Ceiling rose and wide light fitting

[ruthcon]

Hi! I have purchased a polystyrene ceiling rose and a new light fitting. The problem is the ceiling attachment of the light fitting has a diameter of 12cm- do I have to cut out a 12cm hole from the middle of the ceiling rose in order to fit it?
The central circle in the centre of the ceiling rose is much smaller than this so it would mean cutting into midway through the next ring (which has the flower shape in it)... Feel like this would look a mess and crumble everywhere!
Have attached images of the rose and the fitting. Any pointers gratefully received! Thanks

 

[OwainDIYer]

No, you drill a small hole in the decorative rose and feed the cables through from above. Then affix the light fitting onto (below) that.
If it won't sit solidly over the flower effect you will need a decorative rose with a larger flat centre, or a different fitting.

 

[ruthcon]

Thanks so much Owain!

 

[ebee]

Points to consider:-

Any hole in polystyrene should have a barrier (collet, bush, grommet) to prevent cable coming into contact with polystyrene - It causes plasticiser to leach out of the cable, becomes brittle and then the sheathing/insulation of the cable becomes brittle, any movement of the cable (including vibration/settling can then cause particles of cable to crumble off causing likelihood of shorts/overheating/fire and electric shock risk - this will not happen today/tomorrow/next week/next month or even, possibly, this year but it will happen eventually. That is why contact should be prevented.

The fixing to the "ceiling side" of the base should be in contact with something solid like a timber or a plasterboard ceiling or even lathe and plaster (with joist above for fixing screws) that way changing lamps is not going to be an issue causing movement during lamp change.

Is it credible that any heat from the fitting can travel up to the base and therefore the decorative rose? Probably not but needs considering.

If there were to be a terrific heat event, example a fire, it could cause A/ toxic fumes and B/ molten polystyrene to drop from the ceiling onto a person trying to escape, there have been instances in the past of such incidents with polystyrene tiles on ceilings, however one would hope that modern roses would have some anti-flammable coating inbuilt.

Is there an easier viable alternative?

You could help to mitigate one aspect (more important if the rose also creates a cavity to the ceiling for the lamp base) whilst the rose and cables in place then plaster and skim the centre cut out portion and once dried out will create a solid base to mount the light fitting. Again a lot of messing about, is it worth the effort?