ceiling-fanelectricallightingreceptacle
I have a concrete ceiling with an old-style electrical box that has a stud for a hickey, but does not have the traditional mounting holes for fixture screws, like the box in this diagram:
Can I install a ceiling fan using a hickey and crossbar kit to provide a mounting location for the ceiling fan bracket?
The box is embedded in concrete so replacing it is not practical. I'm confident it will support the weight of the fan but I'm worried the crossbar might not provide enough stability.
The bare copper wire and any green insulated wires are meant to be connected together, making it a "party of three" as you stated in your question. That said there is another consideration to take into account as well. These safety ground wires are also meant to be connected to a common ground point of the electrical box as well.
If one of these wires (green or bare copper) coming out of your box already attaches to a safety ground point in the box then you have no more to do than the "party of three" connections.
If neither of these two wires are connected to the electrical box safety ground then it will be necessary to add an additional pigtail green or bare copper wire to the box safety ground and join it with the other three making a "party of four" connection.
Add hickeys until you can hang a box like this from it. Grind off the tabs if you don't like them, paint it to match the ceiling. You will probably need a bushing to make the connection from the last hickey to the new box.
Having pulled the wires through the hickeys, install the relay. Add a cross bar to hang more hickeys, from which you hang the light. Without a 'gap' in the hickeys, you've nowhere to put the relay.
Take the relay with you to the store, find a box and add a hickey; check if it will still fit a cross bar with another hickey sticking into it, with the relay inside, and still have room for wires coming from both hickeys.
I would endeavor to use that company's switches instead of the relay you can't fit, however I am not familiar with them or if they would fit your setup.
The relay doesn't need to be in that box; it just needs the wires... somehow.
Best Answer
You have two issues:
Strength of the hickey - Some hickeys are cast from cheap pot metal and would be sketchy. Some are steel but bent in the shape of a U with one open side, also problematic. Heavier cast iron ones with support on both sides wold probably be better.
Strength of the crossbar - Also an issue. consider a heavier duty type or even a full round. Then consider doubling the cross bar up with small bolts joining the pair.
Supplement - In line with other answers and comments, there are real risks installing a fan with other than a properly rated fan box. Perhaps most important is the security of the box itself. The fan depends on the plate, the plate on the hickey, the hickey on the stud and the stud on the box. Is the box well enough attached that it can't be loosened by fan vibration? Also, if the plate is not pulled tight against the box, the fan is balanced on the single point of the extension coming from the hickey.