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I have lighting/wall circuit which I didn't put in place so don't have definitive information on its layout so bear with me.

I want to put the Shelly 1L into the circuit at the switch.

What I know

  • There is a 20amp breaker for the room (which when turned off, turns off the ceiling lights and wall sockets)
  • The switch does not have a neutral wire.
  • The switch has two black wires and a green/ground - one black leads on to white at the back of the box.
  • Wiring Gauge not written on cables. Looks to be 14?
  • There are 3 ceiling bulbs. LED so may need a bypass
  • The Shelly 1A is my only option in the absence of a neutral wire.
  • The Shelly 1L supports 4.1A which is obviously far less than the 20 on the breaker.

Can I put the 4.1A Shelly into the circuit at the light switch?

I assume the lighting and wall switches are on separate parallel parts of the circuit (something like this) and therefore the load on the lighting part (and therefore the Shelly) is only as much as is drawn from the bulbs and the wall sockets do not affect this?

Edits/Updates

I have added a couple of photos below having managed to pull things out a bit further.

To address some of the points in Harper's answer-

Can I put the 4.1A Shelly into the circuit?

Certifications aside, from a learning perspective is this possible? I will be looking at the UL products instead but out of interest would this have worked? With a neutral present I can get the Shelly 1 or 2.5 instead.

It depends. Both electrical and building codes require that every room have one light switch in the usual location(s) that works, and controls a light.

It is my understanding that the switch always functions as normal even with a Shelly in the circuit. This would be true if I installed it at the ceiling rose. I'm putting a Shelly in and the original switch is present?

#12 copper solid is the universal donor, allowed in all lighting and common receptacle circuits.

Can't see any writing on the wires in the switch. The ones in the LED controller are 18AWG it seems. Can't tell what the ones in the switch are but marginally thicker than the ones in the ceiling. Perhaps 14?

Switches don't normally have neutral wires, as they would have no use for them.

However, look in the back of the box. If power came to the switch first, with cable wiring methods there will be a pair of white wires tied with a wire-nut. Those would be neutral.

You appear to be spot on here. Having managed to pull the switch out properly i can see further into the back of the box and the 2nd black wire leads to a white one in a nut (see picture).

And honestly, the lamp box or rose is likely to have more room for it than a switch box.

There doesn't appear to be much room at all at the rose as theres some sort of LED controller up there (photo #2)

Switch switch

Ceiling ceiling

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  • The Shelly devices will only accept #14 wire because they're not rated at 20A (source: Experience installing them). If your bulbs are incandescent, I think the Shelly will work w/o the bypass. I know the Shelly 1 is UL listed, but I'm not sure about all the other varieties. For some reason, the Shelly site won't load for me ATM, so I can't check.
    – FreeMan
    Commented Dec 3, 2021 at 18:33
  • My question i suppose is more is the shelly safe to put into this circuit given they're not rated up to 20A as you say. If my understanding is correct, there would never be a >4.1 amp load on the Shelly assuming i didn't suddenly add lots of lights (which i have no plans). For example if I plug a high wattage item into a socket i.e. a pair of hair straighteners, that load goes across the breaker, and never the shelly, right? Commented Dec 3, 2021 at 18:35
  • Switch should only control the lights. In some cases it might also control an outlet. Simple test is to plug a desk lamp into each outlet(top and bottom) with the switch off.
    – crip659
    Commented Dec 3, 2021 at 19:19
  • Yep I’ve checked that. switch controls no outlets, only ceiling lights Commented Dec 3, 2021 at 19:21
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    @Harper-ReinstateMonica interesting - Shelly do have some UL certified products but the Shelly 1L doesn't appear to be one of them. For example - 1 ul and list of UL products Commented Dec 3, 2021 at 19:24

1 Answer 1

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Can I put the 4.1A Shelly into the circuit

Not in North America. Anything that goes into AC mains electrical equipment there needs to be certified by an independent Recognized Testing Lab such as Underwriter's Laboratories (UL) or ETL as to its safety. This assures that it's built not to start fires, e.g. proper PCB design, quality components, plastics which will not self-ignite if heated and will not emit toxic smoke foreclosing a chance of escape.

