Garden supply

[HandySparks]

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.

 

[Richard]

Short conduit link to double pole masterseal switch for lights. 1.5mm² HiTuf or NYY-J clipped to wall to each light

Could that be a Masterseal switched fused connection unit with a 3amp fuse in instead?

Rich

 

[Octopus]

Does anyone know of some nice looking bulkhead lights or maybe some wall mounted spots that will take a surface run cable?

I find my small round file rather useful in such cases!

 

[mickys86]

Could that be a Masterseal switched fused connection unit with a 3amp fuse in instead?

Rich

Is what I was thinking

 

[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]

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

 

[HandySparks]

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]

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]

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.

 

[HandySparks]

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.

 

[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]

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.

 

[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]

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]

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.