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Old 08-25-2010, 06:05 PM   #1
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Ceiling Fan Circuit Problem


Hello everyone, first post.

When I had my house built (4 years ago) I had all the bedrooms pre-wired for ceiling fans. I specifically asked the electrician to run a 3-wire (white/black/red) so that I could use a single switch to control both the fan and light (Lutron slider switch with 3 speed fan and dimmer for the light). I had no issues with the other rooms, but this last one has thrown me for a loop.

My Normal Fan Install Routine:
Since the switch is already installed and the fan box mounted in the ceiling, all I need to do is determine which color wire is for the fan and which is for the light. I opened the fan box and separated the wires (with wire nuts on) and turned the light switch on. I then use my pen-style voltage detector to pick the red or black wire with current.

The Problem:
This time the detector was indicating that BOTH wires had current (not normal).

My investigation:
I opened up the wall switch box and pulled out the switch to see how the wires were connected. It is a two gang box with the other switch for the 4 o/h can lights. Here's what I saw...
Wiring --
- Power comes into the bottom box from one 14/2 wire
- The can lights go out the top right through another 14/2
- The fan/light goes out the top left through a 14/3
- All three whites are tied together and the black from the source feeds the two switches
- Everything on the fan switch (according to mfg diagram) was wired correctly

My Tests:
I pulled out my Fluke MM and disconnected the wires running from the switch to the fan. With the switch isolated from any load I tested the switch for voltage and here is what I got
- With the light switch on the light wire (red to ground) gave me 117V, the fan (yellow to ground) gave me 1V. The opposite was true with the opposite switch on (Fan 117V, light 1V).
- So I concluded that the switch was working properly, or at least according to my assumptions of what it should do.
- Then thinking that the wires between the switch and the ceiling box may be shorted (by a stray nail or other cut) I tested the black and red wires for continuity (one of the functions on my MM). But, I got no warning for it.
- Next I hooked the switch back to the wires (Y-B, R-R) and tested the voltage at the ceiling box.
- With the light switch was on I got 114V for the light (red to white) and 32V (!!!) for the fan (black to white)

No I know there is something really wrong....

To finish the test I did the other switch and got 114V (b-w) and 37V (r-w). Just for fun I did the voltage across the two and got 65V for the black to red wires.

Any ideas, please help!?!?!?

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Old 08-25-2010, 06:24 PM   #2
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Join Date: Sep 2007
Location: Maryland
Posts: 7,316
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Ceiling Fan Circuit Problem


It sounds like you are using a digital meter and are reading phantom voltage.

If you want to check the operation you could wire a simple bulb socket to the ceiling wires and test the switch operation.

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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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