Garden Lighting

[Charlie]

Apologies if this has been covered a number of times, but I had difficulty trying to find an existing post that covered my situation exactly.

I want to install 3 LV garden lights, I was planning on using 3x 20w LV lights (with stakes in the ground).

I was planning on running 1.5mm cable at 240v from the house (separate circuit) and under some decking (total distance 10m) Then have an external transformer mounted under the decking followed by 3 lamps (evenly spaced over 10m)

My question is:

1. What should I run the external 240v 1.5mm cable in (can I just put it conduit or does it need to be SWA)?
2. What type of cable/conduit should I use on the the LV side of the transformer?
3. How should I join the lamps to this cable? Will it be possible to join inside the fitting or should I T-Off using an external JB or split the cable and crimp it.

Ady advice would be greatly appreciated.

Charlie

[David Hansen]

On 14 May 2007 04:54:28 -0700 someone who may be Charlie wrote this:-

That is certainly covered by existing posts. Suitable wiring systems are many and varied.

The manufacturers undoubtedly recommend a type and size of cable, including maximum lengths.

That depends on the design of the lamps. No doubt the manufacturers provide advice on this.

[Charlie]

Dave,

Thanks for your reply:

I agree, I just found there were *too* many and they were *too* varied. There are number of ways to skin a cat, want to make sure my skinning is OK.

Some say SWA, some say a rigid conduit. I was interested to know what the general consensus was.

Again some say split the cable, crimp and heat shrinkwrap, others suggest T. Was again looking for some guidance.

[David Hansen]

On 14 May 2007 05:30:48 -0700 someone who may be Charlie wrote this:-

You have not asked whether the way you intend to do it is acceptable. You have asked an open question and that is likely to result in open answers.

There are a number of ways to skin a cat.

Do what the manufacturers of the lights you have chosen recommend.

[meow2222]

It may be simpler and cheaper to run the whole length in 12v using thick T&E. Also no exterior joints means no added failure points, no mains outside, no transformer hidden under decking where it will suffer the outdoor conditions etc. Much simpler.

Some halogen TFs use very high freq unsuitable for long cable runs. Play safe and use a toroidal transformer. These are also more reliable.

6mm^2 would give 0.8v drop with 60w 12v load. Adding 3 turns to the tf would raise this to 12v at the lamp end of the run. For thinner cable you'd need to add more turns.

NT

[Charlie]

NT

Thanks for your advice:

Just a couple of questions:

Surely I still need to connect each lamp.

What would you protect the T&E with? Some conduit like this?

you say 6mm^2 T&E do you mean 6mm T&E like this?

[meow2222]

I reckon that would be a good idea ;)

Nothing, unless its in a situation where its liable to get damaged. T&E has been used as standard outdoor mains cable for decades.

6mm^2 T&E is sometimes inaccurately described as 6mm T&E.

NT

[Charlie]

Thanks for you reply, and clearing up a couple of things.

I've not used toroidal transformers before, can you just clarify what you mean by "adding 3 turns".

Charlie

[meow2222]

I thought that would come up :) Mains transformers produce around

0.25v per turn on the secondary winding (except miceowave oven jobs) so you can add 3 turns to up the output voltage to offset the small cable drop. You need a toroidal transformer where the centre fixing can be undone to allow 3 more turns to be put on, stay away from the potted ones.

Toroids are constructed as follows: ring of (laminated) steel this ring is then wound with copper wire. What you do is put 3 more turns of the same thickness wire on (or fatter's ok), over the secondary winding. This 0.75v winding is then connected in series with the 12v winding. Connecting one way round increases V_out, connecting the other way reduces V_out, so a quick test with the bulbs or a meter will tell you which way to connect it.

If this is still unclear - and its very simple once it is clear - maybe find a pic of a toroidal showing how its constructed.

BTW there's another option to 6mm^2 cable, and thats 2 lengths of 2.5, each one having LN&E all connected together, giving a total of

6.5mm^2. Either option is good.

NT

[Charlie]

Gotcha, you mean like Fig 6. at

you just raise the voltage slightly, pre-empting the voltage drop.

Useful if you have 2.5mm cable kicking around and especially as you don't need an earth on the LV side.

Thanks, I'm getting a clear picture in my head. Just one last thing I omitted earlier to keep things simple. I presume I can run LV two cables from the transformer, one for each side of the garden.

Charlie

[meow2222]

thats it - what a good page

Yup. It would be nice to see a voltage adjust feature on tronic transformers to do this, but I never have.

yes.

Sure, why not. But if theyre not both 10m with 60w load on each run you may need to tweak the relative cable sizes to balance the voltages.

NT

[Charlie]

Thanks for all your help.