Garden Wiring

[Thefailsafe2012]

Why end up back at the cu?

 

[Richard Burns]

Ok, so if i do away with all spurring here and continue the ring circuit from the socket in the house > to the shed > to the sockets and switches for lights (which will all be FCU's) for the decking > back to the remaining sockets in the house > before ending back at the CU. If you understand what i mean. Put everything on the ring.

Would that be acceptable?

Skamuk
You really do need to know what you are doing with a circuit before you start planning things. You need to be able to calculate the requirements for the circuits, whether the volt drop exceeds the maximum allowable, whether your accessories are rated for the potential fault current and so on and so forth. I commend your enthusiasm but I cannot commend your level of understanding of electrical installation.
As you have a friend who is prepared to risk their career to sign off your work for you then the best bet would be to ask him what you need to install.
You are aware that by law all electrical power installations across a garden need to be notified to building control or self assessed through a competent persons scheme.
The key points are to design a circuit within the wiring regulations and the building regulations. You should know what these regulations are before deigning a circuit. BS7671 the wiring regulation and the on site guide and the electricians guide to the wiring regulations and approved Document P would assist you to understand the requirements.
You need to differentiate between lighting circuits and socket circuits by fusing them appropriately.
You need to ensure that there is no possibility that cables can be overloaded and overheat (which is where spurs on spurs are not allowed) by using the appropriately sized cable for the design current and protective device.
A ring final circuit using 2.5mm² cable and a 32A mcb should not exceed 100m².
Light switches are rated in general to a 10A maximum load and a lighting circuit should take this into account.
Your hope of extending the ring out into the garden can be done but it would require some interestingly inconvenient rewiring in the house especially if you are using SWA.
The use of multiple FCUs for your lighting circuit seems overkill and seems to indicate that you are not sure how you should do this.
I hope that this gives some useful information but also provides some warnings that maybe you need more information to be able to install this in accordance with the regulations.

 

[nikmet]

skamuk, maybe if your friend could do the install, then you could watch and learn whats needed to complete the job to a good standard, and have the opportunity to see and ask lots of questions as it progresses, you sound very enthusiastic and keen to learn.

 

[skamuk]

Skamuk
You really do need to know what you are doing with a circuit before you start planning things. You need to be able to calculate the requirements for the circuits, whether the volt drop exceeds the maximum allowable, whether your accessories are rated for the potential fault current and so on and so forth. I commend your enthusiasm but I cannot commend your level of understanding of electrical installation.
As you have a friend who is prepared to risk their career to sign off your work for you then the best bet would be to ask him what you need to install.
You are aware that by law all electrical power installations across a garden need to be notified to building control or self assessed through a competent persons scheme.
The key points are to design a circuit within the wiring regulations and the building regulations. You should know what these regulations are before deigning a circuit. BS7671 the wiring regulation and the on site guide and the electricians guide to the wiring regulations and approved Document P would assist you to understand the requirements.
You need to differentiate between lighting circuits and socket circuits by fusing them appropriately.
You need to ensure that there is no possibility that cables can be overloaded and overheat (which is where spurs on spurs are not allowed) by using the appropriately sized cable for the design current and protective device.
A ring final circuit using 2.5mm² cable and a 32A mcb should not exceed 100m².
Light switches are rated in general to a 10A maximum load and a lighting circuit should take this into account.
Your hope of extending the ring out into the garden can be done but it would require some interestingly inconvenient rewiring in the house especially if you are using SWA.
The use of multiple FCUs for your lighting circuit seems overkill and seems to indicate that you are not sure how you should do this.
I hope that this gives some useful information but also provides some warnings that maybe you need more information to be able to install this in accordance with the regulations.

Thanks for your reply Richard. You seem to be very knowledgeable of the rules and regulations. I'm going to seek more information on this from both my electrician friend and my college, but I would love for someone on here to also point me in the right direction as I intend to order the materials asap. I've provided the spec for all equipment being installed and all the materials I intend to use but no one has given me a straight answer in terms of just telling me what exactly is needed.

My understanding is that to do a proper job from top to bottom, there should be two more circuit breakers installed in the existing CU, one for the lights and one for the sockets. A B6 and a B32, and they should be protected by an RCD. The cable for the sockets should be 2.5mm (and not exceeding 100m2 as you stated above), running a ring circuit for the two sockets. I understand that regulations require it should be done properly but it's just a diy job!

My point is - I can't see what the difference between plugging a 20m extension lead with 8 sockets, protected by a 13a fuse in the plug, into the plug socket in the shed, running it to the back of the garden, and plugging 4 lights and 4 appliances into it?

All I'm doing is hard wiring it instead of having all the plugs? So surely running all the lights through fcu's, and the whole circuit through a 13a rcd in the shed it will be safe and equivalent to the above!!!

I know its not the right way of going about it, and its not within the regulations but it will work and be safe, surely thats all that matters here. Id rather overkill with fused switches than not do the job at all. Because I just want her to have something safer than an extension lead up there! Which is what she is using at the moment.

Again thanks for your help and I will be reading into BS7671 and the on site guide and electricians guide.

