Wiring for downlighters

[shawn]

Hi

I am putting in Halogen downlighters into my house, 4 low voltage spots 12v 20 Watts.

What I dont understand is that the transformer I have bought says, that "the output leads must not exceed 2m in length", Im confused to why they have stated only 2 meters.

It looks like im going to need 3 or possible 4 meters in total to get to all the spots from the transformer.

I had just bought 0.75mm 2 core flat flex which I was thinking of running to each of the lights, about 3/4 meters in total, but having read some posts on here im completely confused to know if this is safe or not.

The cabling I have bought says 6 amps 1440 watts, which I thought should of been plenty as I only have 4 - 20 watt 12 Volt spotlights so surely thats only 80 watts. Dont understand the post about the total amps of the circuit. Could anyone give me some advice about what im planning to do , if its safe or not.

If not safe whats the best solution to make my wiring safe please?

 

[the_jinj]

This is probably to do with volt drop over longer cable runs

 

[securespark]

Is that "three quarters" or "three or four"?

Current. 60W @ 12V = 5A. But the length counts too. For two reasons: the main one is voltage drop. The longer the cable, the bigger it needs to be. Second, with electronic tx's, the output lead(s) have to be limited so that radio interference is minimised.

 

[Spark123]

The 1440watts you are referring to is 6amps at 240volts. The cable is still rated at 6amps at the lower voltage, which equates to 72watts.

 

[shawn]

Somebody has suggested that I use two transformers to keep the cable lengths to no greater then 2 mteres. Does that sound the safest way?

Also how do you work out the Amps of the circuit then, was the calulation / formula

Appreciate all the help you guys have given

thxs

 

[the_jinj]

Amps = Watts/Voltage

 

[shawn]

Hopefully last question re ceiling rose wiring

The rose appears to have been identified as loop in wiring circuit, ie two circuit cables plus a switch cable.

I was going to originally wire just 1 transformer. 4 x 20 watt 12 v downlights to it on a 4 metre cable. But with all the advice im thinking that I should get two transformers and wire that to the ceiling rose so that none of the cable lengths are more then 2 metres. Would I be ok using 0.75 2 core flex to each of the downlights, would I also need to upgrade the ceiling rose as I dont know how many amps that is capable of supporting too?

Somebody suggested not wiring into a ceiling rose, but instead replacing the ceiling rose with a junction box, but I cannot see any junctions boxes that look anything like the wiring I have in the ceiling rose ie loop in wiring?

I appreciate any advice thxs

 

[breezer]

here

other suppliers of junction boxes are available

 

[shawn]

Dont think I can work out how to wire the junction box, think its better that I stick with the existing wiring thats already in the ceiling rose, in which case I need to find out if the existing rose I capable of safely supporting 8.3 amps as I need to connect two low voltage transformers to it and 5 20 Watt 12 volt lights. Im guessing there will be no obvious way of telling how many amps the current rose is rated at, and I will have to try and find a celing rose rated at least 8.3 amps

Does this sound OK as I dont have much electrical experience?

 

[breezer]

the jb is the same as the rose you have.

as Eric Morcombe used to say.

"I am playing the right notes, but not necesarily in the right order"

the rose you have and the jb i mentioned are both rated at 5 amps

I would also suggest you sit and draw your rose on paper, count the "groups" of terminals, then count the groups in the jb

spot the difference = none

Oh, and you are worrying about the current on the secondary side of the transformer, the rose you have will be connected to the primary side of the tranformer

 

[shawn]

Hmm now im confused there are 9 terminals on my ceiling rose, all in use and connected. Theres like only 4 on the junction box, I have no clue what would be wired where.

I was hoping that I could just stay with using the exsiting ceiling rose as its easier to see where I need to conect the wires from the transformers, my worry is that if I connect 5 20 watt downlighters 12 volt to the existing rose I may overload it.

 

[breezer]

there probably are 9 terminals in your rose, but look at which are "internaly" connected to each other

.i.e. look closely and you will see the metal the screw goes into (the terminal) is also the same piece of metal for the next terminal. so it is internall conneted.

yours may be grouped like this

3 3 3

or

2 3 3 + earth

 

[shawn]

We have 2 3 3 + earth in the existing rose, however we do not have an earth from the transfomer. does this matter ?

 

[breezer]

no its a plastic boddied trasformer, how ever you should provide an earth at each lamp (Put it in a choc block)

I take it you now see how you can use a jb.

only thing is all jbs must be acessable

 

[shawn]

The transformer is plastic bodied, the downlighters say "No earth conenctionis required -ensure the fitting does not come into contact with any earthed metal" ?