Future proofing for garden lighting

[John Aston]

I have a rectangular garden 24m x 12m, which is walled on all four sides. A path (from my house to my drive way at the bottom of the garden) runs down one side of the garden. At some point in the future, I would like to light the path and the brick walls around the perimeter of the garden. I would also like to install an outdoor 13A double-gang socket about 6m from the house.

To make provision for this now, I intend to run mains cable underground around the perimeter of the garden and install ten 240/12 transformers at approximately 8m intervals along the length of the cable (see diagram below). Each transformer would be rated to feed up to five 20W lamps. Where the path runs, I would like to use inground transformers as there is no foliage to camouflage a wall-mounted transformer.

12m

| | |house| .| |

------.------- |XO....X X| | . | | . | |X . X| | . | 24m | . | |X . X| | . | | . | |X . X X|

---.---------- . | drive | . | way |

X = transformer O = socket ... = path

My questions are:

(1) Should the circuit connecting the transformers to the consumer unit be a radial or ring circuit? (I can easily configure them as either type)

(2) Can I run the outdoor socket off the same circuit as the transformers?

(3) What current rating of mains cable should I use?

(4) What other cable should I lay so that I can switch the garden lights on from the house or the drive way?

(5) I can lay 240V cable underground in either a flexible heavy-duty conduit or SWA sheath. Which would be the best method and how should the connection to the primary flying leads of the inground transformers be made so that it is watertight?

By the way, the reason I want to make these decisions now is so that I can dig the cable trenches, lay the cable and backfill, and then plant up the garden before making a final decision on exact location and type of outdoor lights.

[N. Thornton]

2 points to add. First a 100w transformer feeding say 20w or 40w of lighting will run the bulbs at overvoltage, resulting in short bulb life.

Second, wherever you want a connection later, include a loop in the cable. Pretty obvious but not impossible to overlook :)

Third, anything underground is prone to damp problems.

Fourth old fashioned iron core transformers are more reliable than electronic ones.

Given all this it would seem preferable to cable but not put in TFs, and figure out your lighting types later. Putting 12v TFs in pretty much commits you, and very possibly not to the best option.

Regards, NT

[Ian Stirling]

I would say a generally good plan.

On principle, I'd say put in conduit so if you decide you want outdoor stereo, or wires for security cameras, or .... so that you can pull them through later.

On another topic, can electrics and water share the same conduit? (with the water enclosed in flexible hose)

[Owain]

"John Aston" wrote | (1) Should the circuit connecting the transformers to the consumer unit | be a radial or ring circuit? (I can easily configure them as either | type)

Radial, 6A lighting circuit.

| (2) Can I run the outdoor socket off the same circuit as the transformers?

No, because most transformers will require connection to a circuit of 6A max (or local fusing down, which is a pain). The socket will require a 20A radial circuit with RCD.

| (3) What current rating of mains cable should I use?

Voltage drop etc will have to be calculated.

| (4) What other cable should I lay so that I can switch the garden lights on | from the house or the drive way?

For two-way switching you'll need a triple+earth from the house switch to the drive switch in addition to the circuit cable. In addition that will mean you can only switch on all or none of the lights, which is very inflexible. Rather than lots of wiring, you could consider X10 mains signalling remote control modules.

| (5) I can lay 240V cable underground in either a flexible heavy-duty conduit | or SWA sheath. Which would be the best method

SWA with warning tape laid 6" above.

| and how should the connection to the primary flying leads of the | inground transformers be made so that it is watertight?

Depends on the inground transformers (have you sourced these yet?).

TLCs are IP68 and still seem unsuitable for direct burial

IP68 waterproof enclosure classification protects the transformer from temporary flooding caused by heavy rain or accidental flooding of a room, however the transformer should not be permanently submersed in water. This is because the transformer warms up under normal running conditions and cools down again when switched off. A partial vacuum is created inside the enclosure, which will suck in a little water. This may build up over a period of time and cause the transformer to fail.

I think you would be better off running a radial down each side of the garden (will reduce voltage drop) to 10 wall-mounted big IP rated boxes. like these (lots of sizes available)

or even will provide termination of the SWA and sufficient space to house tranformers and X10 modules. Cables to lights can then be installed through glands at a later date.

Owain

[John Aston]

Thanks for your comprehensive reply. I have a few questions to clarify my understanding...

Would I connect the earth to the consumer unit earth or to an earth electrode at the drive way end?

Probably transformers like these

which have flying lead terminations. I guess that I would either attempt a "waterproof splice" of the primary leads on to the SWA or use a waterproof junction box. I don't know if either is "legal".

So I need two 6A RCBOs in my consumer unit for the outdoor lighting circuits, plus a 20A RCBO for the outdoor socket?

[Lurch]

On Mon, 12 Apr 2004 21:34:44 +0100, in uk.d-i-y "John Aston" strung together this:

To the consumer unit earth. '

The weatherproof junction box is better, not ideal to be buried but if you could place them just below the surface they wouldn't be too bad. Just make sure it's watertight.

You can run the two radials from one 6A MCB, there's no harm in running two though. If you did all the lighting wiring in 1.5mm you could quite easily have one 10A circuit.

[John Aston]

Really? Can you run two radial wires out of a single MCB? I didn't know that the Regs allowed this. Should I protect each radial circuit with its own RCD, or would one 6A RCBO in the consumer unit be sufficient?

[Lurch]

On Mon, 12 Apr 2004 22:07:03 +0100, in uk.d-i-y "John Aston" strung together this:

Yes, an RCBO would do the job. If it was critical that one circuit was left on at all times then split them but there is no problem with running two radials from one RCBO or MCB.