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I have an existing switch that controls an outlet. I'd like to replace it with a smart-home switch, which requires a neutral wire to power the switch itself. However, there is no neutral wire at the switch. It's infeasible to run a new wire because the switch wasn't run with conduit, and I'm not willing to tear up my walls.

It's my understanding that I could use ground as neutral for low power applications such as this. Are there any risks, either safety or electrical reliability of doing so?

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    It guarantees you will never be able to retrofit GFCI, because this is by definition a ground fault. If this is a bathroom or kitchen circuit, or laundry room or outdoor, you really want GFCI. – Harper Dec 8 '16 at 0:09
  • Good point. Happens to be in a safe place for that--an office. The fault would only be visible only on that outlet, right? I'd guess this would be a only few mA draw. They make battery operated switches that last months with mini batteries, so it can't be much. A quick Google shows that a GFCI can trip on current as low as 4-5 mA, so I think there's a pretty good chance this could sneak under that regardless. If that's the only realistic risk, I'd be happy to take it. – glenviewjeff Dec 8 '16 at 0:13
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    My statement WAS NOT all-inclusive of all potential risks. It's amusing how people planning to doing something crazy, always assume this is the only thing on the circuit, so they can avoid thinking about interactions and unintended consequences. Yes, the moment you think it, God sends elves to rewire your house to make that one box a homerun. – Harper Dec 8 '16 at 0:28
  • I know you weren't suggesting this was the ONLY risk. I was saying IF risking tripping a future GFCI were the only risk, I'd be happy to take it. I'm asking on here in order to make sure that I'm not missing an obvious risk. Why the downvote? – glenviewjeff Dec 8 '16 at 0:46
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    Wasn't me, takes a lot more than this to get a downvote from me. My point is depriving this circuit of a GFCI doesn't only deprive this switch/light of GFCI protection, but also every other location in the circuit wherever those may be. – Harper Dec 8 '16 at 2:48
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Yes there are risks to safety.

If anything interupts the ground conductor that leads back to the service entrance, suddenly your switch is energizing the ground on that circuit, so anything connected to it is also going to be energized (i.e. a printer that has a grounded metal chassis suddenly has a live metal chassis).

You guess that this is only a few milliamps, but do you know under all operating conditions that this is the case? Just 10mA is enough current to cause muscular paralysis -- and 100mA is fatal.

You may think that "well yeah, but it would take multiple bad things to happen for this to be a safety hazard"... but you're already doing one of the bad things it would take, so you're one conductor away from a very unsafe situation.

There are some smart switches rated for use without a neutral (but they generally only work with incandescent lamps).

Since you're just controlling a receptacle, the easiest thing to do is use a plug-in lamp or appliance module.

But if you were controlling a ceiling light fixture, you could use an in-line switch module that wires in at the lamp fixture itself instead of at the switch:

enter image description here

You could keep the switch on all the time to supply "line" to the lamp fixture, and use the existing neutral at that fixture, then let the switch module control power to the lamp. Then you can use a batttery operated wall switch to control the lamp module.

  • I'd actually ordered a microswitch that resembles the Insteon one (Aeon Labs equivalent) that could go behind a traditional dumb switch, and had planned to put it behind the switched outlet rather than the switch in order to gain neutral access. The problem is that the microswitch is so big that it won't fit in the outlet's box. The only way to get it to fit in there would be to jut out the outlet's box about 1.5" away from the wall, which would look goofy. – glenviewjeff Dec 8 '16 at 2:55
  • I'd be "shocked" if it used more than 5 mA. Couldn't resist. So I understand you correctly, are you saying that if there was a fault from hot to ground (such as someone playing with a running toaster into the bath,) this device could now provide a conduit that now "hot" ground back through grounded appliances on the office switch circuit? Wouldn't that happen anyhow, even if a smart switch wasn't connected to ground instead of neutral? – glenviewjeff Dec 8 '16 at 3:00
  • They definitely make zwave switches that operate without neutral, but they are few and far between, and difficult to find. I'm probably going to end up using a battery operated motion sensor and ditching the whole switch problem. – glenviewjeff Dec 8 '16 at 3:01
  • If the box is too small, you may be able to replace it with a deeper rework box. My concern is more that if something happened with the ground conductor between this device and the panel, then this device would energize every grounded device on that circuit. While it probably only leaks a small amount of current, I wouldn't be willing to bet anyone's life on it. – Johnny Dec 9 '16 at 5:21
  • Thanks for the great info. @Harper came up with a brilliant workaround for the switch wires. See his answer. – glenviewjeff Dec 9 '16 at 13:17
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Well here's the thing. You say the switch is controlling the wrong outlet anyway. (this is the scourge of modern construction; electrical code allows builders to connect the mandatory switch to an outlet and provision no lights in the room at all. Leaving random tenants responsible for safety lighting is a disaster, ask any first-responder.)

