Hi Nathan! I highlighted the bonding between neutral (central transformer tap) and ground in my panel outside. The black smaller wire with the white stripe goes to the copper pole stuck in the ground nearby. While they are connected together, we are not allowed to use the ground wire as a return as you stated.
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Well I grew up and live in Croatia but there is a lot to your post.
In my old house I had 3 phase electricity. You can have this here if you want it for a private house. Probably you will have to pay something extra but you can have it.
Now as the wiring goes of course that there is a neutral wires in the house. And all appliances and light and basically everything is wired to the ground wire.
But as for light switches goes they have only two wires. One is definitely hot wire, as I test it my self. The other is light wire. When you connect those two wires it will turn on the light. I test this my self on a live setup. I mean why not.
Now, how smart switches with out neutral wire works in that setup? As I understand some of the electricity is flowing from the live wire, through the light back to light wire to power on the switch.
Old smart switches needed capacitors on the bulbs probably because flowing current was too high and the led bulbs will be on even if the light was off. This was not the case with incandescent bulbs. Never generations of smart switches doesnt have this problem because they managed to sort this thing out.
Point is, the smart switch requires BOTH live and Neutral, so if you want to place it in the switch box you do need a neutral, which often isn’t available.
That is why I stated:
But the live wire isn’t always available in the light box either, in which case pulling an extra cable is the only option
My experience from working as an electrician in a prior lifetime in the U.S., I can only recall seeing one house with single-phase service. It was built in the 1920’s.
If you have 110V (US) it could be single phase, but not if built after the 1970’s. If you have a 220V electric dryer or a 220V central air conditioner, you have a split-phase service; two single-phase lines separated electrically by 180-degrees. Split phase is sometimes confused for three-phase, but three-phase service has three live lines, separated electrically by 120-degrees. Rare in a home installation.
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I have just one relay and several dozen of smart switches, so I don’t know.
Well… It depends 
The dependencies around earth/ground and neutral are actually surprisingly complex. There are various types of earthing systems used around the world (see here). In TN−C, neutral actually is the ground (although it is mostly used in industrial settings I think). For residential settings, most of the EU uses TN, except for France where we use TT (obviously we can’t do it the same way as everyone else 
). The US uses TN-C-S and I think the UK too.
I recently stumbled over this while upgrading to a new generator because of reasons (Hi Ciaran !)… And my RCDs wouldn’t work anymore when on generator power, so I had to create my own earth on the neutral, but I wanted to do it right according to code etc etc, and so I ended up in this rabbit hole…
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Don’t know what?
I just this morning installed a Sonoff Mini Extreme Zigbee switch (relay) in my kitchen. It uses the load as the neutral to power the Zigbee chip.
@stevemann - I edited my post to clarify “houses in Italy”. My house in Italy was built in 1979 and it has a 6kW service (max you could get before having to request 3 phase power. The typical Italian power service was 3kW… and maybe still is… but my house is too big for that.
My house here in the US has the typical split-phase 240V 200A service with a nice big green transformer in my front yard. (See post above).
Yup, in Italy it is rare but if you want more than 6kW (double the normal) then you are likely to get three phase power. I did a quick search and found a recent site that confirms that beyond 6kW and up to 10kW it is likely you get 3 phase, so I am guessing that beyond 10kW it is certain. Again, the typical home service is just 3kW.
Don’t know how relay will work in cross switch environment, not us. If he claims it will work with out neutral fine. But I’m not in relays. I installed smart switches because I don’t like relays. If I have a smart devices I would like to see it.
There are plenty of no neutral smart switches. I have several.
I also have some relays installed in the light box and several smart switches with neutrals in the switch box.
My house must have had at least two guys that didnt talk to each other do the original wiring.
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Residential in the US uses this:
The loads in the house are distributed as evenly as possible between B and C. Heavy load appliances like HVAC, dryer, over, cooktop, car chargers, are on A.
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Yeah, that’s TN-C-S (neutral grounded after the transformer and then separate ground wire to loads), it just uses a split phase transformer instead of a three phase one.
