Domestic Garden supply

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HandySparks

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Hi All,
Detached house, about 15 years old, on an estate. Customer wants a socket and some light on his decking area at the end of the garden (for amenity, not security). It's bordered on two sides by brick walls (one is next door's garage).The easiest source is from his detached garage (supplied by a very short existing underground run from the CU in the house).

TN-C-S supply. Garage supply on 30A MCB on RCD side of CU in house (shared with kitchen sockets!). All other socket circuits are also on this single RCD.
Garage has 2 way CU, 16A sockets, 6A lights. No spare ways in either board.

I'm intending to take the garden supply via a SFCU with 13A fuse off the garage sockets circuit. Through wall to plastic adaptable box. 3 core 2.5mm² SWA, 30m long, down wall and underground to MK masterseal double socket on wall by decking. Short conduit link to double pole masterseal switch for lights. 1.5mm² HiTuf or NYY-J clipped to wall to each light (3off ?).

Any earth fault in the garden will trip out all the house sockets; not ideal but that's how it is. 2.5mm² is ok for, say, 2.5kW load (eg large garden power tool) and still be OK for VD on lights. 2 core SWA would be slightly cheaper, but I like the security of one core for the CPC. Not measured Ze yet, but it would have to pretty high for the Zs not to be OK.

The underground cable run will be in a narrow strip of gravel between the brick wall and a slab path. No digging likely but as it'll only be a few inches down, I'm inclined to supply a piece of
polythene cable duct for the customer to bury and then I can pull the swa through when he's done.


Any comments generally?

In particular on the supply to the lights being protected by the 13A fuse in the SFCU? I think it's OK. The cable rating is higher than this; it's only the wiring inside the lights (whatever they end up having) that may be a problem, but it's a small fixed load.

Does anyone know of some nice looking bulkhead lights or maybe some wall mounted spots that will take a surface run cable? Most domestic lights are designed only for back entry, which is not possible in this case.
 
E

Engineer54

The underground cable run will be in a narrow strip of gravel between the brick wall and a slab path. No digging likely but as it'll only be a few inches down, I'm inclined to supply a piece of
polythene cable duct for the customer to bury and then I can pull the swa through when he's done.
If you install your SWA in a heavy duty plastic pipe/conduit or similar mechanical protection, then it's fine to use the gravel strip. Just don't lay it under the gravel without protection, the sheath will be compromised within a short period of time.
 

Guitarist

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The lighting will definitely need protecting by a 3A fused SFCU as the switch, however you do it.
Btw, 25mm water pipe is fantastic for protecting swa underground, and it's very cheap from scr....x :)
 
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HandySparks

HandySparks

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The lighting will definitely need protecting by a 3A fused SFCU as the switch, however you do it.
Btw, 25mm water pipe is fantastic for protecting swa underground, and it's very cheap from scr....x :)
Thanks for the replies so far chaps.

I was trying to avoid an external SFCU for the lights as the MK one needs the cover lifting to access the switch, which I don't much like for a light switch (although I suppose I could fit a seperate light switch as well). However, I see that S'fix sell one by Masterplug/Nexus (S'fix 27437), where the swich can be operated through a flexible membrane.

Guitarist: Why do you think the lighting supply needs fusing down to 3A? Is is just to follow the usual manufacturer's instructions or is it something fundamental?

I like the idea of using water pipe. (I assume you mean the MDPE blue pipe.) Locally, I've been offered prices for the 63mm twin wall corrugated cable duct at about £100 inc VAT per 50m roll, so water pipe from S'fix would be a big saving. Rather than the blue pipe I'm going to see if I can get hold of the similar black cable duct, although I suspect it will be more expensive, as it is used in smaller quantities. What do people think of using blue water pipe as cable duct? I suppose a piece of warning tape on top helps to identify it as electrical.

Doesn't anyone know of "nice" external light fittings that take surface run cable without modifying them with drill and file. The ones the customer bought would have required a hole in both some stainlees steel trim and the blastic body behind, and would be very difficult to fit a gland to.
 

tigerpaul

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Can't see any problem using water pipe.
Just slap a sticker on every now and then for additional information for the end user.
 

Guitarist

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The MDPE water pipe is fairly indestructible, so a perfect defence for the already sturdy swa. Doesn't really matter that it's blue, although I do use warning tape above it underground, and make it visible where it exits the ground, so it's obvious what it is for. Yes, I was referring to most manufacturers instructions that their light fittings must have 6A CPD maximum. 3A is just a common size for customers to replace and gives good protection.
 
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HandySparks

HandySparks

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I spoke to the ELECSA tech helpline today and asked the question about using blue water pipe as protection for an electrical cable. The answer was that it's OK.

I'm still looking for a source of low cost black underground ducting anyway, even if not used on this job.

I found this:
Black Twinwall Duct 40mm x 50m Coil - P/PM398
Didn't know you could get the twin wall stuff in 40mm OD. Might be useful where you need a tight bend. At 32mm ID it's still big enough for an easy pull through of typical domestic sizes of SWA.
 
