Thanks for great diagram! I've been looking for something this precise for the better part of the day! Looks like I have it wired properly. The only difference is that the proximity of everything lets me use 2 wire in place of the 3 wire - I have the power-in black hooked directly to the switch white. Is there anything else that could cause the buzz? I'm going to wire a plug to the fixtures and try them individually on a different circuit, see what I get.

How did you determine that those wires where hot? Have you opened up the light/fan to see how that is wired up?

Hi! Maybe what I was trying to describe is not called a switch loop. Maybe I should have given an example of what I am talking about. Let's take my brother's "den + 2 bedrooms" circuit. The power comes from the panel to the ceiling fixture box via a 14/2 loomex. From there another 14/2 loomex goes to feed the outlets in the den, and another 14/2 loomex goes to bedroom #1. Also, a 14/3 loomex (bare ground + white + black + red) goes to the switch for the den light. At the fixture box, the whites are wire nutted together, and the bare grounds as well, which are also attached to the box and has a pigtail for the fixture. The blacks are wire-nutted together and the red wire (from the switch) is alone. The hot wire from the chandelier is connected to the red wire and of course the neutral from the chandelier goes to the whites marretted together. The hot black wires are just standing there. Then at the switch (which is mounted on the wall separating the den from bedroom #2), there is the 14/3 from the light fixture box and another 14/2 loomex that goes to bedroom #2. In the den switch box, all grounds are wire-nutted together and attached to the box, all whites (neutrals) are wire-nutted together and the two blacks are wire-nutted together with a pigtail that gets attached to the switch. The other leg of the switch is attached to the red wire that goes to the chandelier. I hope this description makes it clear. Please note that I live in Montreal Canada and I have seen this wiring technique at my aunt's house (built 1964) and also at other friend's houses where I helped with wiring or installing light fixtures. Can someone please tell me if it is still allowed, and if I can use more than one fixture wired this way per branch circuit? Thanks a lot.

Let's clear up a few things. Last time I checked, it was still code-acceptable under some circumstances to use a single pole thermostat to control a 240 volt heater, opening only one hot lead. I don't think it's a good idea, but it's sometimes (maybe often) done. A 240 volt circuit is not 2-phase power. The neutral you use for 120 volts in a 240 volt supply is simply a center tap in the pole transformer. The two halves are in phase; otherwise you couldn't get 240 volts. In the case of a heater, the 240 volt supply could go to the heater with a 2-wire switch loop to the thermostat. I personally wouldn't wire it that way, but I've seen it done. A 240 volt heater fed by 120 volts will use half the current and produce 1/4 the normal output, not 1/2. That's Ohm's law. Power (which is what makes the heat) is proportional to the square of the voltage. P=E^2/R, where P is power, E is voltage, and R is resistance. R is the heater's resistance and it's obviously fixed. A 120 volt heater given 240 volts will use 2 times the current and try to produce 4 times the heat output. If you're lucky, the heater will just stop working. It may get very hot and/or go bang. Do not do this. A quick check for voltage is, as Mike said, to look at the breaker, but be careful. Not all double width breakers are 240 volt. Many GE panels can use a mix of 1/2" and 1" single pole breakers, and 1" and 2" double pole breakers. So you could have 1" 120 volt breakers and 1" 240 volt breakers in a GE panel, though I don't know how likely that is. Other panels use double width breakers that can be tandems (two 120 volt breakers in one). A handle that looks like 2 handles linked together is a pretty certain sign of a 2-pole, 240 volt breaker. A sure way to tell is to use a voltmeter on the live circuit (be careful). Last I saw, crummy-but-accurate-enough digital multimeters (DMMs) were under $10 at the cheap tool place (you know the one I mean). They even sometimes give them away with any purchase.