWICE - I decided to do the job myself. So it's basically just supplying a double socket and light to my shed from a spur taken from an outside plug. The plug itself has a separate RCD connection to the fusebox on its' own. Not sure if that makes any difference but it does mean if it trips nothing else in the house will be affected.
I've taken 2.5mm SWA armoured cable to the shed. Attached to the wall until it reaches the patio, whereupon it is buried about 40cm down, deeper than the sewage pipe I uncovered in the process and with warning tape over the top. Total length of the SWA cable is about 8m.
Once in the shed it supplies a switched FCU (13A). From the FCU I have taken 2.5mm cable to a double socket, plus 1.5mm cable to another FCU, fused at 5m, which then supplies the strip light.
It all works fine, but I gather these days I have to get it signed off for building regs, so I was planning on trying to find another electrician who will just come and sign it off for me. We use one regularly through work so I'm hoping they might take pity on me and come and do it as we are already good clients. Anyway before I do so I wanted to check that I have done the job correctly as I worked it out through google rather than any actual knowledge of electrics.
Thanks in advance!
No, no need to do a Building Regs Certificate (Part P), as it is not a new circuit, and it isnt in a bathroom (or kitchen in Wales).
A Minor Works Certificate would be the most that is needed. This is a one page Cert. that is filled in detailing the work done, and the relevant test results.
I assume someone qualified still needs to do it though?
Nope. It's just a spur. Just need to be a "competent person".
Not me then! Looks like it needs to be tested, and I don't have equipment to do it, although I could presumably get some. More to the point have I made any mistakes with how I have wired it?
I wouldn’t worry about getting it certified, if they didn’t do the install any electrician will cover the minor works cert in so many limitations it’ll be pointless anyway.
From your description it sounds like you’ve got a 2.5 & 1.5 into the switched side of the first spur, if that’s the case I’d change the 1.5 just to make a more secure connection. And if you’ve used metal clad accessories use protection on the knockout holes, grommets minimum but ideally stuffing glands.
No the FCU just has the 2.5mm SWA cable supplying it.
And out from the load side?
The load side has 2.5mm cable to a double socket, and 1.5mm cable to a separate switched FCU fused at 5am which then supplies the light.
From what I can see I could fill in the minor works certificate as long as I can work out how to test it and what equipment I would need to buy. You don't have to be NICEIC certified to do it.
I honestly wouldn't bother with the certificate. I'd just test the RCD tripped appropriately from the shed and leave it there.
You can get various test plugs which generate a 30mA earth leakage current eg
It’s not good practice to have different sized conductors in the same terminal so change the 1.5 feeding the lighting spur to 2.5
If you want to test it yourself you’ll need a continuity tester, an insulation resistance tester, earth fault loop impedance tester, RCD tester and most importantly a copy of BS:7671 to interpret the results, cos if you don’t do that you are just putting numbers in boxes! That little lot will set you back about £700 minimum.
Oh and a knowledge of your supply characteristics, earthing arrangement and protective devices
If you want to test it yourself you’ll need a continuity tester, an insulation resistance tester, earth fault loop impedance tester, RCD tester
Or just buy a multi-tester, not sure why you'd bother buying separate testers....
Thanks for the replies. I think I’ll take on the two simplest suggestions which is to swap the lighting FCU supply to 2.5mm and get an RCD tester, and leave it at that.
Or just buy a multi-tester, not sure why you’d bother buying separate testers
They are much cheaper separately (at the budget, second hand end of the market), I find it easier to do the calibration checking, and if one fails i can bin it and buy another. If you are doing it professionally then maybe it makes less sense.
Thanks for the replies. I think I’ll take on the two simplest suggestions which is to swap the lighting FCU supply to 2.5mm and get an RCD tester, and leave it at that.
Good plan. If you have used new cable and it is wired correctly there isn't a lot to go wrong. An RCD test and a polarity check will be useful and way more than most installations get.
@footflaps I prefer separate testers as opposed to multi, as if one fails you can still do certain work whilst it’s away for repair, and new, separates or multi cost almost the same away.
And if you’re buying second hand it’s probably some poor sods stolen one who’s had his van door ripped off, the same as with most secondhand power tools, plus it’ll need calibrating first
And do these RCD testers give you a value/reading or does it just introduce a fault and trip it? If the latter just press the test button in the DB and spend your money on something nice for your bike, it’ll be more use
I personally wouldn't bother. Our shed runs from a plug socket in the garage. Plugged into it's own RCD, then armoured cable along to the shed where there are two double sockets and two lights run off it. Should anything be faulty, the RCD trips.
It's really just an extension lead !
Testing would also cover the earthing arrangements. What is acceptable depends on how your house is supplied. There's no sensible way of DIYing the earth tests and the rules are quite involved.
Well it all works, I bought a simple tester with integrated RCD tester and it is saying all normal and tripping the RCD as expected, so I am happy with that I think.
