Can two neutrals on different legs of the same circuit be connected together to shared neutral of ceiling fan?

Question

Situation: half way through construction, a change in plans on ceiling fan operation occurred. Wires were originally ran to 3way switches and on to ceiling fan. Then came the decision to separate the fan to be operated by its pull switch (keeping the light kit wall switched). A new 12/2 supply wire was able to be ran on unfinished side of room to get power to box, but I am questioning the neutrals. Maybe I’m overthinking this, but is it ok to have the two separate legs supplying fan and lights (legs are on same circuit) and have the neutrals from both lines wire nutted together with the single/shared neutral line of the ceiling fan?

I wouldn’t normally wire something like this and if it weren’t for code now requiring neutral up to switch box, I would kill that supply line side and just use the other side as supply. Thanks in advance for any wisdom out there!

Answer 1

No, don't do this. The problem with your proposed circuit is that as soon as the two neutral paths are connected at the fan, you no longer control which neutral carries how much return current. The two cables connected at the fan are almost sure to carry unbalanced current.

You can do what you want safely, and prepare for future installation of powered smart switches, but not strictly according to current NEC. You have to wire one way today, then potentially change it around later to accommodate smart switches. It's possible without running any more cables.

With mechanical switches, you want to abandon the run from the basement light to the first 3-way by capping it off at the switch box. (You will use this cable again if you convert to smart switches.) Repurpose the white wires between the fan and the switches to be always-hot, making this run a bog-standard 3-way switch loop:

With smart switches, you will abandon the run from the other basement light to the fan (the "new 12/2"), and reconnect the cable from the first basement light. Depending on the type of smart switch, you may also no longer need the red wire between the switches:

Note: I would never do this in somebody else's house. I would do it in my own house, but I would document it and add it to my "technical debt" list in the "ordinance conformance" section.

Answer 2

There is a simple rule of thumb that keeps you honest, about cabling: No loops. What you just drew there is a loop. You can't have loops.

Think about a tree - trees have many places where they branch or split. But you never see two branches re-merge so they are connected and interchange life fluids. That doesn't happen.

So all wiring must be a tree - unlimited splits involved, but no re-looping back.

This setup has a loopback. It must be cut somewhere to be legal.

Mind you, the cut can be at a device or switch box, by having either a physical or imaginary "partition" separating all non-ground wires). Safety ground wires are allowed to cross the partition/loop/web, but never neutral.

So if you can obtain a fan with separated neutrals for fan and light, or if the fan's instructions include a procedure for having the same effect, then you can indeed have the lamp+its neutral powered off the 3-ways and their accompanying neutral, and the fan+its neutral powered off the branch coming over from the lamps.

The problems with looping are serious -- buzzing wires which then causes metal fatigue, cracking and overheating or arcing... heating in metal bits near this wire, and high EMF which can trouble animals or people who are EMF-sensitive.

When the "tree" plan is followed properly, all currents in each wire are balanced by an equal and opposite current in the other wire(s) of the cable. This causes the EMFs to cancel each other out, because that's the way magnetism works.

Answer 3

While what you ask is possible, and will work OK, it is not recommended for 2 reasons.

1st, I'm pretty sure it is not code.

2nd, you have to think about someone (maybe even yourself) 10, 20, or even 50 years down the road working on the system. There is a potential someone will turn off the breaker and begin to work on the circuit, disconnect the neutral (separating the circuits) then having the load on the other circuit on. This will put 120v on the dangling neutral.

Right now you say both circuits are on the same breaker, but house wiring is more dynamic then people think. If you play with fate, someone down the line will rewire it.

If you go ahead, make sure you place copious notes in the breaker box and near the junction. Also, mark the neutrals with tape or zip ties for better identification.

Is there any chance you can run a completly new wire around the house and just abandon the wire that is incorrect? That would cost a bit more, and personally that would upset my OCD, but I think I could get over that.

Good luck, Mark

Answer 4

There is another choice. I had a fan with a motor and a light with a single hot lead to control both.

There was a semiconductor device in the box in the fan. It was U shaped to fit in the fan box (in my case not in the ceiling box) and maintain a single hot lead through the support pipe from the ceiling to the fan but if you have separate light and motor wires in the pipe, you can fit it in the box in the ceiling.

Here is how it worked.

One would turn the switch on and the light would come on.
Then, one would turn off and back on the switch (in less then a second) and the light would go off and the motor would come on.
Then the second off/on sequence would turn on both the motor and light.
Lather, rinse, repeat.

You can still use your original 3-way switch setup with a controller like this.

---

Another choice is a full-on controller unit. here is an example of something I found on amazon...

I know nothing about this, it is just for illistrative purposes.

Fan controller at Amazon

Zooming in on the pix shows the schematic. Single hot with, no switch(s) in the wall at all.

Order up a second remote and Bobs your uncle.

Answer 5

There are tons of good reasons to rewire or rethink this solution. I just wanted to address the comment about neutral loading being unequal as an issue and calling a wire a dangling neutral. Nothing about this post will help much except clarification. Almost everything else posted is more useful in a practical sense.

The short comment is "who cares?". Assuming the hots that could connect to this neutral are all from the same circuit breaker, the wire should be more than rated for the full current to return along a sing neutral conductor. If you have split the hots across a couple breakers, you might just be creating a slow blow fuse with a burn-dow-the-house feature, but that still isn't a guarantee. Fans don't typically pull huge amounts of current and any short circuit would be short lived and not cause much heating of the wire.

Most likely, it would be fine for a decade or 2 before issues rear their heads, if they ever do.

Still... not a good idea.

Also, a dangling neutral is usually referred too as a common in other electrical systems. It isn't technically a neutral and it can be either hot or neutral. It is simply common to the circuits.