One option is to re-task the switch-loop wires to be an actual hot and neutral. (they are probably black and white already.) You now have always-hot at all outlet locations and at a switch location.

Now install a smart-switch which is powered, but uses wireless or power-line communication to communicate with a remote module at the location you want to switch. You now have a great deal of liberty as to where to put that.

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    Brilliant idea. Just need to carefully label them for future work. If I remember right, they were both black, but either way I'll label them. And yes, that was the plan all along, to use the smart switch to control a device elsewhere. – glenviewjeff Dec 8 '16 at 3:07
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    One is probably taped with black tape. If they are both actually black, that is good news. There's no such thing as black-black Romex, so there must be conduit between switch and outlet. Easy to pull a neutral. – Harper Dec 8 '16 at 3:11
  • They're red and black. Not ideal, but it's definitely some kind of armored or cable (not conduit.) There's the paper wrapping visible inside the box. – glenviewjeff Dec 8 '16 at 3:15
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There are smart switches that do not require a neutral. By design, they "bootleg" some neutral / return current on the ground wire. However, if they are legal and listed, they are tested to limit the bootleg current to some tiny amount that is considered safe by UL.

Generally bootlegging a neutral - using a ground wire as a neutral - is an unsafe practice:

The equipment grounding system (EGS) provides a path so that in the event of a ground fault, there is a low impedance path to complete the circuit, so that sufficient current will flow that the breaker will trip. In typical residential systems in the US wired with nonmetallic cable (Romex) and plastic boxes, the bare wires make up the bulk of the EGS.

Generally the EGS is not carrying current, not energized, even with the power on. In the event of a ground fault it will very, very briefly be energized until the fault is cleared. Faults generally create a dead short and short circuit current is very high.

If someone working on the electrical system, testing, troubleshooting, etc. assumes the EGC is safe, but it's carrying bootleg neutral current, they could receive a shock.

There can be some sharing of EGCs between circuits, retrofit EGCs not run with branch circuits, etc. In these cases even with the circuit you're working on turned off at the breaker, the EGC could carry current from another circuit. So in some of these circumstances, even things like plumbing pipes could wind up carrying some of that bootleg current. If there are multiple not-so-smart devices bootlegging neutral current, it could become more dangerous.

I think most would agree bootlegging a smart switch does not constitute a huge, immanent danger where you ought to get the children out of the house immediately until it's rectified.

But all would agree it's a code violation, and most would agree that re-writing the code to be more convenient for you, or picking and choosing where you're smarter than the code, is some dangerous hubris.

As mentioned in another answer, smart switches with remote units that can be installed at the light are a safe alternative.

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First things first. You asked two important questions I shall answer them in bold.

  1. It's my understanding that I could use ground as neutral for low power applications...

Fact is, per the NEC, manufacturers of smart devices have up to the year 2020 to redesign all of their devices so the do not use the equipment grounding conductor "Green/bare wire" as a neutral. There are exceptions too. The Code reads as follows:

404.22 Electronic Control Switches

Electronic control switches shall be listed. Electronic control switches shall not introduce current on the equipment grounding conductor during normal operation. The requirement to not introduce current on the equipment grounding conductor shall take effect on January 1, 2020

Exception: Electronic control switches that introduce current on the equipment grounding conductor shall be permitted for application covered by 404.2(C). Exception: Electronic control switches that introduce current on the equipment grounding conductor shall be listed and marked for use in replacement or retrofit applications only.

  1. Are there any risks, either safety or electrical reliability of doing so?

Parallel paths is the main reason. Electricity doesn't take the shortest path back to the source, it takes every path possible. Enabling alternative paths can create shock conditions.

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