A lot of cheap and hobby-tier builders simply ignore these safety "annoyances", and take advantage of loopholes in consumer protection apparatus - they sell exclusively via direct mail (including via drop-shippers like Amazon Fulfillment) and as 3rd party sellers on "marketplace" sites.

at the light switch?

It depends. Both electrical and building codes require that every room have one light switch in the usual location(s) that works, and controls a light. (if you walk into a room you've never entered before, you know where to grope for the light switch. That's it.) You are not allowed to eliminate that. (though you can parallel it, i.e. switch on = light forced on; switch off = module controls). So whatever you do, a physical switch must still cause a light to work in the room.

Appears to be 12 or 14 AWG wire based on diameter (Can't see writing on the sheath but will investigate further before getting additional wire for the Shelly)

#12 copper solid is the universal donor, allowed in all lighting and common receptacle circuits.

The switch does not have a neutral wire.
The switch has two black wires and a green/ground.

Switches don't normally have neutral wires, as they would have no use for them.

However, look in the back of the box. If power came to the switch first, with cable wiring methods there will be a pair of white wires tied with a wire-nut. Those would be neutral.

Could it be a switch loop? Nobody makes cables with black-black as the 2 wires. Therefore if it's a switch loop, you are in the conduit wiring method and an actual neutral wire can be pulled into the conduit fairly easily. (trivially for an experienced pro).

The Shelly 1A is my only option in the absence of a neutral wire.

That's not true. A UL-listed smart switch module can be installed anywhere all 3 wires are present:

  • Always-hot (supply)
  • Actual Neutral
  • Switched-hot to the lamp

Your concern is that you have a switch loop that doesn't provide neutral at the switch. Any such switch loop will have all 3 at the lamp... you can simply install the module there.

And honestly, the lamp box or rose is likely to have more room for it than a switch box.

The Shelly 1L supports 4.1A which is obviously far less than the 20 on the breaker.

That's not a concern on a UL-listed (or other NRTL) product. The product safety standards account for this, and require equipment to prove it will fail non-destructively in that gap between "4.1A" and "20A breaker trip".

I assume the lighting and wall switches are on separate parallel parts of the circuit (something like this) and therefore the load on the lighting part (and therefore the Shelly) is only as much as is drawn from the bulbs and the wall sockets do not affect this?

Correct. The only current drawn through the smart device will be the bulbs' draw, if everything is working properly. Of course, if we only built things to be safe when everything is working properly, we wouldn't need circuit breakers or grounds, would we?

Edit

UL listed equipment will wire the same way. However they will be made of materials that are safe to designs that are safe. There's a reason hobby builders like Shelly don't start out UL listed.

The module goes at the ceiling rose only if the wiring is a switch loop which does not have a neutral. (in fact the Shelly 1L is made for this application, probably in a Code-violating way, hence the lack of UL listing). However you DO have neutral at the switch, so you can use any normal smart switch which requires neutral and uses it in a UL-approved fashion.

The switch box has about 26 cubic inches (4x4 steel box + 1-gang mud ring) and only needs 16 c.i. for what's in it now. (no ground allowance is needed since no ground wires are present, except for a pigtail, and pigtails are free. The box grounds via the armored cable). So it may fit, however the Shelly will have poor reception inside a metal box. (yet another detail that UL makes you think about!)

Try a cheapie switch or receptacle with backstab holes. It can be used as a wire gauge. The backstab hole is made to barely fit #14 and reject #12.

So these are LED downlights, which provide a tiny junction splice box barely big enough for what it does there. A module won't fit there.

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  • Hi Harper thanks so much for taking the time to write a comprehensive answer. I've updated my original question with a couple of questions and photos based on your responses. I'd appreciate it if you had a sec to have a look. Thanks again Commented Dec 7, 2021 at 18:36

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