Light switch with no load


(Brandon Willea) #1

I really like the new ecobee switch with Alexa built it, but my house has very old wiring with only 2 wires at the switch and light.
Does anyone know if it would be possible to wire a smart switch without a load, and use a relay at the light to turn it on? Since the relay needs power all the time, would you be able to wire the switch with just line and neutral wires connected?


(Bryan) #2

I’m not sure I fully understand what you are trying to accomplish, but I believe that there is a smart switch that will work without a neutral. Someone will probably chime in here, or can search this forum, as this issue been discussed a number of times.

But if you do use one of those smart switches, you won’t need a relay at the light. Just use a smart bulb. I’m not sure why you would want both a smart switch and a relay at the light.


#3

Strictly speaking, no, there is no way to wire a smart switch without a load because the smart switch itself is a load. That’s why smart switches (generally) require a neutral … so it can realize 120V potential between line and neutral to power itself.

Now, there is the Lutron Caseta switch which operates without a neutral, and I believe they do so by leaking a tiny amount of current through the light bulb itself. This technique isn’t new … X10 switches did that 25 years ago. It works great with incandescent lights because the tiny amount of current flowing through the filament isn’t enough to make it glow. LEDs and CFLs are a bit more problematic because leaking a little current through them may cause them to react in some way. It seems to be the case that Lutron has figured out how to do it with most bulbs successfully. People who have them seem to be happy.


(Brandon Willea) #4

Yes I have a couple lutron caseta switches, they work great with most LEDs but I had to try a couple different bulbs I had lying around to find ones that didn’t flicker when they were supposed to be off.
I was just curious about any workarounds for smart switches that do require a neutral wire.
Wouldn’t the switch theoretically only require line and neutral to power itself? If load isn’t connected to anything wouldn’t it still have power for itself, just not function as a typical “dumb switch”? Just like plugging something into an outlet, you only need the 2 wires.


(Ving) #5

Most people are not aware of the recent change in the NEC 2017 code in 404.2( C ) where the ground conductor can extend to the neutral. But only for these smart switches. And no more than 5 of these on a circuit.

Now I am writing this so you can determine what is possible and what is not.
General rule of thumb is don’t be lazy, don’t take shortcuts.

There are some other NEC codes that work together with this one. If you are not comfortable don’t do this. This is an exception not the normal.

404.2( C ) Switches Controlling Lighting Loads.

The grounded circuit conductor for the controlled lighting circuit shall be installed at the location where switches control lighting loads that are supplied by a grounded general-purpose branch circuit serving bathrooms, hallways, stairways, or rooms suitable for human habitation or occupancy as defined in the applicable building code. Where multiple switch locations control the same lighting load such that the entire floor area of the room or space is visible from the single or combined switch locations, the grounded circuit conductor shall only be required at one location. A grounded conductor shall not be required to be installed at lighting switch locations under any of the following conditions:

(1) Where conductors enter the box enclosing the switch through a raceway, provided that the raceway is large enough for all contained conductors, including a grounded conductor

(2) Where the box enclosing the switch is accessible for the installation of an additional or replacement cable without removing finish materials

(3) Where snap switches with integral enclosures comply with 300.15(E)

(4) Where lighting in the area is controlled by automatic means

(5) Where a switch controls a receptacle load.

The grounded conductor shall be extended to any switch location as necessary and shall be connected to switching devices that require line-to-neutral voltage to operate the electronics of the switch in the standby mode and shall meet the requirements of 404.22.

Exception: The connection requirement shall become effective on January 1, 2020. It shall not apply to replacement or retrofit switches installed in locations prior to local adoption of 404.2© and where the grounded conductor cannot be extended without removing finish materials. The number of electronic lighting control switches on a branch circuit shall not exceed five, and the number connected to any feeder on the load side of a system or main bonding jumper shall not exceed 25. For the purpose of this exception, a neutral busbar, in compliance with 200.2(B) and to which a main or system bonding jumper is connected shall not be limited as to the number of electronic lighting control switches connected.


