OK, as a follow up: The electrician came this morning. He did some testing and determined that we have line, load and neutral (that is the white wire currently in the box) for ceiling fan. We only have line and load for light. He looked at light, and there is a neutral wire running from it to electric plug near switch, but it doesn’t run all the way to the switch.
There is a black wire, the power, which we see running down from light, through electric outlet through to switch. We know it’s the same wire because it tugged on it and you can see it move in the switch box.
Also, what I discovered, thanks to electrician, is that all the neutral wires in the house are connected at the switch box (see image).
So, the plan now is quite simple: Cut the neutral wire in the box and pigtail two neutral wires to it – one for light, the other for fan. That should do it.
I think you should be fine splitting the white wire and using it as neutral. Why don’t you have the electrician do it though? Also, non-contact hot wire detectors do not measure or detect current - they detect the electromagnetic field emanated by the hot wire - they’re technically detecting 60Hz waves coming from the wire and amplifying them to determine if a wire is hot or not.
It’s not uncommon to share neutral with 2 separate lines. Most modern kitchen and bathroom are going this route even on higher 20Amps breaker. The 2 lines need to be on opposite phase (meaning the current will never be able to go above the intended max of 15amp or 20amps whichever it was designed for because they are on opposite phase) and the 2 breakers need to be tagged together.
Saying this. You still need to check your local code.
That is not right. Neutral wires are not usually protected by breakers and having two hot wires share the same neutral wire to close the loop can easily drive a higher-than-rated current through that neutral wire, causing a fire. You can’t have any wire in the home exposed to currents that exceed that wire’s rating. If one hot wire delivers 10A and the other 10A, while they’re both under the 15A rating, the neutral wire is really taking a beating at 20A and will seriously heat up and possibly catch fire. No breaker will interrupt this as the measured current on neither of the two hot wires exceeds 10A… that is really bad.
Most households in the US use a single phase two pole system. It’s technically a 230V with the neutral at the median. They’re not “opposite”. My oven uses a 230V plug (two hot lines, no neutral). I can see what you’re saying about the two currents canceling each other out, but I’m not sure the new NEC approves of sharing a neutral wire between L1 and L2 connected plugs.
For sure, I’m a novice, a newbie and only know what I know about light switch wiring because of what I have researched online and learned here.
That said, in every single video I have seen where someone is replacing a mechanical light switch with a smart switch, I see them pull out a neutral wire like the one in the image below:
The instructions then proceed to suggest you pigtail a wire to the existing neutral wire bundle to plug into the neutral slot of your smart switch. Now, its probably because I’m a noob, but I don’t see what the difference is between what I’ve seen in all these videos, and what I am suggesting for my switch (split the existing neutral wire for each device in the 2 gang switch).
But that’s not what Adrian and Ray are disagreeing about.
They are talking about whether it’s ok for two hot lines to return to one neutral wire in your breaker box. Ady’s a smart dude, but Ray is an electrician, so my money’s on him .
What I don’t agree is with the term “opposite”. It’s the same phase, it’s just a matter of calling it, but yeah, from the reference of the neutral wire, the potential of the two hot lines at any given time are “opposite”. But to have opposite phases, you need to have more than one phase. The system is called single phase. In the UK, the three phase system has a phase shift of 120 degrees between the three phases. The same common-neutral-cuz-they-cancel-out theory does not hold true.
You are fine. Your light is still using its designated neutral wire. The wire you are splitting is used for the switch’s power supply which is negligible.
Special tied breakers are required to ensure all breakers feeding the neutral wire are disconnected (required under 29 CFR 1910.137 & 1910.301, and DOE/ID-10600)
Although technically acceptable under the NEC, it is considered “bad practice” by industrial standards
Industry standards consider it especially bad practice to share neutrals for circuits intended for computer systems
Best-practice recommends that shared or common neutrals be sized up one gage of wire to reduce electrical noise and help prevent overcurrent scenarios.
Based on interpretation, the practice of sharing neutrals may be considered illegal under certain 29 CFR 1910 regulations
Certain DOE – Operation Office Architectural Engineering Standards, dated November 1994, no longer permit the use of “Edison Circuits” in new construction
The Department of Energy has released ESH Bulletin 98-2 which is entitled “EDISON CIRCUITS POSE SAFETY HAZARD” which sites ORPS Report ID-LTC-WASTEMNGT-1997-0013, INEEL Lessons Learned #97283 in its requirement for immediate corrective action in removing all Edison Circuits (shared or common neutrals) from their facilities.
Possibility of over amperage if phases are not aligned properly
Cannot adjust breakers at later dates due to phase alignment issues
Safety hazard for personnel when servicing the equipment as neutral wires may still be “hot” even after the proper lockout/tagout procedures have been implemented
Electrical noise is increased
Possibility that electrical faults occurring on a shared circuit could damage equipment on the other shared circuits
GFCI circuits are nearly impossible to install
Right now, this number 6 is the most troublesome, as current code requires GFCI/AFCI almost everywhere
Thanks for the overkill info. You rock, and as I said, it probably isn’t accepted anymore, see new buildings not permitting it. But he should be fine as he is borrowing the neutral for the sole requirement of the smart switch itself, not to power the bulb. The bulb will continue to use its own dedicated neutral as it did prior to the smart switch installation. I am not a pro of the NEC codes, so a licensed electrician should probably be used. Don’t take my word for it
Unfortunately, I can’t confirm nor deny your claim My kitchen is a commercial grade kitchen with a double fire range and three ovens, individual fridge, individual freezer, etc. The ovens are all 240V with no neutral. You made me pull them all out grrrr But I’ll take your word for it. However, I would personally not use a shared neutral wire, or at least, I would not add a hot wire to an existing one and repurpose the neutral for use with both.
@ady624
Three ovens? I’ll stop by for dinner.
All regular ovens are 240V AC two-phase which results in using only half the current as compared to 120V AC equivalent power. As such, they have no neutral, only ground.
No, it’s not. Also, someone has a fire because of an overheated neutral, that someone will a tough time explaining it to the insurance company. Also, most fire marshalls/inspectors will also refer to 29 CFR 1910.
Well, gentemen (and ladies), the switch is installed, connected to wifi, and working perfectly. I am a little concerned about the neutral based upon the discussion here, but in my case, I really don’t have a choice. My entire apartment shares the same neutral, and has for the xxx years I’ve been here.
Anyway, I thank each and every one of you who participated in this discussion. I learned a lot!
Previous owner ran a home catering business. You’re welcome anytime you’re in Florida. My home has a single phase three wire power system. I do not have two phases in my home, just one phase. One could consider it two phase with a shift of 180 degrees, but they really call it single phase three wire. Also called split phase.
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My kitchen is a commercial grade kitchen with a double fire range and three ovens, individual fridge, individual freezer, etc. The ovens are all 240V with no neutral. You made me pull them all out grrrr 
But I’ll take your word for it. However, I would personally not use a shared neutral wire, or at least, I would not add a hot wire to an existing one and repurpose the neutral for use with both.