I recently purchased in a house built in 1939. The electrical boxes and wiring have been replaced, but the ceiling support bar holding up the box looks original (i.e., flat steel bar attached to the joists). Can this support the new 45 lbs chandelier I want to hang?
The following picture (NOT from my house) is an example of my situation, but I do not have access above the ceiling like the picture.
Best Answer
If the support is as you illustrated, the weight is being held by screws through the support and vertically into the ceiling joist. The load is being held up by screws pointed upward. The strain is downward. All that is holding up the weight is the wood around the threads of two (or maybe four) screws.
In general, wood screws do best when the load is shear (perpendicular to the direction of the screw). Pullout loads are especially vulnerable in older wood that may be deteriorating over time and getting powdery. 1939 is not so old comparatively, but this situation is not ideal.
You might want to consider a replacement box and support that wedges between two joists such as this one. On 16" centers, they are rated for up to 150 lbs and 50 lbs. on 24" centers. For fans, they are rated for less (70lbs. on 16") because of dynamic stresses.
These can be inserted in a 4" hole.