Dimmer for 4-way switch without neutral?
(Brandon Willea) #6

Yes I have read about that as well. If only I had ground in any of my switches/lights/outlets. But, with a 110 year old house, I’m just thankful it isn’t knob and tube.


(Ving) #7

In theory your device would work without the ground though. Not safe because you don’t have a ground. But it will work because you have completed your circuit according to electricity and circuits 101.


(Brandon Willea) #8

So, are you saying theoretically a smart switch like the new ecobee would work with no load, just 2 wires, If you used a relay at the fixture?


(Brandon Willea) #9

This is the best diagram I could find to show what I’m thinking.


#10

OK, so your plan is to wire an Ecobee smart switch in parallel to a micro-relay controlled light fixture, right? I don’t see anything wrong with that, but I’d ask why? Is it that you want Alexa in the wall switch box, and that smart switch wouldn’t actually do anything else? It certainly wouldn’t turn that bulb on and off.

Also, you’d have no way locally in the room to kill power to the fixture with certainty. That may be a code requirement.


(David G) #11

You can power and use a smart switch with just line and neutral without having it switch a connected load. For example if you wanted to use it like a scene controller for another smart device(s).

The problem is that even though you have 2 wires at the switch, neither of them are likely connected back to a neutral at your electrical panel, so you won’t be able to use any smart switch that requires a neutral.


#12

If he is not connecting the light fixture as a load, he will have 2 wires from the fixture to bring line and neutral into the switch box. The fixture box has to have neutral.


(Scott Ainsworth) #13

Typically if you are using a relay up in the light fixture would just use a plain old light switch and connect it to the relay control connections on the relay (there should be a set and they are low voltage). the light switch can be a single switch or a string of properly wired three way switches. The relay looks for the switch to change state (on to off) or (off to on). It will then switch the state of the relay contact. This allows independent control or the light with hub commands or the switch. Understand of course that the light can be ON but the switch in the off position. This of course works like any hard wired three way.

You don’t get any dimming (from the switch) or cute little LED on the switch though.


(David G) #14

Oh yeah, you’re talking about rewiring the load at the fixture to change it to a neutral line, right?

Edit: I didn’t see the white wire on the diagram he made when I looked before - that’s what he drew (oops)

Edit2: He could use SmartLighting to have the relay (or smart bulb) mirror the state of the switch to control it (I have a dummy switch setup that way to control some smart outlets with floor lamps). Still wouldn’t have direct control of the fixture though.


(Brandon Willea) #15

Yes that is the plan. I don’t really care so much about the relay itself, it would just be nice to still be able to use that light fixture. The switch would still be able to control the relay wirelessly via IFTTT or a scene. The relays only purpose is to function as the load wire would have had I had enough wires between the switch and fixture.


#16

Typically, yes. I was just trying to answer his question about whether the specific wiring he proposed would work. Yes, it would in the sense you could have a smart thing and a smart switch. Per my previous comment, still of the opinion that there needs to be a way to manually kill power to the fixture in the same room, and this wouldn’t provide that.


(Scott Ainsworth) #17

Sorry, I intended for my reply to be a response to the diagram he posted.

I see now he is looking for the extra Alexa functionality in the switch. In that case the diagram works but he would need a 4th neutral from the relay to the wirenut joining the neutrals. This is needed to power the electronics in the relay.


#18

What I don’t get is that you have line and load in your box. How are you going to change that to line and Neutral? If there are two wires on the switch now, you have line and load. Even if one of them i s white.


#19

They are only line and load if connected to line and load. The first step of his proposal is to disconnect the two wires at the switch and at the fixture. Then it isn’t line and load any more … it’s two wires. He’s going to use those two wires to connect to line and neutral at the fixture and at the smart switch.


#20

Yes, I get that. But then how is he going to be able to connect the fixture? If you steal the neutral from the fixture to connect to the wire coming into the fixture from the switch, you no longer have a load at the fixture anymore. Do you get what I mean? His diagram relies on power first going to the fixture and then to the switch, which is backwards unless you are “neutral switching”. The power would first go to your switch, then to whatever fixture you are controlling. Otherwise, you don’t really turn power off to the fixture when you turn off the switch. His diagram doesn’t make sense to me.