Changing 2 bath exhaust fans to 1 inline: electrical concerns


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Old 11-05-14, 11:05 AM
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Changing 2 bath exhaust fans to 1 inline: electrical concerns

Hello!

As stated, I am planning to remove ceiling-mounted exhaust fans in my bathrooms, and install an inline fan which will service both bathrooms. I have a couple of questions about the electrical side of the install.

Is there any issue with simply putting the two existing fan control switches in parallel, so that if either switch is closed, the fan will run (even if both happen to be closed at the same time)? This would be my first choice, since I could use the existing switches. I am not sure if both bathrooms' fans are on the same circuit, but I could test to find out.

Is there a better way to handle this, other than a 3-way switch setup?

Thanks for reading!
 
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Old 11-05-14, 11:53 AM
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Probably a better way would be to use the existing wiring from the switch to the existing fan in a switch loop arrangement and install spring-wound timers in each bathroom. The two switch loops would indeed be wired in parallel and then the combination wired in series with the supply and the new fan.
 
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Old 11-05-14, 01:27 PM
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Thanks for the reply! This sounds about like what I had in mind. The timers would be a nice touch. I made a quick & dirty diagram, does it look like I'm on the right track?Name:  wiring-bathrooms.jpg
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Old 11-05-14, 04:20 PM
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That setup will work. ........................................
 
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Old 11-05-14, 07:34 PM
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I assume this is to eliminate the noise of the existing fans? Just my opinion, but I think sometimes just a little noise is desireable.
 
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Old 11-06-14, 12:13 AM
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I would rather listen to the occasional "squeaker" or full-throated fart than constantly be assailed by the roar of a cheap bathroom fan.
 
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Old 11-06-14, 06:27 AM
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Not just to eliminate the noise, but to fix the fact that the existing fans don't work very well and are vented into the attic. If it were just a noise issue, I would have better things to do!
 
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Old 11-06-14, 06:32 AM
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I did some investigating, and the two fans are unfortunately on different breakers, one is on the same wire run as the rest of the master bedroom and the other is on the same run as the adjacent bedroom. I will need to do some poking around to see if the power is introduced at the fan or the switch for each. My diagram just got a whole lot more complicated. Name:  wiring-bathroom-2.jpg
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Last edited by eharshman; 11-06-14 at 06:34 AM. Reason: added picture
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Old 11-06-14, 12:13 PM
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Which is why I suggested spring-wound timers and using the two conductors going from the switch to the fan as a switch leg.

You would abandon the power in the switch box if it went ONLY to the fan or else disconnect the fan wiring from the power. Add a junction box (or two, or three) in the attic as necessary to make up all the wiring and bring the power in from a separate source. Actually a very simple wiring solution.
 
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Old 11-06-14, 08:29 PM
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Furd, I see now why you specified spring wound timers, since they require one less connection. I'm not clear on what a switch leg is, but I'm going to research it and try and diagram it when I get a chance.

I am wondering, could I not remove the power from only one of the existing fan circuits, then connect it to the other fan circuit and the fan in the attic? Then I wouldn't need to bring power in from another source.
 
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Old 11-06-14, 09:42 PM
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A switch leg consists of two wires. One bringing power to the switch and one carrying it away.

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Above is a basic switch loop (leg) however 2011 NEC requires a neutral even if not used.

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So if you have to run new cable and are under 2011 code you could use an electronic timer. However if using just existing cable you would need mechanical timers.

Forgive the crudeness but here is your basic circuit pre 2011.

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Last edited by ray2047; 11-07-14 at 12:35 AM.
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Old 11-07-14, 04:08 PM
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Thanks very much, Ray2047! Those diagrams are very helpful. I saw the first one just before bed, and now you've added two more. I salute you sir. I'm working on figuring out how the fans are currently wired, and will post when I have a diagram. (I'm a fan of diagrams, in case you can't tell.)
 
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Old 11-07-14, 07:30 PM
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I made a diagram of the current wiring setup. I will update the diagram later with my understanding of the correct changes:
  1. Disconnect Guest fan from wire 7 and remove jumper between fan and vanity lights
  2. Move wire 7 to vanity input
  3. Uncap neutral wire from wire 6, mark as hot, connect to Guest fan input (making a switch leg)
  4. Remove existing fans, run wires 1 and 6 (attic end) to new junction boxes
  5. Mark wire 6 (attic end) white wire as hot
  6. Run new wires from junction boxes to new junction box at new fan
  7. Implement rest of circuit as illustrated by ray2047, but with power source at master bath switch
  8. Replace switches with timers after making sure circuit works

Name:  bathroom fan wiring.jpg
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Old 11-07-14, 07:42 PM
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Implement rest of circuit as illustrated by ray2047, but with power source at master bath switch.
Not quiet sure what you mean. Please diagram.
 
