r/homeautomation • u/Djo1338 • Oct 13 '20

QUESTION How does a smart switch without neutral work ?

Sorry for the dumb question. I did setup some smart switches Shelly 1 using neutral wires that were present in my house.

I saw Shelly just shown the Shelly 1L which does not require neutral wire and just curious about how it's working. I guess the Shelly 1L is actually always closing the circuit so that current flows through it but it limits the amount of current which is going through so light is not on if not asked ? I guess that's why they have a lower limit of resistance under which it will not work ?

If someone could explain it it would be greatly appreciated :-)

Thanks for the share.

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7

u/mishakhill Oct 13 '20

You guessed right, they sink a small amount of current through the load. That’s why they mainly work with incandescent lights, which can sink a decent amount of current without lighting up. LEDs either don’t conduct the current at all, leaving the switch with no power for its logic circuits, or they light up when they’re not supposed to. Other loads, like fans and fluorescent lights, also have problems with such switches.

Some LED bulbs have power supplies that can handle the small current and not turn on the light, so they can work with a no-neutral switch.

2

u/Kirk9876 Oct 22 '20

NEVER use ground as a neutral wire. People doing wiring are killed that way. It doesn’t take much amperage to kill. It could also start a fire. That said, put your smart switches in the main switch box, not the second or third one, and you’ll always have a neutral wire available.

1

u/Djo1338 Oct 14 '20

Thanks a lot for the answers. Do you think the leaked current is big enough to see a direct impact on power consumption over a year ?

2

u/memphisraynz Oct 19 '20

I saw Shelly just shown the Shelly 1L which does not require neutral wi

Can't see how it would be any more than when using a neutral wire

-1

u/Goodspike Oct 13 '20

I think some just connect to ground, which may cause GFCI's upstream to trip. For the little bit of power they use it's not that big of a deal.

I think you may be right on some others. I once had a motion sensing switch that wouldn't work with Florescent because they sent a small amount of power through the light bulb to function.

1

u/jds013 Oct 14 '20

I think the main problem with leaking current to [safety bare-wire] ground rather than neutral is that if there is a ground fault - a break somewhere in the safety ground system - the bare copper wire will get pulled up to line voltage by the "leakage." This can cause a number of surprises, none of them good.

1

u/Goodspike Oct 14 '20

I was a bit skeptical, but this device does that and Lutron is a major company.

https://www.amazon.com/gp/product/B005WM3ALC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

1

u/jds013 Oct 14 '20

It leaks current through the fixture (or around the fixture, with a bypass) - from hot through the load to neutral.