Soup said:
I\\\'m currently converting my garage and am installing 8 Mains Halogen downlights(50W) on a single dimmer (dimmer rating 600W).
That's probably close to the limit for the dimmer (they usually need to be derated by 25% for halogen lamps, so your 600W dimmer would actually only cope with 450W). Don't be surprised if it buzzes.
I\\\'m intend to connect to the existing ceiling rose and connecting the lights in series using 1mm2 cable ( recommended minimum ).
For some reason people don't like me pointing this out, but I'm firmly of the opinion that if you let one incorrect term drift by then sooner or later you get confusion that could be dangerous - it is important to always use words that describe what you mean, not what you don't mean.
You don't mean (I hope!!) that you will connect the lights in series, you will (I hope!) connect then in parallel.
1. Should I use a cable that has a higher rating than the recommended minimum, i.e. 1.5mm2 or 2 mm2.
There's no such cable as 2mm. 1.0mm will be perfectly OK, and 1.5mm will bring you no benefits, unless you plan to have these lights a l-o-o-n-n-g-g way apart.
BUT - you may have to use at least the same size cable as is already used for your lighting circuit. If it's 1.0mm, you
may use 1.5mm if you want, but if it's already 1.5mm you
may not be OK with 1.0mm for the additional wiring. What rating is the MCB/fuse? (and is it an MCB or a fuse?)
The safest idea would be to use 1.5mm if that's what the rest of it is.
2. Will I need to change the existing ceiling rose to something more substantial to take 8 halogen lights ?.
I'm surprised you plan to leave it there - a bit ugly, no? But quite substantial enough - roses have to be able to pass the full current of a lighting circuit, which is at least 5A, and could be 10A.