Andrew
And do these RCD testers give you a value/reading or does it just introduce a fault and trip it? If the latter just press the test button in the DB and spend your money on something nice for your bike, it’ll be more use
They just create a 30mA earth current so you can check the RCD goes, which is 99% of what you want. The don't do the 1/2 current, 2x over tests, etc but they're getting quite pedantic. If it trips at 30mA, then it's working infinitely better than not tripping at all......
The one I bought claims to have a ground (PE) error indicator, voltage test and polarity / wiring test in addition to the RCD tester. Just a correct / incorrect indication rather than numeric but I think it'll do.
So it doesn’t tell you if the RCD will trip within the maximum permitted disconnection time then, which is 100% of what you want. Very useful!
Sorry you'll have to explain in idiot proof language! It has an RCD tester, I press it, the RCD trips immediately, but if there is some sort of need to measure how many milliseconds it takes then no...
So it doesn’t tell you if the RCD will trip within the maximum permitted disconnection time then, which is 100% of what you want. Very useful!
Tripping at all is still infinitley better than not tripping at all.
Even if you test one and it shows it passed within x ms, that only tells you what it did when you ran the test, not how well it will behave in the future.
but if there is some sort of need to measure how many milliseconds it takes then no…
More expensive test kit would check it trips within the allocated window, but I wouldn't lose any sleep over it - no one checks their RCDs regualrly to see they all trip quick enough and the world hasn't ended yet.
The extra check is only proving that between manufacture and you installing it, the device hasn't failed - which is getting into very small probabilities....
Footflaps, that last post is, quite frankly, downright dangerous! But also highlights why no self respecting electrician would certify someone else’s work.
There’s a reason why it has to disconnect in a certain time, and that is to reduce the chance of loss of life, simple as that. And whilst you are correct that as with any test in any field it’s only relevant at that time it’s gonna be on your conscience when your wife/husband/kid is flapping about on the floor like a landed fish when it goes wrong!
Using my spidey senses I’d say it was less than 50 milliseconds, and subjectively exactly the same as testing it anywhere else in the house....I’m sure it doesn’t make any difference but the entire house was wired from scratch less than 10 years ago so hopefully that means it’s fairly safe....and on the point of certification if I could actually get someone to bother turning up and doing the job I wouldn’t have ended up doing it myself! It drives me mad how unprofessional some people are - I would get no end of grief if I just decided to not bother getting back to clients who need things doing.
Rant over...
There’s a reason why it has to disconnect in a certain time, and that is to reduce the chance of loss of life, simple as that.
No one is disputing that.
The RCD is designed and tested to do that in the factory, then stuck in a box and shipped.
The install test checks it still works once installed.
Given we know it trips already, we know it's still working (to some extent). So the time test is dealing with the very small probability that is has degraded such that it still trips at 30mA, but takes a longer duration. Which is a very low probability event given RCDs aren't known to degrade in such a manner.
It's up to the OP wether he can live with that, I wouldn't think twice about it.
hopefully that means it’s fairly safe….
If you're serious, get it signed off - Nobody has asked what supply arrangements your house has. If it is TNC-S (quite likely if it is a new-ish house), and you've connected your shed "earth" to the house "earth" you've exported the equipotential zone into the shed which could cause a dangerous situation under certain network faults.
Nobody has asked you what the earth impedance is, or how you have calculated that 8m of 2.5mm SWA on top of your existing system impedance gives a low enough result to trip a breaker in the event of a fault (yes a breaker or fuse, not the RCD)..
A competent electrician will take account of all of this and more before signing it off.
(IANAE)
Nobody has asked you what the earth impedance is, or how you have calculated that 8m of 2.5mm SWA on top of your existing system impedance gives a low enough result to trip a breaker in the event of a fault (yes a breaker or fuse, not the RCD)..
Very easy to check, just cut through an extension lead with a pair of sacrificial side cutters and see if the breaker goes. All my side cutters have holes arced in the blades from forgetting to siwtch off the circuit before starting work......
NB Possibly don't try that at home kids unless you like loud bangs....
@tillydog none of those trivialities matter to Homebase heroes like footflaps, as long as it works to hell with any actual safety features.
With regard to PEN faults and ‘exporting’ the PME you only need to consider that if there are extraneous conductive parts in the shed, so metal gas/water supplies or if the shed is a metal structure
Safe to say I don’t plan on cutting through some live wire to see what happens. Although I did do that by accident once in an old house, and whilst the bang was quite fun, the fuse didn’t even trip in the main fusebox....
I’d like to get it properly signed off really, but getting an electrician out to do a quick job seems to be bordering on impossible. The guy who came out and then let me down was pretty happy about the cable length, and he had planned to take on a significantly longer route than I did. I wasn’t happy with his suggestion to tag some of it along a fence though, I I didn’t consider that to be very safe or sensible.