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Old 11-08-14, 08:30 AM
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ray2047, I just mean that the power seems to be supplied at the switch, rather than at the fan. For both fans, there is a single wire straight from the switch box to the fan, with no junction boxes in between. I am working on a diagram.
 
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Old 11-08-14, 08:42 AM
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Just wanted you to know both fans should be on a switch loop from common power in the original plan. However if you use a switch with power at it you can just run a switch loop from there to the second fan.

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If you use a 3-conductor cable as switch loop you can use an electronic timer and it will meet 2011 NEC code.
 

Last edited by ray2047; 11-08-14 at 09:15 AM.
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Old 11-08-14, 09:32 AM
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Well, it looks like I will need one more conductor to do what I am trying to do. If I use the white wires from the two switches as hot wires, then I have no wire to use as neutral from the fan. Maybe I can pull a 3-conductor wire through the wall? Here is what I have:

Edit: I just saw the diagram you added. Yep, it looks like I am stuck adding new wire in the wall either way.

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Old 11-08-14, 09:35 AM
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Did you see the diagram I added? Just run a 2-conductor cable (or 3-conductor) from the box with power in to the box with the second switch.
 
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Old 11-08-14, 09:48 AM
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.
 

Last edited by ray2047; 11-08-14 at 10:05 AM.
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Old 11-08-14, 09:51 AM
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I need to research how to run wire, is all. It sounds difficult to a newbie and seems to require a lot of new tools. Do they usually staple the wire in place inside the wall, or could I attach a new piece of 14-3 to the end and pull it through using the old wire?
 
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Old 11-08-14, 10:11 AM
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Wires are stapled but you don't remove them, you abandon in place by cutting them short as possible on both ends and shoving out of the box. The new wire is just fished. It does not need to be fastened in to the wall. I have added a diagram above your post on how to wire. A two conductor cable can be used with a mechanical timer so no need to replace if cable already exists.

Technical tip: Only one wire allowed under a screw if two or more you must pigtail or use a continuous wire.

I may have one or two other suggestions. For example if you can access the wire I Xed out in the attic it could be used to go to the master bath box and only a new section added on as needed so you would only need to add a cable to the master bath box.
 
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Old 11-08-14, 10:50 AM
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Alright, I have learned via YouTube how to remove the existing box and I have a fish tape, so I should be good to go adding a new wire.

I think, due to ease of access in the attic, I want to run a new wire to the guest bath switch box instead of the master. (The master bath's wires come into the attic in a spot where I have to crawl 8 feet along joists.)

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Technical tip: Only one wire allowed under a screw if two or more you must pigtail or use a continuous wire.
This is rather unsettling, because the existing wiring breaks this rule in the master bath switch box. The Shower Light switch has two wires under the screw and a third going into a hole in the back of the switch, which I guess is just a spring compressed terminal. I will fix this with a wire nut and a bit of wire before I close everything up.
 

Last edited by eharshman; 11-08-14 at 11:35 AM.
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Old 11-08-14, 11:46 AM
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The Shower Light switch has two wires under the screw and a third going into a hole in the back of the switch
Two wires not allowed by code. Back stabs are less reliable and best practice is to not use them.

Your diagram seems correct.

Finding an old work 3-gang box would be difficult but 2-gang are common so replacing the 2-gang box instead of the 3-gang box makes good sense for a second reason.
 
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Old 11-08-14, 08:19 PM
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I ran the wire through the wall earlier, replaced the switch box and tomorrow I will remove the old fans and get things rolling. Thank you for checking my work, your patience and your efforts making diagrams!
 
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Old 11-11-14, 04:40 PM
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I have finished the wiring work. Everything seems to be working as intended with no issues, so I'm on to running the duct work for the fan.

This diagram is what I ended up doing. The new fan came with a standard NEMA plug built in, so rather than try to splice 14awg wire with the smaller, softer wires in the fan, I opted to install an outlet.

Thanks again for your input, all!

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Old 11-11-14, 05:59 PM
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Thanks for letting us know it worked out.
 
 

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