Low voltage lights - voltage drop/cable size

[st_katharine]

Have trawled through groups but can't find a definitive answer to my question.

I have a 60W transformer and want to run 3 x 20W low voltage lamps from this.

The transformer is "terminated" having three sets of terminals built in so I can connect cables to each 20W light.

The cable running to each light is 1.5m long.

For cable size calculations do I need to take the total load of 60W (3 x 20W) and the total cable length (3 x 1.5m lenghts = 4.5) or simply the load for each light (20W) and the cable length to that light(1.5m).

Using TLC's Low Voltage Lighting Cable Selector, I get a cable size of

2.5mm for the first way, and 1.0mm doing it the other way.

Which is correct?

TLC have a note at the end that says: The actual cable size and runs required to connect several lamps to the same transformer output must be equal to or greater than total load of the run

...but I think this refers to a single output where one cable runs to a junction box serving several lights.

[Gary Cavie]

If you are running seperate feeds from the tranny to each light, then you just need to size the cable for that one lamp - so you are correct with the 1.0mm. If you were daisy chaining the lamps, then you would need to use the larger cable - maybe going 2.5mm to the first lamp, then 1.5, then 1.0!

[Christian McArdle]

With seperate runs, just take the 20W and 1.5m. However, I'd run LV in 2.5mm anyway. It's not expensive or difficult to work with and will reduce voltage drop.

Christian.