Alterations to Garden Radial

[thatguy250]

Hi
I installed a garden radial circuit off a 30ma 13 amp RCD spur from my ring main before part P came in. When I did it, I took 2.5mm cable in a conduit from the house to a socket on the patio, likewise a 1.5mm to a light which is switched from a 3amp fused switch indoors but protected by the same RCD. Then from there, connected 3 core and earth armoured cable rated at '13 amps' which had a picture of a light and a plug socket on it (looking back I now realise is an odd size of ~2.0mm) underground to a double socket and light in the greenhouse. (greenhouse light is on 3rd core on same switch as patio light). After installing, I needed an additional waterproof socket for a pond pump half way along the garden, so I added that to the armoured cable. Total length from house to greenhouse is about 20m. From RCD to current fuse box is about another 15m.
I'm currently having an extension built and new distribution panel put in for the house, and thought it would be a good idea to run a separate 2.5mm T&E cable across house from new panel to garden RCD spur to separate it from ring main. (will get my electrician to connect it into a new 16 amp RCD when it's done, and to clarify, the 13 amp RCD spur is located inside.
Is this setup adequate? I realise there are 3 sockets in the garden, 2 on 2.5mm cable and 1 on 2mm aswell as the 2 lights. Part P red tape would suggest to me that the cable should be 4mm all the way along, but that just seems impractical as, at any one time I'll only ever have a 3 amp pond pump, 3 amp light and maybe a hedge trimmer on the go and would rather not get it replaced. Remember the RCD spur doesn't allow the circuit to exceed 13 amps anyway.
Just want to get your impression before mentioning my garden setup to my electrician, who might have questions. Seems over the top to run a 4mm T&E from distribution panel to the 13amp RCD spur when 2.5mm is perfectly adequate, rated at 25 amps. Voltage drop is minimal, as cable runs through uninsulated ceiling, then straight outside.
thanks
(sorry that was a bit of a long-winded way of explaining the setup, let me know if I need to clarify anything better) [/i][/b]

 

[PrenticeBoyofDerry]

Well it is notifiable work and an application should have been made prior to you starting work, if you now employ an electrician to sign the work of they would be foolish in doing so and should not be doing it.
You stated swa rated at 13A and then said it could carry 2.5mm could carry 25A so what is happening there sure it's protected by 13A spur but can it carry 13A or 25A do you know.
Part P red tape it's a simple application form that is dealt with within a few days.
And did you actually do voltage drop calculation.

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

thatguy250
Did you do the relevant inspection and test during installation and completion of work prior to energizing this installation have your assured it complys to part p and BS7671.
I don't want to be too negative or dramatic, not may style leave that to others but you do realize you have broken the law and could have well endangered lives and created a potential hazard. Just add and your house insurance could be now invalid.

 

[chapeau]

Part P police alert.

Why do you say he broke the law and told him he could have endangered lives in such a 'negative and dramatic' way? He specifically said he installed his garden circuit

before part P came in

. He is now asking for advice on what he needs to plan for before his electrician comes in. Is it against the law to ask for advice? What next, you ask for his address and send the real police around to stop him. In his own home?

 

[thatguy250]

Ye, sorry for confusion
I installed garden circuit before Part P came in. It's a 13 A RCD spur off the indoor ring, currently with 3 plugs and 2 lights. I'm planning pulling a 2.5mm cable from the current fuse box to the 13a RCD in the living room through the ceiling ready for my electrician to connect up to a 20A radial RCD in a new distribution board. So, effectively it will be a 20A radial circuit with an inline 13amp RCD spur. Just to clarify, I'm getting advise to pull a cable, I won't be connecting anything up to the new distribution or doing any work outside.
If it's protected by a 20A RCD, I guess I can just do away with the 13A RCD spur and then it doesn't matter how many plugs are in the garden?
Thanks

 

[thatguy250]

Also, I used TLC's voltage drop thing to check the size of the new cable, but as half is in ceiling and other half is buried outside, depending on which factors I change, sometimes it comes out 2.5mm, other times 4mm. Point is, outside part is protected by an existing 13A RCD spur, so I guess I only need to calculate for the distance of the 20A radial between fusebox to the internal 13A RCD, which comes out at 2.5mm T&E

 

[PrenticeBoyofDerry]

I apologize, I miss understood your post, regarding before part p came.
interpreted it wrongly.
It's always best to use SWA cable on outdoor cabling projects, Your calcs have come up with two different results regarding cable sizing. 2.5 or 4.00mm.
I'd always go top size, 2.5 should be okay on the 13A spur. I personally would have put a 4.00mm in so your in the position to increase the current rating if needs be.
If you now intend to remove the spur and create a circuit from the CU using a 20A MCB or RCBO if it is not RCD protected that to should be okay. But your electrician will be able to tell you what you can do and what is suitable, but the 2.5mm cable current carrying capacity should not be lower than the breaker protecting that circuit.
I hope this was a more helpful post.

 

[ban-all-sheds]

By the sounds of it the best approach would be to have your electrician replace the entire cobbled-together mess.

 

[chapeau]

There is insufficient information to make that recommendation, unless the electrician would be doing it for free of course, but that is not likely.

