Adding the L-box to your existing plaster ceiling would make the edges of your room look lower as the L-box would sit on the perimeter of the room.
With regards to L-Box size 8" is normal, but how wide will your L-Box be? To give a nice look, 1.5-2ft width of the L-Box is sufficient but this differs according to preference and the design you have in mind.

With a 9ft + ceiling height, its is still ok. Have seen houses with 8ft ceilings.

I'll have to check what i'm using but if i'm not mistaken its between a 1.5-2ft wide L-Box.
2 L-Box in a living room no problem dude... As long as it matches your design.



This post has been edited by adrianjc: Nov 29 2011, 06:08 PM

Don't have to redo the entire plaster ceiling. They'll just cut the holes to install the downlights.
Not sure how the aircond and water heater points will affect your plaster ceiling but if you're referring to the embedding the wiring into the wall and the portion of the plaster ceiling that touches the wall... thats no problem either.

One thing you will have to do though is probably repaint the entire plaster ceiling once you're done. Hand prints tend to get left quite easily on plaster ceilings even if the hand is just slightly dirty.

Just make sure they don't throw away the piece of the plaster ceiling that was cut out.

The plaster ceiling guy will need it to patch the hole.

You can but it's not really necessary unless you want to pop-in and look at the fuse box every now and then, especially if your house is prone to tripping and that is a point which needs to be switched back on.

Otherwise the electrical guys are pretty adapt in walking around in your roof. It would makes things easier for you should anything happen in future and you need to access the fuse box. Maybe what you can do is get someone to check whether the fuse box area is suitable for people to climb into the roof as they'll need somewhere to grab and stand on close to the manhole.

If its suitable, maybe consider shifting the manhole from the toilet to the fusebox area. They should be able to reuse the manhole and also the cut out piece to patch back the old hole in the toilet.

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Added on December 27, 2011, 11:33 amIf you're asking whether 3" is sufficient for the light in the L-box to shine out, yup it's sufficient. If you want to install down lights in future the ceiling is too low for down lights based on the 3" board being done to cover the wiring.

One thing to note though, 3" opening for your L-box will make it hard to change the bulbs, etc... in future as the gap would be quite close to the ceiling and can be a pain.

This post has been edited by adrianjc: Dec 29 2011, 06:43 AM