 

[Richard Burns]

If you are not designing it to the regulations then it is unlikely to be safe for all situations, because that is the purpose of the regulations: to ensure a circuit is safe.
The safest way to set this up is to put an 13A FCU at the start of your external circuit and then run what you need out from that FCU. This is the hard wired equivalent of running an extension lead You would be limited to a total current of 13A which could severely limit your capability to run so many halogen floodlights and use the sockets effectively. If you have all the lights on and the patio heater then you could blow the fuse.
A 13A RCD does not exist.
Putting in multiple FCUs, 1 for each light is less safe than having one FCU for the entire lighting circuit.

The reason you are not being given a design guide for how to illegally install an unsafe external garden circuit is because we do not wish you to kill your mum by installing something that you do not understand and could be dangerous.

If you order the materials you have stated and then have them available once you can get on site advice then you will likely find that you have enough materials to create a safe circuit.

 

[skamuk]

If you are not designing it to the regulations then it is unlikely to be safe for all situations, because that is the purpose of the regulations: to ensure a circuit is safe.
The safest way to set this up is to put an 13A FCU at the start of your external circuit and then run what you need out from that FCU. This is the hard wired equivalent of running an extension lead You would be limited to a total current of 13A which could severely limit your capability to run so many halogen floodlights and use the sockets effectively. If you have all the lights on and the patio heater then you could blow the fuse.
A 13A RCD does not exist.
Putting in multiple FCUs, 1 for each light is less safe than having one FCU for the entire lighting circuit.

The reason you are not being given a design guide for how to illegally install an unsafe external garden circuit is because we do not wish you to kill your mum by installing something that you do not understand and could be dangerous.

If you order the materials you have stated and then have them available once you can get on site advice then you will likely find that you have enough materials to create a safe circuit.

Ok that makes sense. So what if I had 2 FCU's at the end of the garden instead of one in the shed, one for the lights and one for the sockets? - Or would this mean that the SWA from the shed to the decking would be unprotected (I figure it will be protected by the circuit breaker in the CU indoors..)

 

[Richard Burns]

You are then putting two accessories (each FCU) on a spur from a ring but a spur should only feed one accessory. (after the fuse there is no problem because the fuse protects the cable.)

Additional edit: Oh yes and I forgot you would also be leaving the shed circuit incorrectly protected.

 

[fylthespider]

interesting posts.
seems like a lot of reading between the lines going on.
to put it blunt, your knowledge/understanding of whats needed isn't up to scratch yet and this is a garden.
don't bugger about with it, unless you can live with frying kids in paddling pool while they're trying to plug in their ipod chargers.

get some more advise on site by someone with the time and patience to take you by the hand through it.

I don't want to come across as patronising (seems like u got the enthusiasm ) but some installs in gardens make me shudder.

having said that, my two pence would be run swa (4mm?) from house CU to shed, 4way rcbo board in shed on a TT, radials out to accessories (either in swa or conduit). avoids exporting TN earths, means you got local(ish) isolation and you can see what the hell is going on.

either way you still need to calc cable sizes, volt drops, rcbo sizes, etc.
all the best.

 

[skamuk]

A 13A RCD does not exist.

But I have seen these for sale everywhere. Is this not a better solution rather than having to change the fuse in an FCU if it blows.

Toolstation > Electrical > Extension Leads & RCDs > SafetySure RCD Spur White

 

[Thefailsafe2012]

That thing still has a fuse in it which will need replacing when it blows! Why can you not run new circuits out of the main cu?

 

[skamuk]

That thing still has a fuse in it which will need replacing when it blows! Why can you not run new circuits out of the main cu?

I can, I just don't want to. Its running the cable from the front to the back of the house from the CU. All cable would have to be hidden in the walls, no conduit or anything like that. Cant pull up laminate flooring and kitchen floor tiles to bury it under the floorboards, so It's kind of my only option.

So if this has a fuse... What is the reason for its existence? Once it blows you can't reset it? I assumed the fuse was there as a backup if the rcd failed?

 

[rmc86uk]

I'll end up running an extension lead in a bin bag at this rate!

This actually made me laugh out loud! I've seen this many times before probably along with other forum members to!


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[brightspark26]

What I've seen before is a fcu in the house off the ring with a 2.5t+e then from there a swa 2.5 3 core to a shed which then goes to 2 fcu 1 for single socket on decking and 1 for decking lights. The ring was supplied from a 17th edition dual RCD consumer unit. The only reason the 2 fcu were fitted in the shed for isolation and the lighting had a 3a fuse in it

 

[ackbarthestar]

Reading this thread it appears that the Garden 'extension' wiring is going to end up as a Pigs ear. If you add spurs on spurs with, no doubt, T&E running all over the place.

IMO I would strip out the existing garden wiring, leaving the outside socket connected to the rfc and run a separate sub mains supply to the Garden shed. This leave you with all the design considerations associated with circuits. Something to consider as you do your electrical course at college and will give you greater impetus to learn all the basic design rules as you go.
You've got a great opportunity to get it right. Look forward to hearing about the outcome....

 

[Thefailsafe2012]

So if this has a fuse... What is the reason for its existence? Once it blows you can't reset it? I assumed the fuse was there as a backup if the rcd failed?

In your case say you we're going to run a lighting circuit off that RCD Spur, you'd fuse it accordingly say for example with a 3A fuse, it also has the RCD function so you are also protecting people from stray shears, pitchforks etc. It's a device used where you would have to meet the requirements of having RCD protected circuits where there is no main RCD so to speak. Similarly you can get IP rated RCD sockets too