Lighting, Light Fixtures, Ceiling and Exhaust Fans - Attic fan mystery

The previous owner of our house had wired an attic fan that would turn on the outdoor light dimly whenever the fan engaged. The fan has a thermostat. The fan stopped working a few months ago. Even though the fan was not turning, the motor gave out a slight hum. I found that if I gave the fan a little spin by hand it would start to spin normally. Thinking that the motor was just worn out or that dirt in the motor was causing too much resistance to allow the blades to turn, I replaced the whole fan. Sure enough the new fan does exactly the same thing. My guess is that the fan is just not getting enough power from the outdoor light circuit. Maybe there's a switch somewhere in the wiring that regulates the power for the fan. Has anyone seen this kind of attic fan wiring before?

It sounds like they wired it to a switch loop instead of a true voltage source. The reduced voltage burned out the motor. You need to find out exactly where and how the cable to it is hooked up. The previous owner of our house had wired an attic fan that would turn on the outdoor light dimly whenever the fan engaged.

Hi clinter, when you wired in the new faw, what did you find for wires? Did you have the option of not connecting that light you mentioned. The idea of a dim light raises the question, as ray mentioned, of a low voltage. I would get the fan going w/o the light and then decide if the light was part of the problem or not.

Bud

I've discovered that the fan is on the same circuit breaker as some interior lights in the house as well as the outdoor lights. But the fan only effects the outdoor lights. I'm not sure where the power cable to the fan is connected to the rest of the system, it's buried in the attic insolation. I'm going to try and trace the cable as far as I can to see how it's spliced into system. Also, when the fan stopped working, the outdoor lights stopped dimming, they now come on full power when ever the thermostat for the fan tries to turn it on.

This is great. It would be embarrassing except that it's so funny. During the winter, when the attic fan never came on, my wife swapped out all of the outdoor light bulbs with some new low-energy twisted bulbs. I pulled them all out and installed regular light bulbs. Guess what, the attic fan now works perfectly. I love that!

You should investigate further. It sounds to me like the lights are feeding the fan via series wiring. (As Ray said ... through a switch leg.) That's a no-no.

If the fan doesn't work with the bulbs removed it is wired wrong. Bet if you measure the voltage at the fan with bulbs in and fan on you get less then 100v..

Either a switch loop or wired them in series rather than parallel. Just a thought.

The fan still works if I remove any of the outdoor bulbs that are on the same circuit, but, it sounds like I may need a professional electrician to inspect the former home owners wiring for quality and safety. Thanks

It needs to be rewired if a bulb affects how it runs.