S

Swicade

Being as handy as it is for protecting SWA cables i'm wondering if there isn't some ruleing somewhere amoungst the 1001 building reg's saying it shouldn't be used as such.

No idea if there is but i'm under the impression pipework underground has a colour coding...kind of a harmonisation protocol for new services.

Blue = water
Yellow = gas
Black ducting = electric
Terracota = waste water

I could easily be wrong (as usual) but something like that rings a bell in the deep depth's of my mind.
 

Strima

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I'd place a length of electrical warning tape on the pipe then another length 200mm below the surface, that way there can be no doubt on the pipes use.
 
1

1shortcircuit

Being as handy as it is for protecting SWA cables i'm wondering if there isn't some ruleing somewhere amoungst the 1001 building reg's saying it shouldn't be used as such.

No idea if there is but i'm under the impression pipework underground has a colour coding...kind of a harmonisation protocol for new services.

Blue = water
Yellow = gas
Black ducting = electric
Terracota = waste water

I could easily be wrong (as usual) but something like that rings a bell in the deep depth's of my mind.
Some of that "warning tape" over the entire length will do the trick:thumbsup
 

rick

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Re. ducting - Tools...tion do some 15mm x 50m flexible ducting for £27 (#92505). A tight fit but you'd get 2.5 SWA into it with care. It's black too.
 

Guitarist

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I spoke to the ELECSA tech helpline today and asked the question about using blue water pipe as protection for an electrical cable. The answer was that it's OK.

I'm still looking for a source of low cost black underground ducting anyway, even if not used on this job.

I found this:
Black Twinwall Duct 40mm x 50m Coil - P/PM398
Didn't know you could get the twin wall stuff in 40mm OD. Might be useful where you need a tight bend. At 32mm ID it's still big enough for an easy pull through of typical domestic sizes of SWA.
I had already checked with Elecsa that it was ok, before using and recommending it, but never any harm in double-checking :)
I have looked long and hard at many other solutions, including black flexible conduit, but water pipe is a fraction of the cost of the equivalent in black (can only assume due to not being so popular), and as long as it is taped along its length, I cannot see an issue.

My belief is that if it is obviously cable ducting, and it provides a high degree of protection, then it can only make the installation safer. I reiterate though, I only use it for protecting swa.
 
S

Swicade

Fully agree it's a good thing to use for extra protection and taped with warning tape and alls good. Was just one of those thing's that lingered in the back of my mind (as these things tend to do).:17:
 
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HandySparks

HandySparks

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Re. ducting - Tools...tion do some 15mm x 50m flexible ducting for £27 (#92505). A tight fit but you'd get 2.5 SWA into it with care. It's black too.
Thanks for that Rick. (The part no is 92502, I think.)
I suspect that the Toolstation stuff is more like the lightweight flexible conduit and therefore may not be much protection against an errant spade or fork (unless you've seen some and know different). Also, as you mention, it may be OK for short runs, but pulling in a long length of SWA needs a decent clearance in the ducting to make life easy.
 
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HandySparks

HandySparks

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While we're on the subject, if you need to get a pulling line into a duct (privided it's not too big on diameter), attach a vacuum cleaner to one end and it'll pull a piece of string through. Dead easy.

A bit of cloth tied to the string might help if it's reluctant.
 

Guitarist

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The beauty of the water pipe is that because it's a smooth bore, the swa cable can easily by pushed in once it's all in position.
 

mike the sparky

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Burdens do 63mm black electric duct 50m for £50/60. Never liked to use blue poly after a farmer cut through one with a grinder to extend his "water supply". lucky man! The water pipe was 100mm to his left
 

brucelee

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When we was on site doing new builds in 80s and 90s the groundworkers used to lay a smooth bore black duct similar to the water pipe but larger bore
Can you get larger bores of this water pipe or similar
I have tried to locate this with no luck whatsoever, as i have just done a job for my brother.
Were I had to dig from house to a New large shed/ workshop at bottom of the garden the total run 34metres the actual dig about 25metres 500-600mm deep hard work to say the least
then he decided to ask me when i had installed some 40mm waste pipe with connectors all glued On the advice of a forum member and some of the blue rope which i had used to draw in the swa 6mm 3 core which was in orignally planned to be 10mm until he saw the price lol
he said Kid
will you run another to the decking we want some decking lights and wall lights on the back, but i want it fed from the shed another run of 15 metres at least but not straight he wanted me to dig a right angle trench
this is someone who gets his house plastered decorated wooden floors fitted wardrobes and then asks to sort his electrics ??
then onto the house to change the existing wylex 4 way wooden backed fuseboard and a volex split single for a new 13 way BG baoard dual RCD
then the fun really started and my black hair is deffo greyer
 

Guitarist

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Burdens do 63mm black electric duct 50m for £50/60. Never liked to use blue poly after a farmer cut through one with a grinder to extend his "water supply". lucky man! The water pipe was 100mm to his left
I think that was the point we were making about making sure it is adequately marked with "electric cable below" tape. I agree, it is madness to simply run cable inside any pipework without adequate marking.
 
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