ceiling support

[ajem]

How much weight can a ceiling hold?
I want to hang a heavy chandelier, but I'm not sure
how much weight the ceiling can hold.

[Clanad]

I'm depending on the installation process we use here in the U.S., but in most cases the actual weight bearing device will be the electrical junction box into which all the wiring will be placed. The junction box is required by code and special ones are designed for chandeliers and ceiling fans. These, as Zac describes, are then attached between two ceiling joists or some other substantial structural members. If the chandelier is a new one in a box it will contain instructions but will probably rely on an adequate junction box already being in place. If your's doesn't have one or it's inadequate, you may want to have a licensed electrician install one for you. This can be simple and inexpensive or complicated and very expensive, depending on the age of the house and structure, etc. Best of luck!.

[wildwood]

Normal light fittings are often suspended from a thin noggin (dwang) between two joists so that they are in the required position, never straight from the plaster. If you have access to the ceiling framing it is a simple matter to strenghten this, otherwise it should be hung straight from a beam.

[Brooksy]

If you have access to a room or loft above, see if you can lift a floorboard to check what`s under there.