Installation of bath vent fan and light.

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Old 06-04-13, 08:30 AM
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Installation of bath vent fan and light.

I installed a new bath vent fan and light by splicing into the circuit between the existing wall switch and vanity light. I installed a junction box in the attic directly above the switch, cut the cable and sliced in a new length of cable for the new fan and light. Connected wires black/black, white/white and ground to ground. When I turn the light switch on the old vanity light comes on but the new fan and light stay off. When the switch is off the old vanity light is off but the new fan and light come on.
From reading other posts on the site it appears I should have pulled the power directly off the old light fixture but this would require cutting into the dry wall as I cannot reach it from the attic. I'm thinking of replacing the old vanity light with a pull chain light or installing a pull chain in the existing light so when the switch is in the on position we could operate the vanity light with the pull chain and when the switch is in the off position the new light and fan will operate. Would there be anything unsafe about this solution? Is there another way to draw power from the switch?
 
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Old 06-04-13, 08:39 AM
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Do you know for sure if you have power at the switch or the light. It can be at either location. If at the switch you have only two wires power is at the light.
 
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Old 06-04-13, 11:47 AM
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Ray:
Thanks for the quick foillow-up. I spoke to the electrical engineer at work and he asked the same question, he's stumped which makes me feel a little less stupid. I'm taking pictures for him tonight and will try to post with thread as well. There is only 1 two-wire cable running from the switch (black, neutral + ground). The wire appears to run from the switch to the existing light and is routed through the attic. The wires are plugged into the back of the switch and I'll pull it tonight to see where they are connected on the switch. I pulled the existing light fixture last night and the box is full of pigtailed wires which leads me to believe the current is routed from an adjacent GFI outlet through the light and to the switch, I'll photo the light wiring as well. Is there anything I can check with the multimeter to better trouble shoot the problem.
 
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Old 06-04-13, 11:54 AM
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I installed a new bath vent fan and light by splicing into the circuit between the existing wall switch and vanity light... [only one] two-wire cable running from the switch
That is a switch loop and has no neutral therefore it can not be used to power the new device.
 
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Old 06-04-13, 04:11 PM
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Welcome to the forums!

There is only 1 two-wire cable running from the switch (black, neutral + ground). The wire appears to run from the switch to the existing light and is routed through the attic. The wires are plugged into the back of the switch and I'll pull it tonight to see where they are connected on the switch.
That sounds like a switch loop. If so, both wires carry ungrounded power. One takes the power from the box behind the vanity light to the switch and the other takes it back to the light. There is no neutral in that cable.

If that's what you cut into to run the cable to your new fan/light combo, here's the part that doesn't make sense:
When I turn the light switch on the old vanity light comes on but the new fan and light stay off. When the switch is off the old vanity light is off but the new fan and light come on.
Without a neutral, the new fan and light will not operate. The switch should have no effect on them.

I'm wondering if they are drawing power in series somehow?

I pulled the existing light fixture last night and the box is full of pigtailed wires which leads me to believe the current is routed from an adjacent GFI outlet through the light and to the switch, I'll photo the light wiring as well. I'm taking pictures,,, tonight and will try to post with thread...

Is there anything I can check with the multimeter to better trouble shoot the problem.
Take all connections in the vanity light box apart. Restore the power and test each black/white pair to determine which cable the power is coming in on. Push the TEST button on the GFCI and see if that kills the incoming power.

If the power does come in at the light, look for a place to splice into it in the attic before it gets to the light - maybe before it gets to the GFCI. If, in fact, the power comes to the light from the GFCI and the panel feed is not accessible in the attic, replacing the 2-conductor cable from the vanity light box up into the attic with a piece of 3-conductor cable will allow you to wire everything the way you want. That should be doable without opening the wall.
 
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