Low Voltage lighting cable size
 

Hi.
I'm planning to connect 4x 50w lv downlights using 2 105va dimmable multi
outlet transformers connected to 2 lights each. All cabling will be in the
loft, replacing an existing ceiling rose fitting. Controlled via a single
dimmer switch.

I have read various articles about the importance of cable size and used the lv
cable size calculator on tlc-direct
(http://www.tlc-direct.co.uk/Technica...ltageDrop.html)

I plan to connect each transformer to a junction box in parallel and connect 2
lights to each JB in parallel. Estimated cable length of 2m between the JB and
each light.

1. Is the total load 100w or 50w in this setup and what would you advise cable
size to be?

2. If 1.5 mm2 is recommended, for example, then would using a thicker cable
such as 2.5mm2 cause a problem? Would a overestimation of cable size impact the
life of the bulbs?

3. If the transformers need to be connected to a JB using additional cable to
that supplied (say 2m also) would standard 2.5mm2 power cable be suitable?

4. I've heard some worrying stories about transformer reliability - any
recommendations on a good reliable make?

5. Would a max 250va dimmer switch be suitable for this setup?

6. Has anyone any advice on improving the angle of light from lv lights but
avoiding glare on computer monitors. I'm thinking of 60 degree beam MR16 lights
to spread light as much as possible but concerned about glare... so many
worries...

Thanks in advice for any advice offered,
Rupertb


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In an earlier contribution to this discussion,
rupertb wrote:

Hi.
I'm planning to connect 4x 50w lv downlights using 2 105va dimmable
multi outlet transformers connected to 2 lights each. All cabling
will be in the loft, replacing an existing ceiling rose fitting.
Controlled via a single dimmer switch.

I have read various articles about the importance of cable size and
used the lv cable size calculator on tlc-direct
(http://www.tlc-direct.co.uk/Technica...ltageDrop.html)

I plan to connect each transformer to a junction box in parallel and
connect 2 lights to each JB in parallel. Estimated cable length of 2m
between the JB and each light.

1. Is the total load 100w or 50w in this setup and what would you
advise cable size to be?

The load from the transformer to the junction box is 100w. The load in each
cable to a lamp from the junction box is 50w. I would use 2.5mm between the
transformer and the box, and 1.5mm to the lamps.

2. If 1.5 mm2 is recommended, for example, then would using a thicker
cable such as 2.5mm2 cause a problem? Would a overestimation of cable
size impact the life of the bulbs?

Make it as fat as you like - you can't have less than zero voltage drop, and
zero is fine!

3. If the transformers need to be connected to a JB using additional
cable to that supplied (say 2m also) would standard 2.5mm2 power
cable be suitable?

Yes.


4. I've heard some worrying stories about transformer reliability -
any recommendations on a good reliable make?

Dunno!

5. Would a max 250va dimmer switch be suitable for this setup?

Possibly - but you may need to use expensive dimmers and transformers to
make them work acceptably. I bought "fully dimmable" transformers and
"compatible" dimmers from Screwfix, and the transformers buzzed something
wrotten when connected to the dimmers - even on the max power setting. In
the end, I sent the dimmers back. The lamps are fine undimmed. [I have 3
banks of 4 x 50w lamps in my L-shaped lounge - with each bank being
separately switchable. Along with some wall lights, this gives a fairly
flexible lighting setup without requiring dimmers].

--
Cheers,
Set Square
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