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Electrical Question (Bathroom Fan)

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Electrical Question (Bathroom Fan)

Old 03-04-2016, 07:37 AM
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Default Electrical Question (Bathroom Fan)

I am in the process of making some improvements to our son's bathroom. One thing I am doing is putting in a new vent fan. I found one I really like that gets great reviews. It has a humidity sensor that you can set the % so it kicks on and off based on that %. It is very energy efficient however, it does not appear to be as simple as just ripping out the old one and replacing it with this one.

The manufacturer's specs state the following:

-Multi switch operation (at the minimum it needs one constant hot wire plus one wall switch)

There is only one switch to operate the current fan. Does the above statement mean that this unit will not operate on one switch? Is there a way around this?

Despite what my friends say, I'm not an idiot, just not an electrician. Thanks for any helpful input.
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Old 03-04-2016, 08:06 AM
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It sounds like the fan will require an additional (always hot) line run if you want both automagic and manual control of the fan.
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Old 03-04-2016, 08:24 AM
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Originally Posted by DFreedom View Post
I am in the process of making some improvements to our son's bathroom. One thing I am doing is putting in a new vent fan. I found one I really like that gets great reviews. It has a humidity sensor that you can set the % so it kicks on and off based on that %. It is very energy efficient however, it does not appear to be as simple as just ripping out the old one and replacing it with this one.

The manufacturer's specs state the following:

-Multi switch operation (at the minimum it needs one constant hot wire plus one wall switch)

There is only one switch to operate the current fan. Does the above statement mean that this unit will not operate on one switch? Is there a way around this?

Despite what my friends say, I'm not an idiot, just not an electrician. Thanks for any helpful input.
You will need a hot bypassing the wall switch. Like what is said above, the automatic feature will not work if you have it wired solely through the wall switch with it in the off position.
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Old 03-04-2016, 08:28 AM
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Yep...depends on how the current wires are routed...but you need one switched leg and an always hot...which may already be in the jb.. if it's a atic space easy to run from any home run jb located close by...if is a split level house and it's on the lower level...pain in the arse..
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Old 03-04-2016, 08:31 AM
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bet it will work if you can remember to always leave switch on. then it will just come off and on by itself. other wise sounds like they want 2 circuits- one to force it on with switch and the other for its auto- mode

there are ways you can accomplish that with your 14/2 existing wire but it is not to code
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Old 03-04-2016, 08:42 AM
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how bout a link?
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Old 03-04-2016, 08:49 AM
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You can wire this two ways, add a hot wire or a neutral wire.

You can run another hot wire up to the fan to operate the automatic feature. Or, you can make the hot constant and run a neutral wire up to the automatic side and switch the neutral on the manual side.

You really don't need to run a separate switch, it's all in the wiring.
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Old 03-04-2016, 09:01 AM
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What if you want to steam it up sometimes?
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Old 03-04-2016, 09:43 AM
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Originally Posted by Jonesyfxr View Post
You can wire this two ways, add a hot wire or a neutral wire.

You can run another hot wire up to the fan to operate the automatic feature. Or, you can make the hot constant and run a neutral wire up to the automatic side and switch the neutral on the manual side.

You really don't need to run a separate switch, it's all in the wiring.
Never switch the neutral. The hot is still hot. Electrocution hazard.
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Old 03-04-2016, 10:28 AM
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Originally Posted by aln View Post
Never switch the neutral. The hot is still hot. Electrocution hazard.
This. Never interrupt or switch a neutral.

The existing fan likely had a hot leg switched from somewhere else. In the switch box connect to the hot side of the switch and run another always hot leg to the new fan. If doing this in new construction you could use a piece of 12/3 or 14/3 romex, but in a retrofit, you probably want to bit the bullet and run another piece of 12/2 or 14/2 from the switch box to the fan box with the neutral / ground unused.
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Old 03-04-2016, 10:34 AM
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My new house had some switched negative (not neutral) wires that I questioned myself. According to my local code that's acceptable, just don't ever switch the grounds.
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Old 03-04-2016, 12:08 PM
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In most bathrooms, the wall switch if fed hot, and only the leg and neutral w/ground are run to the fan. This is done because the fan has a very small area to make the connections in. A new three wire cable will be needed to replace the old cable. Make sure you keep the wire gage the same. Use the black as the continuous hot, and the red as the switch leg.
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Old 03-04-2016, 12:11 PM
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My new house had some switched nuetral wires that I questioned myself. According to my local code that's acceptable, just don't ever switch the grounds.


Neutral is always white, but white isn't always a neutral.
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Old 03-04-2016, 12:15 PM
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Install a double switch and use one to power the humidity sensing side and one for fan-only. You'll have the option of controlling it manually that way.
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Old 03-04-2016, 04:20 PM
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Originally Posted by kenner69 View Post
My new house had some switched nuetral wires that I questioned myself. According to my local code that's acceptable, just don't ever switch the grounds.


Neutral is always white, but white isn't always a neutral.
There used to be a few exceptions where you could use the white wire as an ungrounded (hot) conductor to feed a switch when you were using a cable wiring method (usually Romex) but you have been required to reidentify that wire (typically colored tape) for the last several cycles.
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Old 03-05-2016, 05:19 AM
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Originally Posted by gfretwell View Post
There used to be a few exceptions where you could use the white wire as an ungrounded (hot) conductor to feed a switch when you were using a cable wiring method (usually Romex) but you have been required to reidentify that wire (typically colored tape) for the last several cycles.
Yep and there still installations done that way. One is supposed to mark the white wire utilized as hot by wrapping it with a bit of black tape.

There is a good chance that both circuits that you need are already available, but you'll need to open things up and inspect how it is wired. Most bathroom fans actually need two circuits anyway one for lights and the other for the fan. As such you'll likely find the primary power in actually comes from a junction box you may or may not find and goes directly to the fan unit.

It is from this point where the power is often divided if applicable. This is often done with pcs of romex from the fan units junction box fed to the switch(s) location. The common wire should marked hot utilization with black tape and switched and the circuit is completed.

Maybe the easiest way to maybe see if yours is wired this way is to pop off the switch cover and do what needed that will allow you to observe the switches wiring. If you see black and a white entering and leaving the switch you would be then be golden, because the circuits you're seeking are almost certainly already available at the fan.
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Old 03-05-2016, 05:39 AM
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Redneck it. Take the switch out, wire it to always hot and let the humidity detector do the work.
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Old 03-05-2016, 05:52 AM
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Originally Posted by rocksandblues View Post
bet it will work if you can remember to always leave switch on. then it will just come off and on by itself. other wise sounds like they want 2 circuits- one to force it on with switch and the other for its auto- mode

there are ways you can accomplish that with your 14/2 existing wire but it is not to code
This sounds like the easiest way, just use the one black wire that is the automatic leg at the fan end and always leave the switch on, you will still be able to manually turn it off. The disadvantage of this way is the fan most likely will not work if he is just using the fan for toilet duty in normal non shower conditions. As everyone said the right way is to run another wire.
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Old 03-07-2016, 07:04 AM
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Thanks all!
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Old 03-08-2016, 07:56 PM
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Just installed this same type of fan this week. The one I used would work off of the humidity sensor as long as the switch is in the "on" position. If you want to use it for odor you simply toggle the switch off and back on to operate the fan for odor control then toggle it back off and on again to put the humidity sensor back in control. Check the installation instructions to see if this is a possibility on your fan.
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