Bathroom Fan Wiring Issue

OK, I installed a bathroom vent fan in one of my bathrooms & it worked fine. I installed a double switch assembly in place of the original single light switch & used one for the existing light & the 2nd for the new fan. I used the same hot to power both devices & used a common that had been pulled to the box. This worked perfectly.

Well, I installed another one like this in a different bathroom only a common wasn't pulled to the switch box. I used the same hot to feed the switch for both the existing light & the new fan but had to grab common up in the box above the light. The fan runs just fine & the switch works just fine.... unless the light gets turned out. The fan will run ONLY if the light is on. I don't get it.... common is common, the power switch to the light shouldn't affect this....
Any thoughts?



Texas Fire

 

Assuming you mean neutral you can't go by color. Just because it is white does not mean it is neutral. It could be one side of a switch loop. That would explain the problem.

 

Can you better describe your wiring and the connections you made?

All conductors of the circuit should be run together. You risk overloading the neutral if you grabbed a neutral from another circuit.

 

You also will induce eddy currents in all metallic objects, causing them to heat up.

 

This seemed like a no-brainer.... I had a hot wire feeding a single switch that turned a bathroom light on & off. I swapped the single switch for a double with the intent to use the same hot for both the existing light & newly added fan. I don't see any reason why the neutral for the light circuit couldn't be the neutral for the fan. The light box was only about 2 feet from where the fan was installed. I grabbled the neutral in the light junction box, the white wire going to the light & tied my fan neutral in there. Like I said, works GREAT as long as the light is on. Once I kill the light the fan goes out. Doesn't make sense.... I'm only killing the hot, the neutral for the fan should be "unbroken".... I'm not grabbing just any neutral, its the one for the same circuit & I doubt I'm really overloading anything as the fan doesn't have all that much draw...

TexasFire

 

Where did you take the hot from? Is the supply coming to the light box first, and then switched for the light, or is it also from the light switch box?

 

The hot was at the switch box, the same black hot wire that was feeding the light. My replacement dual switch allowed the option of separating hots or using a common hot feed to switch two outputs. That's the way I chose.....

TexasFire

 

Could you possibly have switched the supply and return hots at the switch? Since it is a switch loop could be possible depending how the original wiring was arranged.

 

I would check your switch wiring. Make sure that you are feeding the second switch correctly and not from the switch side of the first which it sounds like you are doing.

 

Aww... you know I assumed that the black wire was the hot on the switch loop but maybe it wasn't. I didn't check it to ground as I had the power off while I had it apart. I will go back & check that. I'm guessing by your comments that it would matter.....

TexasFire