I just moved into a new home that the builder said was pre-wired for ceiling fans. I bought the first fan and light combination, but when I popped the ceiling junction box cover off and measured AC voltage between red and white or red and copper with the switch on, I only found 46 VAC. I measured 0 volts with the switch off.

The nearest wall outlet measures 122 VAC with the same meter. Since I don't know what is involved with a ceiling fan pre-wire, I don't know if I should be getting full house voltage at each pair of test points mentioned, or if these measurements are normal for ceiling fan wiring. Any suggestions?

Ceiling fans are 120vAC. What sort of switch is controlling the potential fan?

Unfortunately, I discovered my error too late. I should have checked voltage between white and black. When I first opened the ceiling cover plate, I found the copper wire stuck into the same wire nut as the black, so I assumed that the "ceiling fan pre-wire" used black as ground, as in electronics. After I took my voltage measurements, I turned off the wall switch, but I noticed that the copper wire was loose in the wire nut, so I made sure it was secured in there good and tight with the black one before quitting for the day.

This morning, when I came into the office, I mistakenly turned on the wrong switch, heard an explosive crackle (and I swear, a clanking noise) from the ceiling, and reflexively turned it off. I knew immediately that I should not have made an assumption about the copper and black wires. The black had been cut straight across at the end, so I think that the initial grounding blew apart the contact between the two wires, because the breaker did not trip, as far as I know. The insulation at the end of the black wire is charred, but it seems to be OK from about 2 inches back. I'll just follow the fan installation instructions for now, but will post again if I do something else exciting.

Black and red are hot, white is neutral, ground is ground. Connecting black and ground caused a dead short, as I am sure you know by now.

Your initial measure between red and white should have yielded 120vAC.

Let us know how it works out.