We use this here (TT):
There’s also a ground wire (green/yellow), but there are two earth grounds, one by the utility company before the transformer and one per home.
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Just found this:
In the United States National Electrical Code and Canadian Electrical Code, the feed from the distribution transformer uses a combined neutral and grounding conductor, but within the structure separate neutral and protective earth conductors are used (TN-C-S). The neutral must be connected to earth only on the supply side of the customer’s disconnecting switch.
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This is correct. A Ground wire is designed for safety, and as such, no current should ever normally be flowing through it. The only time the ground wire should carry current is when something has failed. By providing a path for the electrical current to flow, the ground wire can save lives. Otherwise, that electricity might flow through a person or pet.
A Neutral wire will have electrical current flowing through it whenever the Light/Load is energized. This is why Neutral wires should never be shared between multiple circuit breakers. Turning off a breaker should ensure that both the Hot and Neutral for that circuit are de-energized. If another circuit is mis-wired to use the same neutral wire, someone may get hurt when working on the system. Thus the reason one should ALWAYS verify that both Hot and Neutral are de-energized when working on a circuit. Even so, someone could flip a nearby switch ON, or plug in a device to an outlet, and energize a mis-wired Neutral wire. Additionally, a mis-wired shared Neutral can easily be overloaded and melt (start a fire) as it has to handle the total current from multiple circuit breakers.
TL/DR - Everyone should hire a licensed electrician if you don’t know what you’re doing. The safety of one’s family is always the highest priority!
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I guess it depends on the country and the electrical system. As far as I’ve seen most devices in the US do require a neutral, or rather, most devices I’d be interested in require one. The ones that don’t typically have less features… for example a dimmer without LED bar.
For those without a neutral, they have no choice (other than rewiring) so that is what they need. For those who do have a neutral, I would go for the model that requires one as it is generally better (more features/less limitations). At least for the US market…
While there are no-neutral switches like that, this is problematic for several reasons. First of all, LED bulbs will start glowing at very low currents. The current drawn by the switch can be enough for that. Or certain LED bulbs will have a conductivity threshold set too high (ie. the switch will not get any power at all). In both cases you will need a capacitor in parallel to the bulb.
Second, a no-neutral switch can never use a relay. It can only use a Triac with a parallel power bleeding / harvesting circuit. Depending on what you do with the switch, having an actual relay to cut off power can be a good thing.
If at all possible, use a smart switch with neutral, even if that means pulling a new N wire from a nearby outlet or so (careful, make sure to pull it from a circuit on the same RCD, or you will trip it).
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I’m not in the us. It’s not a big deal to drop a neutral wire to the light switch in my case. But do I need this ? Well no. Its a light switch. As for a dimmer goes… well you can combine some smart light switches that doesnt require neutral and have decoupled mode with smart bulbs. This is far better than a switch with dimmer mode.
Everything else… well it is device for turning on or off light. Don’t over engineer this.
While there are no-neutral switches like that, this is problematic for several reasons. First of all, LED bulbs will start glowing at very low currents.
No, they will not. That was the problem with first versions that came to the market and needed capacitor to stop led bulbs from gloving. They sort this out a few years ago.
Second, a no-neutral switch can never use a relay. It can only use a Triac with a parallel power bleeding / harvesting circuit. Depending on what you do with the switch, having an actual relay to cut off power can be a good thing.
Are you sure? I have one aquara switch that has decoupled and relay mode. In decoupled mode there is no power to the bulb.
If at all possible, use a smart switch with neutral, even if that means pulling a new N wire from a nearby outlet or so (careful, make sure to pull it from a circuit on the same RCD, or you will trip it).
I don’t need to pull up neutral from outlet because every room has at least two junction boxes and wires can be pulled from there. I didn’t do that because I don’t see any point in doing that. I have a smart switches without neutral for a few years and nothing happened. No one as electrocuted, nothing burned down, switch didn’t melt or anything like that. its like you have a regular switch just a smart one.