One switch providing power to another?

jaysgardenMarch 29, 2011

Question in short:

Can the load side of one single pole switch be used as the

feed/line side to another switch?


I want to install a timer for my bath exhaust fan. The current switch for the exhaust fan is part of a decora double rocker switch where the top rocker controls lights above the sinks and the bottom rocker controls the exhaust fan. This double rocker switch is cut into a very large mirror on the wall. So I want to avoid cutting the mirror to make room for a larger work box.

The attic above the bath is roomy enough to work in and some of the romex is run along the joists and readily accesible.

I was thinking of installing the timer on an adjacent wall,

splicing(in a j-box) into the run in the attic to the exhaust fan and running 12/2 back down to the timer(properly designating the white in this run with black tape).

In this setup the bottom rocker of the double decora switch would "feed" the timer.

Would like to hear some thoughts on this idea whether you think it would work(well it will work) but more importantly if it is OK.


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As a follow up: If I could find a product that was a combination 60 minute timer /single pole switch that could replace one double decora rocker switch that would solve everything but that's a lot to ask in that amount of space.

    Bookmark   March 29, 2011 at 8:40AM
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You can certainly wire a time in series with a switch as you describe. The only question I had was if this circuit is 20 amp, thus requiring 12 gauge wire.

To make this more user-friendly, why not change the existing double rocker switch back to a single switch, and put a switch/timer for the fan in a different location. To me it doesn't make sense to control a single fan from two locations.

    Bookmark   March 29, 2011 at 9:12AM
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Ron Natalie

I've never seen a timer that will fit in the same space as another switch as you're asking. Your other option is to relocate the timer (or the light switch) to another spot on the wall somewhere.

I don't know what your intent is but BROAN makes a fan that incorporates both humidity sensors and timer into the fan.

When the fan switch is on, if you flip it off for less than a second, it will run for 20 minutes and then cut off, until there's a humidity buildup an then it will run until that abates.

    Bookmark   March 29, 2011 at 9:13AM
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Currently from the double decora there is 12/2 running to the fan. I'll install a new timer switch on another wall in the bath and run 12/2 from the timer(switch loop) somewhere in the attic along the 12/2 from the decora where I'll use a j-box and make the appropriate ties namely:
The 12/2 FROM the decora once cut I'll tie the whites together...neutral is now intact to fan.
From the 12/2 to the timer(switch loop) I'll relabel the white as black and tie this "white now labeled black" to the black FROM the decora.
The black FROM the timer will be tied to the black TO the fan.

SO in essence the (bottom rocker switch on the double decora) is used as the line to the new timer.

ron: the current fan is only a few months old so I do not want to go thru the expense of a new one but thatnks for that option on the humidity sensing fan. Did not know one was made like that.

    Bookmark   March 29, 2011 at 1:40PM
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Ron Natalie

I'd actually run a 12/3 with the description you have. Unless you want one of those annoying ticking timers forever, run HOT and NEUTRAL down to the timer and then the switched feed back.

Frankly, I might consider just wire-nutting the connection that went to the original switch together and replace the double switch with a single. Why have two switches in series?

    Bookmark   March 29, 2011 at 5:06PM
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ron: I was considering one of the mechanical timers by Intermatic but may take your advice and get a digital one requiring the neutral.

Also good suggestion on just wire-nutting the the connection at the current double rocker decora. I knew having two switches in series was not typical but could not think of an easy solution without grabbing power from somewhere else.


    Bookmark   March 30, 2011 at 7:06AM
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Ron Natalie

I've got a couple of those multibutton intermatics that give you 15-30-45-60 minutes of time. One's on the receptacle for my wife's straightening iron which she's afraid she'll forget to turn off. The other is on the lights for my wine cellar (room is super insulated so leaving the lights on can really get the cooling unit going hard).

    Bookmark   March 30, 2011 at 2:43PM
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I saw that multibutton one at the store. Does it require the neutral?

    Bookmark   March 31, 2011 at 7:43AM
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Ron Natalie

Yes it does.

    Bookmark   March 31, 2011 at 9:01AM
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Lutron has a timer/dimmer.

Here is a link that might be useful: timer/dimmer

    Bookmark   March 31, 2011 at 9:40PM
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