external cabling

[pls]

I need to install an external socket and a few garden lights (mixture of LV LEDs and GU10 halogen fittings) in my garden (approx 5m from the house) and have a few questions:

1.) For one of the cable runs in the garden I will need to run 3 separately switched circuits for the deck LEDs, pond pump and step lights (LED).It will need to run underground so I was thinking of using polypropylene conduit with 3 lengths of single core conduit cable for each of the switched live circuits. If I bury at the recommended depth (450mm) and cover with slabs, presumably this will offer comparable mechanical protection to SWA as interpreted by the regs? The neutral and earth I would run separately (probably in some left over 2 core SWA)

2.) I need to work out how to power the external socket/lights from the house. The easiest option is to run a spur off the ground floor ring (using a 13A RCD FCU -

and then from that a branch with a 3A FCU for the external lights. Looking at the Collins DIY interpretation of the wiring regs they seem to state that if an external power socket (or light for that matter) is NOT located on the external wall of the house then it has to be run in a separate (RCD protected) circuit direct from the CU. This seems overkill for one outdoor socket and a few lights, and wonder if they are talking about power to an external outbuilding (where potentially the loads would be much higher with separate ring circuits etc)

3.) As part of the lighting, I will be installing three recessed ground lights in the patio ?id=72042&ts=49971)These come preinstalled with 1m of flex to a waterproof junction box which will accept PVC flex. The instructions are rather vague about installation in the ground, presumably the 1m flex will need mechanical protection since the whole light is buried in the patio? I wanted to run SWA to each of the fittings but they won't accept SWA so I was thinking of running the SWA to a IP box on the wall and then run flex from there to the junction box (below ground) if that is permissible? Again difficult to interpret from the regs.

PLS

[Owain]

You *must* run the lives, neutral and earth together in one conduit or cable.

I don't know whether singles in polypropylene conduit is acceptable for burial.

Although 5m isn't really far enough to warrant it, you could run just one circuit and control the switching with X10 or similar switch modules at the lamps.

I think a little more research on suitable cable types and fittings would be beneficial.

Fair enough. You may not actually need the RCD if the socket circuit is already protected by an 30mA RCD at the consumer unit.

Not just a matter of the loads, but also exporting the house earth. I suspect that at 5m from the house, for lighitng, and not installing sockets, you could use a spur.

?id=72042&ts=49971)

Can you put an IP rated box in the ground, within 1 metre of the lights

- under a loose paving slab if the patio is slabbed, if it's tarmaced I don't know.

If you are in England and Wales, Part Pee of the Building Regs will apply.

Owain

[Lurch]

On Mon, 02 Apr 2007 23:15:18 +0100, Owain mused:

Says who?

[Lurch]

On Mon, 02 Apr 2007 21:44:27 GMT, "pls" mused:

I''d run a couple or 3 SWA cables out, or a 7 core SWA.

Coming off the socket circuit via an RCD spur is fine. Even if your sockets are already protected by an RCD then the additional RCD spur will hopefully provide some descrapncy.

I wouldn't use a junction box underground. If the provided flex is too short replace it with a longer length and use flexible conduit for some protection, but keep the runs from the lights to juncrtion boxes as short as possible.

[Clive Mitchell]

In message , Lurch writes

The feed and return of any given circuit should be paired in metal conduit or armoured/screened cable to prevent eddy current issues. Whether this is a supply or two switch wires it's important they be contained together.

It's a similar scenario to making sure that the three phases in distribution equipment are all run through a single hole.

[Lurch]

On Thu, 05 Apr 2007 23:05:22 GMT, Clive Mitchell mused:

Yes but the OP was on about using flexible PVC tube. I know about using a single hole in metal enclosures for live and neutral etc... but Owain said live, neutral and earth together in any conduit or cable.

[Owain]

"Single-core cables (without armour) enclosed in conduits or trunking must be bunched so that the outgoing and return circuits are enclosed in the same conduit or trunking. This must be accepted as a gnereal rule for all ac circuits ... If single-core cables are enclosed in separate metal conduit, trunking or metal armouring, the resultant induction losses could be very marked, and cause considerable voltage drop and overheating of the cables and the enclosure. A voltage drop of 90%, and consuderable overheating, has been known when single-core cables, enclosed separately in magnetic metal have been connected to an ac supply" "Modern Wiring Practice", Steward & Stubbs, 10th Ed

Okay they talk about metallic conduit, but I think it would be Good Practice to adopt anyway.

Owain

[Lurch]

On Sat, 07 Apr 2007 20:12:55 +0100, Owain mused:

Yes, where possible\practicable, but I was under the impression it was for metallic conduits and enclosures only so was just wondering what your source was.

Cheers for quoting the source. ;)