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Wiring a new light/fan combo switch with 3 black and 3 white wires

Wiring a new light/fan combo switch with 3 black and 3 white wires

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  #1  
Old 04-09-15, 01:05 PM
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Wiring a new light/fan combo switch with 3 black and 3 white wires

I'm relatively new to this, and having trouble installing a new DewStop humidity sensor switch--which has connections for hot (black), fan (red) and neutral (white) wires--in place of the old switch--which worked, but used two hot black wires, one of which was linked from the other switch's hot black wire. (I identified the wires I'm calling "hot" with a non-contact tester).

I've tried to diagram the switch box and my old and new configurations below, naming and labeling all six wires. I tried every combination of white/neutral wires connecting to the DewStop's red and white wires, but the new switch did not work under any of the six configurations. The old switch (Switch 1) didn't even work under two of them*.

I also tried keeping the hot black wire linked from Switch 1, and then connecting the other hot black wire to the fan (red) wire, but then the light/fan combo powered by Switch 2 remained permanently on or off, depending on the red/white configuration--and I only tried a few configurations there, because I started to worry about having two hot wires. The new switch did not turn the light/fan combo on or off under any configuration.

Can anyone help me debug this tangle of wires? Which should connect to red, which to black, and which to white?

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*Combinations where neither switch worked: First, when the wire marked White 1 was connected to DewStop's white and White 2 & 3 were connected to DewStop's red; second, when White 3 was connected to DewStop's white and White 1 & 2 were connected to DewStop's red
 
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  #2  
Old 04-09-15, 01:56 PM
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I identified the wires I'm calling "hot" with a non-contact tester
Non contact testers can't determine that. You need a multimeter, preferably analog. While the term hot is slang it generally refers to power in. In most residential boxes there is only one power in wire.

Based on your diagram "old" #1 may be hot but I can"t tell based on your diagram. That should be connected to black of the new switch. Red of the new switch should only connect to the black going to the fan. Please answer the two questions in the diagram below.

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Last edited by ray2047; 04-09-15 at 04:16 PM.
  #3  
Old 04-09-15, 02:01 PM
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The blacks are not neutrals. Neutrals are not connected to regular single pole switches. Special switches like illuminated switches or timers may need a neutral.

The white would only be hot in a switch loop configuration which you do not seem to have.
 
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Old 04-09-15, 04:35 PM
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pcboss and Ray2047, thank you both for your quick replies.

Well, now you know I really am relatively new to this!

I stand corrected: the wires I was calling "hot" are the ones that sounded an alert using the non-contact tester. I do have a multimeter--a Klein MM100 (seems digital?)--but I am not sure how to use it to answer this. I would love any guidance you can give!

Ray2047, I've attached pictures of the two entry points you asked about (first photo is the top one; second is the bottom). I was trying to loosen the locknuts to try to see if the wires came from one or two cables, but the locknuts wouldn't budge, and I didn't want to go too far without making sure I'm on the right track. Can you tell from the pictures? If not, should I try to loosen the locknuts and/or remove the metal switch box to see how many cables I see on the other side?

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Old 04-09-15, 04:51 PM
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With two white and two blacks you have two cables.

I suspect your box is grounded. If so you can take your meter, set it to AC voltage, place one probe on one black wire and the other to the box. Do this until you find one that is 120 volts to ground. That is the feed.
 
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Old 04-09-15, 05:14 PM
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I see three cables. The one with two cables in the top picture and a single cable in the bottom picture that bottom cable should be you feed (power in).
 
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Old 04-09-15, 05:21 PM
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That's really helpful, and you're both absolutely right: I got a reading of 120V from the wire I marked "Black 1", coming from the bottom.

So from Ray's earlier note, "Black 1" (hot) should be connected to the black of the new switch (and, I presume, linked to the other switch in the box like it was in the old configuration so they both get power--can you confirm?)

Then, if I'm reading that same note correctly, red from the new switch connects to the black that was on the old switch ("Black 3").

That just leaves white: does the white from the new switch connect to all three white wires that were previously bundled at the back of the box?
 
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Old 04-09-15, 06:05 PM
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Ok, the good news is that the light/fan combo is now working! But the switch isn't--the light and fan simply stay on. Nothing happens when I press 'off' button, even after I switch it to manual mode.

I suspect the switch may be a dud, but before I give up, can you two brilliant wiring engineers think of anything I might be doing wrong that would make it stay on?
 
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Old 04-09-15, 06:12 PM
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light/fan combo
My diagram does not use a "light/fan combo. It uses a simple switch for the light and the humidistat to switch the fan. Are you saying you want to use two controls for the fan? Post pictures of the combo switch and humidistat switch.
 
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Old 04-09-15, 06:43 PM
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It would appear that the sensor switch will be running a fan/light combo unit.
It would also appear that you have a defective sensor switch.


I have never found anyone that was satisfied with a moisture sensor in a bathroom. I highly recommend and typically install a pushbutton timer. This is especially effective if you want the fan on to clear the air even when not using the shower.

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Old 04-09-15, 06:45 PM
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Photos attached, but I should have clarified that it's not a combo switch--it has only two buttons: on and off, which together power both a light and a fan. At least, they powered both on the old switch...as if the fan in your diagram had a light on the same circuit.

I'm not looking for anything too complex. I would be happy if we could get this new switch to do the same, or to power just the fan (with the light that was linked to the fan joining the other light on Switch 1). I'm not sure which is easier, but for me it'll be a win just as long as it can manage its basic function of turning something on and off!

Thanks again. You're great!

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Old 04-09-15, 07:19 PM
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Temporarily remove the new switch and replace with a single pole switch to check the operations with the current wiring. If it is the way you want the switch to work no wiring changes are needed.

The new switch may be bad.
 
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Old 04-09-15, 07:30 PM
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The old switch works fine again, so it appears the new one is bad.

Thank you so much for helping me solve this puzzle. Now I know how to connect a working new one after I've returned this one. I really appreciate your wonderful responsiveness!
 
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