electricalexhaust-fanfanslightswitch
I just put a new exhaust fan in the bathroom and connected it to existing light switch, which is connected to the bathroom light. When I turned the power back on, the bath light came on but not the fan. When I turned the switch off, the fan turned on and the light turned off.
I figured out that both the white and black on the switch coming from the light are both hot wires.
How do I connect my fan then to run from the same switch?
From what you've described, this is what I think you're wiring should look like. Keep in mind, this is just a guess. I can't see what's going on, and I'm an internet away, so I can't touch/measure/test anything.
The wiring diagram for the switch, can be found in the installation instructions.
If you provide images, and/or a better description of what wires and cables are in each box. I'll be able to provide a better guess, as to how this should be wired.
The diagram is based on your description, and is my best guess as to what your wiring looks like. If you're not sure what to do, or feel like this project is over your head. Do not hesitate to contact a local licensed Electrician.
You should extend the wiring from the light, not the switch. There should be two wires on your light fixture, one grounded (neutral), and one ungrounded (hot) conductor that's controlled by the switch. Extend those wires to the fan, along with a grounding conductor. That will allow the switch to control both the light, and the fan simultaneously.
Best Answer
To simplify things, there are two ways to wire a light switch and a light:
(traditionally, but wiring standards have changed)
If the switch comes first, the cable coming from the switch (A) will provide switched power to whatever you want to put on it.
If the light comes first, the cable between the light and the switch (B) is called a "switch loop". If you open up that cable, it will have a white and black conductor so it looks like hot and neutral, but it's actually playing the role of only the hot. If you were to splice in a fan at position (B), the fan would complete the circuit, and it would run by pulling power through the light.
In most cases the light would also come on, but depending on the electrical characteristics of the light and the fan, only one of them might come on.
When the switch is turned on, it is what completes the circuit to the light, so the power no longer has a reason to run through the fan.
If the above seems true - you spliced into the cable between the light and switch - the only way to wire it correctly would be to run a cable from the light to the fan. The switch box most likely wouldn't have a neutral, so you can't run a new cable from there.