Garden Lighting

0 views
Skip to first unread message

Charlie

unread,
May 14, 2007, 7:54:28 AM5/14/07
to
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

unread,
May 14, 2007, 8:22:11 AM5/14/07
to
On 14 May 2007 04:54:28 -0700 someone who may be Charlie
<charlie...@gmail.com> wrote this:-

>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.

>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)?

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

>2. What type of cable/conduit should I use on the the LV side of the
>transformer?

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

>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.

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


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Charlie

unread,
May 14, 2007, 8:30:48 AM5/14/07
to
Dave,

Thanks for your reply:

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

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.


> >2. What type of cable/conduit should I use on the the LV side of the
> >transformer?
>
> The manufacturers undoubtedly recommend a type and size of cable,
> including maximum lengths.

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

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

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

David Hansen

unread,
May 14, 2007, 9:05:17 AM5/14/07
to
On 14 May 2007 05:30:48 -0700 someone who may be Charlie
<charlie...@gmail.com> wrote this:-

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

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.

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

There are a number of ways to skin a cat.

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

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

meow...@care2.com

unread,
May 14, 2007, 11:16:00 AM5/14/07
to

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

unread,
May 14, 2007, 1:15:58 PM5/14/07
to
> NT- Hide quoted text -
>
> - Show quoted text -


NT

Thanks for your advice:

Just a couple of questions:

>>Also no exterior joints
Surely I still need to connect each lamp.

What would you protect the T&E with? Some conduit like this?
http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331821&ts=62572&id=97987

When you say 6mm^2 T&E do you mean 6mm T&E like this?
http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331782&ts=61167&id=73076

Cheers

Charlie

meow...@care2.com

unread,
May 14, 2007, 6:06:15 PM5/14/07
to
On 14 May, 18:15, Charlie <charlieopens...@gmail.com> wrote:
> On May 14, 4:16 pm, meow2...@care2.com wrote:
> > On 14 May, 12:54, Charlie <charlieopens...@gmail.com> wrote:

> NT
>
> Thanks for your advice:
>
> Just a couple of questions:
>
> >>Also no exterior joints
>
> Surely I still need to connect each lamp.

I reckon that would be a good idea ;)


> What would you protect the T&E with?

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


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

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


NT

Charlie

unread,
May 15, 2007, 6:19:40 AM5/15/07
to

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

meow...@care2.com

unread,
May 15, 2007, 6:57:50 AM5/15/07
to

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

unread,
May 15, 2007, 8:28:39 AM5/15/07
to

Gotcha, you mean like Fig 6. at http://amasci.com/elect/mcoils.html
Neat, you just raise the voltage slightly, pre-empting the voltage
drop.

> 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.

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

>
> NT- Hide quoted text -
>
> - Show quoted text -


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

meow...@care2.com

unread,
May 15, 2007, 11:35:58 AM5/15/07
to


thats it - what a good page


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

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


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

yes.

> > NT- Hide quoted text -
>
> > - Show quoted text -
>
> 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

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

unread,
May 15, 2007, 4:24:02 PM5/15/07
to

Thanks for all your help.

Reply all
Reply to author
Forward
0 new messages