PrenticeBoyofDerry, well done in admitting you misread the post. For what it's worth, if you are an apprentice, you should take the year(s) ahead to learn be more tolerant of people who might be paying your wages when you strike out on your own. If you want recommendations for other work then you should not threaten your punters with life in the nick without possibility of parole for murdering their first born as they used 2.0mm armoured instead of 2.5mm when wiring up their shed.

I do enjoy your posts though. Shame others on here just go missing when they make similar mistakes.

I reckon the OP should go ahead and notify and do it himself.

 

[ban-all-sheds]

There is insufficient information to make that recommendation,

Really?

When I did it, I took 2.5mm cable in a conduit from the house to a socket on the patio,

I am not filled with confidence that this was an appropriate cable or that it has been properly installed.

Then from there, connected 3 core and earth armoured cable rated at '13 amps'

The use of that term does not give me any confidence that the OP knows what he's doing.

(looking back I now realise is an odd size of ~2.0mm)

I've never heard of 2mm² SWA - again it makes me question how much the OP knows.

underground to a double socket and light in the greenhouse. (greenhouse light is on 3rd core on same switch as patio light).

So now we have a DSO and two lights on a 3A circuit.

And we are relying on the armour for the cpc, and therefore being properly terminated at each point.

After installing, I needed an additional waterproof socket for a pond pump half way along the garden, so I added that to the armoured cable.

So now we have two sockets and two lights on a 3A circuit, and at least 4 opportunities to create a dodgy cpc.

thought it would be a good idea to run a separate 2.5mm T&E cable across house from new panel to garden RCD spur to separate it from ring main. (will get my electrician to connect it into a new 16 amp RCD when it's done, and to clarify, the 13 amp RCD spur is located inside.

So the OP is proposing 2 RCDs in series. Another thing which makes me question how much he knows.

Part P red tape would suggest to me that the cable should be 4mm all the way along

His use of the term "red tape" indicates a disregard for regulations.

And his belief that he should be using 4mm² because of Part P is yet another thing which makes me question how much he knows.

but that just seems impractical as, at any one time I'll only ever have a 3 amp pond pump, 3 amp light and maybe a hedge trimmer on the go and would rather not get it replaced. Remember the RCD spur doesn't allow the circuit to exceed 13 amps anyway.

His recognition of the 13A limit together with a belief that he should use 4mm² cable makes me question how much he knows.

Voltage drop is minimal, as cable runs through uninsulated ceiling, then straight outside.

His belief that voltage drop is related to whether the cable runs through insulation makes me question how much he knows.

I reckon the OP should go ahead and notify and do it himself.

I strongly disagree.

 

[chapeau]

His belief that voltage drop is related to whether the cable runs through insulation makes me question how much he knows.

It means he knows more than you.

 

[Aragorn84]

Then from there, connected 3 core and earth armoured cable rated at '13 amps'

The use of that term does not give me any confidence that the OP knows what he's doing.

From how i understood it, it IS actaully 3 core and earth, one live for the socket, one switched live for the light fed from the patio light and one neutral plus earth?

If that is the case it does sound a bit dodgy to me!

 

[ban-all-sheds]

His belief that voltage drop is related to whether the cable runs through insulation makes me question how much he knows.

It means he knows more than you.

I'm always willing to learn.

I await your explanation of how running a cable through insulation affects voltage drop with great interest.

 

[thatguy250]

Wow, so much confusion lol I like it how if anyone ever mentions the word 'garden' in this electrical forum, there's a sudden raising of red flags
anyways, PrenticeBoyofDerry has more or less given me the constructive answers I was looking for. I thankyou good sir I will run a 2.5mm cable from the fuse box through ceiling to the 13amp RCD spur in the living room. Get my electrician to wire it into a 20amp MCB in the new distribution panel so that there aren't 2 RCD's in series. If I decide to make any changes outside at a later date, I will notify building control.
With regard to questions over the lights running on this circuit:
from the 13 amp RCD in the living room, I have a sealed PVC conduit going outside to an IP65 plug socket with a matching switched 3amp fused spur next to it. The yellow strand in the 2.0mm armoured cable comes out of the 3 amp FUSE SPUR to power the lights. The red strand comes out the back of the PLUG SOCKET being supplied by 13amps down the garden to the plug sockets further along. The plugs and lights both share a neutral, and the armoured cable is metal sheathed, earthed and terminated at IP65 glands either end. It's a nice simple setup really. Honest lol. p.s Ban-all-sheds, give up the electrics, you should be an atourney

 

[thatguy250]

I think Ban-all-sheds needs a shed, then he can wire it up and see where I'm coming from
Hope this isn't too complicated a theory, but I was under the impression that if a cable is running through insulation, if it is operating at near full load it is much more likely to get warm, increasing the resistivity of the cable and causing a voltage drop.
Go in the kitchen, wrap a duvet around your kettle cord and tell me how you get on lol

 

[thatguy250]

Oh, and the armoured cable is 2.0mm not 2.5mm. I'm not just being dense. It was a homebase invention. Can't imagine .5mm will ever make any difference though. As I say, it had a picture of a plug socket and a light on roll's packaging, so I'm guessing it can be used for 13amp or 3 amp applications.